The difference between __weak and __block

__weakitself can avoid the problem of circular reference, but it will cause the external object to be released after the object is not accessed inside the block, we can point to the weakobj by declaring a variable inside the block __strong , so that the external object can be held inside the block, To avoid the problem of circular references

__blockThe problem of circular references cannot be avoided by itself, but we can avoid circular references by manually assigning the blockobj to nil within the block. The other point is that the __block modified variables are unique inside and outside the block, so be aware of the potential pitfalls of this feature.

The difference between __weak and __block