Keyboard button "event" efficiency in XNA

Question

I have been trying to figure it out for myself, but all tutorials online and everything I could find, does not really explain my question, so I hope someone here can help me.

I so far have only worked with C# mainly using WPF and if I want to raise an event whey a key is pressed on the keyboard, I simply use the KeyDown event. There I can easily identify the pressed key by e.Key.

Now in XNA everything I have seen is using KeyboardState state = Keyboard.GetState(); to get the state of the keyboard and constantly check in the Update()-method if e.g. state.IsKeyDown(Keys.Left); returns true of false.

And my question is: Is that not really inefficient? If for example my game uses 15 keys for input, I would get the keyboard state and check every single of those 15 keys and that 30 times a second. Is there a reason, why it seems to be so common to use this approach in XNA? The only explanation I could think of, is to make sure everything remains in the Update-method so it will definietly be executed, such that no delayed events cause problems in the game.

Answer 1

A form application and a video game is two completely different beast. In a good video game, the code uses all the threads available. For this reason, having an event start a new thread while none are available is obviously a bad thing, as it could hang another critical thread. There is no loose threads in a game.

A form is reactive to your input. It does virtually nothing while you don't do something. Nobody care if pressing a button in a form take 0.2-0.5 sec of reaction time.

A game is pro-active, and keep checking for them. It update itself for every frame anyway for the AI, physic, sounds, FX, animation and so one, and what goes on screen is always linked to what the user do. The input should always be resolved when the code get to updating the player's actions. So you have to test them anyway! On top, you want the best reaction time possible to your input and the only way to do it is to constantly check them. A 0.2 sec latency to a user input can make a game unplayable. There's coders whose role is solely to reduce the input latency to a minimum.