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POHow to check whether postback caused by a Dynamic link button
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  1. POHow to check whether postback caused by a Dynamic link button
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    copied!<p>I have a button control. On click of this button I need to add a Link Button dynamically. The Link Button needs an event handler. Hence the dynamic Link button is first added in the Page_Load and cleared and added again in the button click handler. Please read <a href="https://stackoverflow.com/questions/14364332/dynamic-controls-event-handlers-working">Dynamic Control’s Event Handler’s Working</a> for understanding the business requirement for this.</p> <p>I have read <a href="https://stackoverflow.com/questions/3175513/on-postback-how-can-i-check-which-control-cause-postback-in-page-init-event">On postback, how can I check which control cause postback in Page_Init event</a> for identifying the control that caused the postback (inside Page_Load). But it is not working for my scenario.</p> <p>What change need to be done to confirm whether the postback was caused by link button (inside Page_Load)?</p> <p><strong>Note</strong>: Refer the following for another scenario where it is inevitable <a href="https://codereview.stackexchange.com/questions/20510/custom-paging-in-asp-net-web-application">https://codereview.stackexchange.com/questions/20510/custom-paging-in-asp-net-web-application</a></p> <p>Note 1: I need to get the postback control ID as the first step inside <code>if (Page.IsPostBack)</code>. I need to add the dynamic link buttons control only if it is a postback from the button or the link button. There will be other controls that causes postback. For such postbacks we should not execute this code.</p> <p>Note 2: I am getting empty string for <code>Request["__EVENTARGUMENT"]</code> in the Page_Load</p> <p><strong>Related Question</strong>: By what <code>event</code>, the dynamic controls will be available in the Page (for using in FindControl). @Tung says - "Your GetPostBackControlId method is properly getting the name of the control that caused the postback, but it is unable to find a control with that id through page.FindControl because the linkbutton has not been created yet, and so page does not know of its existence. "</p> <p><strong>ASPX</strong></p> <pre><code>&lt;%@ Page Language="C#" AutoEventWireup="true" CodeFile="PostbackTest.aspx.cs" Inherits="PostbackTest" MasterPageFile="~/TestMasterPage.master" %&gt; &lt;asp:Content ID="myContent" ContentPlaceHolderID="ContentPlaceHolder1" runat="server"&gt; &lt;div id="holder" runat="server"&gt; &lt;/div&gt; &lt;asp:Button ID="Button1" runat="server" Text="Button" OnClick="TestClick" /&gt; &lt;/asp:Content&gt; </code></pre> <p><strong>CODE BEHIND</strong></p> <pre><code>public partial class PostbackTest : System.Web.UI.Page { protected void Page_Load(object sender, EventArgs e) { if(Page.IsPostBack) { string IDValue = GetPostBackControlId(this.Page); int x = 0; holder.Controls.Clear(); LinkButton lnkDynamic = new LinkButton(); lnkDynamic.Click += new EventHandler(LinkClick); lnkDynamic.ID = "lnkDynamic123"; lnkDynamic.Text = "lnkDynamic123"; holder.Controls.Add(lnkDynamic); } } protected void TestClick(object sender, EventArgs e) { holder.Controls.Clear(); LinkButton lnkDynamic = new LinkButton(); lnkDynamic.Click += new EventHandler(LinkClick); lnkDynamic.ID = "lnkDynamic123"; lnkDynamic.Text = "lnkDynamic123"; holder.Controls.Add(lnkDynamic); } protected void LinkClick(object sender, EventArgs e) { } public static string GetPostBackControlId(Page page) { if (!page.IsPostBack) { return string.Empty; } Control control = null; // First check the "__EVENTTARGET" for controls with "_doPostBack" function string controlName = page.Request.Params["__EVENTTARGET"]; if (!String.IsNullOrEmpty(controlName)) { control = page.FindControl(controlName); } else { // if __EVENTTARGET is null, the control is a button type string controlId; Control foundControl; foreach (string ctl in page.Request.Form) { // Handle ImageButton they having an additional "quasi-property" in their Id which identifies mouse x and y coordinates if (ctl.EndsWith(".x") || ctl.EndsWith(".y")) { controlId = ctl.Substring(0, ctl.Length - 2); foundControl = page.FindControl(controlId); } else { foundControl = page.FindControl(ctl); } if (!(foundControl is Button || foundControl is ImageButton)) continue; control = foundControl; break; } } return control == null ? String.Empty : control.ID; } } </code></pre> <p><strong>REFERENCE</strong></p> <ol> <li><a href="https://stackoverflow.com/questions/3175513/on-postback-how-can-i-check-which-control-cause-postback-in-page-init-event">On postback, how can I check which control cause postback in Page_Init event</a></li> <li><a href="https://stackoverflow.com/questions/14364332/dynamic-controls-event-handlers-working">Dynamic Control’s Event Handler’s Working</a></li> <li><a href="http://aspalliance.com/articleViewer.aspx?aId=895&amp;pId=-1" rel="nofollow noreferrer">Understanding the JavaScript __doPostBack Function</a></li> <li><a href="http://www.dotnetcurry.com/ShowArticle.aspx?ID=203" rel="nofollow noreferrer">Access JavaScript variables on PostBack using ASP.NET Code</a></li> <li><a href="https://stackoverflow.com/questions/9989122/how-does-asp-net-know-which-event-to-fire-during-a-postback">How does ASP.NET know which event to fire during a postback?</a></li> <li><a href="https://stackoverflow.com/questions/4424476/asp-net-how-to-remove-name-attribute-from-server-controls">how to remove &#39;name&#39; attribute from server controls?</a></li> <li><a href="https://stackoverflow.com/questions/3591634/how-to-use-dopostback/3914500#3914500">How to use __doPostBack()</a></li> </ol>
 

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