iOS block中 weakSelf和strongSelf

block在日常开发中非常的常用，并且也十分的简单，但是在block内使用self也会引起循环引用的情况。

void(^myblock)() = ^() {

[self addSubView1];

};

myblock();

一般的解决方法是使用__weak来中断循环引用

__weak __typeof__(self) weakSelf = self;

void(^myblock)() = ^() {

[weakSelf addSubView1];

[weakSelf addSubView2];

};

myblock();

BUT，当self被释放后，也有可能导致weakSelf释放，比如上面的情况中[weakSelf addSubView2]中的weakSelf就有可能被释放，所以还需要

__strong __typeof(self) strongSelf = weakSelf;

来确保后面的weakSelf不被释放，此外在block内涉及使用weakSelf传值的情况也需要注意weakSelf被释放的可能，

__weak __typeof__(self) weakSelf = self;

void(^myblock)() = ^() {

__strong __typeof(self) strongSelf = weakSelf;

[strongSelf addSubView1];

[strongSelf addSubView2];

};

myblock();

总的来说block内涉及到多次使用weakSelf或者类似于通知传值的情况就需要使用strongSelf

这里推荐一个 YYKit 作者关于weakSelf和strongSelf的宏定义写法，使用时

@weakify(self);

@strongify(self);

if (!self) return;

宏定义如下

//--------------------weakSelf和strongSelf------------

#ifndef weakify

#if DEBUG

#if __has_feature(objc_arc)

#define weakify(object) autoreleasepool{} __weak __typeof__(object) weak##_##object = object;

#else

#define weakify(object) autoreleasepool{} __block __typeof__(object) block##_##object = object;

#endif

#else

#if __has_feature(objc_arc)

#define weakify(object) try{} @finally{} {} __weak __typeof__(object) weak##_##object = object;

#else

#define weakify(object) try{} @finally{} {} __block __typeof__(object) block##_##object = object;

#endif

#endif

#endif

#ifndef strongify

#if DEBUG

#if __has_feature(objc_arc)

#define strongify(object) autoreleasepool{} __typeof__(object) object = weak##_##object;

#else

#define strongify(object) autoreleasepool{} __typeof__(object) object = block##_##object;

#endif

#else

#if __has_feature(objc_arc)

#define strongify(object) try{} @finally{} __typeof__(object) object = weak##_##object;

#else

#define strongify(object) try{} @finally{} __typeof__(object) object = block##_##object;

#endif

#endif

#endif

//--------------------end-------------------------