Block 的小技巧

//在block里再改变 指针的属性  设置为weak的strong
//判断string的值是否为NULL 不为NULL执行需要的代码

#define WS(weak_self) _weak typeof(self) weak_self = self
//block的防止循环引用的问题
_weak typeof(self) weak_self = self;

dispath_block block = ^{
    [weakself xxxxxx];
} 

//防止block里面的weak self is nil
_weak type(self) weak_self = self
class.Block = ^{
    _strong typefo(self) strong_self = weak_self
    if(strong_self){//判断weak_self is NULL
    //执行代码
    }else{
    return  //直接返回
    }
}