#1-对于block的理解，mrc和arc的区别

block在ARC和MRC中的声明引用有些区别：

 block可以存储在栈中,也可以在堆中
 默认存储在栈中,不需要管理内存
 存储在堆中的block会对block进行retain操作

copy使栈中的block转移到堆中,并对block会引用的对象进行retain操作
block在堆中时,不想block对引用的对象进行retain操作

• (MRC)前面加__block
• (ARC)前面加__weak
  引用就变成了弱引用，retainCount 不会 +1

1.dog.h (NSObject类)

//block用copy来定义,这样block存在于堆中
//如果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)();

2.dog.m

引用self.age会使retainCount = 2的
因此以__block typeof(self) mySelf = self;方式重新定义self 避免循环引用

#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];
}

3.main.m文件

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

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];
}

• block中引用成员变量情况

 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];
}