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 = selfclass.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    }}