XNA实践键盘篇根据方向键移动图片（三）

接着《XNA试验篇(二)》，我们现在将程序修改为为以下（注意“新增2”与“删除新增”）：

using System;
using System.Collections.Generic;
using Microsoft.Xna.Framework;
using Microsoft.Xna.Framework.Audio;
using Microsoft.Xna.Framework.Content;
using Microsoft.Xna.Framework.GamerServices;
using Microsoft.Xna.Framework.Graphics;
using Microsoft.Xna.Framework.Input;
using Microsoft.Xna.Framework.Media;
using Microsoft.Xna.Framework.Net;
using Microsoft.Xna.Framework.Storage;

namespace MyFirstGame
{
    /// <summary>
    /// This is the main type for your game
    /// </summary>
    public class Game1 : Microsoft.Xna.Framework.Game
    {
        GraphicsDeviceManager graphics;
        SpriteBatch spriteBatch;

        /// <summary>
        /// 定义一个Texture2D的对像（新增）
        /// </summary>
        Texture2D texture;

        /// <summary>
        /// 定义图片坐标（新增2）
        /// </summary>
        Vector2 picPosition;
        /// <summary>
        /// 游戏界面的宽度（新增2）
        /// </summary>
        int clientW = 0;
        /// <summary>
        /// 游戏界面的高度（新增2）
        /// </summary>
        int clientH = 0;
        /// <summary>
        /// 存放按键情况（新增2）
        /// </summary>
        List<Keys> keysList;

        public Game1()
        {
            graphics = new GraphicsDeviceManager(this);
            Content.RootDirectory = "Content";

            keysList = new List<Keys>();//（新增2）
        }

        /// <summary>
        /// Allows the game to perform any initialization it needs to before starting to run.
        /// This is where it can query for any required services and load any non-graphic
        /// related content.  Calling base.Initialize will enumerate through any components
        /// and initialize them as well.
        /// </summary>
        protected override void Initialize()
        {
            // TODO: Add your initialization logic here

            base.Initialize();
        }

        /// <summary>
        /// LoadContent will be called once per game and is the place to load
        /// all of your content.
        /// </summary>
        protected override void LoadContent()
        {
            // Create a new SpriteBatch, which can be used to draw textures.
            spriteBatch = new SpriteBatch(GraphicsDevice);

            //新增
            //等控件初始化完成后，graphics.GraphicsDevic就不会为NULL了
            //将test.jpg的图片以2D的方式画到当前的graphics.GraphicsDevice
            texture = Texture2D.FromFile(graphics.GraphicsDevice, "test.jpg");



            int picW = texture.Width;//获取加载图片的宽度
            int picH = texture.Height;//获取加载图片的高度
            clientW = graphics.GraphicsDevice.Viewport.Width;//设置游戏界面的宽度
            clientH = graphics.GraphicsDevice.Viewport.Height;//设置游戏界面的高度
            int centerX = (clientW - picW) / 2;//求出游戏界面的X坐标中心点
            int centerY = (clientH - picH) / 2;//求出游戏界面的Y坐标中心点
            picPosition = new Vector2(centerX, centerY);

            // TODO: use this.Content to load your game content here
        }

        /// <summary>
        /// UnloadContent will be called once per game and is the place to unload
        /// all content.
        /// </summary>
        protected override void UnloadContent()
        {
            // TODO: Unload any non ContentManager content here
        }

        /// <summary>
        /// Allows the game to run logic such as updating the world,
        /// checking for collisions, gathering input, and playing audio.
        /// </summary>
        /// <param name="gameTime">Provides a snapshot of timing values.</param>
        protected override void Update(GameTime gameTime)
        {
            // Allows the game to exit
            if (GamePad.GetState(PlayerIndex.One).Buttons.Back == ButtonState.Pressed)
                this.Exit();

            //（新增2）开始
            KeyboardState keyboardstate = Keyboard.GetState();//获取键盘输入的键，会保持上一次按键状态
            Keys[] keys = keyboardstate.GetPressedKeys();//
            foreach (Keys key in keys)
            {
                if (keysList.Count == 0)
                {//使用当时的按键
                    KeyBoardHandle(key);
                }
                else
                {
                    //采用存起来的按键
                    foreach (Keys k in keysList)
                    {
                        if (key == k)
                            continue;//跳出与当前按键重复
                        KeyBoardHandle(k);
                    }
                }
            }
            keysList.Clear();
            foreach (Keys k in keys)
                keysList.Add(k);
            ////（新增2）结束
            // TODO: Add your update logic here

            base.Update(gameTime);
        }

        /// <summary>
        /// This is called when the game should draw itself.
        /// </summary>
        /// <param name="gameTime">Provides a snapshot of timing values.</param>
        protected override void Draw(GameTime gameTime)
        {
            GraphicsDevice.Clear(Color.CornflowerBlue);

            // TODO: Add your drawing code here
            //新增
            //绘画驱动开始
            spriteBatch.Begin();
            //将texture加载的图片画到所属的GraphicsDevice上，并定义图片所在的2维坐标，以及图片的着色颜色。
            //spriteBatch.Draw(texture, new Vector2(0.0f, 0.0f), Color.Red);//(取消新增)
            spriteBatch.Draw(texture, picPosition, Color.White);//（新增2）
            //结束GraphicsDevice绘画
            spriteBatch.End();

            base.Draw(gameTime);
        }

        #region 处理键盘按键（新增2）
        private void KeyBoardHandle(Keys key)
        {
            switch (key)
            {
                case Keys.Up:
                    //按向上键的时候
                    MoveUp();
                    break;
                case Keys.Down:
                    //按向下键的时候
                    MoveDown();
                    break;
                case Keys.Left:
                    //按向左键的时候
                    MoveLeft();
                    ; break;
                case Keys.Right:
                    //按向右键的时候
                    MoveRight();
                    ; break;
            }
        }
        #endregion

        #region 移动图片（新增2）左上角的坐标{0,0},向右Y坐标增加，向下X坐标增加
        /// <summary>
        /// 图片向上移动
        /// </summary>
        private void MoveUp()
        {
            if (picPosition.Y > 0)//控制移动边界
                picPosition.Y -= 5;//向上移动5个单位
        }
        /// <summary>
        /// 图片向下移动
        /// </summary>
        private void MoveDown()
        {
            if (picPosition.Y < clientH - texture.Height)//控制移动边界
                picPosition.Y += 5;//向下移动5个单位
        }
        /// <summary>
        /// 图片向左移动
        /// </summary>
        private void MoveLeft()
        {
            if (picPosition.X > 0)//控制移动边界
                picPosition.X -= 5;
        }
        /// <summary>
        /// 图片向右移动
        /// </summary>
        private void MoveRight()
        {
            if (picPosition.X < clientW - texture.Width)//控制移动边界
                picPosition.X += 5;
        }
        #endregion
    }
}

我们需要注意的重要地方有：

 KeyboardState keyboardstate = Keyboard.GetState();//获取键盘输入的键状态

 Keys[] keys = keyboardstate.GetPressedKeys();//获取当前按键信息，在键盘没有按任何键的时候会保持上一次按键状态

请看注释即可。因为都是比较容易一些的函数来的。呵呵