StringBuilder sb = new StringBuilder();
sb.Append("<script language='javascript'>");
sb.Append("var val=window.confirm('Are you sure!');");
sb.Append("window.document.getElementById('TextBox1').value=val;");
sb.Append("__doPostBack('TextBox1','');");
sb.Append("</script>");
this.RegisterStartupScript(System.Guid.NewGuid().ToString(), sb.ToString());

protected void TextBox1_TextChanged(object sender, EventArgs e)
{
if (((TextBox)(sender)).Text != "")
{
if (((TextBox)(sender)).Text.ToUpper() == "TRUE")
{
//确定后执行另一个事件/方法 
}
if (((TextBox)(sender)).Text.ToUpper() == "FALSE")
{
//取消后执行另一个事件/方法 

}

} 
}