ios UIImageView异步加载网络图片2

 //1. NSData dataWithContentsOfURL
//    [self.icon setImage:[UIImage imageWithData:[NSData dataWithContentsOfURL:tempUrl]]];
    
    //2. dispath形式添加到异步处理
//    [self imageDownLoadByUrlASYNC:tempUrl Complete:^(UIImage *image) {
//        [self.icon setImage:image];
//    }];
    //3. 当前我所选用的方式 边下载边加载的方式 用的CGImageRef imageWithCGImage
    _request = [[NSURLRequest alloc] initWithURL:tempUrl];
    _conn    = [[NSURLConnection alloc] initWithRequest:_request delegate:self];
    
    _incrementallyImgSource = CGImageSourceCreateIncremental(NULL);
    
    _recieveData = [[NSMutableData alloc] init];
    _isLoadFinished = false;
    
    self.icon.alpha = .5;
    self.lblTitle.alpha = .5;
    [self.lblTitle setText:appName];

第一种方式，是基本上很少有人用的 是最基础的方式 这种方式有个问题 就是网络不好的情况下会卡主线程，导致程序假死

第二种方式，请款这段实现代码

//
//-(void)imageDownLoadByUrlASYNC:(NSURL *)url Complete:(complete)finished
//{
//    //异步并列执行
//    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
//        UIImage *image = nil;
//        NSError *error;
//        NSData *responseData = [NSData dataWithContentsOfURL:url options:NSDataReadingMappedIfSafe error:&error];
//        image = [UIImage imageWithData:responseData];
//        //跳回主队列执行
//        dispatch_async(dispatch_get_main_queue(), ^{
//            //在主队列中进行ui操作
//            finished(image);
//        });
//        
//    });
//}

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{

        NSError *error;

        UIImage *image = nil;

        SDWebImageManager *manager = [SDWebImageManager sharedManager];

        BOOL existBool = [manager diskImageExistsForURL:url];//判断是否有缓存

        if (existBool) {

            image = [[manager imageCache] imageFromDiskCacheForKey:url.absoluteString];

        }else{

            NSData *responseData = [NSData dataWithContentsOfURL:url options:NSDataReadingMappedIfSafe error:&error];

            image = [UIImage imageWithData:responseData];

        }

        //跳回主队列执行

        dispatch_async(dispatch_get_main_queue(), ^{

            //在主队列中进行ui操作

            __block CGFloat itemW = mWidth;

            __block CGFloat itemH = 0;

            NSLog(@"%f",image.size.width);

            //根据image的比例来设置高度

            if (image.size.width) {

                itemH = image.size.height / image.size.width * itemW;

                if (itemH >= itemW) {

                    if (itemH >= mHeight-64) {

                        NSLog(@"%f",[UIScreen mainScreen].bounds.size.width);

                        UIScrollView *sv = [[UIScrollView alloc]initWithFrame:CGRectMake(0, 64, itemW, mHeight-64)];

                        sv.contentSize = CGSizeMake(itemW, itemH);

                        sv.showsVerticalScrollIndicator = NO;

                        sv.userInteractionEnabled = YES;

                        [self.view addSubview:sv];

                        imageView.frame = CGRectMake(0, 0, itemW, itemH);

                        imageView.contentMode = UIViewContentModeScaleAspectFit;

                        [sv addSubview:imageView];

                    }else{

                        imageView.frame = CGRectMake(0, 64, itemW, itemH);

                        imageView.contentMode = UIViewContentModeScaleAspectFit;

                        [self.view addSubview:imageView];

                    }

                }else{

                    imageView.frame = CGRectMake(0, 64, itemW, itemH);

                    imageView.contentMode = UIViewContentModeScaleAspectFit;

                    [self.view addSubview:imageView];

                }

            }else{

                imageView.frame = CGRectMake(0, 64, mWidth, mHeight-64);

                imageView.contentMode = UIViewContentModeScaleAspectFit;

                [self.view addSubview:imageView];

            }

            [self.myView stopAnimating];

        });

    });

虽然情况跟第一种实现一样，但是将执行代码添加到对应的异步执行中 然后再成功下载之后 获取到image之后 放到主线程执行回调 设置image

第三种方式 需要以下代码 这是我百度到的方式

#pragma mark -- NSURLConnectionDataDelegate

-(void)connection:(NSURLConnection*)connection didReceiveResponse:(NSURLResponse*)response
{
    _expectedLeght=response.expectedContentLength;
    NSLog(@"expectedLength:%lld",_expectedLeght);
    
    NSString*mimeType=response.MIMEType;
    NSLog(@"MIMETYPE%@",mimeType);
    
    NSArray*arr=[mimeType componentsSeparatedByString:@"/"];
    if(arr.count<1||![[arr objectAtIndex:0] isEqual:@"image"])
    {
        NSLog(@"notaimageurl");
        [connection cancel];
        _conn=nil;
    }
}
-(void)connection:(NSURLConnection*)connection didFailWithError:(NSError*)error
{
    NSLog(@"Connection%@error,errorinfo:%@",connection,error);
}
-(void)connectionDidFinishLoading:(NSURLConnection*)connection
{
    NSLog(@"ConnectionLoadingFinished!!!");
    //ifdownloadimagedatanotcomplete,createfinalimage
    if(!_isLoadFinished){
        CGImageSourceUpdateData(_incrementallyImgSource,(CFDataRef)_recieveData,_isLoadFinished);
        CGImageRef imageRef=CGImageSourceCreateImageAtIndex(_incrementallyImgSource,0,NULL);
        UIImage * image=[UIImage imageWithCGImage:imageRef];
        [self.icon setImage:image];
        CGImageRelease(imageRef);
        }
}
-(void)connection:(NSURLConnection*)connection didReceiveData:(NSData*)data
{
    [_recieveData appendData:data];
    
    _isLoadFinished=false;if(_expectedLeght==_recieveData.length){
        _isLoadFinished=true;
        }
    
    CGImageSourceUpdateData(_incrementallyImgSource,(CFDataRef)_recieveData,_isLoadFinished);
    CGImageRef imageRef=CGImageSourceCreateImageAtIndex(_incrementallyImgSource,0,NULL);
    UIImage * image=[UIImage imageWithCGImage:imageRef];
    [self.icon setImage:image];
    CGImageRelease(imageRef);
}

这个方法经过我测试了 非常好用 但是不知道会不会有什么bug 只是刚使用 并且用户体验也会相应增加