When I have use ARC in IOS project,how can I use void *?

1
votes

LooK this method: beginAnimations:context: This is a method of class UIView. The context need parameter which is a type of void-pointer,and I need to send a UIImageView to context. I get a warning,which says void* has been forbidden when I use ARC. So how can I send UIImageView to context except not use ARC.

1
objective-cautomatic-ref-countingvoid-pointers
Use UIView's block animation methods. It's more convenient because you don't neet an animation completion delegate somewhere else. – Nicolas Miari
Plus the docs say to use the block animation methods. – Jack Lawrence
Thanks for help.I will learn to use UIView's block animation methods. – Sky Dragon

1 Answers

0
votes

The comments above provided the correct answer for this particular case (use the block-based animation methods) but in general if you have an API which takes a context void * and you'd like to pass an object, I find it best to convert your id to a CFTypeRef so you can get manual memory management semantics on the pointer (CFTypeRef is a typedef for void *), etc. Note however that this requires that the callback must be called in order to get your object released (i.e. converted back to ARC's built-in management).

Here's an example for some imaginary API I just dreamt up:

- (void) doSomethingWithObject: (id) object {
    // use CFBridgingRetain() to turn object into a manually-retained CFTypeRef/void*
    [someObject performBackgroundTaskWithTarget: self
                                       selector: @selector(bgTask:)
                                        context: CFBridgingRetain(object)];
}

- (void) bgTask: (void *) context
{
    // use CFBridgingRelease() to turn our void*/CFTypeRef into an ARC-managed id
    id object = CFBridgingRelease((CFTypeRef)context);
    ...
}