參考文章:iOS block海洼，你要看的這都有,
block沒那么難
一、Block寫法
1背稼、屬性
@property (nonatomic,copy) void(^myblock)(int);
2贰军、typedef 定義Block類型
typedef void(^responseBlock)(NSDictionary * response,BOOL success);
3、直接寫
- (void)haveFunWithBlock:(void(^)(NSMutableDictionary * dic,BOOL success))funBlock
二蟹肘、Block結(jié)構(gòu)
block內(nèi)部的3個(gè)結(jié)構(gòu)體
// block結(jié)構(gòu)體
struct __main_block_impl_0 {
// impl結(jié)構(gòu)體词疼，即block的主結(jié)構(gòu)體
struct __block_impl impl;
// Desc結(jié)構(gòu)體，即block的描述結(jié)構(gòu)體
struct __main_block_desc_0* Desc;
// block結(jié)構(gòu)體的構(gòu)造函數(shù)
__main_block_impl_0(void *fp, struct __main_block_desc_0 *desc, int flags=0) {
impl.isa = &_NSConcreteStackBlock;
impl.Flags = flags;
impl.FuncPtr = fp;
Desc = desc;
}
};
// impl結(jié)構(gòu)體
struct __block_impl {
void *isa; // 存儲位置帘腹，_NSConcreteStackBlock贰盗、_NSConcreteGlobalBlock、_NSConcreteMallocBlock
int Flags; // 按位承載 block 的附加信息
int Reserved; // 保留變量
void *FuncPtr; // 函數(shù)指針阳欲，指向 Block 要執(zhí)行的函數(shù)舵盈，即__main_block_func_0
};
// Desc結(jié)構(gòu)體
static struct __main_block_desc_0 {
size_t reserved; // 結(jié)構(gòu)體信息保留字段
size_t Block_size; // 結(jié)構(gòu)體大小
} __main_block_desc_0_DATA = { 0, sizeof(struct __main_block_impl_0)};
一、無變量截獲
OC代碼
typedef int (^Block)(void);
int main(int argc, char * argv[]) {
// block實(shí)現(xiàn)
Block block = ^{
return 0;
};
// block調(diào)用
block();
return 0;
}
C代碼
// block方法實(shí)現(xiàn)
static int __main_block_func_0(struct __main_block_impl_0 *__cself) {
return 0;
}
// main函數(shù)
int main(int argc, char * argv[]) {
// block實(shí)現(xiàn)
Block block = ((int (*)())&__main_block_impl_0((void *)__main_block_func_0, &__main_block_desc_0_DATA));
// block調(diào)用
((int (*)(__block_impl *))((__block_impl *)block)->FuncPtr)((__block_impl *)block);
return 0;
}
block實(shí)現(xiàn)：調(diào)用block結(jié)構(gòu)體的構(gòu)造函數(shù)
_main_block_impl_0來實(shí)現(xiàn)block球化，可見秽晚，傳入的兩個(gè)參數(shù)，分別是函數(shù)_main_block_func_0的指針(block方法實(shí)現(xiàn))和_main_block_desc_0結(jié)構(gòu)體筒愚。block調(diào)用：將block作為參數(shù)傳入block中的FuncPtr赴蝇，也即
_main_block_func_0方法，進(jìn)行調(diào)用巢掺。
二句伶、截獲變量
1、截獲變量的block結(jié)構(gòu)體實(shí)現(xiàn)
OC代碼
typedef int (^Block)(void);
int main(int argc, char * argv[]) {
int i = 0;
Block block = ^{
return i;
};
block();
return 0;
}
C代碼
struct __main_block_impl_0 {
struct __block_impl impl;
struct __main_block_desc_0* Desc;
int i;
