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The Support Package includes static "support libraries" that you can add to your Android application in order to use APIs that are either not available for older platform versions or that offer "utility" APIs that aren't a part of the framework APIs.
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/*
 * 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.view;

import android.view.MotionEvent;

/**
 * Helper for accessing features in {@link MotionEvent} introduced
 * after API level 4 in a backwards compatible fashion.
 */
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-{@link android.os.Build.VERSION_CODES#ECLAIR} 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-{@link android.os.Build.VERSION_CODES#ECLAIR} 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-{@link android.os.Build.VERSION_CODES#ECLAIR} 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-{@link android.os.Build.VERSION_CODES#ECLAIR} device,
     * {@link IndexOutOfBoundsException} is thrown.
     */
    public static float getY(MotionEvent event, int pointerIndex) {
        return IMPL.getY(event, pointerIndex);
    }
}