block 的ARC和MRC中的区别

block在ARC和MRC中的声明引用有些区别.

     /**
     block能够存储在栈中,也能够在堆中
     默认存储在栈中,不须要管理内存
     存储在堆中的block会对block进行retain操做
     */
    //(MRC)block在堆中时,不想对block进行retain操做,前面加__block
    //(ARC)前面加__weak或__unsafe_unretained
    //__weak和__unsafe_unretained的区别:__weak则在释放时会对对象赋值nil,后者不会

    //Block_copy使栈中的block转移到堆中,并对block会引用的对象进行retain操做
    //避免block引用的对象进行retain操做,在引用对象声明时前面加__block

1.dog.h (NSObject类)

//block用copy来定义,这样block存在于堆中
//若是block不是copy到堆中,引用完了对象还在,但block被释放了

 #import <Foundation/Foundation.h>
 @interface dog : NSObject
 @property (nonatomic, assign) int age;
 @property (nonatomic, copy) void (^myBlock)();
 @end

2.dog.m

//引用self.age会使retainCount = 2的
//所以以__block typeof(self) mySelf = self;方式从新定义self

2.1 在block nslog中不调用d.age状况下,不须要从新定义self

2.2 在block nslog中调用d.age状况下,须要从新定义self

 #import "dog.h"
 @implementation dog
 - (instancetype)init {
     if (self = [super init]) {
         self.age = 10;
         self.myBlock = ^{
             NSLog(@"%d",mySelf.age);
         };
     }
     return self;
 }
 - (void)dealloc {
        NSLog(@"dog - dealloc");
 //对定义时copy的block进行释放
        Block_release(self.myBlock);
        [super dealloc];
 }
 @end

3.main.m文件

 int main(int argc, const charchar * argv[]) {
 //3.1 block在ARC和MRC中的状况
     blockARC_MRC();
 //3.2 copy block状况
     copyBlock();
     return 0;
 }

3.1 block在ARC和MRC中的状况

     /**
     block能够存储在栈中,也能够在堆中
     默认存储在栈中,不须要管理内存
     存储在堆中的block会对block进行retain操做
     */
    //(MRC)block在堆中时,不想对block进行retain操做,前面加__block
    //(ARC)前面加__weak或__unsafe_unretained
    //__weak和__unsafe_unretained的区别:__weak则在释放时会对对象赋值nil,后者不会
    
    //Block_copy使栈中的block转移到堆中,并对block会引用的对象进行retain操做
    //避免block引用的对象进行retain操做,在引用对象声明时前面加__block

 void blockARC_MRC(){
     __block dog *d = [[dog alloc] init];
     d.age = 12;
     NSLog(@"block引用前:d retainCount = %zd",d.retainCount);
     void (^myBlock)() = ^() {
         NSLog(@"d.age = %d",d.age);
     };
     NSLog(@"block引用后:d retainCount = %zd",d.retainCount);

     Block_copy(myBlock);
     NSLog(@"block copy后:d retainCount = %zd",d.retainCount);
     Block_release(myBlock);
     NSLog(@"block release后:d retainCount = %zd",d.retainCount);
     myBlock();
     NSLog(@"block调用后:d retainCount = %zd",d.retainCount);

     [d release];
 }

3.2 block中引用成员变量状况

//   1.没有调用d.age时,不须要__block
//   2.调用d.age时.必需要__block

 void copyBlock() {
     __block dog *d = [[dog alloc] init];
     d.age = 12;
     NSLog(@"block引用前:d retainCount = %zd",d.retainCount);
     d.myBlock = ^{
         NSLog(@"myBlock -- %d",d.age);
     };
     NSLog(@"block引用后:d retainCount = %zd",d.retainCount);
     d.myBlock();
     NSLog(@"block调用后:d retainCount = %zd",d.retainCount);

     [d release];
 }

-- end