傻瓜学编程之block_2

Posted 2020-10-10 肖无情

block的实质

以一个简单的实现为列子；

- (void)myBlcokTest{
    void (^blk)()=^{
        printf(@“beijinghuanyingni”);
    };
    blk();
}
    

 终端：clang -rewrite-objc 类文件名.m

cpp文件中关键代码：

    static void _I_People_myBlcokTest(People * self, SEL _cmd) {
        void (*blk)()=((void (*)())&__People__myBlcokTest_block_impl_0((void *)__People__myBlcokTest_block_func_0, &__People__myBlcokTest_block_desc_0_DATA));
        ((void (*)(__block_impl *))((__block_impl *)blk)->FuncPtr)((__block_impl *)blk);

    }
    

    
    static void __People__myBlcokTest_block_func_0(struct __People__myBlcokTest_block_impl_0 *__cself) {
        printf("woshinidexiaodaye");
    }
    

    struct __People__myBlcokTest_block_impl_0 {  
        struct __block_impl impl;
        struct __People__myBlcokTest_block_desc_0* Desc;
        __People__myBlcokTest_block_impl_0(void *fp, struct __People__myBlcokTest_block_desc_0 *desc, int flags=0) {
            impl.isa = &_NSConcreteStackBlock;
            impl.Flags = flags;
            impl.FuncPtr = fp;
            Desc = desc;
        }
    };
    
//    第一个成员
    struct __block_impl {
        void *isa;
        int Flags;
        int Reserved;
        void *FuncPtr;
    };
//    第二个成员
    static struct __People__myBlcokTest_block_desc_0 {
        size_t reserved;// 升级版本所需要的区域
        size_t Block_size;//block大小
    } __People__myBlcokTest_block_desc_0_DATA = { 0, sizeof(struct __People__myBlcokTest_block_impl_0)};  

 

运行时的myBlcokTest方法；

 static void _I_People_myBlcokTest(People * self, SEL _cmd) {
        
        void (*blk)()=((void (*)())&__People__myBlcokTest_block_impl_0((void *)__People__myBlcokTest_block_func_0, &__People__myBlcokTest_block_desc_0_DATA));
        
        ((void (*)(__block_impl *))((__block_impl *)blk)->FuncPtr)((__block_impl *)blk);

 }

去掉类型转化

 

static void _I_People_myBlcokTest(People * self, SEL _cmd) {
        __People__myBlcokTest_block_impl_0 blk = __People__myBlcokTest_block_impl_0( __People__myBlcokTest_block_func_0, &__People__myBlcokTest_block_desc_0_DATA));
        
      、、、
    }

__People__myBlcokTest_block_impl_0：是一个结构体 包含两个成员：

struct __block_impl impl;

struct __People__myBlcokTest_block_desc_0* Desc;

以及一个构造函数：
  __People__myBlcokTest_block_impl_0(void *fp, struct __People__myBlcokTest_block_desc_0 *desc, int flags=0) 

 

struct __People__myBlcokTest_block_impl_0 {  
    成员一：    struct __block_impl impl;   // __block_impl结构体

                  struct __block_impl {
                             void *isa;
                             int Flags;
                             int Reserved;
                             void *FuncPtr;
                    };

     成员二：     struct __People__myBlcokTest_block_desc_0* Desc;//__People__myBlcokTest_block_desc_0结构体

                        static struct __People__myBlcokTest_block_desc_0 {
                              size_t reserved;// 升级版本所需要的区域
                               size_t Block_size;//block大小
                         } 

  构造函数：

          构造函数中成员的处理 在后面 构造函数中参数的处理部分解释；
         __People__myBlcokTest_block_impl_0(void *fp, struct __People__myBlcokTest_block_desc_0 *desc, int flags=0)
         {
                impl.isa = &_NSConcreteStackBlock; 
                impl.Flags = flags;
                impl.FuncPtr = fp;
                Desc = desc; 
           }
};

 

通过结构体的构造函数生成一个block实例

 __People__myBlcokTest_block_impl_0 blk = __People__myBlcokTest_block_impl_0( __People__myBlcokTest_block_func_0,
                                                                               &__People__myBlcokTest_block_desc_0_DATA));

 构造函数参数的意义：

参数一：    __People__myBlcokTest_block_func_0  //函数实现地址  在把函数赋值给函数指针的时候可以省略&；
在构造函数参数的意义： 把函数的地址赋值给指针 void *fp
函数的具体实现代码：

static void __People__myBlcokTest_block_func_0(struct __People__myBlcokTest_block_impl_0 *__cself) {
        printf("woshinidexiaodaye");
    }

这里面的__cself是什么后面会解释；

参数二： &__People__myBlcokTest_block_desc_0_DATA // __People__myBlcokTest_block_desc_0的默认初始化
 { 0, sizeof(struct __People__myBlcokTest_block_impl_0) //使用__People__myBlcokTest_block_impl_0的大小进行初始化

具体代码：
 static struct __People__myBlcokTest_block_desc_0 {
        size_t reserved;// 升级版本所需要的区域
        size_t Block_size;//block大小
    } __People__myBlcokTest_block_desc_0_DATA = { 0, sizeof(struct __People__myBlcokTest_block_impl_0)};

 

 函数指针 与指针函数点击这里

构造函数中参数的处理

 __People__myBlcokTest_block_impl_0(void *fp, struct __People__myBlcokTest_block_desc_0 *desc, int flags=0)
           { 
                impl.isa = &_NSConcreteStackBlock;
                impl.Flags = flags;
                impl.FuncPtr = fp;
                Desc = desc;
            } 
赋值之后：

__People__myBlcokTest_block_impl_0(void *fp, struct __People__myBlcokTest_block_desc_0 *desc, int flags=0)
           { 
                impl.isa = &_NSConcreteStackBlock;//_NSConcreteStackBlock用于初始化isa成员  后面具体解释

                impl.Flags = 0;
                impl.FuncPtr =__People__myBlcokTest_block_func_0;
                imlp.Reserved=0;

                Desc =__People__myBlcokTest_block_desc_0_DATA;

            }

  再来看看block的调用：  

     blk();

((void (*)(__block_impl *))((__block_impl *)blk)->FuncPtr)((__block_impl *)blk);

 简化

 ((__block_impl *)blk)->FuncPtr)((__block_impl *)blk); =>(blk ->FuncPtr)(blk)

 获取blk结构体中函数指针FuncPtr 通过该函数指针调用函数 并且参数值为blk   点击这里；

 

这个等价于

(blk ->FuncPtr)(blk) 相当于

   blk -> __People__myBlcokTest_block_func_0（blk）;

再看看

static void __People__myBlcokTest_block_func_0(struct __People__myBlcokTest_block_impl_0 *__cself) {
        printf("woshinidexiaodaye");
    }

说明 __cself 就是blk 本身；