Author: Jonas Bilinkevicius

When to use the OnCreate, OnShow, OnActivate, and OnPaint events of a TForm

Answer:

Stuff that needs to be done to initialize the object (initializing variables and 
nested objects, etc.) should be done in the OnCreate event handler. That gets 
called as part of your constructor logic and is guaranteed to only be called once 
in the life of any object.

Stuff that needs to be drawn should always be done in the OnPaint event handler. 
Drawing for your form (except for other controls or components) must be done there 
or you won't have a chance to refresh it when needed. This gets called lots of 
times in the life of a form.

OnShow gets called when the form is first shown and when it is made visible after 
being hidden. This generally applies only to secondary forms. It should not be used 
to initialize anything.

OnActivate seems to get called at random intervals. Put your hand in that lion's mouth only if you have a surplus of digits ...