Swift 如何在 macOSAppKit 的窗口选项卡上接受拖动项目的放置

布莱恩·韦伯斯特的精彩回答(谢谢！)启发了这个解决方案.

我加了demo code to a fully working project on GitHub.

首先，我们在创建窗口时向window的tab添加一个自定义附件视图.我们传递一个对NSWindowController的引用，以便无论何时在选项卡项上有东西落下时都可以很容易地通知它.

window.tab.accessoryView = TabAccessoryView(windowController: windowController)

该定制accessoryView(TabAccessoryView)是将接受拖放的视图not，因为附件视图与关闭按钮和标题标签一起被限制在NSStackView中，仅覆盖标题标签旁边的标签的一部分.

因此，取而代之的是，我们利用accessoryView是NSTabButton的视图层次 struct 的一部分这一事实来注入另一个定制视图(TabDropTargetView)behind即NSStackView…

class TabAccessoryView: NSView {

    weak private(set) var windowController: NSWindowController?

    private let tabDropTargetView: TabDropTargetView

    init(windowController: NSWindowController? = nil) {
        self.windowController = windowController
        self.tabDropTargetView = TabDropTargetView(windowController: windowController)
        super.init(frame: .zero)
    }

    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }

    override func viewDidMoveToWindow() {
        guard tabDropTargetView.superview == nil else { return }

        // DEBUG: Highlight accessory view
        wantsLayer = true
        layer?.backgroundColor = NSColor.red.withAlphaComponent(0.1).cgColor

        // The NSTabButton close button, title, and accessory view are contained in a stack view:
        guard let stackView = superview as? NSStackView,
              let backgroundView = stackView.superview else { return }

        // Add the drop target view behind the NSTabButton’s NSStackView and pin it to the edges
        backgroundView.addSubview(tabDropTargetView, positioned: .below, relativeTo: stackView)
        tabDropTargetView.translatesAutoresizingMaskIntoConstraints = false
        tabDropTargetView.leadingAnchor.constraint(equalTo: backgroundView.leadingAnchor).isActive = true
        tabDropTargetView.trailingAnchor.constraint(equalTo: backgroundView.trailingAnchor).isActive = true
        tabDropTargetView.topAnchor.constraint(equalTo: backgroundView.topAnchor).isActive = true
        tabDropTargetView.bottomAnchor.constraint(equalTo: backgroundView.bottomAnchor).isActive = true
    }

}

…它将处理丢弃的项目:

class TabDropTargetView: NSView {
    private(set) weak var windowController: NSWindowController?

    let allowedDropTypes: Array<NSPasteboard.PasteboardType> = [.URL, .fileContents, .string, .html, .rtf]

    init(windowController: NSWindowController? = nil) {
        self.windowController = windowController
        super.init(frame: .zero)

        // Tell the system that we accept drops on this view
        registerForDraggedTypes(allowedDropTypes)
    }

    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }

    override func viewDidMoveToWindow() {
        // DEBUG: Highlight drop target view
        wantsLayer = true
        layer?.backgroundColor = NSColor.green.withAlphaComponent(0.05).cgColor
    }

    override func draggingEntered(_ sender: NSDraggingInfo) -> NSDragOperation {
        return .copy
    }

    override func draggingUpdated(_ sender: NSDraggingInfo) -> NSDragOperation {
        return .copy
    }

    override func performDragOperation(_ sender: NSDraggingInfo) -> Bool {
        // Optional: Ignore drags from the same window
        guard (sender.draggingSource as? NSView)?.window != window else { return false }

        // Check if the dropped item contains text:
        let pasteboard = sender.draggingPasteboard
        guard let availableType = pasteboard.availableType(from: allowedDropTypes),
              let text = pasteboard.string(forType: availableType) else {
            return false
        }

        if let windowController = windowController as? WindowController {
            // Use the reference to the tab’s NSWindowController to pass the dropped item
            windowController.handleDroppedText(text)
        }

        return true
    }
}