[RESOLVED] [2005] Testing whether a control exists

[Bulldog]

Is there some easy way to determine if a control exists? The problem I have is that I create an array of controls (labels for example) that gets re-dim'd from time to time. Id like to be able to say, if MyLabel(35).Exists then do something.

I have been using;
If MyPanel.Contains(MyLabel(35)) Then do something

but this craps out if the index is not valid, even if I wrap it in a try/catch.

[Suthey]

Could use a try catch like...

Try
 mycontrol.left = 10
catch
 msgbox("Control does not exist")
End try

If the control does not exist then trying to set the left parameter would raise an error.

Hope this helps

EDIT: Sorry, I missed the last bit of your post. Ignore what I just said

[RobDog888]

Less resources being used to just test it with the TypeOf eval.

If TypeOf MyLabel(35) Is Label Then
    If MyPanel.Contains(MyLabel(35)) Then
        'Meow!
    End If
End If

[Bulldog]

Unfortunately a catch/try does not catch an exception if the index is invalid.

[warrenayen]

For X = 0 To fromForm.Controls.Count - 1
If fromForm.Controls(X).ToString = "DropDownMessage.DropDownMsg" Then
fromForm.Controls(X).Dispose()
Exit For
End If
Next

That's what I did. I created a nifty control that does drop down messages from the bottom of another control. To check if it exists, I check that it's type (to string) = "whatever" and leave the loop when done...

fromForm is the form...BTW...

[kleinma]

For X = 0 To fromForm.Controls.Count - 1
If fromForm.Controls(X).ToString = "DropDownMessage.DropDownMsg" Then
fromForm.Controls(X).Dispose()
Exit For
End If
Next

That's what I did. I created a nifty control that does drop down messages from the bottom of another control. To check if it exists, I check that it's type (to string) = "whatever" and leave the loop when done...

fromForm is the form...BTW...

If TypeOf(fromForm.Controls(X)) Is DropDownMessage.DropDownMsg

would probably be better than checking against a string value. If the name every changes, this method would cause a syntax error and let you know right away. Using a string comparison leaves room for error.

This just goes for your example code, as far as the original thread poster, I would also do what RobDog suggested.

[warrenayen]

No, that's not the name, that is the type, to a string. Everything came up as TextBox or Combobox or Label...

Still, you're probably right. At the time I wrote that code over a year ago I couldn't seem to get it to check the type properly, so I gave up and made it a string...

[kleinma]

No, that's not the name, that is the type, to a string. Everything came up as TextBox or Combobox or Label...

Still, you're probably right. At the time I wrote that code over a year ago I couldn't seem to get it to check the type properly, so I gave up and made it a string...

Yeah I meant name as in the name of the TYPE, not the name of the variable.

You never know when you are going to rework your namespaces to make things more organized, only to have it break because of some string check like that. Its happened to me, which is why I figured I would point it out. May come in handy to others.

[Bulldog]

You guys leave me about five laps behind on this stuff, here's an example of what Im trying to accomplish. Rather than keep tabs on the label indices, I thought it was neater to check whether the control exists and then do the action.

What I dont like about this, is that its written to use an exception as part of the code (instead of an exceptional circumstance like a file not being found or whatever). There are probably all kinds of different ways of doing this example, but Im interested to find a way of doing the equivalent of "If Control.Exists then do something" but without relying on exception throwing to determine the result. This example works fine btw, but it just doesnt look like good coding to me.

Dim a(2, 35) As Label
        Dim t As New TableLayoutPanel
        For i = 0 To 35 - 1
            For j = 1 To 2
                a(j, i) = New Label
                a(j, i).Text = j.Tostring & "/" & i.Tostring
                t.Controls.Add(a(j, i))
            Next
        Next
 
        'At some point in the code I re-dim, for example, here we lose a(35)
        ReDim Preserve a(2, 34)
 
        'In a sub somewhere I want to update the "a" labels
        'Rather than keep track of the current index, I just (try and) detect whether the control exists
        Try
            If t.Contains(a(2, 35)) Then
                MessageBox.Show("Its there!")
            Else
                MessageBox.Show("This message will never get shown")
            End If
        Catch ex As Exception
            MessageBox.Show("Its not there!")
        End Try

[Negative0]

Use the GetUpperBounds function:

Dim a(2, 35) As Label
        MessageBox.Show(a.GetUpperBound(0))     'Returns 2
        MessageBox.Show(a.GetUpperBound(1))     'Returns 35
 
        ReDim Preserve a(2, 34)
        MessageBox.Show(a.GetUpperBound(0))     'Returns 2
        MessageBox.Show(a.GetUpperBound(1))     'Returns 34

[Bulldog]

Aha! that is just perfect. I didnt know I could do that.

Thanks all for commenting.