继承ViewPager实现上下滑动整页

package com.jiajing.administrator.therapeuticapparatus.view;

import java.util.ArrayList;

import android.content.Context;
import android.database.DataSetObserver;
import android.os.Build;
import android.os.Parcel;
import android.os.Parcelable;
import android.support.v4.os.ParcelableCompat;
import android.support.v4.os.ParcelableCompatCreatorCallbacks;
import android.support.v4.view.MotionEventCompat;
import android.support.v4.view.PagerAdapter;
import android.support.v4.view.VelocityTrackerCompat;
import android.support.v4.view.ViewConfigurationCompat;
import android.support.v4.view.ViewPager;
import android.util.AttributeSet;
import android.util.Log;
import android.view.MotionEvent;
import android.view.VelocityTracker;
import android.view.View;
import android.view.ViewConfiguration;
import android.view.ViewGroup;
import android.widget.Scroller;

/**
 * Layout manager that allows the user to flip horizontally or vertically
 * through pages of data. You supply an implementation of a {@link PagerAdapter}
 * to generate the pages that the view shows.
 * 

 * 

 * Note this class is currently under early design and development. The API will
 * likely change in later updates of the compatibility library, requiring
 * changes to the source code of apps when they are compiled against the newer
 * version.
 * 
 */
public class DirectionalViewPager extends ViewPager {
    private static final String TAG = "DirectionalViewPager";
    private static final String XML_NS = "http://schemas.android.com/apk/res/android";
    private static final boolean DEBUG = false;

    private static final boolean USE_CACHE = false;

    public static final int HORIZONTAL = 0;
    public static final int VERTICAL = 1;

    static class ItemInfo {
        Object object;
        int position;
        boolean scrolling;
    }

    private final ArrayList mItems = new ArrayList();

    private PagerAdapter mAdapter;
    private int mCurItem; // Index of currently displayed page.
    private int mRestoredCurItem = -1;
    private Parcelable mRestoredAdapterState = null;
    private ClassLoader mRestoredClassLoader = null;
    private Scroller mScroller;
    private DataSetObserver mObserver;

    private int mChildWidthMeasureSpec;
    private int mChildHeightMeasureSpec;
    private boolean mInLayout;

    private boolean mScrollingCacheEnabled;

    private boolean mPopulatePending;
    private boolean mScrolling;

    private boolean mIsBeingDragged;
    private boolean mIsUnableToDrag;
    private int mTouchSlop;
    private float mInitialMotion;
    /**
     * Position of the last motion event.
     */
    private float mLastMotionX;
    private float mLastMotionY;
    private int mOrientation = HORIZONTAL;
    /**
     * ID of the active pointer. This is used to retain consistency during
     * drags/flings if multiple pointers are used.
     */
    private int mActivePointerId = INVALID_POINTER;
    /**
     * Sentinel value for no current active pointer. Used by
     * {@link #mActivePointerId}.
     */
    private static final int INVALID_POINTER = -1;

    /**
     * Determines speed during touch scrolling
     */
    private VelocityTracker mVelocityTracker;
    private int mMinimumVelocity;
    private int mMaximumVelocity;

    private OnPageChangeListener mOnPageChangeListener;

    private int mScrollState = SCROLL_STATE_IDLE;

    public DirectionalViewPager(Context context) {
        super(context);
        initViewPager();
    }

    public DirectionalViewPager(Context context, AttributeSet attrs) {
        super(context, attrs);
        initViewPager();

