IOS 加载网络图片的方式对比

 //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);
//        });
//        
//    });
//}

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);
}