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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);
//        });
//        
//    });
//}<br><br><br>

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);
}