Removing all controls of a type.

[TomPhillips]

Removing all controls of a type. RESOLVED

I am placing ListBox controls on a form in rows and columns. I then want to remove them and replace them with new ones. When I use code like this:

For Each ctrl As Control In Me.Controls
If TypeOf ctrl Is ListBox Then
ctrl.Dispose()
End If
Next

only every other box gets removed. I can keep running the block over and over till all boxes are gone, but why is this happening and how can I just dispose of all the ListBoxes on a form at once?

 

[TPM]

I delive the answer is by disposing the control your screwing the for each up. For each control loops through useing the controls indexs, an example will help explain;
You have 3 listboxes, there indexes are 0-2. 0 goes through your for each loop and is disposed, now 1's index is 0. But your loop doesn't know that so it move onto control index 1 (which is now your 3rd listbox). What you can do is instead of a for each you could do this:

dim i as integer = 0
while i < me.controls.count
if TypeOf me.controls(i) is listbox Then
me.controls(i).dispose()
Else
i+=1
end if
end while

Note that it'll only increment the control index if the current control isn't deleted.

TPM

 

[TomPhillips]

That was it. Thanks. My brain knew what it had to be but I couldn't put it together. You saved me some time.

 

[jmcilhinney]

Whenever deleting multiple objects from a collection, I always use a for loop counting backwards:

For i as Interger = collection.Count - 1 To 0 Step -1
	collection.RemoveAt(i)
Next

This way, it doesn't matter whether you want to delete all items or just some, as the only items whose indices are affected have already been through the loop.