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；
