Most efficient way to programmatically update and configure forms and controls - vb.net

Question

I am looking for a way to prevent user form controls from appearing one by one when I'm programmatically adding them and for ways to enhance application performance and visual appeal.
Say, I have a Panel_Top in which I programmatically add comboboxes. What is happening is that they appear one by one as they are created and I am looking for a way to suspend the refreshing of the panel and or user form to make all of those programmatically added comboboxes to appear at the same time and faster than it happens right now.
I've tried suspendlayout which doesn't do anything for me or maybe I'm doing it wrong.
MyForm.PanelTop.SuspendLayout = true
And also I've tried to set the Panel_Top to invisible like:
MyForm.Top_Panel.visible = false
Which kind of sorta looks and performs better, or it might be a placebo.
What is the correct approach to this problem?
PS: I do have form set to doublebuffer = true, if that matters

Answer 1

What I tend to do is create a loading modal to appear on top of the form rendering the controls that need to be created/made visible, this can optionally have a progress bar that gets incremented as the control is created/shown. With the loading modal running, the container that needs to add the controls starts with SuspendLayout, adds the controls, and then finished with ResumeLayout.
This makes it so that controls are added/shown while giving the user a visual indicator that something is going on behind the scenes.
Here is a phenomenal example of a loading modal: https://www.vbforums.com/showthread.php?869567-Modal-Wait-Dialogue-with-BackgroundWorker and here is an example of using it:
Private ReadOnly _controlsToAdd As New List(Of Control)()
Private Sub MyForm_Show(sender As Object, e As EventArgs) Handles MyBase.Shown
Using waitModal = New BackgroundWorkerForm(AddressOf backgroundWorker_DoWork,
AddressOf backgroundWorker_ProgressChanged,
AddressOf backgroundWorker_RunWorkerCompleted)
waitModal.ShowDialog()
End Using
End Sub
Private Sub backgroundWorker_DoWork(sender As Object, e As DoWorkEventArgs)
Dim worker = DirectCast(sender, BackgroundWorker)
For index = 1 To 100
_controlsToAdd.Add(New ComboBox() With {.Name = $"ComboBox{index}"})
worker.ReportProgress(index)
Threading.Thread.Sleep(100) ' Zzz to simulate a long running process
Next
End Sub
Private Sub backgroundWorker_ProgressChanged(sender As Object, e As ProgressChangedEventArgs)
Dim percentageCompleted = e.ProgressPercentage / 100
' do something with the percentageCompleted value
End Sub
Private Sub backgroundWorker_RunWorkerCompleted(sender As Object, e As RunWorkerCompletedEventArgs)
PanelTop.SuspendLayout()
PanelTop.Controls.AddRange(_controlsToAdd.ToArray())
PanelTop.ResumeLayout()
End Sub

Answer 2

SuspendLayout() is the correct way to handle this with WinForms.
But first of all, this is a function you call, and not a flag you set.
Secondly, don't forget to call ResumeLayout() at the end of the changes.
Finally, you need to ensure you only call them once when you start to change around the controls in the panel and then again at the very end. If you use them with every control you won't get any benefit.
So the pattern might look something like this:
Public Sub SomeMethod()
PanelTop.SuspendLayout() ' Prevent the panel from updating until you've finished
' Make a bunch of changes
PanelTop.Controls.Clear()
For Each ...
PanelTop.Controls.Add( ... )
Next
PanelTop.ResumeLayout() ' Allow the panel to show all the changes in the same WM_PAINT event
End Sub
You also need to ensure you don't have anything in there like DoEvents()/Invalidate() that might invoke the windows message loop and cause the form to redraw itself.