On Button Click Processing Method

 protected void Page_Load(object sender, EventArgs e)
    {
        this.btnsubmit.Attributes.Add("onclick", DisableTheButton(this.Page, this.btnsubmit));
    }

 #region Button wait event
    private string DisableTheButton(Control pge, Control btn)
    {
        System.Text.StringBuilder sb = new System.Text.StringBuilder();
        sb.Append("if (typeof(Page_ClientValidate) == 'function') {");
        sb.Append("if (Page_ClientValidate() == false) { return false; }} ");
        sb.Append("this.value = 'Processing...';");
        sb.Append("this.disabled = true;");
        sb.Append(Page.GetPostBackEventReference(btn));
        sb.Append(";");
        return sb.ToString();
    }
    #endregion