主要程式脫胎於瘋狂android講義第三版第七章page349

就是用畫板劃出圓球和球拍，並不斷改變座標然後通知重繪，程式碼如下

package org.crazyit.image;

import android.app.Activity;
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.util.DisplayMetrics;
import android.util.Log;
import android.view.Display;
import android.view.KeyEvent;
import android.view.MotionEvent;
import android.view.View;
import android.view.Window;
import android.view.WindowManager;

import java.util.Random;
import java.util.Timer;
import java.util.TimerTask;


public class MainActivity extends Activity
{
    // 桌面的寬度
    private int tableWidth;
    // 桌面的高度
    private int tableHeight;
    // 球拍的垂直位置
    private int racketY;
    // 下面定義球拍的高度和寬度
    private final int RACKET_HEIGHT = 40;
    private final int RACKET_WIDTH = 180;
    // 小球的大小
    private final int BALL_SIZE = 16;
    // 小球縱向的執行速度
    private int ySpeed = 60;
    Random rand = new Random();
    // 返回一個-0.5~0.5的比率，用於控制小球的執行方向
    private double xyRate = rand.nextDouble()-0.5;
    // 小球橫向的執行速度
    private int xSpeed = (int)( ySpeed*xyRate*4 );
    // ballX和ballY代表小球的座標
    private int ballX = rand.nextInt(200)+20;
    private int ballY = rand.nextInt(10)+20;
    // racketX代表球拍的水平位置
    private int racketX = rand.nextInt(200);
    // 遊戲是否結束的旗標
    private boolean isLose = false;
    private GameView mGameView;

    @Override
    public void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        // 去掉視窗標題
        requestWindowFeature(Window.FEATURE_NO_TITLE);
        // 全屏顯示
        getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN, WindowManager.LayoutParams.FLAG_FULLSCREEN);
        // 建立GameView元件
        mGameView = new GameView(this);
        setContentView(mGameView);
        // 獲取視窗管理器
        WindowManager windowManager = getWindowManager();
        Display display = windowManager.getDefaultDisplay();
        DisplayMetrics metrics = new DisplayMetrics();
        display.getMetrics(metrics);
        // 獲得螢幕寬和高
        tableWidth = metrics.widthPixels;
        tableHeight = metrics.heightPixels;
        racketY = tableHeight-300;
        final Handler handler = new Handler()
        {
            public void handleMessage(Message msg)
            {
                if(msg.what == 0x123)
                {
                    mGameView.invalidate();
                }
            }
        };
        final Timer timer = new Timer();
        timer.schedule(new TimerTask() // ①
        {
            @Override
            public void run()
            {
                // 如果小球碰到左邊邊框
                if(ballX<=0 || ballX>=tableWidth-BALL_SIZE)
                {
                    xSpeed = -xSpeed;
                }
                // 如果小球高度超出了球拍位置，且橫向不在球拍範圍之內，遊戲結束
                if(ballY>=racketY-BALL_SIZE && ( ballX<racketX || ballX>racketX+RACKET_WIDTH ))
                {
                    timer.cancel();
                    // 設定遊戲是否結束的旗標為true
                    isLose = true;
                }
                // 如果小球位於球拍之內，且到達球拍位置，小球反彈
                else if(ballY<=0 || ( ballY>=racketY-BALL_SIZE && ballX>racketX && ballX<=racketX+RACKET_WIDTH ))
                {
                    ySpeed = -ySpeed;
                }
                // 小球座標增加
                ballY += ySpeed;
                ballX += xSpeed;
                // 傳送訊息，通知系統重繪元件
                handler.sendEmptyMessage(0x123);
            }
        }, 0, 100);
    }

    @Override
    public boolean onKeyDown(int keyCode, KeyEvent event)
    {

        if(event.getKeyCode() == KeyEvent.KEYCODE_VOLUME_UP || event.getKeyCode() == KeyEvent.KEYCODE_VOLUME_DOWN)
        {
            // 獲取由哪個鍵觸發的事件
            switch(event.getKeyCode())
            {
                // 控制擋板左移
                case KeyEvent.KEYCODE_VOLUME_UP:
                    if(racketX>0)
                    {
                        racketX -= 10;
                    }
                    Log.e("-=-=", "方法被執行");
                    break;
                // 控制擋板右移
                case KeyEvent.KEYCODE_VOLUME_DOWN:
                    if(racketX<tableWidth-RACKET_WIDTH)
                    {
                        racketX += 10;
                    }
                    break;
            }
            // 通知gameView元件重繪
            mGameView.invalidate();
            return true;
        }else
        {
            return super.onKeyDown(keyCode, event);
        }
    }

    @Override
    public boolean onTouchEvent(MotionEvent event)
    {
        racketX = (int)event.getX()-60;
        mGameView.invalidate();
        return true;
    }

    class GameView extends View
    {
        Paint paint = new Paint();

        public GameView(Context context)
        {
            super(context);
            setFocusable(true);
        }

        // 重寫View的onDraw方法，實現繪畫
        public void onDraw(Canvas canvas)
        {
            paint.setStyle(Paint.Style.FILL);
            // 設定去鋸齒
            paint.setAntiAlias(true);
            // 如果遊戲已經結束
            if(isLose)
            {
                paint.setColor(Color.RED);
                paint.setTextSize(40);
                canvas.drawText("遊戲已結束", tableWidth/2-100, 200, paint);
            }
            // 如果遊戲還未結束
            else
            {
                // 設定顏色，並繪製小球
                paint.setColor(Color.rgb(255, 0, 0));
                canvas.drawCircle(ballX, ballY, BALL_SIZE, paint);
                // 設定顏色，並繪製球拍
                paint.setColor(Color.rgb(80, 80, 200));

                canvas.drawRect(racketX, racketY, racketX+RACKET_WIDTH, racketY+RACKET_HEIGHT, paint);

            }
        }
    }
}