__main_block_impl_0(void *fp, struct __main_block_desc_0 *desc, int _i, int flags=0) : i(_i) {
impl.isa = &_NSConcreteStackBlock;
impl.Flags = flags;
impl.FuncPtr = fp;
Desc = desc;
}
};
// main函數(shù)
int main(int argc, char * argv[]) {
int i = 0;
Block block = ((int (*)())&__main_block_impl_0((void *)__main_block_func_0, &__main_block_desc_0_DATA, i));
((int (*)(__block_impl *))((__block_impl *)block)->FuncPtr)((__block_impl *)block);
return 0;
}
與無變量截獲的樣例區(qū)別:
block結(jié)構(gòu)體中多了一個(gè)變量i,但是這個(gè)變量copy之后是const類型(: i(_i)則是c++語法結(jié)構(gòu)體中const類型變量的初始化方式陆淀，即將參數(shù)_i賦值給block結(jié)構(gòu)體中的變量i考余。)
2、block截獲變量的時(shí)機(jī)
block在構(gòu)造的時(shí)刻轧苫，會將參數(shù)i傳入結(jié)構(gòu)體中進(jìn)行初始化楚堤，所以，block會在實(shí)現(xiàn)的地方(非調(diào)用的時(shí)刻)截獲變量，而截獲的變量的值也是實(shí)現(xiàn)時(shí)刻的變量值身冬。
三鳄袍、截獲變量的類型
block可以中的外部變量一共有五種，依次是全局變量吏恭、全局靜態(tài)變量、局部靜態(tài)變量重罪、_block修飾的變量和一個(gè)局部變量（截獲后為const類型）
OC代碼
// block截獲變量樣例代碼
#import <UIKit/UIKit.h>
typedef int (^Block)(void);
int a = 0;
static int b = 0;
int main(int argc, char * argv[]) {
static int c = 0;
int i = 0;
NSMutableArray *arr = [NSMutableArray array];
Block block = ^{
a = 1;
b = 1;
c = 1;
[arr addObject:@"1"];
return i;
};
block();
return 0;
}
C代碼
// block結(jié)構(gòu)體和構(gòu)造函數(shù)
struct __main_block_impl_0 {
struct __block_impl impl;
struct __main_block_desc_0* Desc;
int *c;
NSMutableArray *arr;
int i;
__main_block_impl_0(void *fp, struct __main_block_desc_0 *desc, int *_c, NSMutableArray *_arr, int _i, int flags=0) : c(_c), arr(_arr), i(_i) {
impl.isa = &_NSConcreteStackBlock;
impl.Flags = flags;
impl.FuncPtr = fp;
Desc = desc;
}
};
// block實(shí)現(xiàn)的方法
static int __main_block_func_0(struct __main_block_impl_0 *__cself) {
int *c = __cself->c; // bound by copy
NSMutableArray *arr = __cself->arr; // bound by copy
int i = __cself->i; // bound by copy
a = 1;
b = 1;
(*c) = 1;
((void (*)(id, SEL, ObjectType))(void *)objc_msgSend)((id)arr, sel_registerName("addObject:"), (id)(NSString *)&__NSConstantStringImpl__var_folders_k__6b9p9yt96y9dq8ds8_kvf3kh0000gn_T_main_3c9752_mi_0);
return i;
}
// mian函數(shù)
int main(int argc, char * argv[]) {
static int c = 0;
int i = 0;
NSMutableArray *arr = ((NSMutableArray *(*)(id, SEL))(void *)objc_msgSend)((id)objc_getClass("NSMutableArray"), sel_registerName("array"));
Block block = ((int (*)())&__main_block_impl_0((void *)__main_block_func_0, &__main_block_desc_0_DATA, &c, arr, i, 570425344));
