C# arrow key input for a console app

Question

I have a simple console app written in C#. I want to be able to detect arrow key presses, so I can allow the user to steer. How do I detect keydown/keyup events with a console app?

All my googling has led to info about windows Forms. I don't have a GUI. This is a console app (to control a robot over a serial port).

I have functions written to handle these events, but I have no idea how to register to actually receive the events:

  private void myKeyDown(object sender, KeyEventArgs e)
  {
      switch (e.KeyCode)
      {
          case Keys.Left:
                 ...
          case Keys.Right:
                 ...
          case Keys.Up:
                 ...
      }
  }

  private void myKeyUp(object sender, KeyEventArgs e)
  {
      ... pretty much the same as myKeyDown
  }

This is probably a really basic question, but I'm fairly new to C#, and I've never needed to get this kind of input before.

Update: Many are suggesting I use System.Console.ReadKey(true).Key. This will not help. I need to know the moment a key is held down, when it is released, with support for multiple keys to be held down simultaneously. Also, ReadKey is a blocking call -- which means that the program will stop and wait for a key to be pressed.

Update: It seems that the only viable way to do this is to use Windows Forms. This is annoying, as I cannot use it on a headless system. Requiring a Form GUI to receive keyboard input is ... stupid.

But anyway, for posterity, here's my solution. I created a new Form project in my .sln:

    private void Form1_Load(object sender, EventArgs e)
    {
        try
        {
            this.KeyDown += new KeyEventHandler(Form1_KeyDown);
            this.KeyUp += new KeyEventHandler(Form1_KeyUp);
        }
        catch (Exception exc)
        {
            ...
        }
    }

    void Form1_KeyDown(object sender, KeyEventArgs e)
    {
        switch (e.KeyCode)
        {
            // handle up/down/left/right
            case Keys.Up:
            case Keys.Left:
            case Keys.Right:
            case Keys.Down:
            default: return;  // ignore other keys
        }
    }

    private void Form1_KeyUp(object sender, KeyEventArgs e)
    {
        // undo what was done by KeyDown
    }

Note that if you hold down a key, KeyDown will be called numerous times, and KeyUp will only be called once (when you release it). So you need to handle repeated KeyDown calls gracefully.

Solution 1

A bit late now, but here's how to access keyboard state in a console application.

Note that it's not all managed code as it requires GetKeyState to be imported from User32.dll.

/// <summary>
/// Codes representing keyboard keys.
/// </summary>
/// <remarks>
/// Key code documentation:
/// http://msdn.microsoft.com/en-us/library/dd375731%28v=VS.85%29.aspx
/// </remarks>
internal enum KeyCode : int
{
    /// <summary>
    /// The left arrow key.
    /// </summary>
    Left = 0x25,

    /// <summary>
    /// The up arrow key.
    /// </summary>
    Up,

    /// <summary>
    /// The right arrow key.
    /// </summary>
    Right,

    /// <summary>
    /// The down arrow key.
    /// </summary>
    Down
}

/// <summary>
/// Provides keyboard access.
/// </summary>
internal static class NativeKeyboard
{
    /// <summary>
    /// A positional bit flag indicating the part of a key state denoting
    /// key pressed.
    /// </summary>
    private const int KeyPressed = 0x8000;

    /// <summary>
    /// Returns a value indicating if a given key is pressed.
    /// </summary>
    /// <param name="key">The key to check.</param>
    /// <returns>
    /// <c>true</c> if the key is pressed, otherwise <c>false</c>.
    /// </returns>
    public static bool IsKeyDown(KeyCode key)
    {
        return (GetKeyState((int)key) & KeyPressed) != 0;
    }

    /// <summary>
    /// Gets the key state of a key.
    /// </summary>
    /// <param name="key">Virtuak-key code for key.</param>
    /// <returns>The state of the key.</returns>
    [System.Runtime.InteropServices.DllImport("user32.dll")]
    private static extern short GetKeyState(int key);
}

Solution 2

var isUp = Console.ReadKey().Key == ConsoleKey.UpArrow;

or another example, just for your case:

while (true)
{
   var ch = Console.ReadKey(false).Key;
   switch(ch)
   {
       case ConsoleKey.Escape:
          ShutdownRobot();
          return;
       case ConsoleKey.UpArrow:
          MoveRobotUp();
          break;
       case ConsoleKey.DownArrow:
          MoveRobotDown();
          break;
   }
}

Solution 3

System.Console.ReadKey(true).Key == ConsoleKey.UpArrow

You could put that into a spin, something like:

while(Running)
{
  DoStuff();
  System.Console.ReadKey(true).Key == ConsoleKey.UpArrow
  Thread.Sleep(1)
}

Comments

[Rushyo]

You can call ReadKey in a different thread, see my spinning thread suggestion. Though that doesn't address keyup/keydown stuff.

[Tim]

what about holding down a key, or holding down multiple keys? I don't just want to get the latest key pressed - I want to handle multiple keys being held down (or no keys pressed at all).

[Rushyo]

Then you need to handle keyboard messages directly. Easiest way to do that is using DirectInput on Windows.

[Rushyo]

If you must do it manually, the relevant Win32 functions are GetConsoleWindow and SetWindowsHookEx. Hook the Console's 'WH_CALLWNDPROC' event to trap the raw Windows messages. A console doesn't get much of the abstraction that a Windows Form does, though it may have the functionality you're looking for the fact no one has suggested it implies to me this is your next logical step.

[Rushyo]

If you are intending to create a highly interactive application you might be better off creating a faux-console in a Windows Form. This is a popular technique for creating rudimentary video games UIs.

[Rushyo]

Bear in mind that between every key on a keyboard and the shift, ctrl, alt, etc modifiers you have hundreds of key combinations at your disposal. Hence why it's not exactly standard functionality to want more than that.

[Rushyo]

Duh. Handling multiple arrow keys. Ignore that ;)

[Tim]

Interesting. This would require polling the keyboard on my own, which means I can't just have an event-based app. But it's simple enough to do.

[Ergwun]

Yes, console applications don't typically have a message loop, but there's nothing to stop you rolling your own, and then having the rest of your application be event driven.

[Gerardo Grignoli]

WT actually supports this, but you need to enable win32-input-mode