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Debugging with breakpoints

From: ASP.NET Essential Training

Video: Debugging with breakpoints

Another tool that you can use when you are programming in either Visual Basic or C# and you want to see what's going on inside the code is to set breakpoint. A breakpoint is a way of marking the bit of code, so that when you hit the break point the application is suspended for a moment. As long as the breakpoint is active, you can then inspect the values of variables and other aspects of your application state. For this demonstration I'll start with the file LoopingCSharp. aspx. This file already has the For and the While loops inside the Run Button Click method.

Debugging with breakpoints

Another tool that you can use when you are programming in either Visual Basic or C# and you want to see what's going on inside the code is to set breakpoint. A breakpoint is a way of marking the bit of code, so that when you hit the break point the application is suspended for a moment. As long as the breakpoint is active, you can then inspect the values of variables and other aspects of your application state. For this demonstration I'll start with the file LoopingCSharp. aspx. This file already has the For and the While loops inside the Run Button Click method.

I will save this file under a new name, naming the new version Breakpoints.aspx. You can set a breakpoint on any line of code. You can do this in a couple of ways. One approach to creating breakpoint is to right click on the line and then select Breakpoint, Insert Breakpoint. You will see that that results in selecting the code and highlighting it and you will also see a really large graphic on the left side of the screen in what's called the gutter area, right next to the line numbers.

You can also set and clear breakpoints just by double clicking on that area. So I have double-clicked and you will see that the breakpoint is gone. Then I'll double-click again and you will see that the breakpoint comes back. Now when you set a breakpoint you then have to turn on debugging. By default, in ASP.NET website that's created in Visual Web Developer has debugging turned off. But in order to use the breakpoint and suspend the page as it's running you have to turn debugging on. You can do this through the web.config file explicitly or you can get Visual Web Developer to do it for you just by telling Visual Web Developer that you want to debug the page.

Here is how you do it. I have already set a breakpoint on the For loop. I'll set one on this line with the While loop as well. So now I'll be hitting the breakpoint right before I output the value of the counter variable in both loops. Now I'll go to the menu and select Debug and now for the first time, I'll select Start Debugging. Visual Web Developer detects that this website is not configured to run in Debug mode. So it asks me whether I would like to modify the web.config file to allow debugging. There is also an important note that before you deploy the website to a production environment you should turn debugging off.

I will use the default selection to modify the web.config file and click OK. Visual Web Developer also detects whether Script Debugging is turned on or off. If you want to debug your client side code, you should turn the Script Debugging on. Here though, I'm only debugging server-side code. So I'll say Yes, I want to continue debugging. It takes a moment for the page to be rebuilt and then appear in the web browser. The first time you go into debugging in this context, you may see that the web browser doesn't automatically take focus. If that happens, just click the browser icon down on the task bar.

Now I'll click the Run Code button you will see that I hit the breakpoint in the For loop. The current line that is being suspended is highlighted in yellow and you will also see the breakpoint listed over on the left side. Down at the bottom in the Locals panel, you will see a listing of all available arguments. The counter variable, which was declared inside the function, is listed there with its initial value of 1. Now to continue executing the code, I'll go to the Toolbar and click the Continue button which is a little arrow pointing to the right. Each time I click it executes the code until it gets to another breakpoint and keep your eye down here on the counter variable and you will see that each time I click the Continue button, the counter variable is updating. I'll Continue again and now I'm hitting the breakpoint in the While loop and I'll click it again. One more time and this time because I have gotten out of all the loops, I'll see that the browser comes back and shows me the result of the code.

Now I'm going to execute the breakpoint one more time to show you one very important thing. I'll clear the console and then run the code again. I'll continue a couple of times and you will see that I have hit the output function twice. I'll press Alt+Tab and switch back to the browser and show you that the output doesn't appear in the browser because until you have completed executing the entire page, the content doesn't get sent back to the browser. I will press Alt+Tab again and switch back to Visual Web Developer. I'll click Continue, Continue again and one more time and now I come back to the webpage in the browser because its code has been completed and all of the response has been sent back to the browser and as being displayed appropriately.

So that's basically how you use breakpoints. You place the breakpoint on the line that you want to suspend on while the page is running and then when you hit the breakpoint you will come back to Visual Web Developer and you will be able to use the Locals panel to inspect the data. There are other debugging panels available as well. The Watch panel allows you to put an arbitrary expressions up to a certain point and see what their values are and you can also use the Call Stack, the Immediate Window and the Output panel which you see regularly but which has more detailed information when you are in Debug mode.

When you are done debugging just close the browser and when you come back to Visual Web Developer, it automatically removes those additional panels and shows you the original window layout.

