Module 9: Validating User Input

Transcription

1 Module 9: Validating User Input Table of Contents Module Overview 9-1 Lesson 1: Restricting User Input 9-2 Lesson 2: Implementing Field-Level Validation 9-8 Lesson 3: Implementing Form-Level Validation 9-22 Lab: Validating User Input 9-28 Lab Discussion 9-43

2 Information in this document, including URL and other Internet Web site references, is subject to change without notice. Unless otherwise noted, the example companies, organizations, products, domain names, addresses, logos, people, places, and events depicted herein are fictitious, and no association with any real company, organization, product, domain name, address, logo, person, place, or event is intended or should be inferred. Complying with all applicable copyright laws is the responsibility of the user. Without limiting the rights under copyright, no part of this document may be reproduced, stored in or introduced into a retrieval system, or transmitted in any form or by any means (electronic, mechanical, photocopying, recording, or otherwise), or for any purpose, without the express written permission of Microsoft Corporation. The names of manufacturers, products, or URLs are provided for informational purposes only and Microsoft makes no representations and warranties, either expressed, implied, or statutory, regarding these manufacturers or the use of the products with any Microsoft technologies. The inclusion of a manufacturer or product does not imply endorsement of Microsoft of the manufacturer or product. Links are provided to third party sites. Such sites are not under the control of Microsoft and Microsoft is not responsible for the contents of any linked site or any link contained in a linked site, or any changes or updates to such sites. Microsoft is not responsible for Webcasting or any other form of transmission received from any linked site. Microsoft is providing these links to you only as a convenience, and the inclusion of any link does not imply endorsement of Microsoft of the site or the products contained therein. Microsoft may have patents, patent applications, trademarks, copyrights, or other intellectual property rights covering subject matter in this document. Except as expressly provided in any written license agreement from Microsoft, the furnishing of this document does not give you any license to these patents, trademarks, copyrights, or other intellectual property Microsoft Corporation. All rights reserved. Microsoft, Access, Active Directory, BizTalk, DirectX, Excel, IntelliSense, Internet Explorer, MSDN, Outlook, PowerPoint, SQL Server, Visual Basic, Visual C#, Visual C++, Visual J#, Visual Studio, Win32, Windows, Windows CardSpace, Windows NT, Windows Server, Windows Vista, and WinFX are either registered trademarks or trademarks of Microsoft Corporation in the United States and/or other countries. The names of actual companies and products mentioned herein may be the trademarks of their respective owners. Version 1.1

3 Module 9: Validating User Input 9-1 Module Overview Validation of user input is a critical part of building an application. In most applications that you create, users need to enter information for the application to process. At some point in the entry process, you must check that the information entered is the format and type of data that you expect and notify the user if it is not. You can use input validation techniques at both the field level and the form level to prevent users from entering invalid data. You can also provide error messages that guide users through the process of finding and fixing errors. This module introduces controls that restrict user input on a form. It describes field-level validation and features such as validation events. It also describes how to implement form-level validation and use buttons to accept and cancel user input. Objectives After completing this module, you will be able to: Restrict user input. Implement field-level validation. Implement form-level validation.

4 9-2 Module 9: Validating User Input Lesson 1: Restricting User Input One of the best ways to provide input validation is to restrict user input to only valid data. You can use features of controls to restrict user input on a form. For example, you can use a control that does not allow users to enter anything except numbers when numeric data is required. Objectives After completing this lesson, you will be able to: Describe intrinsic validation. Describe the validation properties of a TextBox control. Explain how to use the MaskedTextBox control.

5 Module 9: Validating User Input 9-3 Introduction to Intrinsic Validation One of the simplest ways to validate user input is to use a control that intrinsically provides the validation that an application requires. Many controls have built-in properties that provide a certain level of intrinsic validation. For example, the DateTimePicker control enables the user to choose only dates and times. Definition Intrinsic validation refers to a control s built-in properties and methods that you can use to restrict and validate user input. For typical data entry requirements, many Microsoft.NET Framework controls exist that automatically restrict the data that users can enter. These controls can save you much time and effort when you want to validate user input. Controls with Intrinsic Validation Properties The following table lists some of the common controls from the Toolbox in Microsoft Visual Studio 2005 that provide intrinsic validation. Control Types of Data Intrinsic Validation Technique TextBox RichTextBox LinkLabel CheckBox RadioButton ComboBox CheckedListBox ListBox ListView Special text requirements Specific values Items in a list Items in a list with graphics and text Restrict and modify data entry in text boxes and labels Restrict values to specific entries identified by the controls Provide a list of valid entries Provide a list of valid entries

6 9-4 Module 9: Validating User Input Control Types of Data Intrinsic Validation Technique DateTimePicker Dates and times Restricts entries to dates or times OpenFileDialog SaveFileDialog Dialog boxes Restrict entries to valid path names and file names

7 Module 9: Validating User Input 9-5 Validation Properties of a TextBox Control The TextBox control is one of the most commonly used controls in applications. It provides several properties that you can use to validate user input. Validation Properties You can use the intrinsic validation properties of the TextBox control to validate and restrict user input in text boxes. For example, you can mask or hide the characters that a user inputs into a text box or specify a maximum number of characters. You can set the following validation properties in a TextBox control at design time or run time to restrict or validate user input: PasswordChar. Masks or hides the characters that a user enters into a text box. If you set this property to an asterisk (*), the user will only see asterisk characters in the text box. Passwords are nearly always hidden in logon dialog boxes. This property does not affect the underlying Text property of the text box. MaxLength. Sets a maximum number of characters that a user can enter into a text box. You can exceed this maximum length when setting the Text property at design time. ReadOnly. Prevents all data entry into a text box. When this property is set to true, users can view the text in the text box, but they cannot edit the text. For example, a text box displays a value that is usually edited but might be read-only because of the state of the application. CharacterCasing. Changes the case of characters in a text box. You can set the case of all characters that a user enters into a text box to uppercase (Upper), lowercase (Lower), or leave the characters unchanged (Normal).