        // We default to horizontal, only change if a value is explicitly
        // specified
        int orientation = attrs.getAttributeIntValue(XML_NS, "orientation", -1);
        if (orientation != -1) {
            setOrientation(orientation);
        }
    }

    void initViewPager() {
        setWillNotDraw(false);
        mScroller = new Scroller(getContext());
        final ViewConfiguration configuration = ViewConfiguration
                .get(getContext());
        mTouchSlop = ViewConfigurationCompat
                .getScaledPagingTouchSlop(configuration);
        mMinimumVelocity = configuration.getScaledMinimumFlingVelocity();
        mMaximumVelocity = configuration.getScaledMaximumFlingVelocity();
        mObserver = new DataSetObserver() {
            @Override
            public void onChanged() {
                dataSetChanged();
            }
        };
    }

    private void setScrollState(int newState) {
        if (mScrollState == newState) {
            return;
        }

        mScrollState = newState;
        if (mOnPageChangeListener != null) {
            mOnPageChangeListener.onPageScrollStateChanged(newState);
        }
    }

    public void setAdapter(PagerAdapter adapter) {

        if (mAdapter != null) {
            this.mAdapter.unregisterDataSetObserver(mObserver);
        }

        mAdapter = adapter;

        if (mAdapter != null) {
            mAdapter.registerDataSetObserver(mObserver);
            mPopulatePending = false;
            if (mRestoredCurItem >= 0) {
                mAdapter.restoreState(mRestoredAdapterState,
                        mRestoredClassLoader);
                setCurrentItemInternal(mRestoredCurItem, false, true);
                mRestoredCurItem = -1;
                mRestoredAdapterState = null;
                mRestoredClassLoader = null;
            } else {
                populate();
            }
        }
    }

    public PagerAdapter getAdapter() {
        return mAdapter;
    }

    public void setCurrentItem(int item) {
        mPopulatePending = false;
        setCurrentItemInternal(item, true, false);
    }

    void setCurrentItemInternal(int item, boolean smoothScroll, boolean always) {
        if (mAdapter == null || mAdapter.getCount() <= 0) {
            setScrollingCacheEnabled(false);
            return;
        }
        if (!always && mCurItem == item && mItems.size() != 0) {
            setScrollingCacheEnabled(false);
            return;
        }
        if (item < 0) {
            item = 0;
        } else if (item >= mAdapter.getCount()) {
            item = mAdapter.getCount() - 1;
        }
        if (item > (mCurItem + 1) || item < (mCurItem - 1)) {
            // We are doing a jump by more than one page. To avoid
            // glitches, we want to keep all current pages in the view
            // until the scroll ends.
            for (int i = 0; i < mItems.size(); i++) {
                mItems.get(i).scrolling = true;
            }
        }
        final boolean dispatchSelected = mCurItem != item;
        mCurItem = item;
        populate();
        if (smoothScroll) {
            if (mOrientation == HORIZONTAL) {
                smoothScrollTo(getWidth() * item, 0);
            } else {
                smoothScrollTo(0, getHeight() * item);
            }
            if (dispatchSelected && mOnPageChangeListener != null) {
                mOnPageChangeListener.onPageSelected(item);
            }
        } else {
            if (dispatchSelected && mOnPageChangeListener != null) {
                mOnPageChangeListener.onPageSelected(item);
            }
            completeScroll();
            if (mOrientation == HORIZONTAL) {
                scrollTo(getWidth() * item, 0);
            } else {
                scrollTo(0, getHeight() * item);
            }
        }
    }

    public void setOnPageChangeListener(OnPageChangeListener listener) {
        mOnPageChangeListener = listener;
    }

    /**
     * Like {@link View#scrollBy}, but scroll smoothly instead of immediately.
     */
    void smoothScrollTo(int x, int y) {
        if (getChildCount() == 0) {
            // Nothing to do.
            setScrollingCacheEnabled(false);
            return;
        }
        int sx = getScrollX();
        int sy = getScrollY();
        int dx = x - sx;
        int dy = y - sy;
        if (dx == 0 && dy == 0) {
            completeScroll();
            return;
        }

        setScrollingCacheEnabled(true);
        mScrolling = true;
        setScrollState(SCROLL_STATE_SETTLING);
        mScroller.startScroll(sx, sy, dx, dy);
        invalidate();
    }

    void addNewItem(int position, int index) {
        ItemInfo ii = new ItemInfo();
        ii.position = position;
        ii.object = mAdapter.instantiateItem(this, position);
        if (index < 0) {
            mItems.add(ii);
        } else {
            mItems.add(index, ii);
        }
    }

    void dataSetChanged() {
        // This method only gets called if our observer is attached, so mAdapter
        // is non-null.

