Android VersionedGestureDetector手势事件

  今天研究了一下PhotoView，发现里面的自定义的手势事件可以支持所有的SDK版本，该事件可以实现拖拽、滑动、缩放功能。下面直接上代码：

public abstract class VersionedGestureDetector {
    static final String LOG_TAG = "VersionedGestureDetector";
    OnGestureListener mListener;

    public static VersionedGestureDetector newInstance(Context context, OnGestureListener listener) {
        final int sdkVersion = Build.VERSION.SDK_INT;
        VersionedGestureDetector detector = null;
        if (sdkVersion < Build.VERSION_CODES.ECLAIR) {
            detector = new CupcakeDetector(context);
        } else if (sdkVersion < Build.VERSION_CODES.FROYO) {
            detector = new EclairDetector(context);
        } else {
            detector = new FroyoDetector(context);
        }

        detector.mListener = listener;

        return detector;
    }

    public abstract boolean onTouchEvent(MotionEvent ev);

    public abstract boolean isScaling();

    public static interface OnGestureListener {
        public void onDrag(float dx, float dy);

        public void onFling(float startX, float startY, float velocityX, float velocityY);

        public void onScale(float scaleFactor, float focusX, float focusY);
    }

    // <2.0 
    private static class CupcakeDetector extends VersionedGestureDetector {

        float mLastTouchX;
        float mLastTouchY;
        final float mTouchSlop;
        final float mMinimumVelocity;

        public CupcakeDetector(Context context) {
            final ViewConfiguration configuration = ViewConfiguration.get(context);
            mMinimumVelocity = configuration.getScaledMinimumFlingVelocity();
            mTouchSlop = configuration.getScaledTouchSlop();
        }

        private VelocityTracker mVelocityTracker;
        private boolean mIsDragging;

        float getActiveX(MotionEvent ev) {
            return ev.getX();
        }

        float getActiveY(MotionEvent ev) {
            return ev.getY();
        }

        public boolean isScaling() {
            return false;
        }

        @Override
        public boolean onTouchEvent(MotionEvent ev) {
            switch (ev.getAction()) {
                case MotionEvent.ACTION_DOWN: {
                    mVelocityTracker = VelocityTracker.obtain();
                    mVelocityTracker.addMovement(ev);

                    mLastTouchX = getActiveX(ev);
                    mLastTouchY = getActiveY(ev);
                    mIsDragging = false;
                    break;
                }
                case MotionEvent.ACTION_MOVE: {
                    final float x = getActiveX(ev);
                    final float y = getActiveY(ev);
                    final float dx = x - mLastTouchX, dy = y - mLastTouchY;

                    if (!mIsDragging) {
                        // Use Pythagoras to see if drag length is larger than
                        // touch slop
                        mIsDragging = FloatMath.sqrt((dx * dx) + (dy * dy)) >= mTouchSlop;
                    }

                    if (mIsDragging) {
                        mListener.onDrag(dx, dy);
                        mLastTouchX = x;
                        mLastTouchY = y;

                        if (null != mVelocityTracker) {
                            mVelocityTracker.addMovement(ev);
                        }
                    }
                    break;
                }

                case MotionEvent.ACTION_CANCEL:
                case MotionEvent.ACTION_UP: {
                    if (mIsDragging) {
                        mIsDragging = false;

                        if (null != mVelocityTracker) {
                            mLastTouchX = getActiveX(ev);
                            mLastTouchY = getActiveY(ev);

                            // Compute velocity within the last 1000ms
                            mVelocityTracker.addMovement(ev);
                            mVelocityTracker.computeCurrentVelocity(1000);

                            final float vX = mVelocityTracker.getXVelocity(), vY = mVelocityTracker.getYVelocity();

                            // If the velocity is greater than minVelocity, call
                            // listener
                            if (Math.max(Math.abs(vX), Math.abs(vY)) >= mMinimumVelocity) {
                                mListener.onFling(mLastTouchX, mLastTouchY, -vX, -vY);
                            }
                        }
                    }

                    // Recycle Velocity Tracker
                    if (null != mVelocityTracker) {
                        mVelocityTracker.recycle();
                        mVelocityTracker = null;
                    }
                    break;
                }
            }
            return true;
        }
    }

    // =2.0 =2.1
    private static class EclairDetector extends CupcakeDetector {
        private static final int INVALID_POINTER_ID = -1;
        private int mActivePointerId = INVALID_POINTER_ID;
        private int mActivePointerIndex = 0;

        public EclairDetector(Context context) {
            super(context);
        }

        @Override
        float getActiveX(MotionEvent ev) {
            try {
                return ev.getX(mActivePointerIndex);
            } catch (Exception e) {
                return ev.getX();
            }
        }

        @Override
        float getActiveY(MotionEvent ev) {
            try {
                return ev.getY(mActivePointerIndex);
            } catch (Exception e) {
                return ev.getY();
            }
        }

        @Override
        public boolean onTouchEvent(MotionEvent ev) {
            final int action = ev.getAction();
            switch (action & MotionEvent.ACTION_MASK) {
                case MotionEvent.ACTION_DOWN:
                    mActivePointerId = ev.getPointerId(0);
                    break;
                case MotionEvent.ACTION_CANCEL:
                case MotionEvent.ACTION_UP:
                    mActivePointerId = INVALID_POINTER_ID;
                    break;
                case MotionEvent.ACTION_POINTER_UP:
                    final int pointerIndex = (ev.getAction() & MotionEvent.ACTION_POINTER_INDEX_MASK) >> MotionEvent.ACTION_POINTER_INDEX_SHIFT;
                    final int pointerId = ev.getPointerId(pointerIndex);
                    if (pointerId == mActivePointerId) {
                        // This was our active pointer going up. Choose a new
                        // active pointer and adjust accordingly.
                        final int newPointerIndex = pointerIndex == 0 ? 1 : 0;
                        mActivePointerId = ev.getPointerId(newPointerIndex);
                        mLastTouchX = ev.getX(newPointerIndex);
                        mLastTouchY = ev.getY(newPointerIndex);
                    }
                    break;
            }

            mActivePointerIndex = ev.findPointerIndex(mActivePointerId != INVALID_POINTER_ID ? mActivePointerId : 0);
            return super.onTouchEvent(ev);
        }
    }

    // >=2.2 add a ScaleGestureDetector
    private static class FroyoDetector extends EclairDetector implements ScaleGestureDetector.OnScaleGestureListener {
        private ScaleGestureDetector mDetector;

        public FroyoDetector(Context context) {
            super(context);
            mDetector = new ScaleGestureDetector(context, this);
        }

        @Override
        public boolean isScaling() {
            return mDetector.isInProgress();
        }

        @Override
        public boolean onScale(ScaleGestureDetector detector) {
            mListener.onScale(detector.getScaleFactor(), detector.getFocusX(), detector.getFocusY());
            return true;
        }

        @Override
        public boolean onTouchEvent(MotionEvent ev) {
            mDetector.onTouchEvent(ev);
            return super.onTouchEvent(ev);
        }

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

        @Override
        public void onScaleEnd(ScaleGestureDetector detector) {
            // NO-OP
        }
    }
}