將圖像加載到UICollectionView異步？

Question

如何將圖像加載到UICollectionview異步？ 裏面下面的方法？

- (PSTCollectionViewCell *)collectionView:(PSTCollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath { 

bookImage = [UIImage imageWithContentsOfFile:[NSString stringWithFormat:@"%@/%@", docPath, [[preview objectAtIndex:indexPath.row] lastPathComponent]]]; 
[[cell grid_image] setImage:bookImage]; 

} 

在viewDidLoad中（）我使用下面的非同步調用來加載圖像， 「預覽」 NSMutablearray

dispatch_queue_t imageLoadQueue = dispatch_queue_create("com.GMM.assamkar", NULL); 

dispatch_async(imageLoadQueue, ^{ 
    //Wait for 5 seconds... 
    usleep(1000000); 
    docPath = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) objectAtIndex:0]; 


    for(int k=0; k <[allImage count] ;k++){ 


     imgURL = [allImage objectAtIndex:k]; 
     [imagePreview addObject:imgURL]; 
     imgData=[NSData dataWithContentsOfURL:[NSURL URLWithString:imgURL]]; 


     [imgData writeToFile:[NSString stringWithFormat:@"%@/%@", docPath, [allImage lastPathComponent]] atomically:YES]; 

    } 

    [[self collectionView] reloadData]; 


}); 

請幫me..Now其花費過多時間用於加載...

Answer 1

此代碼創建串行隊列：

dispatch_queue_t imageLoadQueue = dispatch_queue_create("com.GMM.assamkar", NULL); 

，因此每個任務IN QUEUE在相同的線程中連續執行。因此，對於加載的每個任務而言，您的單個工作線程都會由睡眠維持，從而減慢所有加載過程。

使用異步併發隊列使用類似的東西：

dispatch_queue_t imageLoadQueue = dispatch_queue_create("com.GMM.assamkar", DISPATCH_QUEUE_CONCURRENT); 

Answer 2

爲您的要求使用延遲加載文件。

LazyLoad.h
LazyLoad.m

使用它們像這樣

- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath 
{ 
    UICollectionViewCell *cell=[collectionView dequeueReusableCellWithReuseIdentifier:@"cellIdentifier" forIndexPath:indexPath]; 

    [cell addSubview:[self addViewWithURL:@"http://openwalls.com/image/399/explosion_of_colors_1920x1200.jpg" NFrame:CGRectMake(0, 0, 50, 50)]]; 

    cell.backgroundColor=[UIColor blueColor]; 
    return cell; 
} 

-(UIView*)addViewWithURL:(NSString*)urlStr NFrame:(CGRect)rect 
{ 
    LazyLoad *lazyLoading; 

    lazyLoading = [[LazyLoad alloc] init]; 
    [lazyLoading setBackgroundColor:[UIColor grayColor]]; 
    [lazyLoading setFrame:rect]; 

    [lazyLoading loadImageFromURL:[NSURL URLWithString:urlStr]]; 
    return lazyLoading; 
} 

Download Demo Here

Answer 3

試圖回答您的主要問題： 「我怎樣才能加載圖像到UICollectionview異步？」

我建議你通過「娜塔莎Murashev」 here，這很好地爲我工作提供的解決方案，它的簡單。

如果這裏imgURL = [allImage objectAtIndex:k];在allImage財產你把網址的陣列，那麼像這樣的更新collectionView:cellForItemAtIndexPath:方法：

- (PSTCollectionViewCell *)collectionView:(PSTCollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath 
{ 
    NSURL *url = [NSURL URLWithString:[allImage objectAtIndex:indexPath]]; 

    [self downloadImageWithURL:url completionBlock:^(BOOL succeeded, NSData *data) { 
     if (succeeded) { 
      cell.grid_image.image = [[UIImage alloc] initWithData:data]; 
     } 
    }]; 
} 

相加法downloadImageWithURL:completionBlock:到您的類，它會自動加載異步圖像和更新細胞的CollectionView當圖像被成功下載時。

- (void)downloadImageWithURL:(NSURL *)url completionBlock:(void (^)(BOOL succeeded, NSData *data))completionBlock 
{ 
    NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url]; 
    [NSURLConnection sendAsynchronousRequest:request queue:[NSOperationQueue mainQueue] completionHandler:^(NSURLResponse *response, NSData *data, NSError *error) { 
     if (!error) { 
      completionBlock(YES, data); 
     } else { 
      completionBlock(NO, nil); 
     } 
    }]; 
} 

我看你嘗試預載圖像前視圖出現，所以也許我的解決方案是不是你的東西，但是從你的問題就很難說了。任何方式，你都可以實現你想要的。

Swift 2.2 Swift中的解決方案。

public typealias ImageFetchCompletionClosure = (image: UIImage?, error: NSError?, imageURL: NSURL?) -> Void 

extension String { 
    func fetchImage(completionHandler: (image: UIImage?, error: NSError?, imageURL: NSURL?) -> Void) { 
     if let imageURL = NSURL(string: self) { 
      NSURLSession.sharedSession().dataTaskWithURL(imageURL) { data, response, error in 
       guard 
        let httpURLResponse = response as? NSHTTPURLResponse where httpURLResponse.statusCode == 200, 
        let mimeType = response?.MIMEType where mimeType.hasPrefix("image"), 
        let data = data where error == nil, 
        let image = UIImage(data: data) 
        else { 
         if error != nil { 
          completionHandler(image: nil, error: error, imageURL: imageURL) 
         } 
         return 
       } 
       dispatch_sync(dispatch_get_main_queue()) {() -> Void in 
        completionHandler(image: image, error: nil, imageURL: imageURL) 
       } 
      }.resume() 
     } 
    } 
} 

用法示例：

"url_string".fetchImage { (image, error, imageURL) in 
     // handle different results, either image was downloaded or error received 
    }