SwiftUI如何更改keyUp macOS事件的状态

Question

当从窗口检测到keyUp时，我正在尝试更改状态值。然而，它似乎对我不起作用。这是我的代码

/// Window
class Window: NSWindow {
override func keyUp(with event: NSEvent) {
(contentView as! NSHostingView<ContentView>).rootView.keyPressed(with: event)
}
}
/// ContentView
struct ContentView {
@State var index: Int = 0
var body: some View { ... }
func keyPressed(with event: NSEvent) {
self.index = self.index + 1
}
}

我使用调试器对其进行了测试，显然，keyPressed被成功调用，但索引设置不正确。有人知道为什么吗？或者，在适用于macOS的SwiftUI中收听键盘的正确策略是什么？

Answer 1

这里是一个可能方法的演示。使用Xcode 11.4/macOS 10.15.4 进行测试

其想法是通过注入发布者到环境的值，将生成关键事件的自定义NSWindow与SwiftUI View连接起来。这提供了在视图层次结构的任何级别侦听/处理事件的可能性。

下面是完整的模块(AppDelegate.swift(代码。另请参阅代码中的有用注释。

import Cocoa
import SwiftUI
import Combine
// Environment key to hold even publisher
struct WindowEventPublisherKey: EnvironmentKey {
static let defaultValue: AnyPublisher<NSEvent, Never> = 
Just(NSEvent()).eraseToAnyPublisher() // just default stub
}

// Environment value for keyPublisher access
extension EnvironmentValues {
var keyPublisher: AnyPublisher<NSEvent, Never> {
get { self[WindowEventPublisherKey.self] }
set { self[WindowEventPublisherKey.self] = newValue }
}
}
// Custom window holding publisher and sending events to it. In general 
// it can be any event, but for originated question we limit to keyUp events
class Window: NSWindow {
private let publisher = PassthroughSubject<NSEvent, Never>() // private
var keyEventPublisher: AnyPublisher<NSEvent, Never> { // public
publisher.eraseToAnyPublisher()
}
override func keyUp(with event: NSEvent) {
publisher.send(event)
}
}
// Root demo view
struct DemoKeyPressedView: View {
@Environment(.keyPublisher) var keyPublisher // << access to publisher
@State private var index: Int = 0
var body: some View {
Text("Demo (index)")
.onReceive(keyPublisher) { event in // << listen to events
self.keyPressed(with: event)
}
}

func keyPressed(with event: NSEvent) {
self.index += 1
}
}
@NSApplicationMain
class AppDelegate: NSObject, NSApplicationDelegate {
var window: Window!

func applicationDidFinishLaunching(_ aNotification: Notification) {
// Create the custom window
window = Window(
contentRect: NSRect(x: 0, y: 0, width: 480, height: 300),
styleMask: [.titled, .closable, .miniaturizable, .resizable, .fullSizeContentView],
backing: .buffered, defer: false)
window.center()
window.setFrameAutosaveName("Main Window")
// Create the SwiftUI view that provides the window contents.
let contentView = DemoKeyPressedView()
.frame(minWidth: 400, maxWidth: .infinity, maxHeight: .infinity)
.environment(.keyPublisher, window.keyEventPublisher) // inject publisher
window.contentView = NSHostingView(rootView: contentView)
window.makeKeyAndOrderFront(nil)
}
func applicationWillTerminate(_ aNotification: Notification) {
// Insert code here to tear down your application
}
func applicationShouldTerminateAfterLastWindowClosed(_ sender: NSApplication) -> Bool {
return true
}
}