iPhone - Is there a way to know if a reference is (still) valid?

Let's say I assign an instance var with an object given in parameter. I don't know what this object is, so I don't want to retain it. But, that reference I have to that object can be invalid at some time, for examp开发者_开发百科le if the object is released, or is about to be released (autorelease pool). So, inside my class instance, can I know if the reference I have kept into an instance variable can be used without any risk of crash?

You should retain it and release it when you no longer need it. That is exactly what retain is for.

Kris Van Bael is right, no matter if you know what the object is, if you want to have ownership of it (if it's up to you to ensure that the object is alive), you must retain it. Release it when you don't need it, and set the reference to NIL (for security).

But their is an exception !

Sometimes you don't want to have ownership, the most common example is the delegate. You don't want to retain your delegate, because it probably already retains you, and if both objects release each other in the dealloc method, your app will leak.

But in this case, you shouldn't care about the delegate being deallocated : the delegate should set your "delegate" property to nil in it's dealloc method.

So

• if you have ownership on the object : retain, no choice !
• if the object has ownership on you : assign, and don't worry !

This approach is really dangerous. If your app is not able to track object life cycle, then you must change the code in order to have control of this. Anyway answering to your question: you can protect your instance variable by extra retaining it in your class and then releasing it when it is no more needed. So you don't need to do the check you are asking for.

You should set any released reference to NIL and check for NIL.