NSFilePromiseProviderDelegate 是否也需要是 NSView 或 NSViewController？

Question

我正在学习 AppKit 教程 Supporting Drag and Drop Through File Promises。我下载了演示应用程序。

我试图将 NSFilePromiseProviderDelegate 功能从 ImageCanvasController class（这是一个 NSViewController）提取到一个单独的 class 中。（请参阅下面的代码片段之前和之后。）

在我进行更改之前，将图像从应用程序 canvas 拖出到 Finder 和 Apple Notes 中效果很好。但是在我更改之后，当我拖入 Notes 时没有任何反应，而当我拖入 Finder 时出现此错误：

2022-02-26 23:16:52.713742+0100 MemeGenerator[31536:1975798] *** CFMessagePort: dropping corrupt reply Mach message (0b000100)

是否有任何我需要添加到新 class 中的未记录的协议一致性？或者是否存在某些 NSFilePromiseProviderDelegate 仅在它也是 NSView 或 NSViewController 时才起作用的基本逻辑？在我在网上找到的所有指南中，它总是与视图相关联，但我没有发现任何必须如此的警告。

注意：我想将 promise-provider 功能与视图分开的原因是，这样我可以向 beginDraggingSession 提供多个 NSDraggingItem 对象。 For example, when multiple items are selected, and there is a mouseDragged event on one of them, I could start a dragging session including all the selected items.

之前的代码

class ImageCanvasController: NSViewController, NSFilePromiseProviderDelegate, ImageCanvasDelegate, NSToolbarDelegate {
   
    ...

    /// Queue used for reading and writing file promises.
    private lazy var workQueue: OperationQueue = {
        let providerQueue = OperationQueue()
        providerQueue.qualityOfService = .userInitiated
        return providerQueue
    }()
    
    ...

    func pasteboardWriter(forImageCanvas imageCanvas: ImageCanvas) -> NSPasteboardWriting {
        let provider = NSFilePromiseProvider(fileType: kUTTypeJPEG as String, delegate: self)
        provider.userInfo = imageCanvas.snapshotItem
        return provider
    }
    
    // MARK: - NSFilePromiseProviderDelegate
    
    /// - Tag: ProvideFileName
    func filePromiseProvider(_ filePromiseProvider: NSFilePromiseProvider, fileNameForType fileType: String) -> String {
        let droppedFileName = NSLocalizedString("DropFileTitle", comment: "")
        return droppedFileName + ".jpg"
    }
    
    /// - Tag: ProvideOperationQueue
    func operationQueue(for filePromiseProvider: NSFilePromiseProvider) -> OperationQueue {
        return workQueue
    }
    
    /// - Tag: PerformFileWriting
    func filePromiseProvider(_ filePromiseProvider: NSFilePromiseProvider, writePromiseTo url: URL, completionHandler: @escaping (Error?) -> Void) {
        do {
            if let snapshot = filePromiseProvider.userInfo as? ImageCanvas.SnapshotItem {
                try snapshot.jpegRepresentation?.write(to: url)
            } else {
                throw RuntimeError.unavailableSnapshot
            }
            completionHandler(nil)
        } catch let error {
            completionHandler(error)
        }
    }
}

之后的代码

class CustomFilePromiseProviderDelegate: NSObject, NSFilePromiseProviderDelegate {
    /// Queue used for reading and writing file promises.
    private lazy var workQueue: OperationQueue = {
        let providerQueue = OperationQueue()
        providerQueue.qualityOfService = .userInitiated
        return providerQueue
    }()

    /// - Tag: ProvideFileName
    func filePromiseProvider(_ filePromiseProvider: NSFilePromiseProvider, fileNameForType fileType: String) -> String {
        let droppedFileName = NSLocalizedString("DropFileTitle", comment: "")
        return droppedFileName + ".jpg"
    }

    /// - Tag: ProvideOperationQueue
    func operationQueue(for filePromiseProvider: NSFilePromiseProvider) -> OperationQueue {
        return workQueue
    }

    /// - Tag: PerformFileWriting
    func filePromiseProvider(_ filePromiseProvider: NSFilePromiseProvider, writePromiseTo url: URL, completionHandler: @escaping (Error?) -> Void) {
        do {
            if let snapshot = filePromiseProvider.userInfo as? ImageCanvas.SnapshotItem {
                try snapshot.jpegRepresentation?.write(to: url)
            } else {
                throw RuntimeError.unavailableSnapshot
            }
            completionHandler(nil)
        } catch let error {
            completionHandler(error)
        }
    }
}

class ImageCanvasController: NSViewController, ImageCanvasDelegate, NSToolbarDelegate {

    ...

    func pasteboardWriter(forImageCanvas imageCanvas: ImageCanvas) -> NSPasteboardWriting {
        let delegate = CustomFilePromiseProviderDelegate()
        let provider = NSFilePromiseProvider(fileType: kUTTypeJPEG as String, delegate: delegate)
        provider.userInfo = imageCanvas.snapshotItem
        return provider
    }
}

Answer 1

Does an NSFilePromiseProviderDelegate need to be also an NSView or NSViewController?

没有

delegate是局部变量，在pasteboardWriter(forImageCanvas:)结束时释放。没有委托，文件承诺提供程序将无法工作。解决方案：保持对委托的强引用。

class ImageCanvasController: NSViewController, ImageCanvasDelegate, NSToolbarDelegate {

    let delegate = CustomFilePromiseProviderDelegate()

    ...

    func pasteboardWriter(forImageCanvas imageCanvas: ImageCanvas) -> NSPasteboardWriting {
        let provider = NSFilePromiseProvider(fileType: kUTTypeJPEG as String, delegate: delegate)
        provider.userInfo = imageCanvas.snapshotItem
        return provider
    }
}

NSFilePromiseProviderDelegate 是否也需要是 NSView 或 NSViewController？

Does an NSFilePromiseProviderDelegate need to be also an NSView or NSViewController?

nsview

appkit

swift

nsfilepromiseprovider