Lab 4: Adding a Windows User-Interface

Transcription

1 Lab 4: Adding a Windows User-Interface In this lab, you will cover the following topics: Creating a Form for use with Investment objects Writing event-handler code to interact with Investment objects Using Windows controls to improve access to objects The Investment application developed over labs 2 and 3 is functional but appears clunky when measured against most Windows applications. This is mainly due to the character mode interaction that is used in a console application. In this lab, we will create a new project which makes use of the Investment class but adds a more polished user-interface. 1. Starting the new project Start up Visual Studio as usual, and select to create a new Windows application: From the Start Page in Visual Studio, select the New Project button, and from the New Project dialog box, choose a Visual Basic Windows application. Apply the name InvestmentUI to the project 2. Creating a main User-Interface Configure the default Form in the project. When the project is open, double click on the entry for Form1 in the Solution Explorer, and in the properties window, change its name to frminvestments. Change its caption (the Text property) to Investment Advisor Add a Button to the form (select the Button control from the Toolbox) and configure it using the Properties window so that its Name property is btnaddinvestment and its Text property is Add Investment. Resize the button so that the new text fits snugly and position it just in from the top left of the form Add a ListBox to the form, and change its Name property to lstinvestments. Move it to the right of the button control, and change its size so that it fills most of the form width from the right of the button to the right edge of the form, and it occupies most of the form height The form should appear as shown in figure L4.1. Note that the default form in a Visual Studio Windows program is the one that will automatically show when the project starts up. Now that we have the appearance of the main form in the Windows program set up, we will need to write code for it to create and display investments. For this, we must incorporate the Investment class into the project. A.McMonnies, CIS Page 1 03/11/2003

2 Figure L4.1: The main form of the InvestmentUI application One amendment we must make having changed the name of the form is to alter the project s Start-Up object. This is a setting that defines which form in a Windows program is automatically loaded when the program is run. Currently the program expects Form1 to be the start-up object, but since we have changed its name, we must amend this: Change the Start-Up Object setting by selecting Project Properties from the menus, and selecting frminvestments from the Start-Up Object pull-down list (see figure L4.2) Figure L4.2: Changing the project s Start-Up object 3. Importing the Investment class We can add the existing class that we created in the earlier project directly to our Visual Basic project. In the Solution Explorer, right-click on the project name (InvestmentUI), and from the context menu, select Add Add Existing Item In the Add Existing Item dialog box, navigate to the Lab 3 project (if you have been using the recommended folder structure, click on the up arrow to move to the parent directory, and then A.McMonnies, CIS Page 2 03/11/2003

3 double-click on the Investment directory if not, you need to locate the folder containing project you created for Lab 3) Select the Investment.vb file and click Open (see figure L4.3) Figure L4.3: Adding the existing Investment class to the project 4. Amend the Investment class In the Windows project, we will use the ListBox to manage a collection of Investments. Since the primary purpose of a normal ListBox is to display a list of items as textual descriptions, we will need to add some code to the Investment class to enable this. Each Investment object will be given a Title member, and we will make use of this when we display an investment in the list box. We will also provide an alternative display method so that the summary of an investment can be displayed properly in a Windows MessageBox. Add a Title property to the Investment class. A nominated property can be set to display automatically in a ListBox control provided it is defined as a true property, so adding the property is done in two stages: 1. Define the data member that will store the title of an investment as a Private member variable: Public Class Investment Public Capital As Decimal Public PIR As Single Public Duration As Single Private mytitle As String 'Add this line 'Other code... End Class 2. Add a Property definition to the class code 'Other code... Public Property Title() Get Return mytitle End Get A.McMonnies, CIS Page 3 03/11/2003

4 Set(ByVal Value) mytitle = Value End Set End Property End Class The operation of the property is now defined so that a statement that access the Title of an Investment will be returned the value stored in the mytitle member variable. Updating the Title property will actually cause the mytitle member variable to update. 2. To make the outcome of an investment more useful in a Windows environment, add the following method: Public Overrides Function ToString() As String Return String.Format(" {0} invested at {1}% over {2} years" & _ " produces a return of {3}", Capital, PIR, Duration, ROI) End Function These amendments will make the Investment class more usable in a Windows environment, and also simplify the display of Investment objects in a ListBox. 4. Add User-Interface code to add and display investments A very small amount of code will now suffice to allow our Windows form to interact with Investments. Add code to the Click event handler for btnnewinvestment, as follows: 3. Bring the form designer to the front of the design area by either double-clicking on its entry in the Solution Explorer, or selecting the frminvestments[design] tab at the top of the design area 4. Double-click on the Add Investment button. The form s code window will appear, with the outline of the appropriate event handler in place, ready for you to type the code. Enter all of the statements inside the event handler shown below (all the ones in Bold print) (Note, I have broken up the first line to make it easier to read on the printed page) Private Sub NewInvestment(ByVal sender As System.Object, _ ByVal e As System.EventArgs) Handles btnaddinvestment.click Dim I As New Investment I.Title = InputBox("Enter a title for this investment.") I.Capital = InputBox("Enter the amount to be invested.") I.Duration = InputBox("Enter the number of years to invest for.") I.PIR = InputBox("Enter the Percentage Interest Rate.") lstinvestments.items.add(i) End Sub When you run the application, you should now be able to add an investment by pressing the Add Investment button and entering details as requested. The overall outcome of an investment should appear in the ListBox. This is not ideal, but we need only make a small alteration to make the investments list by Title instead: A.McMonnies, CIS Page 4 03/11/2003

5 Make sure the application is not running (press the Stop button on the toolbar, or close the form by pressing its close button ) Bring the Form design window to the front if it is not there already Select the lstinvestments list box by clicking on it Change the list box s DisplayMember property to Title Run the program and again add an Investment. This time, the Title you gave the Investment should display in the ListBox. To display the details of an Investment, we need only arrange to show any investment that the user selects (form the list box) in a standard MessageBox. Double-Click on the list box in the form designer window. A code window should open up Exercises: with the following event handler outline in place. Simply add the statements shown in bold to the event handler (note that again I have broken up the first line to make it easier to read): Private Sub lstinvestments_selectedindexchanged( _ ByVal sender As System.Object, _ ByVal e As System.EventArgs) _ Handles lstinvestments.selectedindexchanged If lstinvestments.selecteditems.count > 0 Then MessageBox.Show(lstInvestments.SelectedItem.ToString()) End If End Sub 1. In Lab 3, you added a Sub to the main module so that the best of a list of investments could be located and displayed. Add a button to the form (name it btnmax and give it the Text label Maximum Investment) and code it s click event handler to locate the best investment and display its details in a MessageBox. 2. By changing the DisplayMember property of the list box to Title, you set it up to automatically display the Title of each investment added. Try clearing this setting and investigate the effect by comparing a number of investments. Note that you will probably need to make the form and the list box wider to make all of the data visible Having completed this lab, you should be able to: Create a Windows application that uses a form with controls as a user-interface to interact with objects Add code to event handlers that creates objects and interacts with them Display information from individual objects and collections, using windows resources as appropriate A.McMonnies, CIS Page 5 03/11/2003