Completing a Web Form in ASP.NET - How to add code to a form
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To add the functionality required by a web form, you add Visual Basic code to its code-behind file. This code responds to the events that the user initiates on the form. This code also responds to events that occur as a form is processed.
How to use the Code Editor
To create and edit Visual Basic code, you use the Code Editor shown in figure 2-14. The easiest way to display the Code Editor window is to double-click the form or a control in the Web Forms Designer window. That displays the code-behind file for the form.
If you double-click the form in Design view, Sub and End Sub statements for the Load event of the page are generated. If you double-click a control, Sub and End Sub statements for the default event of the control are generated. If you double-click on a button control, for example, an event procedure (or event handler) for the Click event of that control is created. Then, you can enter the code for that procedure between the generated Sub and End Sub statements.
To create procedures for other events, you can use the drop-down lists at the top of the Code Editor window. The list at the left side of the window includes all of the available objects. When you select one of these objects, the list at the right side of the window lists all the events for that object. When you select an event, Visual Studio generates Sub and End Sub statements for the event handler.
You can also code general procedures by entering code directly into the Code Editor window. To create a Sub procedure, for example, you enter a Sub statement. And to create a Function procedure, or just function, you enter a Function statement. When you press the Enter key after entering one of these statements, the End Sub or End Function statement is generated for you. Then, you can enter the code required to implement the procedure between these statements, and you can call the procedure from another procedure.
As you work with the Code Editor, you’ll notice that it provides some powerful features that can help you code more quickly and accurately. One of the most useful of these features is the Auto List Members feature provided by IntelliSense. This feature displays a list of members that are available for an object when you type the object name and a period. Then, you can highlight the member you want by clicking on it, typing the first few letters of its name, or using the arrow keys to scroll through the list. In this figure, you can see the members that are listed for a drop-down list after the first character of the member name is entered. When you press the Tab key, the member you select is inserted into your code.
You can also use the Text Editor toolbar to work with code in the Code Editor. You can use it to perform functions such as commenting or uncommenting several lines of code at once, increasing or decreasing the indentation of several lines of code, and working with bookmarks. If you experiment with this toolbar, you should quickly see how it works.
A project with the Code Editor window displayed
Figure 2-14. How to use the Code Editor
Three ways to open or switch to a file in the Code Editor window
- Select a web form in the Solution Explorer and click the View Code button at the top of the Solution Explorer. Double-click on a Visual Basic file (.aspx.vb or .vb) in the Solution Explorer. Or, click on a tab at the top of the Web Forms Designer (if the file is already open).
Four ways to start an event procedure
- Double-click on a blank portion of a web form to start an event procedure for the Load event of the page.
- Double-click on a control in the Web Forms Designer to start an event procedure for the default event of that control.
- Select a control in the Web Forms Designer, click the Events button in the Properties window (the button with the lightening bolt), and double-click the event you want to create an event procedure for.
- Select a control from the drop-down list at the top left of the Code Editor window, and select an event from the drop-down list at the top right. To create an event procedure for a page event, select (Page Events) from the first drop-down list.
Description
- The Code Editor includes powerful text editing features such as automatic indentation, syntax checking, and statement completion (as shown above).
- To enter a Sub procedure or function, you type the procedure or function from scratch, but Visual Studio will insert the End Sub or End Function statement.
Next: How to use page and control events >>
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 This article is excerpted from the book Murach's ASP.NET 2.0 Web Programming with VB2005, written by Doug Lowe (Murach, 2006; ISBN: 1890774324). Check it out today at your favorite bookstore. Buy this book now.
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