Setting the contents of a CALayer to a CGImageRef on iOS with ARC on

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