Is drawrect more efficient for coregraphcs drawing than using core graphics in touches moved?

Question

My whole app uses touchesMoved for drawing (Coregraphics). Should I be calling [self setNeedsDisplay] from within touchesMoved instead of performing the drawing code in there? Would that stop some lag that I am experiencing? The only reason I didn't try this before posting is because it is going to take me a few hours to convert all drawing to within drawRect and I wanted to know if it would be more would efficient than drawing in touchesMoved?

Answer 1

Yes. You should always keep your drawing in drawRect and use setNeedsDisplay to trigger the actual drawing. This is key to the rendering of views in Cocoa Touch.

For example, if you didn't use this method, you could potentially have drawing code scattered around your class in multiple methods. In addition, this also ensures that your drawing code executes only once during a render cycle. Essentially, calling setNeedsDisplay triggers an invalidation flag that lets your UIView know to redraw itself. Without this, you could be performing extra drawing operations that aren't actually needed due to the render cycle.