        boolean needPopulate = mItems.isEmpty() && mAdapter.getCount() > 0;
        int newCurrItem = -1;

        for (int i = 0; i < mItems.size(); i++) {
            final ItemInfo ii = mItems.get(i);
            final int newPos = mAdapter.getItemPosition(ii.object);

            if (newPos == PagerAdapter.POSITION_UNCHANGED) {
                continue;
            }

            if (newPos == PagerAdapter.POSITION_NONE) {
                mItems.remove(i);
                i--;
                mAdapter.destroyItem(this, ii.position, ii.object);
                needPopulate = true;

                if (mCurItem == ii.position) {
                    // Keep the current item in the valid range
                    newCurrItem = Math.max(0,
                            Math.min(mCurItem, mAdapter.getCount() - 1));
                }
                continue;
            }

            if (ii.position != newPos) {
                if (ii.position == mCurItem) {
                    // Our current item changed position. Follow it.
                    newCurrItem = newPos;
                }

                ii.position = newPos;
                needPopulate = true;
            }
        }

        if (newCurrItem >= 0) {
            // TODO This currently causes a jump.
            setCurrentItemInternal(newCurrItem, false, true);
            needPopulate = true;
        }
        if (needPopulate) {
            populate();
            requestLayout();
        }
    }

    void populate() {
        if (mAdapter == null) {
            return;
        }

        // Bail now if we are waiting to populate. This is to hold off
        // on creating views from the time the user releases their finger to
        // fling to a new position until we have finished the scroll to
        // that position, avoiding glitches from happening at that point.
        if (mPopulatePending) {
            if (DEBUG)
                Log.i(TAG, "populate is pending, skipping for now...");
            return;
        }

        // Also, don't populate until we are attached to a window. This is to
        // avoid trying to populate before we have restored our view hierarchy
        // state and conflicting with what is restored.
        if (getWindowToken() == null) {
            return;
        }

        mAdapter.startUpdate(this);

        final int startPos = mCurItem > 0 ? mCurItem - 1 : mCurItem;
        final int count = mAdapter.getCount();
        final int endPos = mCurItem < (count - 1) ? mCurItem + 1 : count - 1;

        if (DEBUG)
            Log.v(TAG, "populating: startPos=" + startPos + " endPos=" + endPos);

        // Add and remove pages in the existing list.
        int lastPos = -1;
        for (int i = 0; i < mItems.size(); i++) {
            ItemInfo ii = mItems.get(i);
            if ((ii.position < startPos || ii.position > endPos)
                    && !ii.scrolling) {
                if (DEBUG)
                    Log.i(TAG, "removing: " + ii.position + " @ " + i);
                mItems.remove(i);
                i--;
                mAdapter.destroyItem(this, ii.position, ii.object);
            } else if (lastPos < endPos && ii.position > startPos) {
                // The next item is outside of our range, but we have a gap
                // between it and the last item where we want to have a page
                // shown. Fill in the gap.
                lastPos++;
                if (lastPos < startPos) {
                    lastPos = startPos;
                }
                while (lastPos <= endPos && lastPos < ii.position) {
                    if (DEBUG)
                        Log.i(TAG, "inserting: " + lastPos + " @ " + i);
                    addNewItem(lastPos, i);
                    lastPos++;
                    i++;
                }
            }
            lastPos = ii.position;
        }

        // Add any new pages we need at the end.
        lastPos = mItems.size() > 0 ? mItems.get(mItems.size() - 1).position
                : -1;
        if (lastPos < endPos) {
            lastPos++;
            lastPos = lastPos > startPos ? lastPos : startPos;
            while (lastPos <= endPos) {
                if (DEBUG)
                    Log.i(TAG, "appending: " + lastPos);
                addNewItem(lastPos, -1);
                lastPos++;
            }
        }

        if (DEBUG) {
            Log.i(TAG, "Current page list:");
            for (int i = 0; i < mItems.size(); i++) {
                Log.i(TAG, "#" + i + ": page " + mItems.get(i).position);
            }
        }

        mAdapter.finishUpdate(this);
    }

    public static class SavedState extends BaseSavedState {
        int position;
        Parcelable adapterState;
        ClassLoader loader;

        public SavedState(Parcelable superState) {
            super(superState);
        }

