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Using CSS class selectors in server controls

From: ASP.NET Essential Training

Video: Using CSS class selectors in server controls

Website developers who are accustomed to using Cascading Style Sheets to affect the appearance of their HTML elements might be used to using ID selectors. An ID selector is a Cascading Style Sheet selector that applies its properties to only one element of the page matched by the ID. For example, in the current version of the header control the panel with an ID of menuPanel, which is wrapped around the anchor tags that make up the menu, is identified by the phrase menuPanel. I have used the Cascading Style Sheet class of the same name but they aren't related to each other.

Using CSS class selectors in server controls

Website developers who are accustomed to using Cascading Style Sheets to affect the appearance of their HTML elements might be used to using ID selectors. An ID selector is a Cascading Style Sheet selector that applies its properties to only one element of the page matched by the ID. For example, in the current version of the header control the panel with an ID of menuPanel, which is wrapped around the anchor tags that make up the menu, is identified by the phrase menuPanel. I have used the Cascading Style Sheet class of the same name but they aren't related to each other.

If I wanted to modify this panel and I wanted to apply it using an ID selector, I would go back to styles.css and instead of putting a period, I would put in the pound sign. Now I'm taking about the menuPanel ID, rather than the menuPanel class. There is a problem with this approach in ASP.NET that you must know about. When you had cleared an ASP.NET server control such as asp:panel and you place it within a custom control, such as this Header control, at one time the ID is rewritten using a combination of the ID of the control in the page plus the ID of the element within the control.

I am going to demonstrate this by modifying styles.css to use the pound sign instead of the dot. Meaning, I'm matching by ID rather than by class. Then I'll go back to the page Default.aspx and run it in the browser. Notice that the appearance of the menu, including the border around it, the padding and so on, that I had to clear using the class selector that no longer applies. Here's why. I will right click anywhere on the page and select View Source. Then I'll scroll down to the generated code for the panel. Here it is. It's a Div tag with an ID. You will see that the ID consists of the ID of the control instance in the page, which was header 1, and the ID of the control itself within the server control which was menuPanel.

So, they are not matching up with each other. I'll close the text editor and the browser. I'll also show you where the prefix of the ID is coming from. From the declaration of the ID in the instance of the header control. So if you want to use ID selectors to match up your HTML element Ids with Cascading Style Sheet rules, here is what you have to do. I will go back to styles.css and I'll modify my selector to match what will be generated by .NET. header1_menuPanel. I'll save those changes by pressing Ctrl+S, go back to the page and run it again. This time when the menu appears I see the styles kick in, including the border and the padding that I had declared.

Now that I'm matching up by ID, I can go back to the Header file and I no longer need the CSSClass declaration. I'm matching up the menu selector by a combination of the top-level page's ID as it declares the instance of the server control plus the id of the menuPanel. The problem with this approach is that you now have to make sure that you are using exactly the same declaration ID in every single page. If you change it, you will have differences from one page to another. So therefore, my preference when working with ASP.NET server controls, especially those that are embedded within custom controls, is to use class selectors.

These won't be modified at runtime by ASP.NET. So I'll return all these pages to their original settings. I'll put the CSSClass attribute back inside the Header.ascx file. I'll go back to styles.css and change my selector back to a class selector. I'll save all my changes by selecting File > Save All. Go back to the page and run it one more time without debugging. See that the design of the pages is still intact. So again, rule of thumb. When you declare controls within custom controls and you want to apply Cascading Style Sheets to them on a global basis throughout the website, use Cascading Style Sheet classes rather than Ids for the best long term maintainability of your website.

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ASP.NET Essential Training

79 video lessons · 48794 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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