多点触控显示坐标

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(new MTView(this));
    }
    public class MTView extends SurfaceView implements SurfaceHolder.Callback {

        private static final int MAX_TOUCHPOINTS = 10;
        private static final String START_TEXT = "请随便触摸屏幕进行测试";
        private Paint textPaint = new Paint();
        private Paint touchPaints[] = new Paint[MAX_TOUCHPOINTS];
        private int colors[] = new int[MAX_TOUCHPOINTS];

        private int width, height;
        private float scale = 1.0f;

        public MTView(Context context) {
            super(context);
            SurfaceHolder holder = getHolder();
            holder.addCallback(this);
            setFocusable(true); // 确保我们的View能获得输入焦点
            setFocusableInTouchMode(true); // 确保能接收到触屏事件
            init();
        }

        private void init() {
            // 初始化10个不同颜色的画笔
            textPaint.setColor(Color.WHITE);
            colors[0] = Color.BLUE;
            colors[1] = Color.RED;
            colors[2] = Color.GREEN;
            colors[3] = Color.YELLOW;
            colors[4] = Color.CYAN;
            colors[5] = Color.MAGENTA;
            colors[6] = Color.DKGRAY;
            colors[7] = Color.WHITE;
            colors[8] = Color.LTGRAY;
            colors[9] = Color.GRAY;
            for (int i = 0; i < MAX_TOUCHPOINTS; i++) {
                touchPaints[i] = new Paint();
                touchPaints[i].setColor(colors[i]);
            }
        }

        /**
         * 处理触屏事件
         */
        @Override
        public boolean onTouchEvent(MotionEvent event) {
            // 获得屏幕触点数量
            int pointerCount = event.getPointerCount();
            if (pointerCount > MAX_TOUCHPOINTS) {
                pointerCount = MAX_TOUCHPOINTS;
            }

            // 锁定Canvas,开始进行相应的界面处理
            Canvas c = getHolder().lockCanvas();
            if (c != null) {
                c.drawColor(Color.BLACK);
                if (event.getAction() == MotionEvent.ACTION_UP) {
                    // 当手离开屏幕时，清屏
                } else {
                    // 在每一个触点上绘制一个十字和坐标信息
                    for (int i = 0; i < pointerCount; i++) {
                        int id = event.getPointerId(i);
                        int x = (int) event.getX(i);
                        int y = (int) event.getY(i);
                        drawCrosshairsAndText(x, y, touchPaints[id], i, id, c);
                    }

                    // 在每一个触点上绘制一个圆
                    for (int i = 0; i < pointerCount; i++) {
                        int id = event.getPointerId(i);
                        int x = (int) event.getX(i);
                        int y = (int) event.getY(i);
                        drawCircle(x, y, touchPaints[id], c);
                    }
                }

                // 画完后，unlock
                getHolder().unlockCanvasAndPost(c);
            }
            return true;
        }

        /**
         * 画十字及坐标信息
         *
         * @param x
         * @param y
         * @param paint
         * @param ptr
         * @param id
         * @param c
         */
        private void drawCrosshairsAndText(int x, int y, Paint paint, int ptr,
                                           int id, Canvas c) {
            c.drawLine(0, y, width, y, paint);
            c.drawLine(x, 0, x, height, paint);
            int textY = (int) ((15 + 20 * ptr) * scale);
            c.drawText("x" + ptr + "=" + x, 10 * scale, textY, textPaint);
            c.drawText("y" + ptr + "=" + y, 70 * scale, textY, textPaint);
            c.drawText("id" + ptr + "=" + id, width - 55 * scale, textY, textPaint);
        }

        /**
         * 画圆
         *
         * @param x
         * @param y
         * @param paint
         * @param c
         */
        private void drawCircle(int x, int y, Paint paint, Canvas c) {
            c.drawCircle(x, y, 40 * scale, paint);
        }

        /**
         * 进入程序时背景画成黑色，然后把START_TEXT写到屏幕
         */
        public void surfaceChanged(SurfaceHolder holder, int format, int width, int height) {
            this.width = width;
            this.height = height;
            if (width > height) {
                this.scale = width / 480f;
            } else {
                this.scale = height / 480f;
            }
            textPaint.setTextSize(14 * scale);
            Canvas c = getHolder().lockCanvas();
            if (c != null) {
                c.drawColor(Color.BLACK);
                float tWidth = textPaint.measureText(START_TEXT);
                c.drawText(START_TEXT, width / 2 - tWidth / 2, height / 2, textPaint);
                getHolder().unlockCanvasAndPost(c);
            }
        }

        public void surfaceCreated(SurfaceHolder holder) {
        }

        public void surfaceDestroyed(SurfaceHolder holder) {
        }
    }
}