Chapter 6. Multiform Projects The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill

Transcription

1 Chapter 6 Multiform Projects McGraw-Hill 2010 The McGraw-Hill Companies, Inc. All rights reserved.

2 Chapter Objectives - 1 Include multiple forms in an application Use a template to create an About box form Create a new instance of a form's class and show the new form Use the Show, ShowDialog, and Hide methods to display and hide forms Understand the various form events and select the best method for your code McGraw-Hill 2010 The McGraw-Hill Companies, Inc. All rights reserved. 6-2

3 Chapter Objectives - 2 Declare variables with the correct scope and access level for multiform projects Create new properties of a form and pass data values from one form to another Create and display a splash screen Run your project outside of the IDE McGraw-Hill 2010 The McGraw-Hill Companies, Inc. All rights reserved. 6-3

4 Using Multiple Forms Projects can appear more professional if different windows are used for different types of information Example: Display summary information on a well designed form instead of in a message box The first form a project displays is called the startup form A project can have as many forms as you wish McGraw-Hill 2010 The McGraw-Hill Companies, Inc. All rights reserved. 6-4

5 Select Add Windows Form from the Project menu Select from many installed templates in the Add New Item dialog box Choose Windows Forms in Categories list Choose Windows Form as the template Enter a name for the new form and click Add Creating New Forms - 1 McGraw-Hill 2010 The McGraw-Hill Companies, Inc. All rights reserved. 6-5

6 Creating New Forms - 2 After adding a new form, it appears on the screen and is added to the Solution Explorer window While in design time, switch between forms In the Solution Explorer window Select a form name, click View Designer or View Code button Use tabs at top of the Document window If too many tabs to display all of the forms, click the Active Files button to drop down a list and make a selection Each form is a separate class with separate files McGraw-Hill 2010 The McGraw-Hill Companies, Inc. All rights reserved. 6-6

7 Creating New Forms - 3 Click on tabs to switch between forms Drop down the list of active files and make a selection McGraw-Hill 2010 The McGraw-Hill Companies, Inc. All rights reserved. 6-7

8 Adding Existing Form Files to a Project Forms may be used in more than one project Use a form created for one project in a new project A form is saved as three separate files Extensions:.cs,.designer.cs, and.resx To add an existing form to a project, use Project/Add Existing Item Select only the FormName.cs file All three files for that form will be automatically copied into the project folder McGraw-Hill 2010 The McGraw-Hill Companies, Inc. All rights reserved. 6-8

9 Removing Forms from a Project Select the name of the file to be removed in the Solution Explorer and do one of the following: Press the Delete key Right-click the file name and choose Delete Choose Exclude From Project Removes the form from the project but does not delete the files McGraw-Hill 2010 The McGraw-Hill Companies, Inc. All rights reserved. 6-9

10 Creating a New Instance of a Form Each form in a project is a class which can be used to create a new object Similar to controls placed on forms Create a new instance of a form before it can be displayed McGraw-Hill 2010 The McGraw-Hill Companies, Inc. All rights reserved. 6-10

11 An About Box One popular type of form Found in most Windows programs under Help/About Displays the name and version of the program and information about the programmer or company Create an About box by adding controls to a standard Windows form McGraw-Hill 2010 The McGraw-Hill Companies, Inc. All rights reserved. 6-11

12 Using the About Box Template - 1 Choose Add Windows Form from the Project menu Select Windows Forms for Category Select About Box from the Templates list A new form named AboutBox1 is added to the project Set the properties of the controls on the form McGraw-Hill 2010 The McGraw-Hill Companies, Inc. All rights reserved. 6-12

13 Using the About Box Template - 2 A new form created with the About Box template Select the About Box template to add a preformatted AboutBox form to a project McGraw-Hill 2010 The McGraw-Hill Companies, Inc. All rights reserved. 6-13

14 Setting Assembly Information The About Box template form includes the product name, version, copyright, company name and description Open the Project Designer from Project/ProjectName Properties Click the Assembly Information button Fill in desired information in the Assembly Information dialog box Code behind AboutBox form retrieves and displays the entered Assembly Information McGraw-Hill 2010 The McGraw-Hill Companies, Inc. All rights reserved. 6-14

15 Displaying an About Form To display the About Box form (or any form), create a new object of the form's class in code Declare a new instance of the form using the keyword new // Create a new instance of the AboutBox1 form class. AboutBox1 aboutform = new AboutBox1(); Display the form using a Show or ShowDialog method // Show the new aboutform object. aboutform.showdialog(); McGraw-Hill 2010 The McGraw-Hill Companies, Inc. All rights reserved. 6-15

