C# arrow key input for a console app

问题:

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.

回答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);
}

回答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;
   }
}

回答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)
}

回答4:

example code:

        ConsoleKeyInfo kb = Console.ReadKey();
        if (kb.Key == ConsoleKey.LeftArrow)
                Console.WriteLine("Left Arrow pressed");

回答5:

you can do this

bool keyWasPressed = false;
if (consolekey.avalable)
{
keyvar = console.readkey(true);
keyWasPressed = true;
}
if(keyWasPressed)
{
//enter you code here using keyvar
}
else
{
//the commands that happen if you don't press anything
}

回答6:

I have the same issue that you and I found, here, an interesting post using tasks. The original post can be found here: C# Console Application - How do I always read input from the console?

I have to emulate a PWM output through a Raspberry GPIO (using mono C#) to test a LCD backlight. With two simple keys I wanted to change the duty cycle (up/down) and an extra key to stop the program.

I tried this (variables):

static ConsoleKeyInfo key = new ConsoleKeyInfo();
static int counter = 0;
static int duty = 5; // Starts in 50%

Main program:

static void Main(string[] args)
{
// cancellation by keyboard string
    CancellationTokenSource cts = new CancellationTokenSource();
    // thread that listens for keyboard input
    var kbTask = Task.Run(() =>
    {
        while (true)
        {
            key = Console.ReadKey(true);
            if (key.KeyChar == 'x' || key.KeyChar == 'X')
            {
                cts.Cancel();
                break;
            }
            else if (key.KeyChar == 'W' || key.KeyChar == 'w')
            {
                if (duty < 10)
                    duty++;
                //Console.WriteLine("\tIncrementa Ciclo");
                //mainAppState = StateMachineMainApp.State.TIMER;
                //break;
            }
            else if (key.KeyChar == 'S' || key.KeyChar == 's')
            {
                if (duty > 0)
                    duty--;
                //Console.WriteLine("\tDecrementa Ciclo");
                //mainAppState = StateMachineMainApp.State.TIMER;
                // break;
            }
        }
    });

    // thread that performs main work
    Task.Run(() => DoWork(), cts.Token);

    string OsVersion = Environment.OSVersion.ToString();
    Console.WriteLine("Sistema operativo: {0}", OsVersion);
    Console.WriteLine("Menú de Progama:");
    Console.WriteLine(" W. Aumentar ciclo útil");
    Console.WriteLine(" S. Disminuir ciclo útil");
    Console.WriteLine(" X. Salir del programa");

    Console.WriteLine();
    // keep Console running until cancellation token is invoked
    kbTask.Wait();
}

static void DoWork()
{
    while (true)
    {
        Thread.Sleep(50);
        if (counter < 10)
        {
            if (counter < duty)
                Console.Write("─");
                //Console.WriteLine(counter + " - ON");
            else
                Console.Write("_");
                //Console.WriteLine(counter + " - OFF");
            counter++;
        }
        else
        {
            counter = 0;
        }
    }
}

When it's needed to increment the duty cycle, pressing 'W' key makes that the main task changes the duty cycle variable (duty); the same thing with 'S' key to decrement. The program finishes when 'X' key is pressed.