问题
As you read here in most cases a IBOutlet should be weak.
Now as you can read in the development library not all classes support weak references. (e.g. NSTextView). This means you have to use assign:
@property (assign) IBOutlet NSTextView *textView;
If you use a weak reference you will get the following error: "Synthesis of a weak-unavailable property is disallowed because it requires synthesis of an ivar of the __weak object"
What the documentation missed to mention is now you have to set the property again to nil after it's usage e.g. by a dealloc method:
- (void)dealloc
{
self.textView = nil;
}
As far as I understood classes marked with NS_AUTOMATED_REFCOUNT_WEAK_UNAVAILABLE don't support weak references but what is the reason?
回答1:
I think I found the reason why some classes don't support a weak reference:
As you can read here:
Rationale: historically, it has been possible for a class to provide its own reference-count implementation by overriding retain, release, etc. However, weak references to an object require coordination with its class's reference-count implementation because, among other things, weak loads and stores must be atomic with respect to the final release. Therefore, existing custom reference-count implementations will generally not support weak references without additional effort. This is unavoidable without breaking binary compatibility.
来源：https://stackoverflow.com/questions/12882710/iboutlet-for-nstextview-in-a-arc-project