_weak typeof (self) weakself = self

(i) Principles of memory management

1, the default strong, optional weak. Strong, regardless of the member variable or property, each time the pointer is used to point to an object, is equal to automatically call retain (), and call Release () on the old object, so set to nil equals release.
2, as long as an object is pointed to by any strong pointer, then it will not be destroyed, or immediately released, do not wait for Runloop end. All strong pointer variables do not need to be manually set to Nil,ios in Dealloc, and debug can see that all of the variables that were declared are nil, and the first declaration of the variable is finally called Dealloc released.

3, the official proposal Iboutlet add __weak, actually do not add also will automatically release;

4. Use private member variables preferentially, unless you need to expose properties.

5, avoid circular reference, otherwise set nil release manually.

6, block method Common declaration: @property (copy) void (^myblock) (void); If you continue to use block after the current scope is exceeded, it is best to use the Copy keyword to copy to the heap area to prevent the stack variable from being destroyed.

7. It is generally necessary to weak the self before creating the block anonymous function. _weak typeof (self) weakself = Self

typeof (self) is the type that gets to self, so that the definition of weakself is a type of self, plus __weak is to create a reference, the whole sentence is to self define a reference to the nature of the alias;
This is generally used when using block, because the block will copy its internal variables, may cause a reference loop, using the __weak nature of self instead of self, you can cut off the block reference to self, avoid circular reference

_weak typeof (self) weakself = self