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This video is part of

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ASP.NET Essential Training

79 video lessons · 48752 viewers

David Gassner
Author

 
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  1. 18m 44s
    1. Welcome
      1m 42s
    2. Prerequisites
      2m 21s
    3. Using the exercise files
      1m 32s
    4. Upgrading exercise file websites for ASP.NET 4.5 (NEW)
      2m 40s
    5. What's new in ASP.NET 4 (NEW)
      3m 48s
    6. What's new in ASP.NET 4.5 (NEW)
      3m 23s
    7. What's new in this course update (NEW)
      3m 18s
  2. 33m 34s
    1. Understanding how ASP.NET works
      5m 52s
    2. Installing Microsoft Visual Web Developer 2008
      3m 43s
    3. Installing Visual Studio Express 2012 for web (NEW)
      2m 12s
    4. Hello World: Creating your first ASP.NET web site
      4m 28s
    5. Creating pages with dynamic output
      7m 39s
    6. Understanding the development web server
      4m 49s
    7. Exploring the development environment
      4m 51s
  3. 40m 2s
    1. Understanding Microsoft SQL Server
      5m 47s
    2. Installing SQL Server Express
      6m 51s
    3. Exploring SQL Server Management Studio Basic
      4m 23s
    4. Creating a new database
      8m 51s
    5. Connecting to the database in ASP.NET
      5m 35s
    6. Testing SQL queries
      3m 53s
    7. Presenting a dataset in an ASP.NET page
      4m 42s
  4. 25m 31s
    1. Understanding ASP.NET web form pages
      5m 51s
    2. Separating presentation and logic with code files
      4m 17s
    3. Adding web form controls to a page
      5m 25s
    4. Handling postback data in a web form page
      5m 50s
    5. Using data binding expressions
      4m 8s
  5. 48m 37s
    1. Creating a testing environment
      4m 40s
    2. Declaring and using a simple variable
      6m 14s
    3. Declaring and using a complex object
      6m 16s
    4. Using loops
      6m 52s
    5. Using functions
      9m 25s
    6. Using trace statements
      4m 47s
    7. Debugging with breakpoints
      5m 45s
    8. Commenting code
      4m 38s
  6. 17m 43s
    1. Creating web controls
      5m 53s
    2. Registering a user control on a web form page
      3m 25s
    3. Registering controls globally in the web.config file
      3m 53s
    4. Adding public properties to a web control
      4m 32s
  7. 19m 7s
    1. Understanding Cascading Style Sheets (CSS)
      5m 36s
    2. Attaching external CSS files
      3m 12s
    3. Defining a CSS selector
      6m 10s
    4. Using CSS class selectors in server controls
      4m 9s
  8. 30m 34s
    1. Presenting data with the GridView control
      5m 49s
    2. Controlling GridView paging and appearance
      5m 46s
    3. Editing data with the GridView control
      6m 57s
    4. Presenting data with the DataList control
      5m 42s
    5. Formatting data with binding expressions
      6m 20s
  9. 36m 46s
    1. Using the DetailsView control
      7m 33s
    2. Inserting data with the DetailsView control
      6m 36s
    3. Redirecting page requests
      9m 39s
    4. Creating an update page
      6m 20s
    5. Linking to update pages from the list page
      4m 3s
    6. Deleting database records
      2m 35s
  10. 22m 15s
    1. Customizing forms with item editing templates
      6m 7s
    2. Adding validator controls to a form
      6m 40s
    3. Controlling the validation error message display
      6m 24s
    4. Using the ValidationSummary control
      3m 4s
  11. 29m 49s
    1. Creating a query with joined tables
      8m 6s
    2. Replacing control style properties with CSS
      5m 50s
    3. Creating a CSS file for printing
      3m 14s
    4. Suppressing elements in printed web pages
      5m 47s
    5. Selecting data for a report
      6m 52s
  12. 11m 14s
    1. Understanding ViewState and managing postbacks
      4m 36s
    2. Using session variables
      6m 38s
  13. 20m 57s
    1. Turning on forms authentication
      1m 51s
    2. Creating a page to log in users
      4m 18s
    3. Creating a page to set up new users
      4m 6s
    4. Understanding the security database
      3m 27s
    5. Configuring security in the web.config file
      2m 59s
    6. Creating a page to log out users
      4m 16s
  14. 27m 56s
    1. Installing IIS on Windows XP
      6m 32s
    2. Installing ASP.NET 3.5 on Windows XP
      1m 39s
    3. Deploying a site on Windows XP
      5m 9s
    4. Installing Information Internet Services (IIS) on Windows Vista, Windows 7, and Windows 8
      1m 56s
    5. Configuring ASP.NET 3.5 on Windows Vista
      2m 15s
    6. Deploying an application on Windows Vista
      3m 29s
    7. Scripting a database for deployment
      3m 36s
    8. Exporting database scripts in SQL Server Management Studio 2012 (NEW)
      3m 20s
  15. 2m 0s
    1. Where to go from here
      2m 0s

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