iOS: Using UIView's 'drawRect:' vs. its layer's delegate 'drawLayer:inContext:'

Question

I have a class which is a subclass of UIView. I am able to draw stuff inside the view either by implementing the drawRect method, or by implementin

Answer 1

Here're codes of Sample ZoomingPDFViewer from Apple:

-(void)drawRect:(CGRect)r
{

    // UIView uses the existence of -drawRect: to determine if it should allow its CALayer
    // to be invalidated, which would then lead to the layer creating a backing store and
    // -drawLayer:inContext: being called.
    // By implementing an empty -drawRect: method, we allow UIKit to continue to implement
    // this logic, while doing our real drawing work inside of -drawLayer:inContext:

}

-(void)drawLayer:(CALayer*)layer inContext:(CGContextRef)context
{
    ...
}