select all in check box list

Hi experts,
I facing a problem on how to select all the check box with a button at codebehind.
My code is like this:
for (){

CheckBoxList checkBoxL = new CheckBoxList();
        checkBoxL.ID = ID2; 
        checkBoxL.Items.Add("Delete");
        checkBoxL.SelectedIndexChanged += new EventHandler(checkBox_CheckedChanged);
}
 
protected void btnSelectAll_Click(object sender, EventArgs e)
    {
       
    }  


regards
Mike

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