Question

Given

Action closeLoadingAction = new Action(() =>
{
  loadingForm.Close();
  #region - may need to put into second Action
  panelOnMainForm.Controls.AddRange(physdocControls.ToList<Control>().ToArray());
  if (Handle != IntPtr.Zero)
    User32DLL.SetForegroundWindow(this.Handle);//Handle is a property of the mainForm.
  #endregion
});

Sometimes I get handle not created exceptions even though I check the Invoke required.

if(loadingForm.InvokeRequired)
   loadingForm.Invoke(closeLoadingAction);
else
   closeLoadingAction();

The loading form runs on the same thread as the main form. The code you see above runs in a seperate thread. I suspect that I need another check for invoke against the main form. Do I need a second check or is what I have already safe?

Answer 1

The code you see above runs in a seperate thread

Using InvokeRequired like this when you know that the code runs on another thread is a bad anti-pattern. You can do much more useful things with it. Like:

if (!loadingForm.InvokeRequired) {
    throw new InvalidOperationException("Threading race detected");
}
loadingForm.Invoke(closeLoadingAction);

Or the more practical one if you meant to start the loading thread before the loading form’s Load event fired:

while (!loadingForm.InvokeRequired) Thread.Sleep(50);
loadingForm.Invoke(closeLoadingAction);

Or just do it the right way and have the form’s Load event start the thread.