我正在嘗試向macos_ui添加一項功能，該功能允許用戶啟動本機 macOS 顏色選擇器并通過EventChannel.

我能夠啟動選擇器（Cocoa's NSColorPanel），但顏色選擇不會流回來。當我通過 XCode 運行示例應用程式時，我可以看到顏色選擇已注冊，但它們似乎沒有通過EventChannel. 處理這個問題的正確方法是什么？考慮到它們發生在原生 macOS 視圖中，甚至有可能將這些事件流回 Flutter 嗎？

這是我到目前為止的 Swift 代碼：

MacosUIPlugin.swift

import Cocoa
import FlutterMacOS

public class MacOSUiPlugin: NSObject, FlutterPlugin, FlutterStreamHandler {
  private let colorPanelProvider: ColorPanelProvider
  private var eventSink: FlutterEventSink?

  init(colorPanelProvider: ColorPanelProvider) {
    self.colorPanelProvider = colorPanelProvider
    super.init()
  }
  
  public static func register(with registrar: FlutterPluginRegistrar) {
    let channel = FlutterMethodChannel(
      name: "dev.groovinchip.macos_ui",
      binaryMessenger: registrar.messenger)

    let colorSelectionChannel = FlutterEventChannel(
      name: "dev.groovinchip.macos_ui/color_panel",
      binaryMessenger: registrar.messenger)
  
    let colorPanelProvider = ColorPanelProvider()
      
    let instance = MacOSUiPlugin(colorPanelProvider: colorPanelProvider)
    colorSelectionChannel.setStreamHandler(instance)
    registrar.addMethodCallDelegate(instance, channel: channel)
  }

  public func handle(_ call: FlutterMethodCall, result: @escaping FlutterResult) {
    switch call.method {
    case "color_panel":
      colorPanelProvider.openPanel()
      result(true)
    default:
      result(FlutterMethodNotImplemented)
    }
  }
  
  public func onListen(withArguments arguments: Any?, eventSink events: @escaping FlutterEventSink) -> FlutterError? {
    print("listening to MacosUIPluginEvents")
    eventSink = events
    //colorPanelProvider.startStream()
    return nil
  }
  
  public func onCancel(withArguments arguments: Any?) -> FlutterError? {
    eventSink = nil
    return nil
  }
}

extension NSColor {
  var hexString: String {
    let red = Int(round(self.redComponent * 0xFF))
    let green = Int(round(self.greenComponent * 0xFF))
    let blue = Int(round(self.blueComponent * 0xFF))
    let hexString = NSString(format: "#XXX", red, green, blue)
    return hexString as String
  }
}

ColorPanelProvider.swift

import FlutterMacOS

class ColorPanelProvider: NSObject, FlutterStreamHandler {
  var eventSink: FlutterEventSink?
  let colorPanel = NSColorPanel.shared

  func onListen(withArguments arguments: Any?, eventSink events: @escaping FlutterEventSink) -> FlutterError? {
    print("listening to ColorPanelProvider events")
    eventSink = events
    return nil
  }

  func openPanel() {
    colorPanel.setTarget(self)
    colorPanel.setAction(#selector(startStream))
    colorPanel.makeKeyAndOrderFront(self)
    colorPanel.isContinuous = true
    startStream()
  }

  @objc private func currentColor() -> String {
    print("currentColor: \(colorPanel.color.asFlutterHexString)")
    return colorPanel.color.asFlutterHexString
  }

  @objc public func startStream() {
    print("starting ColorPanelProvider stream")
    NotificationCenter.default.addObserver(
      self,
      selector: #selector(currentColor),
      name: NSColorPanel.colorDidChangeNotification,
      object: colorPanel)
    
    eventSink?(currentColor())
  }

  func onCancel(withArguments arguments: Any?) -> FlutterError? {
    eventSink = nil
    return nil
  }
}

extension NSColor {
  var asFlutterHexString: String {
    let red = Int(round(self.redComponent * 0xFF))
    let green = Int(round(self.greenComponent * 0xFF))
    let blue = Int(round(self.blueComponent * 0xFF))
    let hexString = NSString(format: "#XXX", red, green, blue)
    return hexString.replacingOccurrences(of: "#", with: "0xFF") as String
  }
}

uj5u.com熱心網友回復：

你一直在正確的軌道上，但有一些事情需要修復。有三件事：

1. 在MacosUIPlugin.swift你需要聽的colorChannelProvider而不是instance你的register功能。所以你需要更改以下行

colorSelectionChannel.setStreamHandler(instance)

對此：

colorSelectionChannel.setStreamHandler(colorChannelProvider)

2. 在ColorPanelProvider.swift你聽的顏色變化startStream。雖然這是正確的方法，但您必須提交colorPanel發送這些更改的 ，以便該函式可以使用 訪問顏色colorPanel.color。函式簽名應如下所示：

@objc public func startStream(colorPanel: NSColorPanel)

3. 當您將該方法注冊為目標以從instartStream接收更新時，您需要對其進行設定，以便正確呼叫它。因此，將方法的第二行更改為如下所示，一切都像魅力一樣作業：colorPanelopenPanel()

colorPanel.setAction(#selector(startStream(colorPanel:)))

希望這將解決所有問題。如果還有問題，請告訴我。

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