Android 多点触控支持

Question

不知道Android的多点触控支持可靠吗？我读过它遇到了一些问题。

我还想知道，如何定义自定义多点触控手势？例如：3 个手指旋转或 3 个手指保持静止，第四个手指移动。

我遇到过一些资源（developer.android.com 上的 Gestures 或 MotionEvent），但没有明确说明。

问候，

兹德内克

Answer 1

我已经深入研究了 API，找到了一种执行捏合/反向捏合等手势的方法，所以我相信您描述的手势是可能的 - 只需弄清楚如何对它们进行编码即可。下面我粘贴了一个我实现的反向捏合的示例。我希望捏合仅在水平方向时才记录。它不是很干净或可重用的代码，但它应该可以帮助您继续前进。它适用于 Android 2.0.x。我读过多点触控在早期版本上可能存在问题。该示例是我从活动的 onTouchEvent 中调用的一个类，将事件转发到该类。

public class HorizontalReversePinchDetector {

    public boolean onTouchEvent(MotionEvent e) {

        int pointerCount = e.getPointerCount();

        if(pointerCount != 2) {
            Log.d(GESTURE, "not pinching - exactly 2 fingers are needed but have " + pointerCount);
            clearPinch();
            return false;
        }

        int firstIndex = e.getX(0) < e.getX(1) ? 0: 1;
        int secondIndex = e.getX(0) < e.getX(1) ? 1: 0;

        Finger currentLeftFinger = new Finger(e.getX(firstIndex), e.getY(firstIndex));
        Finger currentRightFinger = new Finger(e.getX(secondIndex), e.getY(secondIndex));

        float yDifference = Math.abs(currentLeftFinger.getY() - currentRightFinger.getY());
        if(yDifference > 80) {
            Log.d(GESTURE, "not pinching - fingers too vertically-oriented");
            clearPinch();
            return false;
        }

        if(initialLeftFinger == null) {
            initialLeftFinger = currentLeftFinger;
            initialRightFinger = currentRightFinger;
            Log.d(GESTURE, "not pinching, but might be starting a pinch...");
            return false;
        }

        float leftFingerDistance = initialLeftFinger.getX() - currentLeftFinger.getX();
        float rightFingerDistance = currentRightFinger.getX() - initialRightFinger.getX();

        float xDistanceBetweenFingers = Math.abs(currentLeftFinger.getX() - currentRightFinger.getX());
        if(xDistanceBetweenFingers < minimumDistanceBetweenFingers) {
            Log.d(GESTURE, "pinching, but fingers are not far enough apart...");
            return true;
        }

        if(leftFingerDistance < minimumDistanceForEachFinger) {
            Log.d(GESTURE, "pinching, but left finger has not moved enough...");
            return true;
        }
        if(rightFingerDistance < minimumDistanceForEachFinger) {
            Log.d(GESTURE, "pinching, but right finger has not moved enough...");
            return true;
        }

        pinchCompleted();
        return true;
    }

    private void pinchCompleted() {
        Log.d(GESTURE, "pinch completed");
        if(pinchListener != null) pinchListener.onPinch();
        clearPinch();
    }

    public static interface OnPinchListener {
        void onPinch();
    }

    private void clearPinch() {
        initialLeftFinger = null;
        initialRightFinger = null;
    }

    public void setPinchListener(OnPinchListener pinchListener) {
        this.pinchListener = pinchListener;
    }

    private static class Finger {

        private Finger(float x, float y) {
            this.x = x;
            this.y = y;
        }

        public float getX() {
            return x;
        }

        public float getY() {
            return y;
        }

        private float x;
        private float y;
    }

    private Finger initialLeftFinger;
    private Finger initialRightFinger;
    private OnPinchListener pinchListener;
    private static final float minimumDistanceForEachFinger = 30;
    private static final float minimumDistanceBetweenFingers = 50;
}

从可靠性来看，这段代码是完全可靠的。再次强调，仅适用于 Android 2.0.x。我还没有在该平台的其他版本上进行过测试。