block用法

OC

• block类型实例变量：回传值(^名字)(参数列);
• typedef 回传值(^名字)(参数列);
• 实现体：^(参数列){} 如果没有参数可以省略参数列和圆括弧
• 形參类型：(回传值(^)(参数列))名字
• 返回一个block：(回传值(^)(参数列))名字:(参数类型)参数名,...

Swift

• block类型实例变量：名字:(参数列表)->(返回值)
• typedef 名字 = (参数列表)->(返回值)
• 实现体：{[捕获值列表](参数列表)in 语句}
• 形參类型：名字:(参数列表)->(返回值)

C 函数

• block类型实例变量： 回传值 (*名字)(参数列)
• typedef 回传值 (*名字)(参数列)
• 实现体： 好像没有带参数、返回值之类的匿名函数块
• 形參类型： 回传值(*名字)(参数列)
• 返回一个函数：回传值(*名字((参数类型)参数名1,...))(参数列)

arc问题

arc是引用类型的来说的。值类型的内存管理与arc无关。arc内存管理操作方法：可变拷贝, 不可变拷贝 const, 保持强引用, 保持弱引用
1.给类成员变量赋值
2.给临时变量赋值
3.函数传参
4.闭包捕获
5.作为函数/闭包的返回值返回

深拷贝，浅拷贝是另一个概念

apple object copying

内存管理.png

参考：

• block底层实现
• 内存布局
• objectcopying

-(void)test_7 {
    NSMutableString *p2 = [NSMutableString stringWithString:@"111111111"];
    void (^block)(NSString *p) = ^(NSString *p) {
        NSLog(@"%@", p);
        NSString *p3 = p2;
        p3 = @"33333";
    };
    NSLog(@"%@", p2);
    block(@"helloworld");
    NSLog(@"%@", p2);
    NSLog(@"test6 end!!");
}
-(void)test_6 {
    NSMutableString *p2 = [NSMutableString stringWithString:@"111111111"];
    void (^block)(NSString *p) = ^(NSString *p) {
        NSLog(@"%@", p);
        NSMutableString *p3 = p2;
        [p3 appendString:@"2222222"];
    };
    NSLog(@"%@", p2);
    block(@"helloworld");
    NSLog(@"%@", p2);
    NSLog(@"test6 end!!");
}
-(void)test_5 {
    NSMutableString *p2 = [NSMutableString stringWithString:@"111111111"];
    void (^block)(NSString *p) = ^(NSString *p) {
        NSLog(@"%@", p);
        [p2 appendString:@"2222222"];
    };
    NSLog(@"%@", p2);
    block(@"helloworld");
    NSLog(@"%@", p2);
    NSLog(@"test5 end!!");
}
-(void)test_4 {
    CLGeocoder *coder = [[CLGeocoder alloc]init];
    CLLocation *locaiont = [[CLLocation alloc]initWithLatitude:39.2610740000 longitude:117.1818350000];
    __block NSDictionary *result;
    dispatch_group_t group  = dispatch_group_create();
    dispatch_group_enter(group);
    [coder reverseGeocodeLocation:locaiont completionHandler:^(NSArray * _Nullable placemarks, NSError * _Nullable error) {
        if (error) {
            NSLog(@"%@",error);
            
        } else {
            for ( CLPlacemark * i in    placemarks) {
                NSLog(@"%@",   i.addressDictionary);
                result = i.addressDictionary;
                break;
            }
        }
        dispatch_group_leave(group);
    }];
    dispatch_group_notify(group, dispatch_get_main_queue(), ^{
        NSLog(@"%@",  result );
    });
    NSLog(@"test 4end!!!!");
}
-(void)test_3 {
    __block  NSMutableString *p = [NSMutableString string];
    dispatch_group_t group  = dispatch_group_create();
    dispatch_group_enter(group);
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0)  , ^{
        sleep(5);
        [p appendString: @"hellworooldd!!!!"];
        [p appendString: @"3333333!!!!"];
        [p appendString: @"4444444!!!!"];
        dispatch_group_leave(group);
        
    });
    dispatch_group_notify(group, dispatch_get_main_queue(), ^{
        NSLog(@"%@",  p );
    });
    NSLog(@"end!!!!");
}
-(void)test_2 {
    __block  NSString *p = @"helo";
    dispatch_group_t group  = dispatch_group_create();
    dispatch_group_enter(group);
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0)  , ^{
        sleep(5);
        dispatch_group_leave(group);
        p = @"hellworooldd!!!!";
    });
    dispatch_group_notify(group, dispatch_get_main_queue(), ^{
        NSLog(@"%@",  p );
    });
    NSLog(@"end!!!!");
    
}
-(void)test_1 {
    self.str = @"111111";
    [self performSelectorOnMainThread:@selector(modifyStr) withObject:nil waitUntilDone:false];
    //    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0), ^{
    //        NSLog(@"%@",   self.str);
    //        sleep(3);
    //        NSLog(@"%@",   self.str);
    //    });
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0), ^{
        NSString *p  =  self.str;
        NSLog(@"%@",   p);
        sleep(3);
        NSLog(@"%@",   p);
    });    NSLog(@"test end...");
}
-(void)modifyStr {
    dot;
    self.str = @"222222";
}

作为一个闭包，它需要具备的原则

1，block捕获值，不能被外面的修改而被修改。
2，block捕获值，修改捕获的值，外面可以用到被修改后的结果。