8 9-6 Module 9: Validating User Input How to Use the MaskedTextBox Control The MaskedTextBox control is an advanced version of a text box control that you can use to format and control user input. You specify a mask for the MaskedTextBox that controls the format of data to be entered. For example, you can specify a 16-digit number in groups of four numbers for a credit card number. You can add the MaskedTextBox control to a form in the same way you add any other Toolbox control. Adding a MaskedTextBox control to a form 1. In the Toolbox, expand the Common Controls group. 2. Drag a MaskedTextBox control onto the form. You can then set the properties of the control in the Properties window. Setting properties of a MaskedTextBox control 1. On the form, click the MaskedTextBox control. 2. In the Properties window, set the properties that you want. The main properties are: Mask. Defines a mask for user input at either design time or run time. You can choose a predefined mask or create a custom mask. A phone number, social security number, and zip code are all examples of predefined masks. TextMaskFormat. Determines whether the Text property of the control includes literals and prompt characters of the mask. PasswordChar. Defines the character to display for user input.

9 Module 9: Validating User Input 9-7 Accessing the Values of a MaskedTextBox Control You can access the data that a user enters into a MaskedTextBox control by using the Text property. If you want to exclude the mask, set the TextMaskFormat property of the control to ExcludePromptAndLiterals. If you want to include the mask, set the TextMaskFormat property of the control to IncludePromptAndLiterals. The following code displays the formatted and unformatted Text property of a MaskedTextBox control. [Visual C#] // The mask is a credit card number; a 16-digit number in groups of four numbers. // The user enters into the text box. maskedtextbox1.textmaskformat = MaskFormat.ExcludePromptAndLiterals; MessageBox.Show(maskedTextBox1.Text); // A message box displays the string to the user. maskedtextbox1.textmaskformat = MaskFormat.IncludePromptAndLiterals; MessageBox.Show(maskedTextBox1.Text); // A message box displays the string to the user. [Visual Basic] ' The mask is a credit card number; a 16-digit number in groups of four numbers. ' The user enters into the text box. maskedtextbox1.textmaskformat = MaskFormat.ExcludePromptAndLiterals MessageBox.Show(maskedTextBox1.Text) ' A message box displays the string to the user. maskedtextbox1.textmaskformat = MaskFormat.IncludePromptAndLiterals MessageBox.Show(maskedTextBox1.Text) ' A message box displays the string to the user.

10 9-8 Module 9: Validating User Input Lesson 2: Implementing Field-Level Validation You will often want to validate user data when the user completes each field on a form. You can use Boolean functions to validate data input and the ErrorProvider component to provide messages that help users to correct invalid data input. You can use validation events to ensure that specific data fields contain acceptable data before the user proceeds. Objectives After completing this lesson, you will be able to: Use Boolean functions to validate data. Use the ErrorProvider component. Describe how to set the focus to a control. Explain how to modify user input. Describe validation events. Explain how to use validation events.

11 Module 9: Validating User Input 9-9 How to Use Boolean Functions to Validate Data Boolean functions are useful for testing data to determine if it is valid. For example, you might need to test a variable to determine what type of data it holds and then take action based on the results. Boolean functions use a specific condition to evaluate an expression. Definition A Boolean function evaluates an expression based on certain criteria and returns a true or false value. For example, you can use a Boolean function to determine if the data a user inputs into a date field is a date or a string that you can convert into a date. Common Boolean Functions Microsoft Visual Basic provides many useful Boolean functions. The main Boolean functions are: IsDate. Tests whether a value is a date or can be converted to a date. Returns true if the date is valid; otherwise returns false. IsNumeric. Tests whether a value is a numeric. Returns true if the value is numeric; otherwise returns false. IsError. Tests whether a value is an exception type. Returns true if the value is an exception type; otherwise returns false. IsNothing. Tests whether a value is null. Returns true if the value is null; otherwise returns false. These functions are also available in Microsoft Visual C# code by referencing the Microsoft.VisualBasic assembly and using the Information class in the assembly to access these functions.

12 9-10 Module 9: Validating User Input The System.Text.RegularExpressions namespace contains another valuable Boolean function for validating user input. The Regex class contains an IsMatch method that indicates whether an input string matches a regular expression. The main regular expressions are: [\s]. Expression can contain spaces [\d]. Expression can contain numbers [a-za-z]. Expression can contain alphabet characters 1,50. Expression must contain between 1 and 50 characters Note: For more information on regular expressions, see the Microsoft Visual Studio 2005 Documentation. Examples and Syntax The following code uses the IsNumeric function to test whether a user inputs a numeric value into a text box and displays a message stating whether the value is numeric. [Visual C#] // Import the Visual Basic namespace. using Microsoft.VisualBasic; public class CheckInput private void NumberInput() // Set a string to the user input in the text box. string userinput; userinput = inputtextbox.text; // Display a message that depends on the validity of the input. if (Information.IsNumeric(userInput)) MessageBox.Show(userInput + " is a number."); else MessageBox.Show(userInput + " is not a number."); [Visual Basic] Private Sub CheckInput( ) ' Set a string to the user input in the text box. Dim userinput As String userinput = usertextbox.text ' Display a message that depends on the validity of the input. If IsNumeric(userInput) Then MessageBox.Show(userInput & " is a number.") Else

13 Module 9: Validating User Input 9-11 MessageBox.Show(userInput & " is not a number.") End If End Sub The following code uses the IsMatch method of the Regex class to test whether a user inputs a valid name between 1 and 50 characters with alphabet characters, spaces, single quotes, or periods. [Visual C#] string userinput; userinput = inputtextbox.text; // Display a message that depends on the validity of the input. if MessageBox.Show(userInput + " is a valid name."); else MessageBox.Show(userInput + " is not a valid name."); [Visual Basic] Dim userinput As String userinput = inputtextbox.text ' Display a message that depends on the validity of the input. If Then MessageBox.Show(userInput + " is a valid name.") Else MessageBox.Show(userInput + " is not a valid name.") End If In the IsMatch method parameters, the values between the square brackets are the acceptable characters. The number range in the curly brackets is the minimum and maximum number of acceptable characters. The caret (^) and dollar ($) symbols ensure that the expression consists of the expression and nothing else.

