After reading MJ's explanation of the single case of personal summary

1, the introduction of a single case

Singleton is one of the most common development patterns for iOS.

2, what is a single case

A singleton is a class that creates only one object and allocates only one memory space.

3, single case of the application scenario

1) System of single example: [uiapplication sharedapplication];

2) Application of the single example: QQ background map, etc.

4. Precautions for single case

1) always allocate only one piece of memory to create objects

2) provides a class method that returns an internally unique object (one instance)

3) It is best to ensure that the Init method is initialized only once

5, the creation of a single case

1) Overriding the allocation memory method

// override method for allocating memory + (Instancetype) Allocwithzone: (struct _nszone *) zone{    static  dispatch_once_t Once_token;    Dispatch_once (&once_token, ^{        // guaranteed to allocate only once memory        _instance = [ Super Allocwithzone:zone];            });     return _instance;    }

2) Creating a class method

// Create share Method + (instancetype) shareperson{    static  dispatch_once_t Oncetoken;    Dispatch_once (&oncetoken, ^{       // is only init once        _instance = [[Self Alloc]init];            });     return _instance;}

3) Overriding the Init method

- (instancetype) init{    if (self = [Super init]) {        static  dispatch_once _t Oncetoken;        Dispatch_once (&oncetoken, ^{            // Assignment, initialize resource         });     return Self ;}

6. Single-instance invocation and output results

1) Invocation of a single case

Person * Mark = [person Shareperson];    person * Mary = [[Person alloc]init];    NSLog (@ "Mark---%p  mary----  %p", mark,mary);

2) output of single case

2016-03-02 21:38:30.743 single[2104:190961] Mark---0x7fe6325488e0  mary----  

After reading MJ's explanation of the single case of personal summary