Nick Gravelyn

I started working on a quick game for the latest XNA 7 Day challenge and wanted to simplify my input a bit. I knew I wanted to centralize it all to make things easier, but I also wanted to make the code simpler when I needed to check input. I’m only doing keyboard input, so that helped even more. After a bit of tinkering I came up with a clean solution thanks to extension methods.

First of all, I created a static class to house my current and previous frame’s KeyboardStates as well as my extension methods. The core of the class is really minimal:

public static class KeyboardInputExtensions
{
   private static KeyboardState oldKeyState, newKeyState;

   static KeyboardInputExtensions()
   {
      oldKeyState = newKeyState = Keyboard.GetState();
   }

   public static void Update()
   {
      oldKeyState = newKeyState;
      newKeyState = Keyboard.GetState();
   }
}

Then I just add a call to the KeyboardInputExtensions.Update() method in my game’s Update method and I’m ready to go. Next up: the extension methods. I came up with a fun way to make checking for input look like this:

if (Keys.Space.WasJustPressed())
{
   player.Jump();
}
else if (Keys.X.IsDown())
{
   player.Shoot();
}

I think that looks really clean and makes input checking much quicker than other methods. Supporting this is really easy thanks to a few extension methods I added to my KeyboardInputExtensions class:

public static bool IsDown(this Keys key)
{
   return newKeyState.IsKeyDown(key);
}

public static bool IsUp(this Keys key)
{
   return newKeyState.IsKeyUp(key);
}

public static bool WasJustPressed(this Keys key)
{
   return newKeyState.IsKeyDown(key) && oldKeyState.IsKeyUp(key);
}

public static bool WasJustReleased(this Keys key)
{
   return newKeyState.IsKeyUp(key) && oldKeyState.IsKeyDown(key);
}

Pretty nifty, huh? Anyone else have any fun tricks for simplifying code using extension methods or any other technique?