XNA Menu Not Working | 易学教程

问题

I have a problem with the logic of this code, XNA's Update Method is to fast so when i am trying to icreas the value by 1 every time the down button is pressed on the keyboard, it ends up updating a more than just by 1

Have a look at the code and see if you can think of a better way to do it,

     public void Update(GameTime gameTime)
    {
         var now = Keyboard.GetState();

        KeyboardState old = Keyboard.GetState();

        if (now.IsKeyDown(Keys.Down) && !old.IsKeyUp(Keys.Down))
        {
            properties.Menuposition++;
        }
        else if (now.IsKeyDown(Keys.Up) && !old.IsKeyUp(Keys.Up))
        {
            properties.Menuposition--;
        }
        else if (now.IsKeyDown(Keys.Enter))
        {
            properties.Menuposition = 5;
        }
        old = now;
    }

That was the update method and this is the Draw Method

     public void Draw(GameTime gametime, SpriteBatch spriteBatch)
    {
        if(properties.Menuposition == 0)
        {
            spriteBatch.DrawString(properties.Font, properties.Menu[0], properties.Playpos, Color.White);
            spriteBatch.DrawString(properties.Font, properties.Menu[1], properties.Highscorepos, Color.White);
            spriteBatch.DrawString(properties.Font, properties.Menu[2], properties.Exitpos, Color.White);
        }


        int menueitem = 0;
        Vector2 play = new Vector2(320,117);
        Vector2 highscore = new Vector2(320, 151);
        Vector2 Exit = new Vector2(320,180);

        spriteBatch.DrawString(properties.Font, properties.Menuposition.ToString(),new Vector2(100,100),Color.White);

        if(properties.Menuposition == 1)
        {
            spriteBatch.DrawString(properties.Font, properties.Menu[0], play, Color.Yellow);
            spriteBatch.DrawString(properties.Font, properties.Menu[1], highscore, Color.White);
            spriteBatch.DrawString(properties.Font, properties.Menu[2], Exit, Color.White);
            numberoftime = true;
            menueitem = 1;
        }
        else if(properties.Menuposition == 2)
        {
            spriteBatch.DrawString(properties.Font, properties.Menu[0], play, Color.White);
            spriteBatch.DrawString(properties.Font, properties.Menu[1], highscore, Color.Yellow);
            spriteBatch.DrawString(properties.Font, properties.Menu[2], Exit, Color.White);
           numberoftime = true;
            menueitem = 2;
        }
        else if(properties.Menuposition == 3)
        {

            spriteBatch.DrawString(properties.Font, properties.Menu[0], play, Color.White);
            spriteBatch.DrawString(properties.Font, properties.Menu[1], highscore, Color.White);
            spriteBatch.DrawString(properties.Font, properties.Menu[2], Exit, Color.Yellow);
            numberoftime = true;
            menueitem = 3;
        }

I am thinking of another way to do it but it would mean i would have to change all the code so have a look at it and see if you have a better way of doing this

Thanks and Regards, .....:)

回答1:

 private float timeSinceLastPush = 0;  
    public void Update(GameTime gameTime)
        {
               var now = Keyboard.GetState();
            timeSinceLastPush +=(float)gameTime.ElapsedGameTime.TotalSeconds;

             KeyboardState old = Keyboard.GetState();

       if (now.IsKeyDown(Keys.Down) && !old.IsKeyUp(Keys.Down)&& timeSinceLastPush >0.5 )
            {
                  properties.Menuposition++;
                    timeSinceLastPush = 0;

                }
            else if (now.IsKeyDown(Keys.Up) && !old.IsKeyUp(Keys.Up)&& timeSinceLastPush >0.5)
                {
                    properties.Menuposition--;
                    timeSinceLastPush = 0;
                }
                else if (now.IsKeyDown(Keys.Enter)&& timeSinceLastPush >0.5)
                {
                    properties.Menuposition = 5;
                    timeSinceLastPush = 0;
                }
                old = now;
            }

I added a variable float to hold the time elapsed since last time if it has passed 0.5 seconds do the comand and reset

回答2:

You seem to be trying to get certain keys to activate only once per press. To do that, this code:

public void Update(GameTime gameTime)
{
   var now = Keyboard.GetState();
   KeyboardState old = Keyboard.GetState();

Should be rewritten as:

private KeyboardState now; // suggest rename to something like mCurrentKeyboardState
private KeyboardState old; // suggest rename to something like mLastKeyboardState

...

public void Update(GameTime gameTime)
{
   old = now;
   now = Keyboard.GetState();
   ...

You should also think about putting this input related code into its own class.

来源：https://stackoverflow.com/questions/9889891/xna-menu-not-working

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xna

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