Updating VCL from the same thread that created the UI. Why?

Question

I know that I must call Synchronize to update the vcl from a thread that did not create the controls or send a message to the window.

I have often heard the word not th

Answer 1

Windows controls with handles are not thread-safe (i.e. they cannot be accessed safely by two different threads at the same time), and Delphi wraps the Windows controls to give you the VCL controls. Since the controls ARE accessed by the main GUI thread, you need to leave them alone if you are executing another thread.