How To Pass Control As A Variable - asp.net

Question

This is one of those problems which seems like it should have a simple solution but I can't work out what it is!
How can I pass a control from one sub to another if the first sub doesn't actually call the second? For example, where btnChangeText is in a panel that has a ModalPopupExtender called mpExample, and therefore isn't usually visible:
Protected Sub btnChangeText_Click(sender as object, e as EventArgs) Handles btnChangeText.Click
<SpecifiedTextBox>.Text = "Hello"
End Sub
And then on the main page, visible at all times, is a button associated with each textbox. In this example, it's textbox15:
Protected Sub btnChangeTextBox15_Click(sender as object, e as EventArgs) Handles btnChangeTextBox15.Click
<Set TextBox15 as variable>
mpExample.Show()
End Sub
I know it's a silly example - believe me when I say that the real application I want to make of this actually makes sense! But the point is that I want to somehow store the name of the control to be updated by the first sub when the second sub is run.
If I was calling the first sub from the second it'd be easy, I'd just pass it as an argument, but I'm not. The first sub is called from a button click and is an independent action from the running of the second sub.
I don't seem to be able to use a session variable (my first thought) because I can't find any way to store the control name as a string and then convert it back to an actual control when the first sub runs. That'd be the easiest answer if somebody could tell me how to do it.

Answer 1

One approach would be to store the control's ID as a string in a Session variable, and then use the FindControl method to grab the control in your 2nd Click event.
Protected Sub btnChangeTextBox15_Click(sender as object, e as EventArgs) Handles btnChangeTextBox15.Click
Session("currentTextBox") = TextBox15.ID
mpExample.Show()
End Sub
Protected Sub btnChangeText_Click(sender as object, e as EventArgs) Handles btnChangeText.Click
Dim currentTextBox As TextBox
currentTextBox = CType(Page.FindControl(Session("currentTextBox")),TextBox)
currentTextBox.Text = "Hello"
End Sub
Note that if your TextBox15 control is inside some kind of container (a Panel or something), you'll need to use that container's FindControl method, rather than Page.FindControl.
Another approach is to store the TextBox itself in a Session variable, and then pull that out to set the text in your other method. Note that this only works if the methods are both called in the same request (which doesn't sound like it would work for your use-case). Here's what that would look like:
Protected Sub btnChangeTextBox15_Click(sender as object, e as EventArgs) Handles btnChangeTextBox15.Click
Session("currentTextBox") = TextBox15
mpExample.Show()
End Sub
Protected Sub btnChangeText_Click(sender as object, e as EventArgs) Handles btnChangeText.Click
Dim currentTextBox As TextBox
currentTextBox = CType(Session("currentTextBox"), TextBox)
currentTextBox.Text = "Hello"
End Sub