Question

I am working on a game tutorial with XNA but I am modifying it slightly. Instead of adding projectiles to an array based on a duration, I am trying to add them to the array by pressing the SpaceBar. So this way the user has some control over firing the missiles.

  if (currentKeyboardState.IsKeyDown(Keys.Space))
  {
      AddProjectile(player.Position + new Vector2(player.Width / 2, 0));
  }



   private void AddProjectile(Vector2 position)
   {
       Projectile projectile = new Projectile();
       projectile.Initialize(GraphicsDevice.Viewport, projectileTexture, position);
       projectiles.Add(projectile);
   }

However I am running into a minor problem. Since I am using the method IsKeyDown() missiles will be added to the projectiles array until the space bar is released. Is there a method that will register a key press rather than IsKeyDown().

Answer 1

Add a field that keeps track of the previous keyboard state

KeyboardState _previousKeyboardState = Keyboard.GetState();

You will update this state at the end of the Update. You can now do edge detection:

KeyboardState currentKeyboardState = Keyboard.GetState();
if(_previousKeyboardState.IsKeyUp(Keys.Space) 
   && currentKeyboardState.IsKeyDown(Keys.Space))
{
    //action
}
_previousKeyboardState = currentKeyboardState; //update previous state

The thinking is: If on previous pass the key had not been pressed, but now it is pressed, do this action.