find control on page using vb.net - asp.net

Question

I'm using the FindControl function to look for a control on the page. It seems super simple and straight forward on MSDN but I can't get it to find the control. The page I'm using has a MasterPageFile that prepends more to the id that I give the contorl in the aspx file. A simple example that isn't working:
aspx page
<%# Page Title="Inventory Control Test" Language="VB" AutoEventWireup="false" MasterPageFile="~/Site.master" CodeFile="Default2.aspx.vb" Inherits="Sales_ajaxTest_Default2" %>
<asp:Content ID="conHead" ContentPlaceHolderID="head" Runat="Server">
</asp:Content>
<asp:Content ID="conBody" ContentPlaceHolderID="MainBody" Runat="Server">
<asp:Button ID="saveAllBtn" runat="server" Text="Save All" />
</asp:Content>
code behind
Partial Class Sales_ajaxTest_Default2
Inherits System.Web.UI.Page
Protected Sub saveAllBtn_Click(sender As Object, e As System.EventArgs) Handles saveAllBtn.Click
Dim myControl1 As Control = FindControl("ctl00_MainBody_saveAllBtn")
If (Not myControl1 Is Nothing) Then
MsgBox("Control ID is : " & myControl1.ID)
Else
'Response.Write("Control not found.....")
MsgBox("Control not found.....")
End If
End Sub
End Class
I get that msgbox isn't a web thing I'm just using it for this example.
If i use "saveAllBtn", which is the id given to the control, in the FindControl I get "control not found". If I try this, on a stand alone page without a masterpage it works fine.
If I inspect the element using chrome I find that the ID of the button has been changed to "ctl00_MainBody_saveAllBtn" but if I use that in the FindControl I still get "control not found"

Answer 1

When you use FindControl you would specify the "server ID" (what you named it) of the control, not the final rendered "client ID" of the control. ex:
Dim myControl as Control = MainBody.FindControl("saveAllBtn")
However, in your specific example, since you are in the saveAllBtn.Click event, the control you are looking for is actually the sender parameter (because you clicked on that button to trigger the event you are in) ex:
Dim myControl as Button = CType(sender, Button)

Answer 2

If you just want to find saveAllBtn control, wweicker's second method using CType(sender, Button) is the prefer one.
However, if you want to find other control by name, you cannot use just FindControl. You need to find the control recursively, because it is nested inside other controls.
Here is the helper method -
Protected Sub saveAllBtn_Click(sender As Object, e As EventArgs)
Dim button = TryCast(FindControlRecursive(Me.Page, "saveAllBtn"), Button)
End Sub
Public Shared Function FindControlRecursive(root As Control, id As String) As Control
If root.ID = id Then
Return root
End If
Return root.Controls.Cast(Of Control)().[Select](Function(c) FindControlRecursive(c, id)).FirstOrDefault(Function(c) c IsNot Nothing)
End Function
Note: My VB code might be a bite weird, because I wrote in C# and converted to VB using converter.

Answer 3

FindControl does not work recursively. You must start at one point (Me, for example), and if that is not the control your looking for, search the Controls collection of your starting point. And so forth.