轉載地址：部落格地址
ARC下
@property (nonatomic, weak/assign) id delegate;
相當於
- (void)setDelegate:(id)delegate
{
if (_delegate != delegate) {
_delegate = delegate;
}
}

MRC下
@property (nonatomic, strong/retain/copy) id delegate;
相當於

• (void)setDelegate:(id)delegate
  {
  if (_delegate != delegate) {
  [_delegate release];
  _delegate = [delegate retain/copy];
  }
  }