14 9-12 Module 9: Validating User Input How to Use the ErrorProvider Component With the ErrorProvider component, you can display an icon to the user to communicate that something is incorrect. This component has an advantage over a message box because it does not require users to close a window before they can continue. When the user moves the pointer over the error icon, a tooltip displays helpful information. You add the ErrorProvider component to a form in the same way you add any other Toolbox control. Adding an ErrorProvider component to a form 1. In the Toolbox, expand the Components group. 2. Drag an ErrorProvider component onto the form. You can set the properties of an ErrorProvider component in the Properties window. Setting properties of a ErrorProvider component 1. On the form, click the ErrorProvider component. 2. In the Properties window, set the properties that you want. The main properties are as follows: Icon. Defines the picture on the icon that indicates the error. BlinkStyle. Defines whether the error icon blinks when an error is set. BlinkRate. Defines the rate in milliseconds at which the error icon blinks.

15 Module 9: Validating User Input 9-13 The SetError Method When you display an error message to a user, you can explain the error to the user and communicate how to correct the problem. The key method of the ErrorProvider component is the SetError method, which specifies the error message string to display and the control to associate with the error icon. The first argument of the SetError method specifies the control to associate with the error icon. The second argument specifies the error text to display as a tooltip. When the user corrects the error, you should set the error message to an empty string so that the error icon disappears. Writing Code for an ErrorProvider Component You add code to the Validating event of a control to validate the contents of the control. When you move between controls, the Validating event of the first control is raised when the second control receives focus, provided that the second control has the CausesValidation property set to True. If the validation fails, use the ErrorProvider component to display an error message and icon to the user. You can also set the focus back to the control if you want the user to input valid data before they can continue. The following code sets the error message for a text box control if the text box contains more than 10 characters or contains non-alphabet characters. [Visual C#] // If the user input is invalid, set the error message, otherwise clear it. if myerrorprovider.seterror(userinput, "Please enter 10 characters or fewer."); else errorprovider1.seterror(userinput, ""); [Visual Basic] ' If the user input is invalid, set the error message, otherwise clear it. If Then errorprovider1.seterror(userinput, "Please enter 10 characters or fewer.") Else errorprovider1.seterror(userinput, "") End If You can also use the ErrorProvider with bound data controls. When working with bound data, you can set the DataSource property of the ErrorProvider component to automatically collect error messages from a database.

16 9-14 Module 9: Validating User Input How to Set the Focus on a Control When a user enters invalid data and moves to another control, you can direct users to the invalid data by setting focus on the control. Most controls have two methods called Focus and SelectAll that you can use to aid users when they enter invalid data. You can use these methods to set focus on the invalid control and select all the data in the control. These methods are particularly useful when you combine the control focus with an informative message. Methods The two methods that are helpful to users that enter invalid data are: Focus. Set focus on a specific control. SelectAll. Select all text within a specific control. On a Microsoft Windows Form that contains several text boxes, only the text box that has focus can receive data input from the user. If a user enters invalid data, you can use the Focus method to keep the focus on the appropriate control until valid data is input. After you set the focus on a control, you can also use the SelectAll method to select all the text of the control to simplify the re-entry of data for the user. Example The following code calls the Focus and SelectAll methods on a text box if the text box does not contain a date value. This example also uses the ErrorProvider component to display an error if the data is invalid. [Visual C#] // If the text box does not contain a date, set the error message, set focus on // the control, and select all the text of the control. if (!Microsoft.VisualBasic.Information.IsDate(textBox1.Text))

17 Module 9: Validating User Input 9-15 errorprovider1.seterror(textbox1, "Please enter a valid date."); textbox1.focus(); textbox1.selectall(); else errorprovider1.seterror(textbox1, null); [Visual Basic] ' If the text box does not contain a date, set the error message, set focus on ' the control, and select all the text of the control. If Not IsDate(textBox1.Text) Then errorprovider1.seterror(textbox1, "Please enter a valid date.") textbox1.focus() textbox1.selectall() Else errorprovider1.seterror(textbox1, Nothing) End If Order of Focus Events When the focus of a control changes because the user moves away from the control or because the application calls the Focus method, focus events occur in the following order: 1. Enter. Occurs when the control is entered 2. GotFocus. Occurs when the control receives focus 3. LostFocus. Occurs when the control loses focus 4. Leave. Occurs when the input focus leaves the control 5. Validating. Occurs when the control is validating 6. Validated. Occurs when the control is finished validating When the focus arrives at a control whose CausesValidation property set to true, the control that previously had focus will be validated. For example, if the focus is on a first name text box, and the user tabs to a last name text box, the Validating event of the first name text box will only be raised if the CausesValidation property of the last name text box is set to true.

18 9-16 Module 9: Validating User Input How to Modify User Input In some cases, you might need to ensure that user input is in a particular format for example, to insert valid data into a database. You can use methods of the String class to convert the case of a string, replace characters in a string, and remove blank spaces from a string. Methods and Functions to Modify User Input The String class provides many methods that you can use to modify user input. These methods return a new modified string. The main methods in the String class that modify user input are: ToLower. Converts all characters in the string to lowercase. ToUpper. Converts all characters in the string to uppercase. Trim. Removes all occurrences of a set of specified characters from the start and end of the string. Insert. Inserts a string at a specified index position within another string. Replace. Replaces all occurrences of a specified string within another string. Remove. Deletes a specified number of characters from the string beginning at a specified position. In Visual Basic, you can also use several functions to modify user input. The following functions return a new modified string and possess similar functionality to the methods of the String class: LCase. Converts all characters in the string to lowercase. UCase. Converts all characters in the string to uppercase.

