Button Redirect Page in Iframe

T1.aspx

//HTML
<asp:Button runat="server" ID="btnTask1" OnClick="ShowTask" Text="Task1" CommandArgument="Task1" />
<asp:Button runat="server" ID="btnTask2" OnClick="ShowTask" Text="Task2" CommandArgument="Task2" />
<asp:Button runat="server" ID="btnTask3" OnClick="ShowTask" Text="Task3" CommandArgument="Task3" />
<iframe src="T2.aspx"></iframe>

//C#
public void ShowTask(object sender, EventArgs e)
{
this.Page.ClientScript.RegisterStartupScript(this.GetType(),this.GetType().Name,string.Format("window.frames[0].location.href = 'T2.aspx?Task={0}'", ((Button)sender).CommandArgument),true);
}

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T2.aspx

//HTML
<asp:Label runat="server" ID="lblTask"></asp:Label>

//C#
protected void Page_Load(object sender, EventArgs e)
{
    this.lblTask.Text = this.Request.QueryString.Get("Task");
}