        @Override
        public void writeToParcel(Parcel out, int flags) {
            super.writeToParcel(out, flags);
            out.writeInt(position);
            out.writeParcelable(adapterState, flags);
        }

        @Override
        public String toString() {
            return "FragmentPager.SavedState{"
                    + Integer.toHexString(System.identityHashCode(this))
                    + " position=" + position + "}";
        }

        public static final Creator CREATOR = ParcelableCompat
                .newCreator(new ParcelableCompatCreatorCallbacks() {
                    @Override
                    public SavedState createFromParcel(Parcel in,
                                                       ClassLoader loader) {
                        return new SavedState(in, loader);
                    }

                    @Override
                    public SavedState[] newArray(int size) {
                        return new SavedState[size];
                    }
                });

        SavedState(Parcel in, ClassLoader loader) {
            super(in);
            if (loader == null) {
                loader = getClass().getClassLoader();
            }
            position = in.readInt();
            adapterState = in.readParcelable(loader);
            this.loader = loader;
        }
    }

    @Override
    public Parcelable onSaveInstanceState() {
        Parcelable superState = super.onSaveInstanceState();
        SavedState ss = new SavedState(superState);
        ss.position = mCurItem;
        ss.adapterState = mAdapter.saveState();
        return ss;
    }

    @Override
    public void onRestoreInstanceState(Parcelable state) {
        if (!(state instanceof SavedState)) {
            super.onRestoreInstanceState(state);
            return;
        }

        SavedState ss = (SavedState) state;
        super.onRestoreInstanceState(ss.getSuperState());

        if (mAdapter != null) {
            mAdapter.restoreState(ss.adapterState, ss.loader);
            setCurrentItemInternal(ss.position, false, true);
        } else {
            mRestoredCurItem = ss.position;
            mRestoredAdapterState = ss.adapterState;
            mRestoredClassLoader = ss.loader;
        }
    }

    public int getOrientation() {
        return mOrientation;
    }

    public void setOrientation(int orientation) {
        switch (orientation) {
            case HORIZONTAL:
            case VERTICAL:
                break;

            default:
                throw new IllegalArgumentException(
                        "Only HORIZONTAL and VERTICAL are valid orientations.");
        }

        if (orientation == mOrientation) {
            return;
        }

        // Complete any scroll we are currently in the middle of
        completeScroll();

        // Reset values
        mInitialMotion = 0;
        mLastMotionX = 0;
        mLastMotionY = 0;
        if (mVelocityTracker != null) {
            mVelocityTracker.clear();
        }

        // Adjust scroll for new orientation
        mOrientation = orientation;
        if (mOrientation == HORIZONTAL) {
            scrollTo(mCurItem * getWidth(), 0);
        } else {
            scrollTo(0, mCurItem * getHeight());
        }
        requestLayout();
    }

    @Override
    public void addView(View child, int index, ViewGroup.LayoutParams params) {
        if (mInLayout) {
            addViewInLayout(child, index, params);
            child.measure(mChildWidthMeasureSpec, mChildHeightMeasureSpec);
        } else {
            super.addView(child, index, params);
        }

        if (USE_CACHE) {
            if (child.getVisibility() != GONE) {
                child.setDrawingCacheEnabled(mScrollingCacheEnabled);
            } else {
                child.setDrawingCacheEnabled(false);
            }
        }
    }

    ItemInfo infoForChild(View child) {
        for (int i = 0; i < mItems.size(); i++) {
            ItemInfo ii = mItems.get(i);
            if (mAdapter.isViewFromObject(child, ii.object)) {
                return ii;
            }
        }
        return null;
    }