19 Module 9: Validating User Input 9-17 Trim. Removes all leading and trailing spaces in the string. Replace. Replaces all occurrences of a specified string within another string a specified number of times. Visual C# does not provide equivalents to functions. However, you can reference the Microsoft.VisualBasic assembly and use the Strings class in this assembly to use these functions in Visual C# code. Example The following code calls the Trim and ToLower methods of the String class to remove all spaces in leading and trailing spaces in a string and convert all characters to lowercase. [Visual C#] // Remove all leading and trailing spaces from a string and convert to lowercase. string fullname = " Thomas Andersen "; fullname = fullname.trim(); fullname = fullname.tolower(); [Visual Basic] ' Remove all leading and trailing spaces from a string and convert to lowercase. Dim fullname As String = " Thomas Andersen " fullname = fullname.trim() fullname = fullname.tolower() The example converts the fullname string to thomas andersen with no leading or trailing spaces.

20 9-18 Module 9: Validating User Input What Are Validation Events? Sometimes you will need to check user input before you allow the user to move to another field on a form. Many Windows Forms controls provide two validation events: the Validating event and the Validated event. You can use these events to ensure that specific fields in your application contain accurate data before the user moves on to other fields. CausesValidation Property You can use the CausesValidation property to raise the Validating event for a control. This Boolean property is available on the Windows Forms controls in the Toolbox. When you set the CausesValidation property to true for a control, and the user moves to the control, the Validating event for the previous control is raised. When you set the CausesValidation property to false, and the user moves between the two controls, the Validating event for the first control is not raised. The CausesValidation property is set to true by default. Validating Event The Validating event is raised after the Leave event and before the Validated event. This event is normally raised after the user enters data in a control and then moves to another control. You can implement the event handler for the Validating event to contain any validation code that you need for a specific control. Validated Event The Validated event is raised after the Validating event. The Validated event is normally raised after the user enters data in a control, moves to another control, and the validation of the control is successful. You can implement the event handler for the

21 Module 9: Validating User Input 9-19 Validated event to contain any code that you need for a specific control after validation has occurred.

22 9-20 Module 9: Validating User Input How to Use Validation Events You can use the Validating and Validated events of a control to implement validation for user input. You can implement event handlers for these events to provide full programmatic control over validation and perform complex validation checks. Example of the Validating Event In the Validating event handler, you can write code to manage the validation of controls. The following code sets the error message in the Validating event for a text box control if the text box is null or empty. [Visual C#] // Validating event handler for the textbox1 control. private void textbox1_validating(object sender, CancelEventArgs e) // If the control is null or empty, set an error message, otherwise clear it. if (String.IsNullOrEmpty(textBox1.Text)) myerrorprovider.seterror(textbox1, "Please enter a value."); else errorprovider1.seterror(textbox1, ""); [Visual Basic] ' Validating event handler for the textbox1 control. Private Sub textbox1_validating(byval sender As System.Object, ByVal e As _ System.ComponentModel.CancelEventArgs) Handles textbox1.validating ' If the control is null or empty, set an error message, otherwise clear it. If String.IsNullOrEmpty(textBox1.Text) Then errorprovider1.seterror(textbox1, "Please enter a value.")

23 Module 9: Validating User Input 9-21 Else errorprovider1.seterror(textbox1, "") End If End Sub Example of the Validated Event In the Validated event handler, you can write code to manage controls that depend on the recently validated control. The following code illustrates the interaction between the Validating and Validated events. If the text in the control is null or an empty string, the Validating event handler cancels the event, selects the text in the control, and sets the ErrorProvider component. If the data is valid, the Validated event handler occurs and clears the ErrorProvider component? [Visual C#] // Validating event handler for the textbox1 control that sets the error message. private void textbox1_validating(object sender, CancelEventArgs e) // If the control is null or empty, cancel the event, set focus on // the control, select all the text, and set an error message for the control. if (String.IsNullOrEmpty(textBox1.Text)) e.cancel = true; textbox1.focus(); textbox1.selectall(); errorprovider1.seterror(textbox1, "Please enter a value."); // Validated event handler for the textbox1 control that clears the error message. private void textbox1_validated(object sender, CancelEventArgs e) errorprovider1.seterror(textbox1, ""); [Visual Basic] ' Validating event handler for the textbox1 control that sets the error message. Private Sub textbox1_validating(byval sender As Object, _ ByVal e As System.ComponentModel.CancelEventArgs) Handles textbox1.validating ' If the control is null or empty, cancel the event, set focus on ' the control, select all the text, and set an error message for the control. If String.IsNullOrEmpty(textBox1.Text) Then e.cancel = True textbox1.focus() textbox1.selectall() errorprovider1.seterror(textbox1, "Please enter a value.") End If End Sub ' Validated event handler for the textbox1 control that clears the error message. Private Sub textbox1_validated(byval sender As Object, _ ByVal e As System.EventArgs) Handles textbox1.validated ' errorprovider1.seterror(textbox1, "") End Sub

24 9-22 Module 9: Validating User Input Lesson 3: Implementing Form-Level Validation In some scenarios, you will want to perform data validation near the end of the formcompletion process to minimize the number of error messages and interruptions to which a user must respond. Objectives After completing this lesson, you will be able to: Describe how to validate multiple fields on a form. Designate accept and cancel buttons for a form.

25 Module 9: Validating User Input 9-23 How to Validate Multiple Fields on a Form You can implement validation for multiple fields on a form in various ways. You can provide visual cues to users so that they know all the required fields are valid. If the user enters an invalid field, you can set the focus on the control and select the text to be corrected. Providing Visual Cues to the User You should provide visual clues to users when you implement form-level validation. Users can then see when data is missing or incorrect. For example, a form might contain a set of personal details that must be completely filled in before the user can continue. You can provide a visual clue that more data is required by disabling the OK button on a form until all fields are valid. Example of Providing Visual Cues The following code enables an OK button if all three text boxes are valid; otherwise, the button is disabled. The GetError method of an ErrorProvider component accepts a control as the parameter and returns the error message associated with the control. [Visual C#] private void CheckValidation() // If all three text boxes do not contain an error, enable the OK button, // otherwise disable the OK button. if (String.IsNullOrEmpty(myErrorProvider.GetError(textBox1)) && String.IsNullOrEmpty(myErrorProvider.GetError(textBox2)) && String.IsNullOrEmpty(myErrorProvider.GetError(textBox3))) okbutton.enabled = true; else

