如何降低 android ScaleGestureDetector.SimpleOnScaleGestureListener 的灵敏度答案

【问题标题】：How to reduce sensitivity of android ScaleGestureDetector.SimpleOnScaleGestureListener如何降低 android ScaleGestureDetector.SimpleOnScaleGestureListener 的灵敏度
【发布时间】：2017-03-27 09:50:51
【问题描述】：

我有一个自定义的 SwipeRefreshLayout，里面有一个自定义的 GridView。我想根据捏/缩放手势更改该 GridView 的列号。我已经成功实施了。问题是，尺度太敏感了。

例如，我的列号为 3-5。缩放到 3 或 5 很容易，但要变成 4 则很难，因为缩放本身太敏感了。

这是我的自定义 SwipeRefreshLayout 类

/**
 * This class contains fix from http://stackoverflow.com/questions/23989910/horizontalscrollview-inside-swiperefreshlayout
 */
public class CustomSwipeRefreshLayout extends SwipeRefreshLayout {

    private int mTouchSlop;
    private float mPrevX;
    private ScaleGestureDetector mScaleGestureDetector;
    private ScaleListener mScaleListener;

    public CustomSwipeRefreshLayout(Context context, AttributeSet attrs) {
        super(context, attrs);
        mTouchSlop = ViewConfiguration.get(context).getScaledTouchSlop();
    }

    public void setScaleListener(Context context, ScaleListener scaleListener) {
        this.mScaleListener = scaleListener;
        mScaleGestureDetector = new ScaleGestureDetector(context, new MyOnScaleGestureListener());
    }

    @Override
    public boolean onInterceptTouchEvent(MotionEvent event) {
        if (mScaleGestureDetector != null) {
            mScaleGestureDetector.onTouchEvent(event);
        }

        switch (event.getAction() & MotionEvent.ACTION_MASK) {
            case MotionEvent.ACTION_POINTER_DOWN:
                setEnabled(false);
                if (mScaleListener != null) {
                    mScaleListener.onTwoFingerStart();
                }
                break;
            case MotionEvent.ACTION_POINTER_UP:
                setEnabled(true);
                mPrevX = MotionEvent.obtain(event).getX();
                if (mScaleListener != null) {
                    mScaleListener.onTwoFingerEnd();
                }
                break;
            case MotionEvent.ACTION_DOWN:
                mPrevX = MotionEvent.obtain(event).getX();
                break;

            case MotionEvent.ACTION_MOVE:
                final float eventX = event.getX();
                float xDiff = Math.abs(eventX - mPrevX);

                if (xDiff > mTouchSlop) {
                    return false;
                }
        }

        return super.onInterceptTouchEvent(event);
    }

    class MyOnScaleGestureListener extends ScaleGestureDetector.SimpleOnScaleGestureListener {

        private static final String TAG = "MyOnScaleGestureListene";

        @Override
        public boolean onScale(ScaleGestureDetector detector) {
            if (mScaleListener != null) {
                // Too sensitive, must change to other approach
                float scaleFactor = detector.getScaleFactor();
                Log.d(TAG, "onScale: " + scaleFactor);
                if (scaleFactor > 1F) {
                    mScaleListener.onScaleUp(scaleFactor);
                } else if (scaleFactor < 1F) {
                    mScaleListener.onScaleDown(scaleFactor);
                } else {
                    // no scale
                }
            }
            return true;
        }

        @Override
        public boolean onScaleBegin(ScaleGestureDetector detector) {
            return true;
        }

        @Override
        public void onScaleEnd(ScaleGestureDetector detector) {
        }
    }

    public interface ScaleListener {
        void onTwoFingersStart();

        void onTwoFingersEnd();

        void onScaleUp(float scaleFactor);

        void onScaleDown(float scaleFactor);
    }
}

有什么办法可以降低 ScaleGestureDetector.SimpleOnScaleGestureListener 的灵敏度？如果没有办法，有什么办法可以解决吗？

这是一个显示问题的短视频 https://www.youtube.com/watch?v=0MItDNZ_o4c

【问题讨论】：

标签： java android scale gesture gesture-recognition

【解决方案1】：

你应该有一个公差距离，这在 Android 世界中被称为“slop”。如果手势小于那个容差，你应该忽略它。

private static final int SPAN_SLOP = 7;

...

@Override
public boolean onScale(@NonNull ScaleGestureDetector detector) {
    if (gestureTolerance(detector)) {
        // performing scaling
    }
    return true;
}

private boolean gestureTolerance(@NonNull ScaleGestureDetector detector) {
    final float spanDelta = Math.abs(detector.getCurrentSpan() - detector.getPreviousSpan());
    return spanDelta > SPAN_SLOP;
}

作为示例，您可以看到由@rallat 制作的展示开源应用程序。

在这里您可以找到source code 和presentation at GOTO Copenhagen 2016。

【讨论】：

为什么 SPAN_SLOP 是 7？是像素吗？如果是这样，您认为将其转换为 dp 会更好吗？
我试过了，不符合我的要求，因为如果我的手指太慢，spanDelta 总是会重置。如果我的手指太快，仍然很难得到 4 个列号。
正如您从docs 看到的那样，它是以像素为单位的值。基本上，您应该测试并为您的用例找到合适的容差值。
但是从您提供的代码中，我想到了使用detector.getCurrentSpan() 保存初始距离，并在每次调用onScale 时将其直接与detector.getCurrentSpan() 进行比较。

