Which delegate proxy objects in iOS use weak and assign?

When defining delegate objects, we often see that we can use weak and assign but which one is more appropriate?

First: Using assign, the declared object even if the object is destroyed, but the pointer is still present, thus causing the declared object to become a wild pointer, which results in a memory leak.

With weak, when the object is destroyed, it will be delegate = nil, so that there is no wild pointer to this situation.

So the answer is obviously that when we define proxy objects, we usually use weak to decorate them.

Which delegate proxy objects in iOS use weak and assign?