MotionEventCompat.java

/*
 * Copyright (C) 2011 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package android.support.v4.viewpager;

import android.view.MotionEvent;

/**
 * Helper for accessing newer features in MotionEvent.
 */
public class MotionEventCompat {
    /**
     * Interface for the full API.
     */
    interface MotionEventVersionImpl {
        public int findPointerIndex(MotionEvent event, int pointerId);
        public int getPointerId(MotionEvent event, int pointerIndex);
        public float getX(MotionEvent event, int pointerIndex);
        public float getY(MotionEvent event, int pointerIndex);
    }

    /**
     * Interface implementation that doesn't use anything about v4 APIs.
     */
    static class BaseMotionEventVersionImpl implements MotionEventVersionImpl {
        @Override
        public int findPointerIndex(MotionEvent event, int pointerId) {
            if (pointerId == 0) {
                // id 0 == index 0 and vice versa.
                return 0;
            }
            return -1;
        }
        @Override
        public int getPointerId(MotionEvent event, int pointerIndex) {
            if (pointerIndex == 0) {
                // index 0 == id 0 and vice versa.
                return 0;
            }
            throw new IndexOutOfBoundsException("Pre-Eclair does not support multiple pointers");
        }
        @Override
        public float getX(MotionEvent event, int pointerIndex) {
            if (pointerIndex == 0) {
                return event.getX();
            }
            throw new IndexOutOfBoundsException("Pre-Eclair does not support multiple pointers");
        }
        @Override
        public float getY(MotionEvent event, int pointerIndex) {
            if (pointerIndex == 0) {
                return event.getY();
            }
            throw new IndexOutOfBoundsException("Pre-Eclair does not support multiple pointers");
        }
    }

    /**
     * Interface implementation for devices with at least v11 APIs.
     */
    static class EclairMotionEventVersionImpl implements MotionEventVersionImpl {
        @Override
        public int findPointerIndex(MotionEvent event, int pointerId) {
            return MotionEventCompatEclair.findPointerIndex(event, pointerId);
        }
        @Override
        public int getPointerId(MotionEvent event, int pointerIndex) {
            return MotionEventCompatEclair.getPointerId(event, pointerIndex);
        }
        @Override
        public float getX(MotionEvent event, int pointerIndex) {
            return MotionEventCompatEclair.getX(event, pointerIndex);
        }
        @Override
        public float getY(MotionEvent event, int pointerIndex) {
            return MotionEventCompatEclair.getY(event, pointerIndex);
        }
    }

    /**
     * Select the correct implementation to use for the current platform.
     */
    static final MotionEventVersionImpl IMPL;
    static {
        if (android.os.Build.VERSION.SDK_INT >= 5) {
            IMPL = new EclairMotionEventVersionImpl();
        } else {
            IMPL = new BaseMotionEventVersionImpl();
        }
    }

    // -------------------------------------------------------------------

    /**
     * Synonym for {@link MotionEvent#ACTION_MASK}.
     */
    public static final int ACTION_MASK = 0xff;

    /**
     * Synonym for {@link MotionEvent#ACTION_POINTER_DOWN}.
     */
    public static final int ACTION_POINTER_DOWN = 5;

    /**
     * Synonym for {@link MotionEvent#ACTION_POINTER_UP}.
     */
    public static final int ACTION_POINTER_UP = 6;

    /**
     * Synonym for {@link MotionEvent#ACTION_HOVER_MOVE}.
     */
    public static final int ACTION_HOVER_MOVE = 7;

    /**
     * Synonym for {@link MotionEvent#ACTION_SCROLL}.
     */
    public static final int ACTION_SCROLL = 8;

    /**
     * Synonym for {@link MotionEvent#ACTION_POINTER_INDEX_MASK}.
     */
    public static final int ACTION_POINTER_INDEX_MASK  = 0xff00;

    /**
     * Synonym for {@link MotionEvent#ACTION_POINTER_INDEX_SHIFT}.
     */
    public static final int ACTION_POINTER_INDEX_SHIFT = 8;

    /**
     * Call {@link MotionEvent#getAction}, returning only the {@link #ACTION_MASK}
     * portion.
     */
    public static int getActionMasked(MotionEvent event) {
        return event.getAction() & ACTION_MASK;
    }

    /**
     * Call {@link MotionEvent#getAction}, returning only the pointer index
     * portion
     */
    public static int getActionIndex(MotionEvent event) {
        return (event.getAction() & ACTION_POINTER_INDEX_MASK)
                >> ACTION_POINTER_INDEX_SHIFT;
    }

    /**
     * Call {@link MotionEvent#findPointerIndex(int)}.
     * If running on a pre-{@android.os.Build.VERSION_CODES#HONEYCOMB} device,
     * does nothing and returns -1.
     */
    public static int findPointerIndex(MotionEvent event, int pointerId) {
        return IMPL.findPointerIndex(event, pointerId);
    }

    /**
     * Call {@link MotionEvent#getPointerId(int)}.
     * If running on a pre-{@android.os.Build.VERSION_CODES#HONEYCOMB} device,
     * {@link IndexOutOfBoundsException} is thrown.
     */
    public static int getPointerId(MotionEvent event, int pointerIndex) {
        return IMPL.getPointerId(event, pointerIndex);
    }

    /**
     * Call {@link MotionEvent#getX(int)}.
     * If running on a pre-{@android.os.Build.VERSION_CODES#HONEYCOMB} device,
     * {@link IndexOutOfBoundsException} is thrown.
     */
    public static float getX(MotionEvent event, int pointerIndex) {
        return IMPL.getX(event, pointerIndex);
    }

    /**
     * Call {@link MotionEvent#getY(int)}.
     * If running on a pre-{@android.os.Build.VERSION_CODES#HONEYCOMB} device,
     * {@link IndexOutOfBoundsException} is thrown.
     */
    public static float getY(MotionEvent event, int pointerIndex) {
        return IMPL.getY(event, pointerIndex);
    }
}