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如何异步加载图像？这就是我目前正在做的事情（借用开源代码来加载图像缩略图）：

- (UIImage*)thumbnailListView:(ThumbnailListView*)thumbnailListView
                 imageAtIndex:(NSInteger)index
{
    NSURL* url = [NSURL URLWithString:[recommendedArray objectAtIndex:index]] ;

//  [[cell grid_image] setImage:[UIImage imageWithData:[NSData dataWithContentsOfURL:url]]];



NSString *docPath = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) objectAtIndex:0];
BOOL isImageLoaded = YES;
UIImage *bookImage = [UIImage imageWithContentsOfFile:[NSString stringWithFormat:@"%@/%@", docPath, [[recommendedArray objectAtIndex:index] lastPathComponent]]];

if(bookImage == nil)
    isImageLoaded = NO;

if(!isImageLoaded){
    UIImage *thumbnailImage =[UIImage imageNamed:@"App-icon-144x144.png"];}
else{
    UIImage *thumbnailImage = [UIImage imageWithData:[NSData dataWithContentsOfURL:[NSURL URLWithString:[NSString stringWithFormat:@"%@",[recommendedArray objectAtIndex:index]]]]];
      return thumbnailImage;

}



}

我尝试将以下内容添加到该方法中，但它会为 NSURL 产生错误：

dispatch_queue_t imageLoadQueue = dispatch_queue_create("com.g.load", NULL);

dispatch_async(imageLoadQueue, ^{
    //Wait for 5 seconds...
    usleep(1000000);

    NSArray *docPath = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) objectAtIndex:0];    

    for(int k=0; k < [images count];k++){
        NSLog(@"Loading %d Image", k);
        NSString *imgURL = [images objectAtIndex:k];
        NSData *imgData = [[NSData alloc] initWithContentsOfURL:[NSURL URLWithString:imgURL]];
        [imgData writeToFile:[NSString stringWithFormat:@"%@/%@", docPath, [imgURL lastPathComponent]] atomically:YES];
    }

    [[self collectionView] reloadData];
    NSLog(@"DONE WITH ALL IMAGES");
});

错误

[NSURL length]: unrecognized selector sent to instance 0x12ea7240
2013-04-18 11:18:35.456 AssamKart[3084:14d03] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[NSURL length]: unrecognized selector sent to instance 0x12ea7240'
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4 回答 4

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在方法内部-> 

- (UIImage*)thumbnailListView:(ThumbnailListView*)thumbnailListView
                     imageAtIndex:(NSInteger)index

使用这个->

NSURLConnection *aNSURLConnection= [[NSURLConnection alloc]initWithRequest:<#(NSURLRequest *)#> delegate:<#(id)#> startImmediately:<#(BOOL)#>];

和内部代表

- (void)connectionDidFinishLoading:(NSURLConnection *)connection; 获取图像数据并实现您的逻辑，在这里您将再次调用

- (UIImage*)thumbnailListView:(ThumbnailListView*)thumbnailListView
                     imageAtIndex:(NSInteger)index

递归方法，直到你recommendedArray筋疲力尽。

于 2013-04-18T05:43:40.377 回答
0

使用 AsyncImageView。

https://github.com/nicklockwood/AsyncImageView

AsyncImageView *imageView = [[AsyncImageView alloc] initWithFrame:CGRectMake(Your Frame)];
imageView.contentMode = UIViewContentModeScaleAspectFill;
imageView.clipsToBounds = YES;
NSURL *URL =  [NSURL URLWithString:[NSString stringWithFormat:URL]];
[AsyncImageLoader defaultCache];
[[AsyncImageLoader sharedLoader]loadImageWithURL:URL target:self success:@selector(successSelector) failure:@selector(failureSelector)];
于 2013-04-18T10:09:01.080 回答
0

就这样做，

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{

    for (int k=0; k<[images count]; k++) {
    NSString *imgURL = [images objectAtIndex:k];
    NSData* data = [NSData dataWithContentsOfURL: [NSURL URLWithString:imgURL]];
    [data writeToFile:[NSString stringWithFormat:@"%@/%@", docPath, [imgURL lastPathComponent]] atomically:YES];

    }
});
于 2013-04-18T06:36:41.067 回答
0

您可以使用SDWebImage从 Internet 下载您的图像并使用以下方法：

[imageView setImageWithURL:[NSURL URLWithString:@"http://www.domain.com/path/to/image.jpg"]
               placeholderImage:[UIImage imageNamed:@"placeholder.png"]];
于 2013-04-18T09:00:13.577 回答