iOS Automatic memory management ARC

Today, a BUG broke out in the company, leading to 5000+crash.

Roughly, the delegate in UIKit visited the already released interface, which is the use of wild pointers to cause crash.

Come back and demonstrate the discovery

@property (nonatomic, assign) id<mycelldelegate> Delegate;//1@property (nonatomic, weak) id<mycelldelegate > DELEGATE;//2

Most of the UIKit's delegate are statements like 1.

Because iOS doesn't have ARC before 5, it's written assign for compatibility.

So what's the difference between assign and weak?

__strong nsstring *yourstring = [[NSString alloc] initwithutf8string: "Your string"];__weak nsstring *mystring = YourStrin   G   yourstring = nil;  __unsafe_unretained nsstring *theirstring = myString; Now all the pointers are nil

Weak attribute, if the point of memory is released, then automatically points to nil;

So using weak is not a wild pointer.

and assign and unsafe_unretained, always point to a memory address, if the memory is released, you will become a wild pointer

As follows

__strong nsstring *yourstring = @ "Your String";   __weak nsstring *mystring = yourstring;  __unsafe_unretained nsstring *theirstring = myString;   yourstring = nil; Now the yourstring and mystring pointers are nil, and theirstring is not nil, but it is a wild pointer.

So when we use the delegate in UIKit, we want to avoid responding to delegate's VC, or View-like instances being released prematurely, resulting in crash

Our own delegate can be written directly into weak, which avoids circular references and does not produce wild pointers.

Ps:assign can only be used in the definition of a property, the definition of a variable could be used in a similar unsafe_unretained

That's all ...

iOS Automatic memory management ARC