暂停和恢复单人游戏的背景音轨

Question

I am trying to simply add a pause and resume feature in my ping pong video game project. I Here is what I have tried:

 using System;
 using System.Collections.Generic;
 using System.Linq;
 using Microsoft.Xna.Framework;
 using Microsoft.Xna.Framework.Audio;
 using Microsoft.Xna.Framework.Content;
 using Microsoft.Xna.Framework.Graphics;
 using Microsoft.Xna.Framework.Input;
 using Microsoft.Xna.Framework.Media;

 namespace Ping_Pong
{
/// <summary>
/// This is the main type for your game
/// </summary>  
public class Game1 : Microsoft.Xna.Framework.Game
 {

 ...
 protected override void Update(GameTime gameTime)
 {


    KeyboardState press = Keyboard.GetState();

    if (press.IsKeyDown(Keys.P)==true)
    {
        pressed = !pressed;

        if (pressed == true)
        {
            MediaPlayer.Pause();
        }
        // do something 
        if (pressed ==false)
        {
            MediaPlayer.Resume();
        }
    }
    // update the ball's location on the screen
    MoveBall();
    // update the paddles' locations on the screen
    MovePaddles();

    base.Update(gameTime);
}
 ...
}
}

when I run this, sometimes it will pause and sometimes it will do nothing. How can I modify this so that I can make sure that it works properly?

Answer 1

IsKeyDown(Keys.P) returns true on every frame that "P" is being held down, not just on a single frame when that key is first pressed. Since Update() is probably getting called around 60 times a second, pressed is being flipped back and forth between true and false even if you just tap the P button for a fraction of a second. (This is why the code works some of the time; you have about a 50% chance of letting go of the P button on the desired state.)

One way to differentiate between a pressed event that should only fire once and a button being held down continuously is by looking for changes between the current KeyboardState and the previous one. This code below will turn pause/unpause the MediaPlayer each time the P key is struck.

Declare as class members:

private KeyboardState keyboardState, lastKeyboardState;

And then change the relevant code in Update() to:

keyboardState = Keyboard.GetState();

if (keyboardState.IsKeyDown(Keys.P) && lastKeyboardState.IsKeyUp(Keys.P))
{
    // P button has been pressed - change MediaPlayer state
    if (MediaPlayer.State == MediaState.Paused) // Paused to playing
        MediaPlayer.Resume();
    else if (MediaPlayer.State == MediaState.Playing) // Playing to paused
        MediaPlayer.Pause();
}

lastKeyboardState = keyboardState;