26 9-24 Module 9: Validating User Input okbutton.enabled = false; [Visual Basic] Private Sub CheckValidation() ' If all three text boxes do not contain an error, enable the OK button, ' otherwise disable the OK button. If String.IsNullOrEmpty(myErrorProvider.GetError(textBox1)) AndAlso _ String.IsNullOrEmpty(myErrorProvider.GetError(textBox2)) AndAlso _ String.IsNullOrEmpty(myErrorProvider.GetError(textBox3)) Then okbutton.enabled = True Else okbutton.enabled = False End If End Sub Validating All Fields on a Form Together In some scenarios, it can be more efficient to validate multiple fields at the same time rather than each field individually. You can validate all fields on a form at same time by writing validation code in the Click event handler for an OK button or another button with similar functionality. Example of Validating All Fields on a Form Together The following code in the event handler for the OK button validates three text boxes at the same time. A message displays to the user and the form closes if all the controls are valid. [Visual C#] // Event handler for the Click event of the OK button. private void okbutton_click(object sender, EventArgs e) // If all three text boxes do not contain an error, display a message and // close the form, otherwise just display a message. if (String.IsNullOrEmpty(myErrorProvider.GetError(textBox1)) && String.IsNullOrEmpty(myErrorProvider.GetError(textBox2)) && String.IsNullOrEmpty(myErrorProvider.GetError(textBox3))) MessageBox.Show("All input data is valid.", "Input Correct!"); this.close(); else MessageBox.Show("Input data with an error symbol is invalid.", "Input Incorrect"); [Visual Basic] ' Event handler for the Click event of the OK button. Private Sub okbutton_click(byval sender As System.Object, _ ByVal e As System.EventArgs) Handles okbutton.click ' If all three text boxes do not contain an error, display a message and ' close the form, otherwise just display a message.

27 Module 9: Validating User Input 9-25 If String.IsNullOrEmpty(myErrorProvider.GetError(textBox1)) AndAlso _ String.IsNullOrEmpty(myErrorProvider.GetError(textBox2)) AndAlso _ String.IsNullOrEmpty(myErrorProvider.GetError(textBox3)) Then MessageBox.Show("All input data is valid.", "Input Correct!") Me.Close Else MessageBox.Show("Input data with an error symbol is invalid.", _ "Input Incorrect") End If End Sub

28 9-26 Module 9: Validating User Input How to Designate Accept and Cancel Buttons for a Form In Windows Forms applications, it is good practice to assign ENTER and ESC key functionality to a form because this makes it easier to use the form. By using the ENTER key, users can quickly accept their actions; with the ESC key, users can quickly cancel their actions. You can set this functionality by using the AcceptButton and CancelButton properties of a form. Designating an Accept Button You can assign any button on a form to be the accept button of the form. This button is also known as the default button. When the user presses ENTER, the Click event handler for the accept button is invoked, regardless of which control on the form has focus. An exception to this rule is when another button has focus. In this case, the Click event handler for the button with focus is invoked. Assigning a Button control as the accept button 1. In design view, click the form. 2. In the Properties window, set the AcceptButton property of the form to the name of the Button control. Designating a Cancel Button Similarly, you can assign any button on a form to be the cancel button of the form. When the user presses ESC, the Click event handler for the cancel button is invoked, regardless of the control in focus. For example, you can write code in the Click event handler of the cancel button to take no action and close the form.

29 Module 9: Validating User Input 9-27 Assigning a Button control as the cancel button 1. In design view, click the form. 2. In the Properties window, set the CancelButton property of the form to the name of the Button control. You can also assign the accept and cancel buttons in code. The following example assigns the accept and cancel buttons of a form to the okbutton and cancelbutton controls respectively. [Visual C#] // Set the accept button for the current form. this.acceptbutton = okbutton; // Set the cancel button for the current form. this.cancelbutton = cancelbutton; [Visual Basic] ' Set the accept button for the current form. Me.AcceptButton = okbutton ' Set the cancel button for the current form. Me.CancelButton = cancelbutton

30 9-28 Module 9: Validating User Input Lab: Validating User Input After completing this lab, you will be able to: Use an ErrorProvider component. Provide visual cues to the user by enabling an OK button. Estimated time to complete this lab: 50 minutes Lab Setup For this lab, you will use the available virtual machine environment. Before you begin the lab, you must: Start the 4994A-LON-DEV-09 virtual machine. Log on to the virtual machine with the user name Student and the password Pa$$w0rd. Lab Scenario You are a new developer in the Adventure Works organization, a fictitious bicycle manufacturer. You are currently learning how to create a Windows Forms application by working on a version of a sales application. In this lab, you will add validation features to the existing application.

31 Module 9: Validating User Input 9-29 Exercise 1: Using the ErrorProvider Component on a Form In this exercise, you will add an ErrorProvider component to the NewSalesPersonForm form. You will also add validation code to three different text boxes by implementing event handlers for the Validating event and Validated event of the control. The principal tasks for this exercise are as follows: Add an ErrorProvider component to the NewSalesPersonForm form. Add specific validation code to three text boxes. Open the Adventure Works Sales application 1. Start Microsoft Visual Studio On the File menu, point to Open, and then click Project/Solution. 3. In the Open Project dialog box, open the SalesApplication.sln solution file for the starter Sales application. If you are using Visual C#, the solution file is located in the E:\Labfiles\Starter\CS\SalesApplication folder. If you are using Visual Basic, the solution file is located in the E:\Labfiles\Starter\VB\SalesApplication folder. 4. In Solution Explorer, double-click NewSalesPersonForm. The NewSalesPersonForm form is displayed in design view. Add an ErrorProvider component to NewSalesPersonForm 1. In the Toolbox, in the Components group, drag an ErrorProvider component to the form. This creates an ErrorProvider component in the component tray below the form. 2. In the Properties window, set the (Name) property of the ErrorProvider component to validerrorprovider Add validation code to the nametextbox control 1. On the form, click the nametextbox control. 2. In the Properties window, click Events, and then double-click the Validating event. This creates an event handler for the Validating event of the control.

