What's the difference between 'weak' and 'assign' in delegate property declaration
The only difference between weak and assign is that if the object a weak property points to is deallocated, then the value of the weak pointer will be set to nil, so that you never run the risk of accessing garbage. If you use assign, that won't happen, so if the object gets deallocated from under you and you try to access it, you will access garbage.
For Objective-C objects, if you're in an environment where you can use weak, then you should use it.