How do you rename runtime generated checkboxes in runtime generated groupboxes? - vb.net

Question

I am having an issue changing runtime generated checkbox names in runtime generated groupboxes. I am using multiple groupboxes, and then taking all of the rows in a database and creating checkboxes for them. The checkbox names are as follows ""chkClass" & intGroupBoxNumber & intCurrentRow". Upon deletion of a groupbox, I renumber all of the current group boxes, and would like the checkbox names to change as well to the new groupbox number, if this makes any sense. My code is as follows:
strControlName = "grpGroup" & strIBResult
Try
intGroupBoxOldYLocation = Me.Controls(strControlName).Location
Me.Controls(strControlName).Dispose()
MessageBox.Show("Deleted: " & strControlName)
intRenameGroup = strIBResult + 1
Try
strControlName = "grpGroup" & intRenameGroup
strControlNewName = "grpGroup" & intRenameGroup - 1
Me.Controls(strControlName).Location = intGroupBoxOldYLocation
Me.Controls(strControlName).Text = "Group " & intRenameGroup - 1
Me.Controls(strControlName).Name = strControlNewName
MessageBox.Show("Changed: " & strControlName & " to: " & strControlNewName)
Do While intCurrentClassRow < intTotalClassRows
strCheckBoxOldName = "chkClass" & intRenameGroup & intCurrentClassRow
strCheckBoxNewName = "chkClass" & intRenameGroup - 1 & intCurrentClassRow
MessageBox.Show("Renaming: " & strCheckBoxOldName & " to: " & strCheckBoxNewName)
Me.Controls(strCheckBoxOldName).Name = strCheckBoxNewName
intCurrentClassRow += 1
MessageBox.Show("Renamed: " & strCheckBoxOldName & " to: " & strCheckBoxNewName)
Loop
intCurrentClassRow = 0
intRenameGroup += 1
intGroupBoxNewYIncrement = intGroupBoxOldYLocation.Y + Me.Controls(strControlNewName).Height + 50
Do
strControlName = "grpGroup" & intRenameGroup
strControlNewName = "grpGroup" & intRenameGroup - 1
Me.Controls(strControlName).Location = New Point(intCurrentXPosition, intGroupBoxNewYIncrement)
Me.Controls(strControlName).Text = "Group " & intRenameGroup - 1
Me.Controls(strControlName).Name = strControlNewName
Do While intCurrentClassRow < intTotalClassRows
strCheckBoxOldName = "chkClass" & intRenameGroup & intCurrentClassRow
strCheckBoxNewName = "chkClass" & intRenameGroup - 1 & intCurrentClassRow
Me.Controls(strCheckBoxOldName).Name = strCheckBoxNewName
intCurrentClassRow += 1
MessageBox.Show("Renamed: " & strCheckBoxOldName & " to: " & strCheckBoxNewName)
Loop
intCurrentClassRow = 0
intRenameGroup += 1
intGroupBoxNewYIncrement = intGroupBoxNewYIncrement + Me.Controls(strControlNewName).Height + 50
Loop
Catch ex As Exception
MessageBox.Show("Control: " & strControlName & " does not exist")
MessageBox.Show(ErrorToString)
End Try
Catch ex As Exception
'MessageBox.Show("Control: " & strControlName & " never existed")
MessageBox.Show("Please enter a valid group number to delete.", "Invalid Entry")
Exit Sub
End Try
I am pretty sure my trouble now exists at the Me.Controls(strCheckBoxOldName).Name = strCheckBoxNewName
The error is as follows: "Object reference not set to an instance of an object"
Is there a different method to reference that runtime generated groupbox?
Thanks. Sorry if this is confusing!

Answer 1

The form's Controls collection only contains the top-level controls that are placed directly on the form. If you load a control into a container control, such as a GroupBox, you must find it in that container control's Controls collection.
So, instead of doing this:
Me.Controls(strCheckBoxOldName).Name = strCheckBoxNewName
You should be doing something like this:
Me.Controls(strControlName).Controls(strCheckBoxOldName).Name = strCheckBoxNewName

Answer 2

I would temporarily comment out the try/catch blocks. Then the application will break at the offending statement and you won't have to be just "pretty sure" where the problem is. Then, check the values of the associated variables (highlight, shfit-F9). You'll probably find that one of the objects has a value of nothing. This causes the error message you mentioned.