【解决方案2】：

我能够解决问题以满足我的要求。 @azizbekian 的回答并没有真正满足我的要求，因为spanDelta 总是在我的手指太慢而我的手指太快时重置，它可以缩放，但仍然很难得到 4 列。但是从他的代码示例中，我能够创建一个解决方法。

我只需要使用detector.getCurrentSpan()保存初始比例距离（跨度）

@Override
public boolean onScaleBegin(ScaleGestureDetector detector) {
    mInitialDistance = detector.getCurrentSpan();
    return true;
}

然后每次调用onScale()时直接与detector.getCurrentSpan()比较。如果发生缩放，则使用mInitialDistance = detector.getCurrentSpan(); 重置初始距离。

@Override
public boolean onScale(ScaleGestureDetector detector) {
    if (gestureTolerance(detector)) {
        if (mScaleListener != null) {
            float scaleFactor = detector.getScaleFactor();
            if (scaleFactor > 1F) {
                mScaleListener.onScaleUp(scaleFactor);
                mInitialDistance = detector.getCurrentSpan();
            } else if (scaleFactor < 1F) {
                mScaleListener.onScaleDown(scaleFactor);
                mInitialDistance = detector.getCurrentSpan();
            }
        }
    }
    return true;
}

private boolean gestureTolerance(@NonNull ScaleGestureDetector detector) {
    final float currentDistance = detector.getCurrentSpan();
    final float distanceDelta = Math.abs(mInitialDistance - currentDistance);
    return distanceDelta > mScaleTriggerDistance;
}

这是我的自定义 SwipeRefreshLayout 的完整代码

public class MyCustomSwipeRefreshLayout extends SwipeRefreshLayout {

    private static final String TAG = "OneTouchRefreshFreeSwip";
    private static final float DEFAULT_SCALE_TRIGGER_DISTANCE = 48;// in dp
    private int mTouchSlop;
    private float mPrevX;

    private ScaleGestureDetector mScaleGestureDetector;
    private ScaleListener mScaleListener;

    private float mScaleTriggerDistance;
    private float mInitialDistance;

    public MyCustomSwipeRefreshLayout(Context context, AttributeSet attrs) {
        super(context, attrs);
        mTouchSlop = ViewConfiguration.get(context).getScaledTouchSlop();
    }

    public void setScaleListener(Context context, ScaleListener scaleListener) {
        this.mScaleListener = scaleListener;
        mScaleGestureDetector = new ScaleGestureDetector(context, new MyOnScaleGestureListener());
        mScaleTriggerDistance = Util.dp2px(DEFAULT_SCALE_TRIGGER_DISTANCE, context);
    }

    @Override
    public boolean onInterceptTouchEvent(MotionEvent event) {
        if (mScaleGestureDetector != null) {
            mScaleGestureDetector.onTouchEvent(event);
        }

        switch (event.getAction() & MotionEvent.ACTION_MASK) {
            case MotionEvent.ACTION_POINTER_DOWN:
                setEnabled(false);
                if (mScaleListener != null) {
                    mScaleListener.onTwoFingersStart();
                }
                break;
            case MotionEvent.ACTION_POINTER_UP:
                if (mScaleListener != null) {
                    mScaleListener.onTwoFingersEnd();
                }
                mPrevX = MotionEvent.obtain(event).getX();
                setEnabled(true);
                return true;
            case MotionEvent.ACTION_DOWN:
                mPrevX = MotionEvent.obtain(event).getX();
                break;

            case MotionEvent.ACTION_MOVE:
                final float eventX = event.getX();
                float xDiff = Math.abs(eventX - mPrevX);

                if (xDiff > mTouchSlop) {
                    return false;
                }
        }

        return super.onInterceptTouchEvent(event);
    }

    private boolean gestureTolerance(@NonNull ScaleGestureDetector detector) {
        final float currentDistance = detector.getCurrentSpan();
        final float distanceDelta = Math.abs(mInitialDistance - currentDistance);
        return distanceDelta > mScaleTriggerDistance;
    }

    class MyOnScaleGestureListener extends ScaleGestureDetector.SimpleOnScaleGestureListener {

        @Override
        public boolean onScale(ScaleGestureDetector detector) {
            if (gestureTolerance(detector)) {
                if (mScaleListener != null) {
                    float scaleFactor = detector.getScaleFactor();
                    if (scaleFactor > 1F) {
                        mScaleListener.onScaleUp(scaleFactor);
                        mInitialDistance = detector.getCurrentSpan();
                    } else if (scaleFactor < 1F) {
                        mScaleListener.onScaleDown(scaleFactor);
                        mInitialDistance = detector.getCurrentSpan();
                    }
                }
            }
            return true;
        }

        @Override
        public boolean onScaleBegin(ScaleGestureDetector detector) {
            mInitialDistance = detector.getCurrentSpan();
            return true;
        }

        @Override
        public void onScaleEnd(ScaleGestureDetector detector) {
        }
    }

    public interface ScaleListener {
        void onTwoFingersStart();

        void onTwoFingersEnd();

        void onScaleUp(float scaleFactor);

        void onScaleDown(float scaleFactor);
    }
}

【讨论】：