1.Block的本质是一个结构体指针, 回调原理: 通过当前的block对应的结构体指针找到对应的结构体,然后在结构体中找到对应的函数名称, 最后调用函数 . 2.通过__block \ static \ 全局变量 修饰或定义的变量,传入到 block 对应的结构体中实质时传入了对应的变量地址& a, 所以修改变量后block 内部的变量也随着响应的改变. 3.局部静态变量则传入的是实际的值, 所以即便修改原来的变量 block 内部的值仍不会变化. EG: ObjC 代码: #import <Foundation/Foundation.h>
// 局部变量
void test1(){
int a = 10 ;
void (^block)() = ^{
NSLog( @"test1 a = %d" , a);
};
a = 20 ;
block();
}
// 局部静态变量
void test2(){
static int a = 10 ;
void (^block)() = ^{
NSLog( @"test2 a = %d" , a);
};
a = 20 ;
block();
}
//__block 修饰
void test3(){
__block int a = 10 ;
void (^block)() = ^{
NSLog( @"test3 a = %d" , a);
};
a = 20 ;
block();
}
// 全局变量调用
int a = 30 ;
void test4(){
a = 50 ;
void (^block)() = ^{
NSLog( @"test4 a = %d" , a);
};
a = 20 ;
block();
}
int main( int argc, const char * argv[]) {
@autoreleasepool {
test1(); //10
test2(); //20
test3(); //20
test4(); //20
}
return 0 ; } 编译过后的c++代码; struct __test1_block_impl_0 { struct __block_impl impl;
struct __test1_block_desc_0* Desc;
int a;
__test1_block_impl_0( void *fp, struct __test1_block_desc_0 *desc, int _a, int flags= 0 ) : a(_a) {
impl.isa = &_NSConcreteStackBlock;
impl.Flags = flags;
impl.FuncPtr = fp;
Desc = desc;
}
};
static void __test1_block_func_0( struct __test1_block_impl_0 *__cself) {
int a = __cself->a; // bound by copy
NSLog((NSString *)&__NSConstantStringImpl__var_folders_0n_2blpmxd960zf5lxdfdrd9l9r0000gn_T_main_504a7b_mi_0, a);
}
static struct __test1_block_desc_0 {
size_t reserved;
size_t Block_size;
} __test1_block_desc_0_DATA = { 0 , sizeof ( struct __test1_block_impl_0)};
void test1(){
int a = 10 ;
void (*block)() = (( void (*)())&__test1_block_impl_0(( void *)__test1_block_func_0, &__test1_block_desc_0_DATA, a));
a = 20 ;
(( void (*)(__block_impl *))((__block_impl *)block)->FuncPtr)((__block_impl *)block);
}
struct __test2_block_impl_0 {
struct __block_impl impl;
struct __test2_block_desc_0* Desc;
int *a;
__test2_block_impl_0( void *fp, struct __test2_block_desc_0 *desc, int *_a, int flags= 0 ) : a(_a) {
impl.isa = &_NSConcreteStackBlock;
impl.Flags = flags;
impl.FuncPtr = fp;
Desc = desc;
}
};
static void __test2_block_func_0( struct __test2_block_impl_0 *__cself) {
int *a = __cself->a; // bound by copy
NSLog((NSString *)&__NSConstantStringImpl__var_folders_0n_2blpmxd960zf5lxdfdrd9l9r0000gn_T_main_504a7b_mi_1, (*a));
}
static struct __test2_block_desc_0 {
size_t reserved;
size_t Block_size;
} __test2_block_desc_0_DATA = { 0 , sizeof ( struct __test2_block_impl_0)};
void test2(){
static int a = 10 ;
void (*block)() = (( void (*)())&__test2_block_impl_0(( void *)__test2_block_func_0, &__test2_block_desc_0_DATA, &a));
a = 20 ;
(( void (*)(__block_impl *))((__block_impl *)block)->FuncPtr)((__block_impl *)block);
}
struct __Block_byref_a_0 {
void *__isa;
__Block_byref_a_0 *__forwarding;
int __flags;
int __size;
int a;
};
struct __test3_block_impl_0 {
struct __block_impl impl;
struct __test3_block_desc_0* Desc;
__Block_byref_a_0 *a; // by ref
__test3_block_impl_0( void *fp, struct __test3_block_desc_0 *desc, __Block_byref_a_0 *_a, int flags= 0 ) : a(_a->__forwarding) {
impl.isa = &_NSConcreteStackBlock;
impl.Flags = flags;
impl.FuncPtr = fp;
Desc = desc;
}
};
static void __test3_block_func_0( struct __test3_block_impl_0 *__cself) {
__Block_byref_a_0 *a = __cself->a; // bound by ref
NSLog((NSString *)&__NSConstantStringImpl__var_folders_0n_2blpmxd960zf5lxdfdrd9l9r0000gn_T_main_504a7b_mi_2, (a->__forwarding->a));
}
static void __test3_block_copy_0( struct __test3_block_impl_0*dst, struct __test3_block_impl_0*src) {_Block_object_assign(( void *)&dst->a, ( void *)src->a, 8 );}
static void __test3_block_dispose_0( struct __test3_block_impl_0*src) {_Block_object_dispose(( void *)src->a, 8 );}
static struct __test3_block_desc_0 {
size_t reserved;
size_t Block_size;
void (*copy)( struct __test3_block_impl_0*, struct __test3_block_impl_0*);
void (*dispose)( struct __test3_block_impl_0*);
} __test3_block_desc_0_DATA = { 0 , sizeof ( struct __test3_block_impl_0), __test3_block_copy_0, __test3_block_dispose_0};
void test3(){ __attribute__((__blocks__(byref))) __Block_byref_a_0 a = {(void*)0,(__Block_byref_a_0 *) &a , 0, sizeof(__Block_byref_a_0), 10}; void (*block)() = ((void (*)())&__test3_block_impl_0((void *)__test3_block_func_0, &__test3_block_desc_0_DATA, (__Block_byref_a_0 *) &a , 570425344)); (a.__forwarding->a) = 20 ;
(( void (*)(__block_impl *))((__block_impl *)block)->FuncPtr)((__block_impl *)block);
}
int a = 30 ;
struct __test4_block_impl_0 {
struct __block_impl impl;
struct __test4_block_desc_0* Desc;
__test4_block_impl_0( void *fp, struct __test4_block_desc_0 *desc, int flags= 0 ) {
impl.isa = &_NSConcreteStackBlock;
impl.Flags = flags;
impl.FuncPtr = fp;
Desc = desc;
}
};
static void __test4_block_func_0( struct __test4_block_impl_0 *__cself) {
NSLog((NSString *)&__NSConstantStringImpl__var_folders_0n_2blpmxd960zf5lxdfdrd9l9r0000gn_T_main_504a7b_mi_3, a);
}
static struct __test4_block_desc_0 {
size_t reserved;
size_t Block_size;
} __test4_block_desc_0_DATA = { 0 , sizeof ( struct __test4_block_impl_0)};
void test4(){
a = 50 ;
void (*block)() = (( void (*)())&__test4_block_impl_0(( void *)__test4_block_func_0, &__test4_block_desc_0_DATA));
a = 20 ;
(( void (*)(__block_impl *))((__block_impl *)block)->FuncPtr)((__block_impl *)block);
}
int main( int argc, const char * argv[]) {
{ __AtAutoreleasePool __autoreleasepool;
test1();
test2();
test3();
test4();
}
return 0 ; }
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