ios: why NSManagedObjectID object cannot be weak reference?

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?

Why do you store `NSManagedObjectID` in a property? It may not work as you expect, take a look at this answer: http://stackoverflow.com/a/2821001/2128900 — Michał Ciuba, Oct 22 '14 at 08:38
I add this code '@synthesize locatedMessageID = _locatedMessageID; ', got the same error. — Zhang Jiuzhou, Oct 24 '14 at 02:56

Mundi · Answer 1 · 2015-08-31T11:20:31.693

-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.

edited Aug 31 '15 at 11:20

answered Oct 22 '14 at 14:42

Mundi

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Actually, do the opposite. A managed object is a collection of references to things in the context, identified by the managed object id - this is why using the object ID is often preferable to using the managed object. – quellish Oct 23 '14 at 02:09

ios: why NSManagedObjectID object cannot be weak reference?

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