几种重要的倒序传值方式

来源：互联网发布：博客助赢软件cpzyrj 编辑：程序博客网时间：2024/04/29 15:56

 今天跟大家分享四种常用的传值方式，这四种都非常重要！如果文中有什么错误的地方，还请大家指出，本人一定改正！

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/*我的需求：在需要下载图片的地方（ViewController）创建一个DownloadImage的对象，然后调用下载的方法，下载完毕后将下载下来的图片返回给ViewController，显示到界面上/
/*第一种：代理传值/

model.h@protocol  DownloadImageDelegate <NSObject>@required-(void)downloadImageFinished: (UIImage *)image;@end@interface DowndloadImage : NSObject@property (nonatomic,assign) id<DownloadImageDelegate>delegate;@endmodel.m-(void)downloadImageWithUrlStr: (NSString *)urlStr{    /**异步调用全局的子线程，下载图片*/    dispatch_queue_t queue = dispatch_get_global_queue(0, 0);    dispatch_async(queue, ^{        NSURL *url = [NSURL URLWithString:urlStr];        NSData *data = [NSData dataWithContentsOfURL:url];        UIImage *image = [UIImage imageWithData:data];        /**下载图片完成后异步调用主线程*/        dispatch_queue_t queue = dispatch_get_main_queue();        dispatch_async(queue, ^{ /**如果_delegate里面有内容，而且[_delegate respondsToSelector:@selector(downloadImageFinished:)]这个方法已经调用，则进入这个if执行语句*/            if (_delegate && [_delegate respondsToSelector:@selector(downloadImageFinished:)]) {                /**线程间的通信*/                [_delegate performSelector:@selector(downloadImageFinished:) withObject:image];            }        });   });}ViewController.h只要遵守这个协议就OK。ViewController.m/**1.创建一个DownloadImage的对象*/    DowndloadImage *downloadImage = [[DowndloadImage alloc] init];/**2.设置代理，让本类来实现方法*/    downloadImage.delegate = self;/**3.给下载图片类传一个图片*/    [downloadImage downloadImageWithUrlStr:@"http://e.hiphotos.baidu.com/image/pic/item/5fdf8db1cb13495405b54f62544e9258d1094a08.jpg"];/**4.实现协议方法*/-(void)downloadImageFinished:(UIImage *)image{    _iamgeView = [[UIImageView alloc]initWithFrame:self.view.bounds];    _iamgeView.image = image;    [self.view addSubview:_iamgeView];}//到这里就传值OK了！

/*第二种：通知传值,这个传值和代理传值差不多，但有本质上的区别/

model.h@interface DowndloadImage : NSObject/**通知传值*/@property (nonatomic, assign) id target;@property (nonatomic, assign) SEL action;@endmodel.m-(void)downloadImageWithUrlStr: (NSString *)urlStr{    /**异步调用全局的子线程，下载图片*/    dispatch_queue_t queue = dispatch_get_global_queue(0, 0);    dispatch_async(queue, ^{        NSURL *url = [NSURL URLWithString:urlStr];        NSData *data = [NSData dataWithContentsOfURL:url];        UIImage *image = [UIImage imageWithData:data];        /**下载图片完成后异步调用主线程*/        dispatch_queue_t queue = dispatch_get_main_queue();        dispatch_async(queue, ^{            /**通知传值*/            if (_target &&[_target respondsToSelector:_action]) {                [_target performSelector:_action withObject:image];            }        });   });}ViewController.h这个方法.h里面什么都不用写哦ViewController.m/**设置target用通知传值*/    downloadImage.target = self;    downloadImage.action = @selector(downloadImageFinished:); DowndloadImage *downloadImage = [[DowndloadImage alloc] init];/**给下载图片类传一个图片*/ [downloadImage downloadImageWithUrlStr:@"http://e.hiphotos.baidu.com/image/pic/item/5fdf8db1cb13495405b54f62544e9258d1094a08.jpg"];/**实现指定的方法*/-(void)downloadImageFinished:(UIImage *)image{    _iamgeView = [[UIImageView alloc]initWithFrame:self.view.bounds];    _iamgeView.image = image;    [self.view addSubview:_iamgeView];}通知传值到这就OK了。

/*第三种：block方式的回调，用block进行传值/

model.h/**1.定义一个block类型，block的名字是DownloadFinishBlock，无返回值*/typedef void (^DowndloadFinish)(UIImage *image);@interface DowndloadImage : NSObject{    DowndloadFinish _block;}/**写一个成员变量的set方法*/-(void)setBlock: (DowndloadFinish)block;@endmodel.m-(void)downloadImageWithUrlStr: (NSString *)urlStr{    /**异步调用全局的子线程，下载图片*/    dispatch_queue_t queue = dispatch_get_global_queue(0, 0);    dispatch_async(queue, ^{        NSURL *url = [NSURL URLWithString:urlStr];        NSData *data = [NSData dataWithContentsOfURL:url];        UIImage *image = [UIImage imageWithData:data];        /**下载图片完成后异步调用主线程*/        dispatch_queue_t queue = dispatch_get_main_queue();        dispatch_async(queue, ^{                /**4.block 调用属性block，把image作为参数毁掉给ViewController*/            if (_block) {            _block(image);            }        });   });}/**写block的set方法*/-(void)setBlock:(DowndloadFinish)block{    _block = block;}ViewController.h这个方法.h也不用写任何东西哦ViewController.m DowndloadImage *downloadImage = [[DowndloadImage alloc] init];/**给下载图片类传一个图片*/ [downloadImage downloadImageWithUrlStr:@"http://e.hiphotos.baidu.com/image/pic/item/5fdf8db1cb13495405b54f62544e9258d1094a08.jpg"];//用setBlock的方式来传一个参数    [downloadImage setBlock:^(UIImage *image) {        _iamgeView = [[UIImageView alloc]initWithFrame:self.view.bounds];        _iamgeView.image = image;        [self.view addSubview:_iamgeView];    }];

/**第四种：

列表内容

通知中心传值*/
/*~~~~~~~~~~~~~~~~~通知不同于代理的是，它可以一对多的进行传递/

model.hdefine kDownloadFinishNotification @"kDownloadFinishNotification"model.m-(void)downloadImageWithUrlStr: (NSString *)urlStr{    /**异步调用全局的子线程，下载图片*/    dispatch_queue_t queue = dispatch_get_global_queue(0, 0);    dispatch_async(queue, ^{        NSURL *url = [NSURL URLWithString:urlStr];        NSData *data = [NSData dataWithContentsOfURL:url];        UIImage *image = [UIImage imageWithData:data];        /**下载图片完成后异步调用主线程*/        dispatch_queue_t queue = dispatch_get_main_queue();        dispatch_async(queue, ^{        /**生成通知中心,传递数据*/            [[NSNotificationCenter defaultCenter] postNotificationName:kDownloadFinishNotification object:image];         });   });}ViewController.h这里也什么都不用写ViewController.m/**注册通知中心添加一个观察者，当我post这个kDownloadFinishNotification通知的时候，self将执行selector对应的方法*/[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(downloadImageFinishedNotification:) name:kDownloadFinishNotification object:nil];/**通知中心传值*/-(void)downloadImageFinishedNotification: (NSNotification *)noti{    UIImage *image = noti.object;    _iamgeView = [[UIImageView alloc]initWithFrame:self.view.bounds];    _iamgeView.image = image;    [self.view addSubview:_iamgeView];}

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