问题
The following code compiles fine with manual memory management, but fails under ARC:
CALayer *layer = [CALayer layer];
layer.contents = [[UIImage imageNamed:@"dial.png"] CGImage];
The error is:
Automatic Reference Counting Issue: Implicit conversion of a non-Objective-C pointer type 'CGImageRef' (aka 'struct CGImage *') to 'id' is disallowed with ARC
How can I get this running with ARC?
回答1:
CoreFoundation objets aren't managed by ARC. ARC only works with Objective-C objets and does not implicitly know how to transfer the ownership when casting from (or to) an non-object pointer type.
You need to tell ARC how the ownership of the objet is transferred during the cast:
layer.contents = (__bridge id) [[UIImage imageNamed:@"dial.png"] CGImage];
回答2:
Just cast the result of -CGImage to a id, as it is complaining about implicit conversions...
layer.contents = (id) [[UIImage imageNamed:@"dial.png"] CGImage];
来源：https://stackoverflow.com/questions/8577894/setting-the-contents-of-a-calayer-to-a-cgimageref-on-ios-with-arc-on