Question

在Objective-C中，有一个Photos Framework a.k.a. PhotoKit，可让iOS开发人员访问iPhone和iPad上的照片库，并检索照片/视频及其元数据。

Mac开发人员将如何执行类似的任务？似乎PhotoKit仅适用于iOS 8.0。是否有相当于Mac OS X的照片框架？

Answer 1

用法：

@import MediaLibrary;

- (void) awakeFromNib
{
  NSDictionary *options = @{
     MLMediaLoadSourceTypesKey: @(MLMediaSourceTypeImage),
     MLMediaLoadIncludeSourcesKey: @[MLMediaSourcePhotosIdentifier]
  };

  MLMediaLibrary *mediaLibrary = [[MLMediaLibrary alloc] initWithOptions:options];
  self.mediaLibrary = mediaLibrary;

  [mediaLibrary addObserver:self
                 forKeyPath:@"mediaSources"
                    options:0
                    context:(__bridge void *)@"mediaLibraryLoaded"];

  [mediaLibrary mediaSources]; // returns nil and starts asynchronous loading
}

- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object 
                        change:(NSDictionary *)change context:(void *)context
{
   if (context == (__bridge void *)@"mediaLibraryLoaded") {
      // Media Library is loaded now, we can access mediaSources
      MLMediaSource *mediaSource = [self.mediaLibrary.mediaSources objectForKey:@"com.apple.Photos"];
   }
}

库背后的概念是你必须要求它读取一个对象的属性，它返回一个空的引用。然后使用键值观察器订阅此属性，并等待它加载。然后你可以用相同的原理检索下一个孩子等等......

Answer 2

根据Pierre F的回答，我扩展了显示所有照片的网址的代码：

- (void)applicationDidFinishLaunching:(NSNotification *)aNotification {

    NSDictionary *options = @{
                              MLMediaLoadSourceTypesKey: @(MLMediaSourceTypeImage),
                              MLMediaLoadIncludeSourcesKey: @[MLMediaSourcePhotosIdentifier]
                              };

    self.mediaLibrary = [[MLMediaLibrary alloc] initWithOptions:options];

    [self.mediaLibrary addObserver:self
                        forKeyPath:@"mediaSources"
                           options:0
                           context:(__bridge void *)@"mediaLibraryLoaded"];

    [self.mediaLibrary.mediaSources objectForKey:MLMediaSourcePhotosIdentifier];
}


- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object
                        change:(NSDictionary *)change context:(void *)context
{
     MLMediaSource *mediaSource = [self.mediaLibrary.mediaSources objectForKey:MLMediaSourcePhotosIdentifier];

    if (context == (__bridge void *)@"mediaLibraryLoaded")
    {
        [mediaSource addObserver:self
                            forKeyPath:@"rootMediaGroup"
                               options:0
                               context:(__bridge void *)@"rootMediaGroupLoaded"];

        [mediaSource rootMediaGroup];
    }
    else if (context == (__bridge void *)@"rootMediaGroupLoaded")
    {
        MLMediaGroup *albums = [mediaSource mediaGroupForIdentifier:@"TopLevelAlbums"];

        for (MLMediaGroup *album in albums.childGroups)
        {
            NSString *albumIdentifier = [album.attributes objectForKey:@"identifier"];

            if ([albumIdentifier isEqualTo:@"allPhotosAlbum"])
            {
                self.allPhotosAlbum = album;

                [album addObserver:self
                        forKeyPath:@"mediaObjects"
                           options:0
                           context:@"mediaObjects"];

                [album mediaObjects];

                break;
            }
        }
    }
    else if (context == (__bridge void *)@"mediaObjects")
    {
        NSArray * mediaObjects = self.allPhotosAlbum.mediaObjects;

        for(MLMediaObject * mediaObject in mediaObjects)
        {
            NSURL * url  = mediaObject.URL;

            NSLog(url.path);
        }
    }
}

Answer 3

尽管这不是正式的文档 API，但w0lfschild发布了Apple's PhotoKit framework for macOS的标头。该API看起来与iOS十分相似，因此也许您可以仅使用iOS文档来弄清楚。除了MediaLibrary Framework，您还可以对库进行更改。

以编程方式访问Mac OS X上的照片库：适用于Mac的PhotoKit / Photos Framework

3 个答案: