John's Technology Blog

RadioButton CheckedChanged event doesn't fire if default value is checked

Posted at: March 27, 2012
Related Topic(s): ASP.NET

Whether a bug or by design, if you have a radio button with autopostback set to true and you set the default value to true, the CheckedChanged event will not fire if the RadioButton is the trigger for an AJAX UpdatePanel but outside of the panel.

This can be reproduced using the following sample code:

Markup:

<asp:ScriptManager ID="ScriptManager" runat="server"></asp:ScriptManager>
<p><asp:RadioButton ID="rdoOne" runat="server" AutoPostBack="true" Checked="true" GroupName="Radios" OnCheckedChanged="rdoOne_CheckedChanged" Text="One" /></p>
<p><asp:RadioButton ID="rdoTwo" runat="server" AutoPostBack="true" GroupName="Radios" OnCheckedChanged="rdoTwo_CheckedChanged" Text="Two" /></p>
<asp:UpdatePanel ID="panResult" runat="server">
	<ContentTemplate>
		<p><asp:Literal ID="litResult" runat="server"></asp:Literal></p>
	</ContentTemplate>
	<Triggers>
		<asp:AsyncPostBackTrigger ControlID="rdoOne" EventName="CheckedChanged" />
		<asp:AsyncPostBackTrigger ControlID="rdoTwo" EventName="CheckedChanged" />
	</Triggers>
</asp:UpdatePanel>

protected void rdoOne_CheckedChanged(object sender, EventArgs e)
{
	litResult.Text = "One " + DateTime.Now;
}
protected void rdoTwo_CheckedChanged(object sender, EventArgs e)
{
	litResult.Text = "Two " + DateTime.Now;
}

rdoOne.InputAttributes["checked"] = "true"

rdoOne.Attributes.Add("onclick", "javascript:setTimeout('__doPostBack(\\'" + rdoOne.ClientID.Replace("_", "$") + "\\',\\'\\')', 0)");

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