ios - 如何为下载图像的对象编写类，但有一个进度 block 和一个完成 block 来广播下载？

Question

我是使用 Objective-C 进行 block 编程的新手，我进行了搜索以尝试找到这个问题的答案，如果这是一个愚蠢的问题，我深表歉意。

我正在写一个类来包装 Imgur下载。它是 NSObject 的子类并使用 NSURLSession。我正在使用单例模式，让我可以轻松地在一行中启动下载，并在完成后获取图像下载的进度和 UIImage 本身。

- (void)downloadImageWithURL:(NSURL *)URL
              progressBlock:(void (^)(CGFloat percentageDownlaoded))progressBlock
          completionHandler:(void (^)(UIImage *downloadedImage, NSURLResponse *response, NSError *error))completionHandler;

但是我很困惑如何在类本身中实现它。这是我的完整类(class)文件:

+ (instancetype)sharedClient {
    static ImgurClient *sharedClient = nil;

    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        sharedClient = [[ImgurClient alloc] init];
    });

    return sharedClient;
}

- (id)init {
    self = [super init];

    if (self) {
        self.session = [NSURLSession sessionWithConfiguration:[NSURLSessionConfiguration defaultSessionConfiguration] delegate:self delegateQueue:nil];
    }

    return self;
}

#pragma mark - External Download Methods

/**
 * Asynchronously downloads the image for the given URL.
 */
- (void)downloadImageWithURL:(NSURL *)URL
              progressBlock:(void (^)(CGFloat percentageDownlaoded))progressBlock
          completionHandler:(void (^)(UIImage *downloadedImage, NSURLResponse *response, NSError *error))completionHandler {
}

/**
 * Asynchronously downloads the thumbnail for the given URL at the specified size.
 */
- (void)downloadThumbnailWithID:(NSURL *)URL
                           size:(CSImgurThumbnailSize)size
                  progressBlock:(void (^)(CGFloat percentageDownlaoded))progressBlock
              completionHandler:(void (^)(UIImage *downloadedImage, NSURLResponse *response, NSError *error))completionHandler {
}

#pragma mark - NSURLSessionDelegate Methods

- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask didWriteData:(int64_t)bytesWritten totalBytesWritten:(int64_t)totalBytesWritten totalBytesExpectedToWrite:(int64_t)totalBytesExpectedToWrite {
}

- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask didResumeAtOffset:(int64_t)fileOffset expectedTotalBytes:(int64_t)expectedTotalBytes {
}

- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask didFinishDownloadingToURL:(NSURL *)location {
}

我该如何构建这个类？我是否拥有表示进度的属性，然后将其放入适当的方法中？

如果有人能阐明或提供解释链接，我将不胜感激。

Answer 1

这是它的部分草图，我将专注于一个 block 来给你一个想法，你必须自己填写所有其他部分，否则这个答案会很大。您需要向 sharedClient 添加属性以保存 block 。

如果你先输入 block 的类型，会容易得多，即

typedef void (^PercentageDownloadedBlock)(CGFloat percentageDownlaoded);

然后你可以声明你的属性为

@property (copy, nonatomic)     PercentageDownloadedBlock   thePercentageBlock;

然后做这样的事情:

- (void)downloadThumbnailWithID:(NSURL *)URL
                           size:(CSImgurThumbnailSize)size
                  progressBlock:(PercentageDownloadedBlock)progressBlock
              completionHandler:(completionHandlerBlock)completionHandler
{
    self.thePercentageBlock = progressBlock;
    start the connection
    ...
}


- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask didWriteData:(int64_t)bytesWritten totalBytesWritten:(int64_t)totalBytesWritten totalBytesExpectedToWrite:(int64_t)totalBytesExpectedToWrite 
{
    CFFloat progress = do calculation of progress
    self.thePercentageBlock(progress);
    ...
}

等等