Question

I have a textbox with a Css class called ‘required’. When a user click a button, I’d like to add additional Css Class to the textbox called ‘error’ without removing the ‘required’ class. I want to accomplish this from code-behind.

Answer 1

You can set the CssClass property of the ASP.NET Textbox control. To add more than one CSS class for an element, just separate it with a space:

MyTextBox.CssClass = "class1 class2";

You can put this in your OnClick event handler:

<asp:TextBox ID="MyTextBox" runat="server" OnClick="MyTextBox_Click" />

Then in code-behind:

void MyTextBox_Click(Object sender, EventArgs e) {
    MyTextBox.CssClass = "class1 class2";
}