我的OS X应用程序如何接受来自Photos.app的图片文件的拖放？

Question

从新的Photos.app拖动图片时,作为拖动信息的一部分,粘贴板中不会传递任何URL.我的应用程序已经正确处理从iPhoto,Photo Booth,Aperture传递的图像......

我尝试从Photos.app拖动图片:Finder或Pages处理正确,但不是TextEdit或预览.Photos.app与存储在其库中的图片的工作方式似乎有所不同.

Answer 1

在深入了解NSPasteboard并逐步浏览应用程序之后,我意识到Photos.app正在粘贴板中传递"承诺文件",并在Apple的邮件列表中找到了这个帖子,其中包含一些答案:http://prod.lists.apple.com/档案/可可开发/ 2015 /月/ msg00448.html

以下是我在处理文件拖放到文档中的类中最终解决它的方法.该类是一个视图控制器,用于处理通常的拖放方法,因为它位于响应器链中.

便捷方法检测拖动的发件人是否具有任何与文件相关的内容:

- (BOOL)hasFileURLOrPromisedFileURLWithDraggingInfo:(id <NSDraggingInfo>)sender
{
    NSArray *relevantTypes = @[@"com.apple.pasteboard.promised-file-url", @"public.file-url"];
    for(NSPasteboardItem *item in [[sender draggingPasteboard] pasteboardItems])
    {
        if ([item availableTypeFromArray:relevantTypes] != nil)
        {
            return YES;
        }
    }
    return NO;
}

我还有一种方法来提取URL,如果它不是"承诺文件":

- (NSURL *)fileURLWithDraggingInfo:(id <NSDraggingInfo>)sender
{
    NSPasteboard *pasteboard = [sender draggingPasteboard];
    NSDictionary *options = [NSDictionary dictionaryWithObject:@YES forKey:NSPasteboardURLReadingFileURLsOnlyKey];
    NSArray *results = [pasteboard readObjectsForClasses:[NSArray arrayWithObject:[NSURL class]] options:options];
    return [results lastObject];
}

最后是用于处理drop的方法.这不完全是我的代码,因为我简化了拖动到便利方法的内部处理,允许我隐藏特定于应用程序的部分.我还有一个特殊的类来处理文件系统事件,FileSystemEventCenter作为练习留给读者.此外,在这里介绍的情况下,我只处理拖动一个文件.您必须根据自己的情况调整这些部件.

- (NSDragOperation)draggingEntered:(id <NSDraggingInfo>)sender
{
    if ([self hasFileURLOrPromisedFileURLWithDraggingInfo:sender])
    {
        [self updateAppearanceWithDraggingInfo:sender];
        return NSDragOperationCopy;
    }
    else
    {
        return NSDragOperationNone;
    }
}

- (NSDragOperation)draggingUpdated:(id <NSDraggingInfo>)sender
{
    return [self draggingEntered:sender];
}

- (void)draggingExited:(id <NSDraggingInfo>)sender
{
    [self updateAppearanceWithDraggingInfo:nil];
}

- (void)draggingEnded:(id <NSDraggingInfo>)sender
{
    [self updateAppearanceWithDraggingInfo:nil];
}

- (BOOL)prepareForDragOperation:(id <NSDraggingInfo>)sender
{
    return [self hasFileURLOrPromisedFileURLWithDraggingInfo:sender];
}

- (BOOL)performDragOperation:(id <NSDraggingInfo>)sender
{
    // promised URL
    NSPasteboard *pasteboard = [sender draggingPasteboard];
    if ([[pasteboard types] containsObject:NSFilesPromisePboardType])
    {
        // promised files have to be created in a specific directory
        NSString *tempPath = [NSTemporaryDirectory() stringByAppendingPathComponent:[[NSUUID UUID] UUIDString]];
        if ([[NSFileManager defaultManager] createDirectoryAtPath:tempPath withIntermediateDirectories:NO attributes:nil error:NULL] == NO)
        {
            return NO;
        }

        // the files will be created later: we keep an eye on that using filesystem events
        // `FileSystemEventCenter` is a wrapper around FSEvent
        NSArray *filenames = [sender namesOfPromisedFilesDroppedAtDestination:[NSURL fileURLWithPath:tempPath]];
        DLog(@"file names: %@", filenames);
        if (filenames.count > 0)
        {
            self.promisedFileNames = filenames;
            self.directoryForPromisedFiles = tempPath.stringByStandardizingPath;
            self.targetForPromisedFiles = [self dropTargetForDraggingInfo:sender];
            [[FileSystemEventCenter defaultCenter] addObserver:self selector:@selector(promisedFilesUpdated:) path:tempPath];
            return YES;
        }
        else
        {
            return NO;
        }
    }

    // URL already here
    NSURL *fileURL = [self fileURLWithDraggingInfo:sender];
    if (fileURL)
    {
        [self insertURL:fileURL target:[self dropTargetForDraggingInfo:sender]];
        return YES;
    }
    else
    {
        return NO;
    }
}

- (void)promisedFilesUpdated:(FDFileSystemEvent *)event
{
    dispatch_async(dispatch_get_main_queue(),^
     {
         if (self.directoryForPromisedFiles == nil)
         {
             return;
         }

         NSString *eventPath = event.path.stringByStandardizingPath;
         if ([eventPath hasSuffix:self.directoryForPromisedFiles] == NO)
         {
             [[FileSystemEventCenter defaultCenter] removeObserver:self path:self.directoryForPromisedFiles];
             self.directoryForPromisedFiles = nil;
             self.promisedFileNames = nil;
             self.targetForPromisedFiles = nil;
             return;
         }

         for (NSString *fileName in self.promisedFileNames)
         {
             NSURL *fileURL = [NSURL fileURLWithPath:[self.directoryForPromisedFiles stringByAppendingPathComponent:fileName]];
             if ([[NSFileManager defaultManager] fileExistsAtPath:fileURL.path])
             {
                 [self insertURL:fileURL target:[self dropTargetForDraggingInfo:sender]];
                 [[FileSystemEventCenter defaultCenter] removeObserver:self path:self.directoryForPromisedFiles];
                 self.directoryForPromisedFiles = nil;
                 self.promisedFileNames = nil;
                 self.targetForPromisedFiles = nil;
                 return;
             }
         }
    });
}