java - 绘制圆圈而不删除先前的圆圈

Question

目前，我每次单击屏幕时都会绘制圆圈，但是当我绘制一个圆圈时，我之前绘制的圆圈就会被删除。有没有办法继续点击并使上一个圆圈保留在屏幕上？

public boolean onTouchEvent(MotionEvent event) {
    switch (event.getActionMasked()) {
        case MotionEvent.ACTION_DOWN:
            drawCirc = true;
            xTouch = event.getX();
            Log.d("keyboard", "xpos" + xTouch);
            yTouch = event.getY();
            break;

        case MotionEvent.ACTION_UP:
            drawCirc = false;
    }
    return true;
}


public void onDraw(Canvas canvas) {
    super.onDraw(canvas);
    Paint paint = new Paint();
    paint.setColor(Color.RED);
    if(drawCirc) {
        if (xTouch < 150 && xTouch>0) {
                paint.setColor(Color.RED);
                canvas.drawCircle(150, 500, 100, paint);
                invalidate();
        }
    }
}

Answer 1

问题是您没有保存旧点。您需要创建一个配对列表或 map 并保存所有点。

final List<Pair<Integer, Integer> points = new ArrayList();

public boolean onTouchEvent(MotionEvent event) {
    switch (event.getActionMasked()) {
        case MotionEvent.ACTION_DOWN:
            drawCirc = true;
            xTouch = event.getX();
            Log.d("keyboard", "xpos" + xTouch);
            yTouch = event.getY();
            points.add(new Pair(xTouch, yTouch));
            break;

        case MotionEvent.ACTION_UP:
            drawCirc = false;
    }
    return true;
}


public void onDraw(Canvas canvas) {
    super.onDraw(canvas);
    Paint paint = new Paint();
    paint.setColor(Color.RED);
    if(drawCirc) {
        for (Pair<Int, Int> point : points) {
            xTouch = point.first;
            yTouch = point.second;
            if (xTouch < 150 && xTouch>0) {
                paint.setColor(Color.RED);
                canvas.drawCircle(150, 500, 100, paint);
            }
        }
    }
 }

上面的代码应该让您大致了解要做什么。