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;

05-02 16:46