32 9-30 Module 9: Validating User Input 3. In the namespace declaration section at the top of the file, reference the System.Text.RegularExpressions namespace that provides regular expression functionality. 4. In the nametextbox_validating event handler, implement the IsMatch method of the Regex class to check if the nametextbox control contains only: Alphabetic characters Spaces Periods Single quotes Between 1 and 50 characters 5. If the validation of the nametextbox control is incorrect: Cancel the event. Set the focus on the nametextbox control. Select all the text of the nametextbox control. Call the SetError method of the ErrorProvider component, passing the nametextbox control and the string Name invalid as parameters. Your code should resemble the following. [Visual C#] using System.Text.RegularExpressions;... private void nametextbox_validating(object sender, CancelEventArgs e) // If the name is invalid, cancel the event, set focus on the text box, // select all the text, and set an error message. if e.cancel = true; nametextbox.focus(); nametextbox.selectall(); validerrorprovider.seterror(nametextbox, "Name invalid"); [Visual Basic] Imports System.Text.RegularExpressions... Private Sub nametextbox_validating(byval sender As System.Object, ByVal e As _ System.ComponentModel.CancelEventArgs) Handles nametextbox.validating ' If the name is invalid, cancel the event, set focus on the text box, ' select all the text, and set an error message.

33 Module 9: Validating User Input 9-31 If Not Regex.IsMatch(nameTextBox.Text, "^[a-za-z\s'.]1,50$") Then e.cancel = True nametextbox.focus() nametextbox.selectall() validerrorprovider.seterror(nametextbox, "Name invalid") End If End Sub 6. On the View menu, click Designer. 7. On the form, click the nametextbox control. 8. In the Properties window, double-click the Validated event. 9. In the nametextbox_validated event handler, call the SetError method of the ErrorProvider component and pass the nametextbox control and an empty string as parameters. Your code should resemble the following. [Visual C#] private void nametextbox_validated(object sender, EventArgs e) // Clear the error message if the name is valid. validerrorprovider.seterror(nametextbox, ""); [Visual Basic] Private Sub nametextbox_validated(byval sender As System.Object, ByVal e As _ System.EventArgs) Handles nametextbox.validated ' Clear the error message if the name is valid. validerrorprovider.seterror(nametextbox, "") End Sub Add validation code to the phonemaskedtextbox control 1. On the View menu, click Designer. 2. On the form, click the phonemaskedtextbox control. 3. In the Properties window, click Properties, click the Mask property, and then click the ellipsis ( ) button. 4. In the Input Mask dialog box, click the Phone number mask, and then click OK. This adds a US phone number mask to the phonemaskedtextbox control. 5. In the Properties window, click Events, and then double-click the Validating event. 6. If you are using Visual C#: In Solution Explorer, right-click the SalesApplication project, and then click Add Reference. In the Add Reference dialog box, select Microsoft.VisualBasic, and then click OK.

34 9-32 Module 9: Validating User Input In the namespace declaration section at the top of the file, add a using statement to reference the Microsoft.VisualBasic namespace that provides Visual Basic functions. 7. In the phonemaskedtextbox_validating event handler, exclude the mask from the Text property by setting the TextMaskFormat property of the control to ExcludePromptAndLiterals. 8. If the Text property of the phonemaskedtextbox control is not a number or is not 10 characters in length: Cancel the event. Set the focus on the phonemaskedtextbox control. Select all the text of the phonemaskedtextbox control. Call the SetError method of the ErrorProvider component, passing the phonemaskedtextbox control and the string Phone number invalid as parameters. Your code should resemble the following. [Visual C#] using Microsoft.VisualBasic;... private void phonemaskedtextbox_validating(object sender, CancelEventArgs e) // Exclude prompt and literals from the text box. phonemaskedtextbox.textmaskformat = MaskFormat.ExcludePromptAndLiterals; // If the phone number is not a number or is fewer than 10 digits, cancel the // event, set focus on the text box, select all the text, and set an error // message. if (!Information.IsNumeric(phoneMaskedTextBox.Text) phonemaskedtextbox.text.length!= 10) e.cancel = true; phonemaskedtextbox.focus(); phonemaskedtextbox.selectall(); validerrorprovider.seterror(phonemaskedtextbox, "Phone number invalid"); [Visual Basic] Private Sub phonemaskedtextbox_validating(byval sender As System.Object, ByVal e _ As System.ComponentModel.CancelEventArgs) Handles phonemaskedtextbox.validating ' Exclude prompt and literals from the text box. phonemaskedtextbox.textmaskformat = MaskFormat.ExcludePromptAndLiterals ' If the phone number is not a number or is fewer than 10 digits, cancel the ' event, set focus on the text box, select all the text, and set an error ' message.

35 Module 9: Validating User Input 9-33 If Not IsNumeric(phoneMaskedTextBox.Text) OrElse Not _ phonemaskedtextbox.text.length = 10 Then e.cancel = True phonemaskedtextbox.focus() phonemaskedtextbox.selectall() validerrorprovider.seterror(phonemaskedtextbox, "Phone number invalid") End If End Sub Note: In a production application, you might need to validate additional criteria for the phone number. 9. On the View menu, click Designer. 10. On the form, click the phonemaskedtextbox control. 11. In the Properties window, double-click the Validated event. 12. In the phonemaskedtextbox_validated event handler, call the SetError method of the ErrorProvider component and pass the phonemaskedtextbox control and an empty string as parameters. Your code should resemble the following. [Visual C#] private void phonemaskedtextbox_validated(object sender, EventArgs e) // Clear the error message if the phone number is valid. validerrorprovider.seterror(phonemaskedtextbox, ""); [Visual Basic] Private Sub phonemaskedtextbox_validated(byval sender As System.Object, _ ByVal e As System.EventArgs) Handles phonemaskedtextbox.validated ' Clear the error message if the phone number is valid. validerrorprovider.seterror(phonemaskedtextbox, "") End Sub Add a mask and validation code to the dobmaskedtextbox control 1. On the View menu, click Designer. 2. On the form, click the dobmaskedtextbox control. 3. In the Properties window, click Properties, click the Mask property, and then click the ellipsis ( ) button. 4. In the Input Mask dialog box, click the Short date mask, and then click OK. This adds a date mask to the dobmaskedtextbox control. 5. In the Properties window, click Events, and then double-click the Validating event.