((int (*)(__block_impl *))((__block_impl *)block)->FuncPtr)((__block_impl *)block);
return 0;
}
1樱哼、全局變量a、和靜態(tài)全局變量b為第一類剿配，block可以直接修改搅幅。
2、局部靜態(tài)變量c呼胚，從block構(gòu)造函數(shù)可以看出此處傳入的是c的指針茄唐，所以可以更改c
3、局部基本變量i蝇更，局部對象arr沪编，可以發(fā)現(xiàn)i不能修改，而arr因?yàn)槭菍ο竽昀梢詫ο筮M(jìn)行操作（但不能對給arr重新指向其他地址）蚁廓，這時(shí)需要注意的是，block內(nèi)部的i和arr均為const類型厨幻，所以均不能對其進(jìn)行修改
四相嵌、_block作用
__block會將局部變量拷貝到堆上，并生成一個(gè)帶有指向自己的_forwarding指針况脆，然后傳入_forwarding給結(jié)構(gòu)體構(gòu)造函數(shù)饭宾。
OC代碼
// 使用_block的樣例
#import <UIKit/UIKit.h>
typedef int (^Block)(void);
int main(int argc, char * argv[]) {
__block int i = 2;
Block block = ^{
i = 1;
arr = [NSMutableArray array];
return i;
};
block();
return 0;
}
C代碼
// 執(zhí)行xcrun -sdk iphonesimulator9.3 clang -rewrite-objc main.m后代碼
// __block為變量i創(chuàng)建的結(jié)構(gòu)體，其中成員i為i的值格了，forwarding為指向自己的指針
struct __Block_byref_i_0 {
void *__isa;
__Block_byref_i_0 *__forwarding;
int __flags;
int __size;
int i;
};
// block結(jié)構(gòu)體
struct __main_block_impl_0 {
struct __block_impl impl;
struct __main_block_desc_0* Desc;
__Block_byref_i_0 *i; // by ref
__main_block_impl_0(void *fp, struct __main_block_desc_0 *desc, __Block_byref_i_0 *_i, __Block_byref_arr_1 *_arr, int flags=0) : i(_i->__forwarding) {
impl.isa = &_NSConcreteStackBlock;
impl.Flags = flags;
impl.FuncPtr = fp;
Desc = desc;
}
};
五看铆、block的存儲類型
isa表示的三種存儲位置_NSConcreteStackBlock、_NSConcreteGlobalBlock笆搓、_NSConcreteMallocBlock
1性湿、_NSConcreteGlobalBlock
全局聲明實(shí)現(xiàn)的block
局部block未截取任何變量
// a、全局聲明實(shí)現(xiàn)的block
// clang編譯后可發(fā)現(xiàn)isa指針為_NSConcreteGlobalBlock
#import <UIKit/UIKit.h>
typedef int (^Block)(void);
Block globalBlock = ^{
return 0;
};
int main(int argc, char * argv[]) {
globalBlock();
return 0;
}
// b满败、局部block未截取任何變量
// clang編譯后可發(fā)現(xiàn)isa指針為_NSConcreteStackBlock肤频，這就看出了clang的不準(zhǔn)確的地方，從此以后算墨，我們通過NSLog打印宵荒。此處NSLog打印出的為_NSConcreteGlobalBlock。
#import <UIKit/UIKit.h>
typedef int (^Block)(void);
int main(int argc, char * argv[]) {
Block globalBlock = ^ {
return 0;
};
globalBlock();
NSLog(@"%@", globalBlock);
return 0;
}
2、_NSConcreteStackBlock
ARC環(huán)境下报咳，大部分情況下編譯器通常會將創(chuàng)建在棧上的 block 自動(dòng)拷貝到堆上侠讯，只有當(dāng)block 作為方法或函數(shù)的參數(shù)傳遞時(shí)，編譯器可能不會自動(dòng)調(diào)用 copy 方法暑刃。
id getBlockArray()
{
int val = 10;
NSLog(@"%@", ^{NSLog(@"blklog:%d", val);});
return [[NSArray alloc] initWithObjects:
^{NSLog(@"blk0:%d", val);},
^{NSLog(@"blk1:%d", val);}, nil];
}
3厢漩、_NSConcreteMallocBlock
常用的都是MallocBlock
