C# Monitor Clipboard changes console

Question

I am working on a console application that is supposed to catch the event when the clipboard content changes. There is an API in WinRT for this, Windows.ApplicationModel.DataTransfer.Clipboard.ContentChanged. I have already tested this on a WinForms and WPF application, and it works perfectly. However I am experiencing problems when doing this in a console application. The code is pretty basic. When doing it on a WinForms application, I simply write this line of code:

public MyApp()
{
    InitializeComponent();
    Windows.ApplicationModel.DataTransfer.Clipboard.ContentChanged += OnClipboardChanged;

}


public async void OnClipboardChanged(Object sender, Object e)
{
   MyCodeHere
}

However when trying to do the same in my console application:

class Program
{

    [STAThread]
    static void Main(string[] args)
    {
        Windows.ApplicationModel.DataTransfer.Clipboard.ContentChanged += OnClipboardChanged;
    }

    public static void OnClipboardChanged(Object sender, Object e)
    {
        Console.WriteLine("Hello");
    }
}

Yet the console just exits after starting it. If I put "Console.ReadKey" then it still errors but does not exit. Neither way invokes the event I have written in Main. I want the console to be running and not end, even if there is a clipboard change. So it should constantly run in the background, and everytime the clipboard changes then it should just WriteLine a "Hello" to the console. I have gone through all the other answers but none of them works for me, because they want to manipulate the clipboard whereas I am invoking an event on the content change of the clipboard. Thanks for all the help!

Another question, will there be any perfomance difference if I use C++/winRT instead?

Answer 1

In a console context, you must ensure windows messages are processed as clipboard depends on it, so for example, you can use Winforms' DoEvents method (if you don't have a real window and nothing pumps messages):

class Program
{
    static void Main()
    {
        Windows.ApplicationModel.DataTransfer.Clipboard.ContentChanged += (s, e) => Console.WriteLine("ContentChanged");
        Console.WriteLine("Press any key to quit");
        do
        {
            System.Windows.Forms.Application.DoEvents();
            if (Console.KeyAvailable)
                break;

            Thread.Sleep(100); // for example
        }
        while (true);
    }
}

To enable Winforms support in a .NET 5 Console project, here is the simplest way of doing it (you don't even need to add the Windows.SDK nuget package), just modify the.csproj to something like this:

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>net5.0-windows10.0.19041.0</TargetFramework>
    <UseWindowsForms>true</UseWindowsForms>
    <DisableWinExeOutputInference>true</DisableWinExeOutputInference>
  </PropertyGroup>

</Project>

If you don't have .NET 5, or don't want to reference Winforms, then you can declare your own message pump using P/Invoke, like this:

class Program
{
    [STAThread]
    static void Main()
    {
        Windows.ApplicationModel.DataTransfer.Clipboard.ContentChanged += (s, e) => Console.WriteLine("ContentChanged");
        Console.WriteLine("Press any key to quit");
        do
        {
            while (GetMessage(out var msg, IntPtr.Zero, 0, 0) != 0)
            {
                TranslateMessage(ref msg);
                DispatchMessage(ref msg);
            }
            if (Console.KeyAvailable)
                break;

            Thread.Sleep(100);
            Console.Write(".");
        }
        while (true);
    }

    [StructLayout(LayoutKind.Sequential)]
    private struct MSG
    {
        public IntPtr hwnd;
        public int message;
        public IntPtr wParam;
        public IntPtr lParam;
        public int time;
        public POINT pt;
        public int lPrivate;
    }

    [StructLayout(LayoutKind.Sequential)]
    private struct POINT
    {
        public int x;
        public int y;
    }

    [DllImport("user32")]
    private static extern int GetMessage(out MSG lpMsg, IntPtr hWnd, int wMsgFilterMin, int wMsgFilterMax);

    [DllImport("user32")]
    private static extern bool TranslateMessage(ref MSG lpMsg);

    [DllImport("user32")]
    private static extern IntPtr DispatchMessage(ref MSG lpmsg);
}