Android(安卓)自定义 View 之弹球游戏

主程序代码：
package com.toby.personal.testlistview;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.support.v7.app.AppCompatActivity;import android.util.DisplayMetrics;import android.view.Display;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 AppCompatActivity {    final private static String TAG = "Toby_Test";    final private static int MSG_WHAT = 170411;    private boolean isOver = false;    // 桌面的宽高    private int tableWidth;    private int tableHeight;    // 球拍的垂直位置    private int racketY;    // 球拍的宽高    private final int RACKET_WIDTH = 70;    private final int RACKET_HEIGHT = 20;    // 小球的大小    private final int BALL_SIZE = 12;    // 小球的纵向速度    private int ySpeed = 20;    private Random random = new Random();    // 返回一个介于 -0.5 ~ 0.5 之间的比率，用于控制小球的运行方向    private double xyRate = random.nextDouble() - 0.5;    // 小球的横向速度    private int xSpeed = (int) (ySpeed * xyRate * 2);    // 小球的坐标    private int ballX = random.nextInt(200) + 20;    private int ballY = random.nextInt(10) + 20;    // 球拍的水平位置    private int racketX = random.nextInt(200);    // 球拍上次的 x 坐标    private float racketLastX = racketX;    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        requestWindowFeature(Window.FEATURE_NO_TITLE);        getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN,                WindowManager.LayoutParams.FLAG_FULLSCREEN);        final GameView gameView = new GameView(this);        setContentView(gameView);        WindowManager windowManager = getWindowManager();        Display display = windowManager.getDefaultDisplay();        DisplayMetrics metrics = new DisplayMetrics();        display.getMetrics(metrics);        tableWidth = metrics.widthPixels;        tableHeight = metrics.heightPixels - 400;        racketY = tableHeight - 80;        final Handler handler = new Handler() {            @Override            public void handleMessage(Message msg) {                if (msg.what == MSG_WHAT) {                    gameView.invalidate();                }                super.handleMessage(msg);            }        };        gameView.setOnTouchListener(new View.OnTouchListener() {            @Override            public boolean onTouch(View v, MotionEvent event) {                float x = event.getX();                if (x < racketLastX) {                    if (racketX > 0) racketX -= 10;                } else {                    if (racketX < tableWidth - RACKET_WIDTH) racketX += 10;                }                racketLastX = x;                return true;            }        });        final Timer timer = new Timer();        timer.schedule(new TimerTask() {            @Override            public void run() {                if (ballX <= 0 || ballX >= tableWidth - BALL_SIZE) {                    xSpeed = -xSpeed;                }                if (ballY >= racketY - BALL_SIZE                        && (ballX < racketX || ballX > racketX + RACKET_WIDTH)) {                    timer.cancel();                    isOver = true;                } else if (ballY <= 0 || (ballY >= racketY - BALL_SIZE                        && ballX > racketX && ballX <= racketX + RACKET_WIDTH)) {                    ySpeed = -ySpeed;                }                ballY += ySpeed;                ballX += xSpeed;                handler.sendEmptyMessage(MSG_WHAT);            }        }, 0, 100);    }    class GameView extends View {        Paint paint = new Paint();        public GameView(Context context) {            super(context);            setFocusable(true);            paint.setStyle(Paint.Style.FILL);            paint.setAntiAlias(true);        }        @Override        protected void onDraw(Canvas canvas) {            super.onDraw(canvas);            canvas.drawColor(Color.GRAY);            if (isOver) {                paint.setColor(Color.RED);                paint.setTextSize(40);                canvas.drawText("Game Over!", 50, 200, paint);            } else {                paint.setColor(Color.rgb(240, 240, 80));                canvas.drawCircle(ballX, ballY, BALL_SIZE, paint);                paint.setColor(Color.rgb(80, 80, 200));                canvas.drawRect(racketX, racketY, racketX + RACKET_WIDTH, racketY + RACKET_HEIGHT,                        paint);            }        }    }}
运行效果：
显示效果
本文参考文献：《疯狂Android讲义 : 第2版》
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