如何使多个球从顶部掉落？

Question

public class MovingBagView extends View {

    private Bitmap bag[] = new Bitmap[2];
    private int bagX;
    private int bagY = 1000;
    private int bagSpeed;
    private Boolean touch = false;
    private int canvasWidth, canvasHeight;
    private int yellowX = 500, yellowY, yellowSpeed = -16;
    private Paint yellowPaint = new Paint();
    private int score;
    private Bitmap backgroundImage;
    private Paint scorePaint = new Paint();
    private Bitmap life[] = new Bitmap[2];

    public MovingBagView(Context context) {
        super(context);
        bag[0] = BitmapFactory.decodeResource(getResources(), R.drawable.bag1);
        bag[1] = BitmapFactory.decodeResource(getResources(), R.drawable.bag2);
        backgroundImage = BitmapFactory.decodeResource(getResources(), R.drawable.background);
        yellowPaint.setColor(Color.YELLOW);
        yellowPaint.setAntiAlias(false);
        scorePaint.setColor(Color.BLACK);
        scorePaint.setTextSize(40);
        scorePaint.setTypeface(Typeface.DEFAULT_BOLD);
        scorePaint.setAntiAlias(true);
        life[0] = BitmapFactory.decodeResource(getResources(), R.drawable.heart);
        life[1] = BitmapFactory.decodeResource(getResources(), R.drawable.heart_grey);
        bagX = 10;
        score = 0;
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        canvasWidth = canvas.getWidth();
        canvasHeight = canvas.getHeight();
        canvas.drawBitmap(backgroundImage, 0, 0, null);
        int minBagX = bag[0].getWidth();
        int maxBagX = canvasWidth - bag[0].getWidth() * 2;
        bagX = bagX + bagSpeed;
        if (bagX < minBagX) {
            bagX = minBagX;
        }
        if (bagX >= maxBagX) {
            bagX = maxBagX;
        }
        bagSpeed = bagSpeed + 2;
        if (touch) {
            canvas.drawBitmap(bag[1], bagX, bagY, null);
        }
        else {
            canvas.drawBitmap(bag[0], bagX, bagY, null);
        }
        yellowY = yellowY - yellowSpeed;
        if (hitBallChecker(yellowX, yellowY)) {
            score = score + 10;
            yellowY = -100;
        }
        if (yellowY < 0) {
            yellowY = canvasHeight + 21;
            yellowX = (int)Math.floor(Math.random() * (maxBagX - minBagX)) + maxBagX;
        }
        canvas.drawCircle(yellowX, yellowY, 15, yellowPaint);
        canvas.drawText("Score : " + score, 20, 60, scorePaint);
        canvas.drawBitmap(life[0], 500, 10, null);
        canvas.drawBitmap(life[0], 570, 10, null);
        canvas.drawBitmap(life[0], 640, 10, null);
    }

    public boolean hitBallChecker(int x, int y) {
        if (bagY < y && y < (bagY + bag[0].getHeight()) && bagX < x && x < (bagX + bag[0].getWidth())) {
            return true;
        }
        return false;
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        if (event.getAction() == MotionEvent.ACTION_DOWN) {
            touch = true;
            bagSpeed = -22;
        }
        return true;
    }
}

我已经弄清楚了如何使球从屏幕顶部掉落。该代码应该使多个黄色球从屏幕顶部掉落，但是只有一个黄色球掉落。随机的黄色小球应该从顶部掉落，并且从不同的位置掉落。您可以在下面查看其预览：

Answer 1

要实现此目的，您应该考虑创建一个自定义对象Ball

public class Ball{
    public int x;
    public int y;
    public int speed;

    public Ball(int x, int y, int speed){
         this.x = x;
         this.y = y;
         this.speed = speed;
    }
}

然后，您可以在ArrayList中添加多个Ball，然后在draw()中迭代遍历数组中的每个Ball，并对每个Ball进行相同的操作。

for(int i = 0; i < balls.length(); i++){
    Ball ball = balls.get(i);
    ball.y -= ball.speed;
    // check for collisions
    // draw ball
}