RadioButtons CheckedChanged event

I have 20 radiobuttons on the page and I want to know which one of them was clicked.

protected void Page_Load(object sender, EventArgs e)
{
    Button newBTN = new Button();

    newBTN.Text = "Button 1";
    PlaceHolder1.Controls.Add(newBTN);
    for (int i = 0; i < 20; i++)
    {
       RadioButton r = new RadioButton();
       r.ID = i.ToString();
       r开发者_如何学C.CheckedChanged += RadioButton1_CheckedChanged;
       PlaceHolder1.Controls.Add(r);
    }
}

New Updated code.. NOTE: THE CODE DOESNT RELATE TO THE ABOVE CODE.

      public List<int> ThreadID2Treat { get { return ViewState["Checked"] == null ? null : (List<int>)ViewState["Checked"]; } set { ViewState["Checked"] = value; } }
protected void CheckBox1_CheckedChanged(object sender, EventArgs e)

{

var rad = (CheckBox)sender;
int threadID = int.Parse(rad.ID.ToString());
ThreadID2Treat.Add(threadID); 

}

public void DeleteButton_Clicked(object sender, EventArgs e)
{
    foreach (var item in ThreadID2Treat)
    {
        UsefulStaticMethods.DeleteThreads(item);
    }
}

How do i find out?

var rad = (RadioButton)sendder;
Response.Write("RadioButton Id :" + rad.Id.ToString());

You could try the above.

Update :
To get all select radio buttons in PlaceHolder make sure the AutoPostBack is not set on the radio buttons. You dont need to add CheckChanged Event. "r.CheckedChanged += RadioButton1_CheckedChanged;" <= remove.

StringBuilder stringBuilder = new StringBuilder();
    foreach (var control in placeHolder1.Controls)
    {
        var rad = control as RadioButton;
        if (rad != null)
        {
            if (rad.Checked)
                stringBuilder.AppendLine(String.Format("Radion Button Checked : {0}", rad.ID));
        }
    }

    Response.Write(stringBuilder.ToString());

With the parameter sender you have a direct reference to the event-source control.

var rb = (RadioButton)sender;

If you want to trigger this event and the postback directly, you must set the RadioButton's AutoPostBack-Property to true.

 protected void RadioButton1_CheckedChanged(object sender, EventArgs e)
    {
        if (sender is RadioButton)
        {

            RadioButton radioButton = (RadioButton)sender;
            //Code to use radioButton's properties to do something useful.
            // get the radio button by its ID
            string id = radioButton.ID;  



        }
    }

You can try this.

RadioButton r = sender as RadioButton;
Response.Write(r.Id);

Cast sender as RadioButton:

RadioButton r = sender as RadioButton;
if(r != null)
{
    //Do stuff
}