如何从其他类线程调用UI方法？UDP监听线程传参问题

我的UDP监听类线程运行正常，但不知道如何把recData字符串传递给UI方法UpdateCommand？我已经在UpdateCommand里用了Dispatcher，但不知道怎么在ListenForUDPPackages()里调用这个方法，试了好几种调用方式都不行，求帮忙。

namespace SoftEKA
{
   
    
    public delegate void OnDataReceivedHandler(string newData);
    public class UDPListener
    {
        private int portToListen = 5001;
        private volatile bool listening;
        Thread UDPListeningThread;
        public string recData;
        public event OnDataReceivedHandler DataReceived;

        // constructor
        public UDPListener()
        {
            this.listening = false;
        }

        // starts the UDPListener-Thread
        public void StartListener(int exceptedMessageLength)
        {
            if (!this.listening)
            {
                UDPListeningThread = new Thread(ListenForUDPPackages);
                this.listening = true;
                UDPListeningThread.Start();
            }
        }
        // stops the UDPListener-Thread
        public void StopListener()
        {
            this.listening = false;
        }
 
        // receives incoming UDP-Messages
        public void ListenForUDPPackages()
        {      
            UdpClient listener = null;
            try
            {
                listener = new UdpClient(portToListen);
            }
            catch (SocketException)
            {
                //do nothing
            }

            if (listener != null)
            {
                {
                    IPEndPoint groupEP = new IPEndPoint(IPAddress.Any, portToListen);
                    //MainWindow MW = new MainWindow();

                    try
                    {
                        while (true)
                        {
                            // received message as array of byte
                            byte[] data = listener.Receive(ref groupEP);

                            Console.WriteLine($"Received broadcast from {groupEP} :");
                            Console.WriteLine($"{Encoding.ASCII.GetString(data, 0, data.Length)}");
                            recData = Encoding.ASCII.GetString(data, 0, data.Length);
                            MessageBox.Show(recData);

                             ------>  here!! Calling the UI-method UpdateCommand(recData)

                            if (DataReceived != null)
                                DataReceived(recData);
                            else
                                Console.WriteLine("Null ausgeloest");
                        }
                    }
                    catch (SocketException e)
                    {
                        Console.WriteLine(e);
                    }
                    catch (Exception e)
                    {
                        Console.WriteLine(e.ToString());
                    }
                    finally
                    {
                        listener.Close();
                        Console.WriteLine("Done listening for UDP broadcast");
                    }
                }
            }
        }
    }


    
    public partial class MainWindow : Window
    {
        SoundPlayer soundPlayer = new SoundPlayer(@"c:\Users\Klaus\Music\beep.wav");

        Socket client = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp);
        IPEndPoint ep = new IPEndPoint(IPAddress.Parse("192.168.178.255"), 5000);

        UDPListener listener = new UDPListener();


    
        public MainWindow()
        {
            InitializeComponent();

            listener.StartListener(1024);

        }


       public void UpdateCommand(string data)
        {
            this.Dispatcher.Invoke(() => { Command.Text = data; });
        }
}

解决方法 #

你已经定义了DataReceived事件，这是解耦UDP监听逻辑和UI逻辑的正确方式，不需要在UDPListener类里直接调用UI方法，按以下步骤修改：

• 在MainWindow构造函数中订阅事件
  修改MainWindow的构造函数，添加事件订阅：

  public MainWindow()
  {
      InitializeComponent();
      // 订阅DataReceived事件，收到数据时触发处理方法
      listener.DataReceived += Listener_DataReceived;
      listener.StartListener(1024);
  }
  

• 实现事件处理方法
  在MainWindow中添加事件处理方法，调用你的UpdateCommand：

  private void Listener_DataReceived(string newData)
  {
      UpdateCommand(newData);
  }
  

• 修复UDPListener的循环控制
  你当前的while(true)会导致StopListener方法失效，改成用listening变量控制循环：

  // 替换ListenForUDPPackages中的while循环
  while (listening)
  {
      byte[] data = listener.Receive(ref groupEP);
  
      Console.WriteLine($"Received broadcast from {groupEP} :");
      Console.WriteLine($"{Encoding.ASCII.GetString(data, 0, data.Length)}");
      recData = Encoding.ASCII.GetString(data, 0, data.Length);
      // 注意：后台线程不能直接调用MessageBox，如需弹窗请用Dispatcher
      // Application.Current.Dispatcher.Invoke(() => MessageBox.Show(recData));
  
      DataReceived?.Invoke(recData); // 简化事件触发写法
  }
  

• 优化事件触发写法
  把原来的if (DataReceived != null) DataReceived(recData);改成空合并运算符的写法DataReceived?.Invoke(recData);，更简洁安全。

这样修改后，UDP监听线程收到数据时会触发DataReceived事件，MainWindow订阅该事件后调用UpdateCommand，通过Dispatcher更新UI元素，完全符合WPF的线程模型要求。

内容的提问来源于stack exchange，提问作者Klaus Dilper