iOS单例

• 声明两个全局的静态实例
  static dispatch_once_t _oneToken;
static ExampleManager _instance;

• 重写allocWithZone方法.此方法为对象分配空间必须调用方法.

+(ExampleManager *)shareInstance{
    dispatch_once(&_oneToken, ^{
        _instance = [[ExampleManager alloc] init];
    });
    return _instance;
}

• 保证copy时相同

-(id)copyWithZone:(NSZone *)zone{
    return _instance;
}

• 释放资源

-(void)destroyInstance{
   
/*
只有置成0,GCD才会认为它从未执行过.它默认为0.这样才能保证下次再次调用shareInstance的时候,再次创建对象.
*/
    _oneToken = 0; 
    _instance = nil;
}

用法实例

ExampleManager *example = [ExampleManager shareInstance];

[[ExampleManager shareInstance] destroyInstance];