When it comes time to present errors or other messages in iOS with UIAlertView it is immediately obvious that a more convenient interface would involve the use of blocks. A search on GitHub shows just about every iOS developer has had the same thought and had a crack at it.
After reviewing the better options (I.e. those that actually had a README with more than a few lines of content) on GitHub it appeared that one of the challenges was how to handle memory. This stems from the wrapper becoming the delegate for the UIAlertView but not having a strong reference from the caller. I saw various solutions to this, most involving adding a extra retain call to keep everything around until the delegate methods were called.
Since my project is using ARC I looked for a solution that
didn’t involve marking the wrapper file as non-ARC and
retain. The solution I came up with was to use
objc_setAssociatedObject. This Objective-C runtime
function allows one object to be associated with another using various
memory management strategies. I used this to associate the UIAlertView
blocks based wrapper with the UIAlertView.
init method the wrapper instance is associated with its UIAlertView:
objc_setAssociatedObject(alertView, _cmd, self, OBJC_ASSOCIATION_RETAIN);
Note that I’m using the implicit second argument to the method, its
_cmd as the key for the associated object. This was
suggested in a tweet by Bill Bumgarner.
alertView:didDismissWithButtonIndex:, the association
dealloc of the wrapper called as a result and the
UIAlertView also released.
SEL key = @selector(initWithTitle:message:); objc_setAssociatedObject(self.alertView, key, nil, OBJC_ASSOCIATION_RETAIN);