C#/WPF：在启动时在单独的线程上创建和运行事件

Question

我尽量避免在 stackoverflow 上提出一些看起来微不足道的问题。上次我问一个问题时，我得到了很多否定的回答，所以我想我会尝试自己解决这个问题。所以大概一个月，两本书，还有一些视频教程之后，我还是很困惑。 :)

我的 MainWindow.xaml.cs 类的第 39 行根据我的调试器被调用，但注释 30 或 31 似乎没有触发 UI 上的任何内容，有一次它确实触发了，但它也给了我一个运行-时间错误。在被难住了几周之后，我休息了一下，开始做其他事情，所以我不确定我做了什么来消除运行时错误。所以，现在我正在寻求帮助，拜托:)

更新

MainWindow.xaml.cs 第 45 行返回的异常：

“对象，因为不同的线程拥有它。”

我的 MIDI 课：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using NAudio.Midi;

namespace StaveHelper
{
public sealed class  MIDIMain 
{
    private static MIDIMain midiMain = null;
    public static int noteOnNumber;
    public static int noteOffNumber;
    public MidiIn midiIn;
    public bool noteOn;
    private bool monitoring;
    private int midiInDevice;

    private MIDIMain()
    {
        GetMIDIInDevices();
    }

    public static MIDIMain GetInstance()
    {
        if (null == midiMain)
        {
            midiMain = new MIDIMain();
        }
        return midiMain;
    }


    public string[] GetMIDIInDevices()
    {
        //Get a list of devices
        string[] returnDevices = new string[MidiIn.NumberOfDevices];

        //Get the product name for each device found
        for (int device = 0; device < MidiIn.NumberOfDevices; device++)
        {
            returnDevices[device] = MidiIn.DeviceInfo(device).ProductName;
        }
        return returnDevices;
    }

    public void StartMonitoring(int MIDIInDevice)
    {
        if (midiIn == null)
        {
            midiIn = new MidiIn(MIDIInDevice);
        }
        midiIn.Start();
        monitoring = true;
    }

    public void midiIn_MessageReceived(object sender, MidiInMessageEventArgs e)
    {
        //int noteNumber;
        // Exit if the MidiEvent is null or is the AutoSensing command code  
        if (e.MidiEvent != null && e.MidiEvent.CommandCode == MidiCommandCode.AutoSensing)
        {
            return;
        }

        if (e.MidiEvent.CommandCode == MidiCommandCode.NoteOn)
        {
            // As the Command Code is a NoteOn then we need 
            // to cast the MidiEvent to the NoteOnEvent  
            NoteOnEvent ne;
            ne = (NoteOnEvent)e.MidiEvent;
            noteOnNumber = ne.NoteNumber;
        }

        if (e.MidiEvent.CommandCode == MidiCommandCode.NoteOff)
        {
            NoteEvent ne;
            ne = (NoteEvent)e.MidiEvent;
            noteOffNumber = ne.NoteNumber;
        }        
    }

    //// send the note value to the the MainWindow for display
    //public int sendNoteNum(int noteNumber)
    //{
    //    noteOnNumber = noteNumber;
    //    noteOn = true;
    //    return noteOnNumber;
    //}
}

}

我的 MainWindow.xaml.cs

using System;
using System.Collections.Generic;
using System.Text;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Shapes;
using NAudio.Midi;
using System.Threading;
using System.Windows.Threading;

namespace StaveHelper
{
/// <summary>
/// Interaction logic for MainWindow.xaml
/// </summary>
public  partial class MainWindow : Window
{
    Config config;
    MIDIMain midiMain;

    public delegate void mon(object sender, MidiInMessageEventArgs e);
    public MainWindow()
    {
        this.InitializeComponent();

        // Insert code required on object creation below this point.
        midiMain = MIDIMain.GetInstance();
        config = new Config();
        config.load_MIDIIn_Devices();
        //Thread t = new Thread(monitorNotes);
        midiMain.midiIn.MessageReceived += new EventHandler<MidiInMessageEventArgs>(monitorNotes); 
    }

    public void monitorNotes(object sender, MidiInMessageEventArgs e)  //LINE 39: MONITOR NOTES
    {

        switch ( MIDIMain.noteOnNumber)
        {
            case 30:
                C3.Opacity = 100;               //LINE 45: "The calling thread cannot access this 
                C3Dot.Opacity = 100;            //object because a different thread owns it."
                break;
            case 31:
                D3Dot.Opacity = 100;
                break;
        }
    }

    ~MainWindow()
    {

    }

    private void btnConfig_Click(object sender, RoutedEventArgs e)
    {
        config.Show();
    }


}
}

所以看来答案是要改变：

switch ( MIDIMain.noteOnNumber)
    {
        case 30:
            C3.Opacity = 100;               //LINE 45: "The calling thread cannot access this 
            C3Dot.Opacity = 100;            //object because a different thread owns it."
            break;
        case 31:
            D3Dot.Opacity = 100;
            break;
    }
}

进入

switch ( MIDIMain.noteOnNumber)
        {
            case 60:
                C3.Dispatcher.BeginInvoke(
                    System.Windows.Threading.DispatcherPriority.Normal,
                    new System.Windows.Threading.DispatcherOperationCallback
                        (delegate
                        {
                            C3.Opacity = 100;
                            C3Dot.Opacity = 100;
                            MIDIMain.noteOffNumber = -1;
                            return null;
                        }), null);
                 break;
            case 61:
                D3Dot.Dispatcher.BeginInvoke(
                    System.Windows.Threading.DispatcherPriority.Normal,
                    new System.Windows.Threading.DispatcherOperationCallback
                        (delegate
                        {
                            D3Dot.Opacity = 100;
                            D3Dot.Opacity = 100;
                            MIDIMain.noteOnNumber = -1;
                            return null;
                        }), null);
                break;
        }

感谢大家的帮助！

Answer 1

您的例外是因为您试图从后台线程修改 WPF GUI 组件。您需要使用调度程序。这里有很多关于堆栈溢出的问题可以对此提供帮助。例如，您可以使用来自this answer的代码

yourControl.Dispatcher.BeginInvoke(
   System.Windows.Threading.DispatcherPriority.Normal, 
   new System.Windows.Threading.DispatcherOperationCallback(delegate
   {
        // update your GUI here    
        return null;
   }), null);

Answer 2

如果您查看StartMonitoring() 方法 - 如果midiIn 为空，它会创建一个新实例然后调用Start() 但在这种情况下没有人订阅MessageReceived 所以看来您忘记了在这种情况下订阅midiIn.MessageReceived 事件并且永远不会调用方法midiIn_MessageReceived。所以noteOnNumber 没有赋值，因为只有在这种方法中 (midiIn_MessageReceived) 我看到了一个代码，它为noteOnNumber 变量赋值。

尝试更新 StartMonitoring() 方法：

if (midiIn == null)
{
   midiIn = new MidiIn(MIDIInDevice);
   midiIn.MessageReceived += midiIn_MessageReceived;
}