36 9-34 Module 9: Validating User Input 6. In the dobmaskedtextbox_validating event handler, call the IsDate Visual Basic function method to check if the Text property of dobmaskedtextbox control can be converted to a date. 7. If the dobmaskedtextbox control cannot be converted to a date: Cancel the event. Set the focus on the dobmaskedtextbox control. Select all the text of the dobmaskedtextbox control. Call the SetError method of the ErrorProvider component, passing the dobmaskedtextbox control and the string Date of birth invalid as parameters. 8. If the dobmaskedtextbox control can be converted to a date: Convert the Text property of the dobmaskedtextbox control to a date. Add 18 years to the date. If the date is greater than or equal to today s date: Cancel the event. Set the focus on the dobmaskedtextbox control. Select all the text of the dobmaskedtextbox control. Call the SetError method of the ErrorProvider component, passing the dobmaskedtextbox control and the string Person is under 18 as parameters. Your code should resemble the following. [Visual C#] private void dobmaskedtextbox_validating(object sender, CancelEventArgs e) // If the date of birth is not a date, cancel the event, set focus on the // text box, select all the text, and set an error message. if (!Information.IsDate(dobMaskedTextBox.Text)) e.cancel = true; dobmaskedtextbox.focus(); dobmaskedtextbox.selectall(); validerrorprovider.seterror(dobmaskedtextbox, "Date of birth invalid"); else // Convert the date and add 18 years. DateTime dateofbirth = DateTime.Parse(dobMaskedTextBox.Text); dateofbirth = dateofbirth.addyears(18); // If the date of birth is fewer than 18 years in the past, cancel the // event, set focus on the text box, select all the text, and set an // error message. if (dateofbirth >= DateTime.Now)

37 Module 9: Validating User Input 9-35 e.cancel = true; dobmaskedtextbox.focus(); dobmaskedtextbox.selectall(); validerrorprovider.seterror(dobmaskedtextbox, "Person is under 18"); [Visual Basic] Private Sub dobmaskedtextbox_validating(byval sender As System.Object, ByVal _ e As System.ComponentModel.CancelEventArgs) Handles dobmaskedtextbox.validating ' If the date of birth is not a date, cancel the event, set focus on the ' text box, select all the text, and set an error message. If Not IsDate(dobMaskedTextBox.Text) Then e.cancel = True dobmaskedtextbox.focus() dobmaskedtextbox.selectall() validerrorprovider.seterror(dobmaskedtextbox, "Date of birth invalid") Else ' Convert the date and add 18 years. Dim dateofbirth As DateTime = DateTime.Parse(dobMaskedTextBox.Text) dateofbirth = dateofbirth.addyears(18) ' If the date of birth is fewer than 18 years in the past, cancel the ' event, set focus on the text box, select all the text, and set an ' error message. If dateofbirth >= DateTime.Now Then e.cancel = True dobmaskedtextbox.focus() dobmaskedtextbox.selectall() validerrorprovider.seterror(dobmaskedtextbox, "Person is under 18") End If End If End Sub Note: In a production application, you might also need to validate additional criteria such as whether the date of birth is in the past. 9. On the View menu, click Designer. 10. On the form, click the dobmaskedtextbox control. 11. In the Properties window, double-click the Validated event. 12. In the dobmaskedtextbox_validated event handler, call the SetError method of the ErrorProvider component and pass the dobmaskedtextbox control and an empty string as parameters. Your code should resemble the following. [Visual C#] private void dobmaskedtextbox_validated(object sender, EventArgs e) // Clear the error message if the date of birth is valid. validerrorprovider.seterror(dobmaskedtextbox, "");

38 9-36 Module 9: Validating User Input [Visual Basic] Private Sub dobmaskedtextbox_validated(byval sender As System.Object, ByVal e As _ System.EventArgs) Handles dobmaskedtextbox.validated ' Clear the error message if the date of birth is valid. validerrorprovider.seterror(dobmaskedtextbox, "") End Sub Build and test the application 1. On the Build menu, click Build Solution. Verify that the solution builds without any errors. 2. On the Debug menu, click Start Debugging. 3. On the application, click New Sales Person. This opens the NewSalesPersonForm form. 4. In the Name box, type an invalid name. For example, an invalid name contains numbers, unusual symbols, or is greater than 50 characters in length. 5. To remove focus from the Name box, press TAB or click another control. This invokes the Validating event of the Name box. 6. Verify that the focus is set to the Name box, all the text is selected, and an error symbol appears next to the box. 7. Move the pointer over the error symbol and verify that a pop-up box displays the text Name invalid. 8. In the Name box, type a valid name, and then click the Phone box. This invokes the Validated event of the Name box. 9. Verify that the error symbol disappears. 10. In the Phone box, type an invalid phone number. For example, an invalid phone number is not 10 digits in length. 11. To remove focus from the Phone box, press TAB or click another control. 12. Verify that an error symbol appears next to the Phone box. 13. Move the pointer over the error symbol and verify that a pop-up box displays the text Phone number invalid. 14. In the Phone box, type a valid phone number, and then click the DoB box. 15. Verify that the error symbol disappears. 16. In the DoB box, type an invalid date.

39 Module 9: Validating User Input 9-37 For example, an invalid date is not a date or is fewer than 18 years in the past. 17. To remove focus from the DoB box, press TAB or click another control. 18. Verify that an error symbol appears next to the DoB box. 19. Move the pointer over the error symbol and verify that a pop-up box displays the text Date of birth invalid or Person is under 18, depending on the invalid date. 20. In the DoB box, type a valid date, and then remove focus from the DoB box. 21. Verify that the error symbol disappears. 22. Close the form and application.

