title: radiobutton.checked always is false after postback
body: <p>I have 3 <strong>radiobutton</strong> control and a submit <strong>button</strong> in my aspx page which are inside a <strong>Content</strong> control.</p>
  
  <pre><code>&lt;asp:Content ID="Content1" ContentPlaceHolderID="MainContent" runat="server"&gt;
       &lt;asp:Panel ID="Panel1" runat="server"&gt;
            &lt;asp:RadioButton ID="rd0" runat="server" GroupName="g1" Checked="true" /&gt;
            &lt;asp:Image ID="img0" runat="server" ImageUrl="/image/img0.png" /&gt;
            &lt;asp:RadioButton ID="rd1" runat="server" GroupName="g1" /&gt;
            &lt;asp:Image ID="img1" runat="server" ImageUrl="/image/img1.png" /&gt;
            &lt;asp:RadioButton ID="rd2" runat="server" GroupName="g1" /&gt;
            &lt;asp:Image ID="img2" runat="server" ImageUrl="/image/img2.png" /&gt;
       &lt;/asp:Panel&gt;
       &lt;asp:Button ID="btnSubmit" runat="server" Text="Submit" /&gt;
  &lt;/asp:Content&gt;
  </code></pre>
  
  <p>The user can select one of these radiobuttons and press submit button.
  Now in code behind i want to diagnose which radiobutton is selected,</p>
  
  <pre><code>RadioButton checkedButton;
  if (rd0.Checked)
     checkedButton = rd0;
  
  else if (rd1.Checked)
     checkedButton = rd1;
  
  else
     checkedButton = rd2;
  </code></pre>
  
  <p>but the checked property of all of the radiobuttons is false.</p>
  
  <p>I have even set the checked property of the first radiobutton to true but it becomes to false after postback again.</p>