    @Override
    protected void onAttachedToWindow() {
        super.onAttachedToWindow();
        if (mAdapter != null) {
            populate();
        }
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        // For simple implementation, or internal size is always 0.
        // We depend on the container to specify the layout size of
        // our view. We can't really know what it is since we will be
        // adding and removing different arbitrary views and do not
        // want the layout to change as this happens.
        setMeasuredDimension(getDefaultSize(0, widthMeasureSpec),
                getDefaultSize(0, heightMeasureSpec));

        // Children are just made to fill our space.
        mChildWidthMeasureSpec = MeasureSpec.makeMeasureSpec(getMeasuredWidth()
                - getPaddingLeft() - getPaddingRight(), MeasureSpec.EXACTLY);
        mChildHeightMeasureSpec = MeasureSpec.makeMeasureSpec(
                getMeasuredHeight() - getPaddingTop() - getPaddingBottom(),
                MeasureSpec.EXACTLY);

        // Make sure we have created all fragments that we need to have shown.
        mInLayout = true;
        populate();
        mInLayout = false;

        // Make sure all children have been properly measured.
        final int size = getChildCount();
        for (int i = 0; i < size; ++i) {
            final View child = getChildAt(i);
            if (child.getVisibility() != GONE) {
                if (DEBUG)
                    Log.v(TAG, "Measuring #" + i + " " + child + ": "
                            + mChildWidthMeasureSpec + " x "
                            + mChildHeightMeasureSpec);
                child.measure(mChildWidthMeasureSpec, mChildHeightMeasureSpec);
            }
        }
    }

    @Override
    protected void onSizeChanged(int w, int h, int oldw, int oldh) {
        super.onSizeChanged(w, h, oldw, oldh);

        // Make sure scroll position is set correctly.
        if (mOrientation == HORIZONTAL) {
            int scrollPos = mCurItem * w;
            if (scrollPos != getScrollX()) {
                completeScroll();
                scrollTo(scrollPos, getScrollY());
            }
        } else {
            int scrollPos = mCurItem * h;
            if (scrollPos != getScrollY()) {
                completeScroll();
                scrollTo(getScrollX(), scrollPos);
            }
        }
    }

    @Override
    protected void onLayout(boolean changed, int l, int t, int r, int b) {
        mInLayout = true;
        populate();
        mInLayout = false;

        final int count = getChildCount();
        final int size = (mOrientation == HORIZONTAL) ? r - l : b - t;

        for (int i = 0; i < count; i++) {
            View child = getChildAt(i);
            ItemInfo ii;
            if (child.getVisibility() != GONE
                    && (ii = infoForChild(child)) != null) {
                int off = size * ii.position;
                int childLeft = getPaddingLeft();
                int childTop = getPaddingTop();
                if (mOrientation == HORIZONTAL) {
                    childLeft += off;
                } else {
                    childTop += off;
                }
                if (DEBUG)
                    Log.v(TAG,
                            "Positioning #" + i + " " + child + " f="
                                    + ii.object + ":" + childLeft + ","
                                    + childTop + " " + child.getMeasuredWidth()
                                    + "x" + child.getMeasuredHeight());
                child.layout(childLeft, childTop,
                        childLeft + child.getMeasuredWidth(),
                        childTop + child.getMeasuredHeight());
            }
        }
    }

    @Override
    public void computeScroll() {
        if (DEBUG)
            Log.i(TAG, "computeScroll: finished=" + mScroller.isFinished());
        if (!mScroller.isFinished()) {
            if (mScroller.computeScrollOffset()) {
                if (DEBUG)
                    Log.i(TAG, "computeScroll: still scrolling");
                int oldX = getScrollX();
                int oldY = getScrollY();
                int x = mScroller.getCurrX();
                int y = mScroller.getCurrY();

                if (oldX != x || oldY != y) {
                    scrollTo(x, y);
                }

                if (mOnPageChangeListener != null) {
                    int size;
                    int value;
                    if (mOrientation == HORIZONTAL) {
                        size = getWidth();
                        value = x;
                    } else {
                        size = getHeight();
                        value = y;
                    }

                    final int position = value / size;
                    final int offsetPixels = value % size;
                    final float offset = (float) offsetPixels / size;
                    mOnPageChangeListener.onPageScrolled(position, offset,
                            offsetPixels);
                }

