iOS：为什么NSManagedObjectID对象不能弱引用？

Question

I have a weak property:

@property (nonatomic,weak) NSManagedObjectID *locatedMessageID;

App will crash when calling -(void)setLocatedMessageId . The error is:

EXC_BAD_INSTRUCTION(code=EXC_I386_INVOP).

To solve this problem, only replace 'weak' keyword to 'assign'.

@property (nonatomic,assign) NSManagedObjectID *locatedMessageID;

But is it safe? Why I cannot use weak property here?

Answer 1

NSManagedObjectID is not advisable. Use the object itself instead. You have convenient access to all associated objects and attributes - there is really no need to explicitly fetch the object again based on the object ID.

Contrary to the comment below, you are better off with the object itself.