16 Showing a Form Show method displays a form as modeless Both forms are open and a user can navigate from one form to the other ShowDialog method displays a form as modal A user must respond to the form in some way No other program code can execute until the user responds to, hides, or closes a modal form McGraw-Hill 2010 The McGraw-Hill Companies, Inc. All rights reserved. 6-16

17 The Show and ShowDialog Methods General Form FormObjectName.Show(); FormObjectName.ShowDialog(); Examples SummaryForm asummaryform = new SummaryForm(); asummaryform.show(); SummaryForm asummaryform = new SummaryForm(); asummaryform.showdialog(); The code is generally placed in a menu item or button s click event handler McGraw-Hill 2010 The McGraw-Hill Companies, Inc. All rights reserved. 6-17

18 Hiding or Closing a Form Close a form using the Close method asummaryform.close(); The Close method behaves differently for a modeless form (using the Show method) compared to a modal form (using the ShowDialog method) Modeless Close destroys the form instance and removes it from memory Modal Close only hides the form instance If the same instance is displayed again, any data from the previous ShowDialog will still be there Using the form's Hide method sets the form object's Visible property to False and keeps the form object in memory ready to be redisplayed McGraw-Hill 2010 The McGraw-Hill Companies, Inc. All rights reserved. 6-18

19 Responding to Form Events Two primary events to write code for FormName.Load Occurs only the first time a form is loaded into memory FormName.Activated Occurs after the Load event, just as control is passed to a form Occurs each time the form is shown A good location to place initializing steps or set the focus in a particular place on the form McGraw-Hill 2010 The McGraw-Hill Companies, Inc. All rights reserved. 6-19

20 The Sequence of Form Events - 1 Load Occurs the first time a form is displayed Activated Occurs each time the form is shown Place initialization or SetFocus events here Paint Occurs each time any portion of the form is redrawn Happens each time a change is made or the form is moved or uncovered McGraw-Hill 2010 The McGraw-Hill Companies, Inc. All rights reserved. 6-20

21 The Sequence of Form Events - 2 Deactivate Occurs when the form is no longer the active form When a user clicks another window or the form is about to be hidden or closed FormClosing Occurs as the form is about to close FormClosed Occurs after the form is closed McGraw-Hill 2010 The McGraw-Hill Companies, Inc. All rights reserved. 6-21

22 Writing Event Handlers for Selected Events To write an event handler for a form event other than the Load event Click on the form to show its properties in the Properties window Click the Events button Double-click the desired event to create an empty event handler Properties button Events button Double-click on the event McGraw-Hill 2010 The McGraw-Hill Companies, Inc. All rights reserved. 6-22

23 Variables and Constants in Multiform Projects Private variables and constants within a form (or other class) cannot be seen by code in other classes Private is the default access level To declare variables as Public makes them available to all other classes Public variables present security problems and violate the principles of object oriented programming (OOP) The correct approach for passing variables from one form object to another is to set up properties of the form s class Use a property method to pass values from one form to another McGraw-Hill 2010 The McGraw-Hill Companies, Inc. All rights reserved. 6-23

24 Creating Properties in a Class Set a new property of a form class Need a private class-level variable to store the value Available only to methods and property blocks within the class Need public property methods to allow other classes to view and/or set the property When program creates objects from a class Need to assign values to the properties Class controls access to its properties through property methods McGraw-Hill 2010 The McGraw-Hill Companies, Inc. All rights reserved. 6-24

25 Property Blocks A class allows its properties to be retrieved or set with accessor methods in a property block get accessor method retrieves a property value Similar to a method declared with a return value Before the closing brace a return value must be assigned set accessor method assigns a value to the property Uses the value keyword to refer to the incoming value for the property Property block declared as public to allow external objects to access it Data type of incoming value for a set must match type of the return value of the corresponding get McGraw-Hill 2010 The McGraw-Hill Companies, Inc. All rights reserved. 6-25

26 The Property Block General Form // Class-level variable to hold the value internally. private DataType MemberVariable; public DataType PropertyName { get { return MemberVariable; } set { // Statements, such as validation. MemberVariable = value; } } Holds value of property internally Property name to "outside world". Use a "friendly" name Keyword that refers to the incoming value assigned to the property McGraw-Hill 2010 The McGraw-Hill Companies, Inc. All rights reserved. 6-26

27 The Property Block - Example private string lastnamestring; public string LastName { get { return lastnamestring; } set { lastnamestring = value; } } Holds the value of the property Name of property Retrieve the value of the property Assign a value to the property McGraw-Hill 2010 The McGraw-Hill Companies, Inc. All rights reserved. 6-27

