get http value default.aspx to default.aspx

Drag a textbox, button on the same page

public partial class _Default : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{

if (!string.IsNullOrEmpty(Request.QueryString["TextBoxVal"]))
{
string textboxvalue = Request.QueryString["TextBoxVal"];
}
}
protected void Button1_Click(object sender, EventArgs e)
{
Response.Redirect("Default.aspx?TextBoxVal=" + TextBox1.Text);
}
}