從《block-底層數據結構》中,我們知道block的本質就是就是OC對象,他也有isa指針,它既然是對象,那它是屬於什麼類型呢?那這章節,我們來探討下block的類型
block有三種類型,可以通過調用class方法或者isa指針查看具體類型,最終都是繼承NSBlock類型。
NSGlobalBlock (__NSConcreteGlobalBlock)
NSStackBlock (__NSConcreteStackBlock)
NSMallocBlock (__NSConcreteMallocBlock)
先來簡單的看下下面的代碼,通過代碼分析block的類型。
int main(int argc, const char * argv[]) {
@autoreleasepool {
// insert code here...
void (^block)(void) = ^() {
NSLog(@"Hello, World!");
};
NSLog(@"%@",[block class]);
NSLog(@"%@",[[block class] superclass]);
NSLog(@"%@",[[[block class] superclass] superclass]);
NSLog(@"%@",[[[[block class] superclass] superclass] superclass]);
NSLog(@"%@",[[[[[block class] superclass] superclass] superclass] superclass]);
}
return 0;
}
// 控制檯打印
2018-07-02 14:55:39.799788+0800 block的類型[17627:1408539] __NSGlobalBlock__
2018-07-02 14:55:39.799954+0800 block的類型[17627:1408539] __NSGlobalBlock
2018-07-02 14:55:39.799970+0800 block的類型[17627:1408539] NSBlock
2018-07-02 14:55:39.799984+0800 block的類型[17627:1408539] NSObject
2018-07-02 14:55:39.799993+0800 block的類型[17627:1408539] (null)
Program ended with exit code: 0
從控制檯的打印,可以得出的結論__NSGlobalBlock__--> __NSGlobalBlock --> NSBlock--> NSObject
,最終block也是繼承於NSObject。(結論一:block繼承於NSObject)
int main(int argc, const char * argv[]) {
@autoreleasepool {
// insert code here...
// Global:沒有訪問auto變量
void (^block1)(void) = ^() {
NSLog(@"Hello, World!");
};
// Stack:訪問了auto變量
auto int age = 10;
void (^block2)(void) = ^(){
NSLog(@"%d",age);
};
NSLog(@"%@,%@,%@",[block1 superclass],[block2 superclass],[^{
NSLog(@"%d",age);
} class]);
}
return 0;
}
// 控制檯打印
2018-07-02 15:06:59.997872+0800 block的類型[17735:1426379] __NSGlobalBlock, __NSMallocBlock, __NSStackBlock__
Program ended with exit code: 0
從上面代碼的打印的三個block中,可以看出block有三種,分別是__NSGlobalBlock, __NSMallocBlock, __NSStackBlock_
。(結論二:block的三種類型__NSGlobalBlock, __NSMallocBlock, __NSStackBlock_)
那我們如何區分block到底是NSGlobalBlock
、NSStackBlock
還是NSMallocBlock
呢?下面我們來看再來看下面的代碼,我舉些例子讓大家知道如何區分block的類型。
NSGlobalBlock
int a = 20;
int main(int argc, const char * argv[]) {
@autoreleasepool {
// insert code here...
// NSGlobalBlock:沒有訪問auto變量
void (^block1)(void) = ^ {
NSLog(@"Hello");
};
NSLog(@"%@",[block1 class]);
static int age = 10;
void (^block2)(void) = ^ {
NSLog(@"age is %d",age);
};
NSLog(@"%@",[block2 class]);
void (^block3)(void) = ^ {
NSLog(@"a is %d",a);
};
NSLog(@"%@",[block3 class]);
}
return 0;
}
// 控制檯打印
2018-07-02 15:24:40.575459+0800 block的類型2[17895:1449262] __NSGlobalBlock__
2018-07-02 15:24:40.575640+0800 block的類型2[17895:1449262] __NSGlobalBlock__
2018-07-02 15:24:40.575651+0800 block的類型2[17895:1449262] __NSGlobalBlock__
Program ended with exit code: 0
來分析一下上面的代碼,block1、block2、block3都沒有訪問auto變量,blcok1直接打印“Hello”
,block2訪問了靜態變量age
,block3訪問的是全局變量a
,他們三者的類型都是NSGlobalBlock類型,所以可以得知(結論三:①NSGlobalBlock:沒有訪問auto變量)
NSStackBlock
int main(int argc, const char * argv[]) {
@autoreleasepool {
// insert code here...
// NSStackBlock:訪問auto變量
auto int age = 10;
void (^block)(void) = ^ {
NSLog(@"age is %d",age);
};
NSLog(@"%@",[block class]);
}
return 0;
}
//控制檯打印
// ARC環境下打印的結果
2018-07-02 16:03:21.152819+0800 block的類型2[18168:1493595] __NSMallocBlock__
Program ended with exit code: 0
// MRC環境下打印的結果
2018-07-02 16:08:01.000861+0800 block的類型2[18204:1499788] __NSStackBlock__
Program ended with exit code: 0
從上面代碼的控制檯打印輸出的block類型是NSMallockBlock
,爲什麼是NSMallockBlock
?因爲這是在ARC(自動管理內存)環境下,蘋果自動幫我們將block做了複製操作,這個我們後面的章節再討論,所以這裏我們要把ARC調成MRC的環境下,再打印,NSStackBlock
纔是block真實類型。(結論三:②NSStackBlock:訪問了auto變量)
NSMallocBlock
int main(int argc, const char * argv[]) {
@autoreleasepool {
// insert code here...
// NSMallocBlock:NSStackBlock copy後就是NSMallocBlock,NSMallocBlock是存在堆空間
auto int age = 10;
void (^block)(void) = [^ {
NSLog(@"age is %d",age);
} copy];
NSLog(@"%@",[block class]);
}
return 0;
}
//控制檯打印
// MRC環境下打印的結果
2018-07-02 16:08:01.000861+0800 block的類型2[18204:1499788] __NSMallocBlock__
Program ended with exit code: 0
NSStackBlock
copy後就是NSMallocBlock
,NSMallocBlock
是存在堆空間的。
(結論三:③NSMallocBlock:NSStackBlock調用了copy)
再來看看一下兩張圖。
每一種類型的block調用copy後的結果如下所示
總結:綜合上面的分析我們得出三個結論
結論一:block繼承於NSObject
結論二:block的三種類型__NSGlobalBlock, __NSMallocBlock, __NSStackBlock_
結論三:
①NSGlobalBlock:沒有訪問auto變量
②NSStackBlock:訪問了auto變量
③NSMallocBlock:NSStackBlock調用了copy