28 Read-Only Properties In some instances, a property can be retrieved by an object but not changed Write a property block that contains only a get (creates a read-only property) // Private class-level variable to hold the property value. private decimal paydecimal; // Property block for read-only property. public decimal Pay { get { return paydecimal; } } McGraw-Hill 2010 The McGraw-Hill Companies, Inc. All rights reserved. 6-28

29 Write-only Properties A property that can be assigned by an object but not retrieved Write a property block that contains only a set (creates a write-only property) // Private class-level variable to hold the property value. private decimal hoursdecimal; // Property block for write-only property. public decimal Hours { set { hoursdecimal = value; } } McGraw-Hill 2010 The McGraw-Hill Companies, Inc. All rights reserved. 6-29

30 Applying the Properties to Multiple Forms - 1 From a main form, pass a total to a summary form The summary form Create a private variable (totalsummarysalesdecimal) to hold the value for the total Create a property set method (TotalSales) to allow the value to be assigned The main form Pass the value from the private variable (totalsalesdecimal) to the property of the summary form (TotalSales) Stored internally in the SummaryForm as totalsummarysalesdecimal Assign the private variable (totalsalesdecimal) to the property of the summary form (TotalSales) Show the summary form McGraw-Hill 2010 The McGraw-Hill Companies, Inc. All rights reserved. 6-30

31 public partial class SummaryForm : Form { private decimal totalsummarysalesdecimal; public decimal TotalSales { set { totalsummarysalesdecimal = value; } } //... More code for the rest of the form class Applying the Properties to Multiple Forms - 2 //Event-handling method in the main calculation form. private void summarybutton_click(object sender, EventArgs e) { // Display the summary form. SummaryForm asummaryform = new SummaryForm(); } asummaryform.totalsales = totalsalesdecimal; asummaryform.showdialog(); McGraw-Hill 2010 The McGraw-Hill Companies, Inc. All rights reserved. 6-31

32 Passing Summary Values among Forms To maintain the value of a property for multiple instances of a class Declare the property as static Static variables retain their value for every object instantiated using the new keyword Static keyword is used on both the private variable and property method A static keyword in a property method creates a public property that can be accessed from anywhere in the project A specific object of the class does not have to be instantiated McGraw-Hill 2010 The McGraw-Hill Companies, Inc. All rights reserved. 6-32

33 A Splash Screen Displays a logo or window while a program is loading Splash screens tell the user the program is loading and starting Makes a large application appear to load and start faster McGraw-Hill 2010 The McGraw-Hill Companies, Inc. All rights reserved. 6-33

34 Creating a Splash Screen Simply another form in a project Eliminate the title bar and close button Timer component will control length of time splash screen appears Set the StartPosition to CenterScreen Leave Text property blank Set ControlBox to false Add graphics and any additional information on the form Many programs display AssemblyInfo on Splash screen McGraw-Hill 2010 The McGraw-Hill Companies, Inc. All rights reserved. 6-34

35 Controlling the Time a Splash Form Displays In a large application, the splash form displays while the rest of the application loads For a small application, use a Timer component to hold the form on the screen Add a Timer component to the splash form Set the Enabled property to true Set the Interval property to the number of milliseconds Example: set to 5000 for 5 seconds The timer s Tick event fires when the interval passes Close the form in the Tick event handler McGraw-Hill 2010 The McGraw-Hill Companies, Inc. All rights reserved. 6-35

36 Making the Splash Form Display First - 1 C# Programs begin execution in the Program.cs file, which appears in the Solution Explorer Open Program.cs in the Editor Add the code to instantiate and show the splash form Using ShowDialog, the main form does not appear until the splash form closes Using Show, the main form appears behind the splash form McGraw-Hill 2010 The McGraw-Hill Companies, Inc. All rights reserved. 6-36

37 Making the Splash Form Display First - 2 The Program.cs file with the code added to show the splash form static void Main() { Application.EnableVisualStyles(); Application.SetCompatibleTextRenderingDefault(false); SplashForm asplashform = new SplashForm(); asplashform.showdialog(); Application.Run(new MainForm()); } Add these two statements to display the splash form MainForm is the name of the startup form Change this if you change the startup form McGraw-Hill 2010 The McGraw-Hill Companies, Inc. All rights reserved. 6-37

38 Running Your Program Outside the IDE The.exe file is in the project s bin\debug folder It can be moved to another computer, placed on the system desktop, or used as a shortcut, like any other application To copy the.exe file to another computer, make sure it has the correct version of the Microsoft.NET Framework The framework can be downloaded for free from the Microsoft Web site You can change the program's icon in the Project Designer (Project/ProjectName Properties) Application tab, click Browse button next to Icon and browse to another file with an.ico extension Recompile after setting a new icon McGraw-Hill 2010 The McGraw-Hill Companies, Inc. All rights reserved. 6-38