How to determine which button caused postback

Question

I have 2 button controls. When I click one i'm trying to determine which one caused a postback in the page load. How to do determine this?

Why don't you handle the buttons' [click-event](http://msdn.microsoft.com/en-us/library/system.web.ui.webcontrols.button.click.aspx)? Then you would have two different handlers, one for each button. Apart from that: [Determining the Control that Caused a PostBack](http://ryanfarley.com/blog/archive/2005/03/11/1886.aspx) — Tim Schmelter, Apr 19 '12 at 14:15
@huMptyduMpty - fair point, but you might argue that Tim's comment and my answer are worth preserving in their own right? — CJM, Apr 19 '12 at 15:29

score 3 · Answer 1 · edited Apr 19 '12 at 14:27

3

What about using CommandName and CommandArgument has shown in this example. This way you can have just one handler.

<asp:Button id="Button1"
       Text="Sort Ascending"
       CommandName="Sort"
       CommandArgument="Ascending"
       OnCommand="CommandBtn_Click" 
       runat="server"/>

  <asp:Button id="Button2"
       Text="Sort Descending"
       CommandName="Sort"
       CommandArgument="Descending"
       OnCommand="CommandBtn_Click" 
       runat="server"/>

edited Apr 19 '12 at 14:27

abatishchev

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answered Apr 19 '12 at 14:21

Kris Krause

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like: var button = sender as Button; – Govind Malviya Apr 19 '12 at 14:28
@Govind: Right. `sender is Button2`, `sender as Button2`, `((Button)sender)).ID` and many other ways. But in general good advise. – abatishchev Apr 19 '12 at 14:32

score 2 · Answer 2 · answered Apr 19 '12 at 14:22

2

Do you come from a Classic ASP background? When I first used ASP.NET, the same question occurred to me.

Consider an alternative approach:

Rather than detect the postback in the Form_Load, and then figure out what triggered it, create a specific event handler for each of your buttons. This is the whole point of Web Forms - so you can develop apps in very similar ways as you would Windows applications.

answered Apr 19 '12 at 14:22

CJM

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The reason why I want to know from the form load rather than and create a specific event is that im creating a dynamic table, and as you know I have to re-create it every time I do a postback. Well im noticing that its causing my page to slow down, and im seeing in this one instance that when I dont need to use that particular function to re-create that table but I dont know what button/control caused that postback – Will Apr 20 '12 at 12:12
In this case, you can use the `Request["__EVENTTARGET"]` method explained above (and mark as the answer) – Darbio May 10 '13 at 01:31

score 1 · Answer 3 · answered Apr 07 '14 at 16:31

Really input with type button sends its value within post request. For example if you have you'll get in Post button-name=Quote like it's simple text input. So you can just check if post contains value for the button using code like following (sorry for my vb):

Dim isQuote As Boolean = HttpContext.Current.Request.Form(SubmitQuote.UniqueID) IsNot Nothing

so if it's not Nothing (null) then post has been sent by SubmitQuote button.

BTW for me HttpContext.Current.Request("__EVENTTARGET") didn't work either.

score 1 · Answer 4 · answered Feb 22 '15 at 16:29

In my implementation there are several forms on my page; if a post-back was triggered by certain button controls further operations are necessary.

The controls are of the following type, which do not populate Request["__EVENTTARGET"]

Button (at the root of the form)
Image Button (nested within a Datagrid)

I determine if the following button controls instigated the post-back, by reviewing that the UniqueID of the control was passed to the form request within the Page_Load sub:

- ASP.NET:
    <asp:Button ID="Button1" runat="server" />
    <asp:Button ID="Button2" runat="server" />

To simply handle whether the following nested image button instigated the post-back I take advantage of the OnClientClick attribute which calls to a javascript function that will populate the value of a supplementary hidden field control with the UniqueID of the instigating control, then review the hidden control value similarly in the Page_Lode sub:

- ASP.NET:
    <script type="text/javascript">
        function SetSource(SourceID) {
            var hiddenField = document.getElementById("<%=HiddenField1.ClientID%>");
            hiddenField.value = SourceID;
        }
    </script>

    <asp:HiddenField ID="HiddenField1" runat="server" Value="" />
    <asp:ImageButton ID="ImageButton1" runat="server" OnClientClick="SetSource(this.id)" />

The Page_Load would then implement by some means:

-VB.NET
     Private Sub Page_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Me.Load
        ' ...
        If Not Page.IsPostBack Then
            If Not String.IsNullOrEmpty(Me.Page.Request.Form(Button1.UniqueID)) Then
                ' ...
            ElseIf Not String.IsNullOrEmpty(Me.Page.Request.Form(Button2.UniqueID)) Then
                ' ...
            ElseIf Not Me.Page.Request.Form(HiddenField1.UniqueID) Is Nothing _
                And Not String.IsNullOrEmpty(Me.Page.Request.Form(HiddenField1.UniqueID)) Then
                ' ...
                HiddenField1.Value = String.Empty
            Else
                ' ...
            End If
        End If
    End Sub

This is the JavaScript method, but an alternative approach would be [this answer](https://stackoverflow.com/a/12273424/2912011). — David Rogers, Nov 01 '18 at 19:59

score 0 · Answer 5 · answered Apr 19 '12 at 14:24

0

on page load check this

String ButtonID = Request["__EVENTTARGET"];

answered Apr 19 '12 at 14:24

Govind Malviya

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Thats nice. I didnt know this technique. – Kamran Pervaiz Apr 19 '12 at 14:46
1

This gives you the `UniqueID` of the object which sent the request. e.g. `button.UniqueID` – Darbio May 10 '13 at 01:25
Doesn't work with buttons with submit buttons. – Ishikawa Sep 29 '22 at 13:47

How to determine which button caused postback

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