Should I create new Pens/Brushes per Paint request or keep them throughout the application lifecycle?

Question

I have an application that does a lot of drawing, let\'s pretend it\'s a Viso-like application. It has objects that have multiple sub-objects that are drawn, things can

Answer 1

You'll only know the performance impact by testing on your particular application, but the framework doesn't seem to have a problem keeping a few pens around for the life of the application. The first time you call Pens.Black, it creates a black pen and caches it. You get the same object back for future calls, and it's never explicitly disposed (Pens.Black.Dispose() will actually throw an exception). However, you don't want to blindly create pens and leave them to be disposed when the application ends, because you'll be leaking unmanaged memory. A couple of options spring to mind depending on the pattern of usage in your app.

Give each object a private Pen that's created when ForeColor is set and reused for all painting. You should make your object IDisposable so that it can dispose of that Pen properly.

If you're using relatively few distinct colours but lots of objects use each colour, you may not want each object to hold on to its own Pen. Create some cache class that keeps a Dictionary and hands them out through a PenCache.GetPen(ForeColor). Like using Pens.Black, you can now forget about disposing them. A problem arises if you use a colour briefly, then don't need it again. The Pen got cached, so you're stuck with it in memory forever. You could keep a Dictionary> instead, allowing cached pens to be eventually garbage collected if they're no longer needed.

That last option may be the best general purpose solution, avoiding gratuitous creation and disposal while letting the garbage collector make sure that orphaned pens don't cause too much memory trouble. It may, of course, not be any better in your particular case.