40 9-38 Module 9: Validating User Input Exercise 2: Providing Visual Cues to the User by Enabling an OK Button In this exercise, you will initially disable the OK button by setting the Enabled property of the button to false. You will create three Boolean values and a method to enable and disable the OK button, depending on the validity of the Name, Phone, and DoB boxes. You will also set the OK button to be the accept button for the NewSalesPersonForm form. The principal tasks for this exercise are as follows: Set the Enabled property of the OK button to false. Create three Boolean values and a method to set the Enabled property of the OK button to true if the controls are valid. Set the Boolean values and call the CheckValidation method in the Validating event handlers. Set the accept button for the NewSalesPersonForm form. Set the Enabled property of the OK button to false 1. On the View menu, click Designer. 2. In design view, double-click the form. This creates a Load event handler for the form. 3. In the NewSalesPersonForm_Load event handler, set the Enabled property of the OK button to false. This disables the OK button when the form loads. You will add code to enable the OK button when all the text box controls are valid. Your code should resemble the following. [Visual C#] private void NewSalesPersonForm_Load(object sender, EventArgs e) // Disable the OK button. okbutton.enabled = false; [Visual Basic] Private Sub NewSalesPersonForm_Load(ByVal sender As System.Object, _ ByVal e As System.EventArgs) Handles MyBase.Load ' Disable the OK button. okbutton.enabled = False End Sub

41 Module 9: Validating User Input 9-39 Create three Boolean values and the CheckValidation method 1. In the NewSalesPersonForm class, declare three private Boolean values to store the validity of the text box controls. 2. Set all three Boolean values to false. 3. In the NewSalesPersonForm class, create a private method called CheckValidation that accepts no parameters and does not return a value. 4. In the CheckValidation method, enable the OK button if all the three Boolean values are true, otherwise disable the OK button. Your code should resemble the following. [Visual C#] // Create three Boolean values. private bool validname = false; private bool validphone = false; private bool validdate = false;... private void CheckValidation() // If all three Boolean values are true, enable the OK button, otherwise // disable the OK button. if (validname && validphone && validdate) okbutton.enabled = true; else okbutton.enabled = false; [Visual Basic] ' Create three Boolean values. Private validname As Boolean = False Private validphone As Boolean = False Private validdate As Boolean = False... Private Sub CheckValidation() ' If all three Boolean values are true, enable the OK button, otherwise ' disable the OK button. If validname AndAlso validphone AndAlso validdate Then okbutton.enabled = True Else okbutton.enabled = False End If End Sub

42 9-40 Module 9: Validating User Input Set the Boolean values and call the CheckValidation method in the Validating event handlers 1. In all three Validating event handlers, set the corresponding Boolean value to false and disable the OK button when validation fails. Note: In the dobmaskedtextbox_validating event handler, you need to set the corresponding Boolean value to false and disable the OK button inside both if statements. 2. In all three Validated event handlers, set the corresponding Boolean value to true and call the CheckValidation method. In the following example, the italicized text is specific for each Validating and Validated event handler. Your code should resemble the following. [Visual C#] private void control_validating(object sender, CancelEventArgs e) // If the control is invalid, cancel the event, set focus on the // text box, select all the text, and set an error message. if (!control is valid) e.cancel = true; control.focus(); control.selectall(); validerrorprovider.seterror(control, control error message); // Set the corresponding Boolean value to false and disable the OK button. controlboolean = false; okbutton.enabled = false; private void control_validated(object sender, EventArgs e) // Clear the error message if the control is valid. validerrorprovider.seterror(control, ""); // Set the corresponding Boolean value to true. controlboolean = true; // Call the method to check validation. CheckValidation(); [Visual Basic] Private Sub control_validating(byval sender As System.Object, ByVal e As _ System.ComponentModel.CancelEventArgs) Handles control.validating ' If the control is invalid, cancel the event, set focus on the ' text box, select all the text, and set an error message. If Not control is valid Then e.cancel = True control.focus() control.selectall() validerrorprovider.seterror(control, control error message)) ' Set the corresponding Boolean value to false and disable the OK button. controlboolean = False

43 Module 9: Validating User Input 9-41 okbutton.enabled = False End If End Sub Private Sub control_validated(byval sender As System.Object, ByVal e As _ System.EventArgs) Handles control.validated ' Clear the error message if the control is valid. validerrorprovider.seterror(control, "") ' Set the corresponding Boolean value to true. controlboolean = True ' Call the method to check validation. CheckValidation() End Sub Set the accept button for the NewSalesPersonForm form 1. On the View menu, click Designer. 2. In design view, click the form. 3. In the Properties window, click Properties, and then set the AcceptButton property to okbutton. This sets the accept button of the form to the OK button. Build and test the application 1. On the Build menu, click Build Solution. Verify that the solution builds without any errors. 2. On the Debug menu, click Start Debugging. 3. On the application, click New Sales Person. 4. In the Name box, type a valid name. 5. In the Phone box, type a valid phone number. 6. In the DoB box, type a valid date, and then remove focus from the control. The OK button will become enabled because all the controls on the form are valid. 7. In the Phone box, type an invalid phone number, and then remove focus from the control. The OK button will become disabled because at least one control on the form is invalid. 8. In the Phone box, type a valid phone number, remove focus from the control, and then press ENTER. This invokes the Click event handler of the OK button because this is the accept button of the form. 9. In the message box, click OK.

44 9-42 Module 9: Validating User Input 10. Close the application. Results Checklist The following is a checklist of results for you to verify that you have performed this lab successfully. Ensure that you: Added an ErrorProvider component to the NewSalesPersonForm form and implemented validation code for three text box controls. Enabled the OK button if all the three text box controls are valid. Lab Shutdown After you complete the lab, you must shut down the 4994A-LON-DEV-09 virtual machine and discard any changes. Important: If the Close dialog box appears, ensure that Turn off and delete changes is selected and then click OK.

45 Module 9: Validating User Input 9-43 Lab Discussion Discuss the following questions: Why might an ErrorProvider component be considered more useful than a message box? What are the key properties of an ErrorProvider component? How would you override validation and close a form that still contains invalid data? What is the disadvantage of overriding validation and closing a form that still contains invalid data?