Question

从新的Photos.app中拖动图片时，作为拖动信息的一部分，粘贴板中不会传递任何URL。我的应用已正确处理从例如iPhoto，Photo Booth，Aperture，...

我尝试从Photos.app中拖动图片：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/archives/cocoa-dev/2015/Apr/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，它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;
}

我还有一种方法可以在不是“承诺文件”的情况下提取URL：

- (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];
}

最后是用于处理丢弃的方法。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，在此处显示的情况下，我只处理拖动一个文件。你必须根据自己的情况调整这些部分。

- (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;
             }
         }
    });
}

Answer 2

Apple在10.12中使用NSFilePromiseReceiver使这一点变得更容易了。它仍然是一个漫长而繁琐的过程，但稍微不那么重要。

这是我如何做到的。我实际上把它分成了一个扩展名，但是我已经为这个例子简化了它。

    override func performDragOperation(_ sender: NSDraggingInfo) -> Bool {

        let pasteboard: NSPasteboard = sender.draggingPasteboard()

            guard let filePromises = pasteboard.readObjects(forClasses: [NSFilePromiseReceiver.self], options: nil) as? [NSFilePromiseReceiver] else {
                return
            }
            var images = [NSImage]()
            var errors = [Error]()

            let filePromiseGroup = DispatchGroup()
            let operationQueue = OperationQueue()
            let newTempDirectory: URL
            do {
        let newTempDirectory = (NSTemporaryDirectory() + (UUID().uuidString) + "/") as String
        let newTempDirectoryURL = URL(fileURLWithPath: newTempDirectory, isDirectory: true)

        try FileManager.default.createDirectory(at: newTempDirectoryURL, withIntermediateDirectories: true, attributes: nil)
            }
            catch {
                return
            }

            filePromises.forEach({ filePromiseReceiver in

                filePromiseGroup.enter()

                filePromiseReceiver.receivePromisedFiles(atDestination: newTempDirectory,
                                                         options: [:],
                                                         operationQueue: operationQueue,
                                                         reader: { (url, error) in

                                                            if let error = error {
                                                                errors.append(error)
                                                            }
                                                            else if let image = NSImage(contentsOf: url) {
                                                                images.append(image)
                                                            }
                                                            else {
                                                                errors.append(PasteboardError.noLoadableImagesFound)
                                                            }

                                                            filePromiseGroup.leave()
                })

            })

            filePromiseGroup.notify(queue: DispatchQueue.main,
                                    execute: {
// All done, check your images and errors array

            })
}

我的OS X应用程序如何接受来自Photos.app的图片文件的拖放？

2 个答案: