Is there anything special I need to do to get the Paint message sent to a Control in C#?

Question

I have three classes derived from Control...Class1, Class2 and Class3.

Class1 is the parent. It contains a list of Class2 objects, which, in turn, each contain a list of Class3 objects.

Each class overrides the OnPaint method to paint itself.

Class1 and Class2 paint themselves fine but Class3.OnPaint is never called.

Do I need to do anything special (perhaps in Class2.OnPaint) to ensure that Class3 objects get invalidated and receive the Paint message?

Answer 1

OnPaint will only get called if there is a visible region that has been invalidated (either because it became un-obscured or because it was manually invalidated.)

Can you post some simplified snippets of code that exhibit the problem?

Answer 2

By "contains as list" do you mean that (1) the child controls have been added to .Controls on the parent control, or (2) that you have a list of controls as a variable within the parent control?

If (1) is the case, you can force a paint of the parent control and all child controls by calling .Refresh() on the parent control. Calling .Invalidate() will not necessarily mean that the control or its children will be painted right away.

If (2) is the case, you should add the controls to .Controls on the parent control to ensure they will be painted.

Answer 3

Try this in the constructor of the control.

this.SetStyle(ControlStyles.UserPaint, true);

Answer 4

I think the Controls has to be chained together using the Controls collection in each of them, so any parent control should have the child control(s) added to its Controls collection which I think how the OnPaint event gets populated.

Answer 5

My bad! I wasn't setting the Location of Class3 controls relative to their parent control and, being larger values than the Size of the parent control, they were always off-screen.

Thanks for your help!