Add CSS class to a div in code behind

Question

I have a div and I am trying to add a CSS class to it in code but I receive the following error when I try

Property or indexer 'System.Web.UI.HtmlControls.HtmlControl.Style' cannot be assigned to -- it is read only 

I am using the following code:

protected void BTNEvent_Click(object sender, ImageClickEventArgs e) {     BtnventCss.Style= "hom_but_a";                  } 

Can anyone please help me?

Answer 1

What if:

 <asp:Button ID="Button1" runat="server" CssClass="test1 test3 test-test" /> 

To add or remove a class, instead of overwriting all classes with

   BtnventCss.CssClass = "hom_but_a" 

keep the HTML correct:

    string classname = "TestClass";      // Add a class     BtnventCss.CssClass = String.Join(" ", Button1                .CssClass                .Split(' ')                .Except(new string[]{"",classname})                .Concat(new string[]{classname})                .ToArray()        );       // Remove a class      BtnventCss.CssClass = String.Join(" ", Button1                .CssClass                .Split(' ')                .Except(new string[]{"",classname})                .ToArray()        ); 

This assures

• The original classnames remain.
• There are no double classnames
• There are no disturbing extra spaces

Especially when client-side development is using several classnames on one element.

In your example, use

   string classname = "TestClass";      // Add a class     Button1.Attributes.Add("class", String.Join(" ", Button1                .Attributes["class"]                .Split(' ')                .Except(new string[]{"",classname})                .Concat(new string[]{classname})                .ToArray()        ));       // Remove a class      Button1.Attributes.Add("class", String.Join(" ", Button1                .Attributes["class"]                .Split(' ')                .Except(new string[]{"",classname})                .ToArray()        )); 

You should wrap this in a method/property ;)