I try to use RadioGroup.CheckedItems for getting the checked item from client when it does a postback.

But I always get count equal to 0, could radiogroup be used this way ?

or I need use extra parameter to do that ?

ASPX
  <ext:ResourceManager ID="ResourceManager1" runat="server">
           </ext:ResourceManager>
    <ext:FormPanel ID="FormPanel1" runat="server" ButtonAlign="Right" Height="300" Padding="5"
        Title="Title" Width="300">
       <Content>
         
           <ext:RadioGroup ID="radioGroup01" runat="server">
           </ext:RadioGroup>
           <ext:CheckboxGroup ID="checkboxGroup01" runat="server">
           </ext:CheckboxGroup>
           <ext:Button ID="Button1" runat="server" Text="Submit">
            <DirectEvents>
                <Click OnEvent="Button1_OnClicked">
                    <EventMask ShowMask="true" MinDelay="100" />
                </Click>
            </DirectEvents>
           </ext:Button>
           <ext:Label ID="Label1" runat="server">
           </ext:Label>
           <ext:DisplayField ID="DisplayField1" runat="server">
           </ext:DisplayField>
       </Content>
    </ext:FormPanel>
C# code
 public IList<TestDataItem> DemoDataSource { get; set; }

    protected void Page_Load(object sender, EventArgs e)
    {
        DemoDataSource = getDemoData();

        if (X.IsAjaxRequest == false)
        {
            initGroup();
        }


    }

    private void initGroup()
    {
        radioGroup01.Vertical = true;
        radioGroup01.ColumnsNumber = 1;
        foreach (TestDataItem item in DemoDataSource)
        {
            Radio radio = new Radio();
            radio.Checked = false;
            radio.InputValue = item.ItemValue;
            radio.BoxLabel = item.ItemText;
            radioGroup01.Items.Add(radio);

            Checkbox checkbox = new Checkbox(false, item.ItemText);
            checkbox.InputValue = item.ItemValue;
            checkboxGroup01.Items.Add(checkbox);
        }
    }

    protected void Button1_OnClicked(object sender, DirectEventArgs args)
    {
        DisplayField1.Text = "Radio Checked Count:" + radioGroup01.CheckedItems.Count.ToString() + " Checkbox Checked Count:" + checkboxGroup01.CheckedItems.Count.ToString();
    }

    // for test
    private IList<TestDataItem> getDemoData()
    {
        IList<TestDataItem> demoDataList = new List<TestDataItem>();

        demoDataList.Add(new TestDataItem("XXXX", "0"));
        demoDataList.Add(new TestDataItem("YYYY", "3"));
        demoDataList.Add(new TestDataItem("ZZZZ", "4"));
        return demoDataList;
    }

    public class TestDataItem
    {
        public string ItemValue { get; set; }
        public string ItemText { get; set; }

        public TestDataItem(string text, string value)
        {
            ItemValue = value;
            ItemText = text;
        }
    }