Home > ASP.NET and Dynamic Languages > Previous Topics > Walkthrough: Debugging

To create a file system Web site and an ASP.NET Web page

1. In Visual Studio, in the File menu, click New Web Site. The New Web Site dialog box is displayed.

2. In the Language list, click a dynamic language such as IronPython to make it the default language for the Web site.

   Note  You can use statically compiled languages in the same Web application by creating pages and components in different programming languages.

3. Under Visual Studio installed templates, click ASP.NET Web Site.
4. In the Location box, select the File System box, and then enter the name of the folder where you want to keep the pages of your Web site. For example, type the folder name C:\DebugWebSite.
5. Click OK. Visual Studio creates the folder and a new page named Default.aspx.

To add a page to the Web site

1. Close the Default.aspx page.
2. In Solution Explorer, right-click the name of your Web site and then click Add New Item.
3. Under Visual Studio installed templates, select Web Form.
4. In the Name box, enter DebugPage.aspx. The language defaults to your selected dynamic language.
5. Make sure that the Place code in separate file check box is checked.

   In this walkthrough, you are creating a page with the code in a separate file. The code for ASP.NET pages can be located either in the page or in a separate class file.

Note  In this release, there are small differences in the way breakpoints and watches can be set, depending on whether the code is in the page or in a separate file. The walkthrough calls out these differences.

6. Click Add.

To add controls and code for debugging

1. Switch to Design view, and then from the Standard tab of the toolbox, drag the following controls onto the page and set their properties as indicated:

   Control	Properties
   Label	ID: CaptionLabel Text: (empty)
   TextBox	ID: NumberTextBox Text: (empty)
   Button	ID: SquareButton Text: Square
   Label	ID: ResultLabel Text: (empty)

   Note  For this walkthrough, the layout of the page is not important.

2. Right-click the page and click View Code.

   In this release, event handlers must be coded and bound manually. You cannot create them by double-clicking a control in Design view or by selecting an event in the Properties window.

3. Add an event handler for the button's Click event, with logic to call a function named Square to square the number entered by the user. The handler might look like the following example.

   Note   The code example deliberately does not include error checking.

   		
   def SquareButton_Click(sender, e):
       number = float(NumberTextBox.Text)
       result = Square(number)
       ResultLabel.Text = '%s squared is %8.2f' % \
           (NumberTextBox.Text, result)
   

   IronPython
   
   
4. Switch to DebugPage.aspx and switch to Source view.
5. Bind the event handler to the SquareButton control by adding an OnClick attribute, as shown in the following example.

   <asp:Button ID="SquareButton" runat="server" Text="Square"
       OnClick="SquareButton_Click" />

6. Right-click the page and click View Code to return to the code file
7. Create the Square function that squares the number. Include a bug in the code, so that the function adds the number to itself instead of multiplying it.
   
   

   		
   def Square(number):
       return number + number
   

   IronPython
   
   
8. Add code to set the text of the CaptionLabel control to Enter a number: if this is the first time the page is running, and thereafter to Enter another number:. The handler will look like the following.
   
   

   		
   def Page_Load(sender, e):
       postback = sender.IsPostBack
       if IsPostBack:
           CaptionLabel.Text = "Enter another number: "
       else:
           CaptionLabel.Text = "Enter a number: "
   

   IronPython
   
   

   You can use the IsPostBack property by itself, as shown in the if statement, or qualified by sender, as shown in the assignment statement. When it is used by itself, it is recognized as a property of the script page just as it is in C# and Visual Basic. In the assignment statement, sender.IsPostBack is used because later in the walkthrough it illustrates a limitation of debugging in the current release.

   Note  In this case, sender and the implicit page reference happen to be the same, because Page_Load handles a page event.

9. Save the page.
10. Press CTRL+F5 to run the page without debugging.
11. Enter a number (other than 2) and press the Square button.

    Notice that the result is incorrect, because there is an intentional bug in the program.

12. Close the browser.

To set breakpoints

1. In Source view, set a breakpoint on the following line:
   
   

   		
   postback = sender.IsPostBack
   

   IronPython
   
   

   Note  When your code is in a separate file, you can toggle breakpoints by pressing F9, by right-clicking a line and choosing Breakpoint, or by clicking in the margin to left of the line. In this release, the only mechanism that works for code embedded in a Web page is clicking in the margin.

2. Set another breakpoint on the following line of the SquareButton_Click handler:
   
   

   		
   result = Square(number)
   

   IronPython
   
   

To run the debugger

1. In the Debug menu, click Start Debugging (or press F5) to run the page in debug mode.

   Note  The first time you debug, you will be prompted to modify the Web.config file to enable debugging. Debugging is disabled by default, for better performance.

   Because the breakpoint is in the Page_Load event handler, the page has not finished processing yet. The browser is open, but the page is not yet displayed.

2. Click the postback variable and press SHIFT+F9 to display its value in a Quick Watch window. The value is null.

Note  In this release, the Locals window, the Watch and QuickWatch windows, and the Immediate window are limited to local variables in IronPython, and do not yet work in Managed JScript.

3. Press F10 to execute the assignment statement, and check the value of postback (IronPython only) to see that it is now false.
4. In the Debug menu, click Windows and then click Locals.

   This opens the Locals window, which displays the values of variables and objects that are in scope at the current line being executed (IronPython only). The value of postback is false.

   Notice that sender, IsPostBack, CaptionLabel, and SquareButton do not appear in the Locals window.

5. In the Immediate window, use the question mark operator to examine the value of postback (IronPython only).

   The Immediate window display will look like the following:

   >? postback
   >false

6. In the Debug menu, click Windows, click Watch, and then click Watch 1 (IronPython only).

   Note:  If you are using Visual Studio Express Edition, the debugger offers only a single Watch window.

7. Right-click postback, then click Add Watch to add the postback variable to the watch.

   Note  In the current release, you cannot right-click to add a watch if the code is in the page instead of in a separate file. Instead, you can enter the name of the variable in the first cell of the Name column in the Watch window.

8. Press F10 several times to step through the if statement.

   When the last line of the if statement has executed, the execution pointer pauses on the next function. The body of the Page_Load method is still in scope, as you can see from examining the Locals window.

9. Press F5 to continue execution and display the page.
10. Enter the value 7 into the text box and click the Square button.

    The debugger is displayed again, with the breakpoint in the Page_Load event handler. Press F10 to execute the line. The Watch window shows that the value of postback is true.

11. Press F5 to continue.

    The debugger processes the Page_Load event handler and enters the SquareButton_Click handler, where it stops on the second breakpoint you set.

12. Press F11 to step into the Square function.
13. Continue stepping through the function until you return from it.

    Notice that the value of result still is not set (IronPython only).

14. Press F11 one more time, and note the incorrect value.

    In the current release, you have to stop the debugger in order to correct the code.

15. Press F5 to continue running the program.