How to select an element by Class instead of ID in ASP.NET?

c# asp.net select css-selectors selection
firedrawndagger picture firedrawndagger · May 4, 2010 · Viewed 43.2k times · Source

I have a few scattered <p> elements on the aspx page which I am grouping together using a class like so - <p class="instructions" runat="server">

In my code behind, using C# I want to hide these elements, using something like instructions.Visible = false;

However I realize I can only do this in codebehind if I use ID but this will result in invalid HTML/CSS Selector since you can't have multiple ID's with the same ID name...

Alternatively is there another way to group the controls if not by class?

EDIT: I can't use JavaScript, so the selection must be done in C# codebehind/ASP.NET

Answer

Sebastian P.R. Gingter picture Sebastian P.R. Gingter · May 4, 2010

The thing is quite easy. In your ASPX:

<p class="instructions" runat="server" OnPreRender="Paragraph_PreRender">

In your codebehind:

protected void Paragraph_PreRender(object sender; EventArgs e)
{
  Control paragraph = (Control)sender;
  paragraph.Visible = !paragraph.CssClass.Contains("instructions");
}

The codebehind will be hooked up automatically to the PreRender event handler in your class. This casts the sender to the control and sets its Visibility dependent on the css class. You just have to adjust the tags and you don't need a lot code traversing your control collection.

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