                // Keep on drawing until the animation has finished.
                invalidate();
                return;
            }
        }

        // Done with scroll, clean up state.
        completeScroll();
    }

    private void completeScroll() {
        boolean needPopulate;
        if ((needPopulate = mScrolling)) {
            // Done with scroll, no longer want to cache view drawing.
            setScrollingCacheEnabled(false);
            mScroller.abortAnimation();
            int oldX = getScrollX();
            int oldY = getScrollY();
            int x = mScroller.getCurrX();
            int y = mScroller.getCurrY();
            if (oldX != x || oldY != y) {
                scrollTo(x, y);
            }
            setScrollState(SCROLL_STATE_IDLE);
        }
        mPopulatePending = false;
        mScrolling = false;
        for (int i = 0; i < mItems.size(); i++) {
            ItemInfo ii = mItems.get(i);
            if (ii.scrolling) {
                needPopulate = true;
                ii.scrolling = false;
            }
        }
        if (needPopulate) {
            populate();
        }
    }

    @Override
    public boolean onInterceptTouchEvent(MotionEvent ev) {
        /*
         * This method JUST determines whether we want to intercept the motion.
       * If we return true, onMotionEvent will be called and we do the actual
       * scrolling there.
       */

        final int action = ev.getAction() & MotionEventCompat.ACTION_MASK;

        // Always take care of the touch gesture being complete.
        if (action == MotionEvent.ACTION_CANCEL
                || action == MotionEvent.ACTION_UP) {
            // Release the drag.
            if (DEBUG)
                Log.v(TAG, "Intercept done!");
            mIsBeingDragged = false;
            mIsUnableToDrag = false;
            mActivePointerId = INVALID_POINTER;
            return false;
        }

        // Nothing more to do here if we have decided whether or not we
        // are dragging.
        if (action != MotionEvent.ACTION_DOWN) {
            if (mIsBeingDragged) {
                if (DEBUG)
                    Log.v(TAG, "Intercept returning true!");
                return true;
            }
            if (mIsUnableToDrag) {
                if (DEBUG)
                    Log.v(TAG, "Intercept returning false!");
                return false;
            }
        }

        switch (action) {
            case MotionEvent.ACTION_MOVE: {
            /*
             * mIsBeingDragged == false, otherwise the shortcut would have
          * caught it. Check whether the user has moved far enough from his
          * original down touch.
          */

         /*
             * Locally do absolute value. mLastMotionY is set to the y value of
          * the down event.
          */
                final int activePointerId = mActivePointerId;
                if (activePointerId == INVALID_POINTER
                        && Build.VERSION.SDK_INT > Build.VERSION_CODES.DONUT) {
                    // If we don't have a valid id, the touch down wasn't on
                    // content.
                    break;
                }

                final int pointerIndex = MotionEventCompat.findPointerIndex(ev,
                        activePointerId);
                final float x = MotionEventCompat.getX(ev, pointerIndex);
                final float y = MotionEventCompat.getY(ev, pointerIndex);
                final float xDiff = Math.abs(x - mLastMotionX);
                final float yDiff = Math.abs(y - mLastMotionY);
                float primaryDiff;
                float secondaryDiff;

                if (mOrientation == HORIZONTAL) {
                    primaryDiff = xDiff;
                    secondaryDiff = yDiff;
                } else {
                    primaryDiff = yDiff;
                    secondaryDiff = xDiff;
                }

                if (DEBUG)
                    Log.v(TAG, "Moved x to " + x + "," + y + " diff=" + xDiff + ","
                            + yDiff);

                if (primaryDiff > mTouchSlop && primaryDiff > secondaryDiff) {
                    if (DEBUG)
                        Log.v(TAG, "Starting drag!");
                    mIsBeingDragged = true;
                    setScrollState(SCROLL_STATE_DRAGGING);
                    if (mOrientation == HORIZONTAL) {
                        mLastMotionX = x;
                    } else {
                        mLastMotionY = y;
                    }
                    setScrollingCacheEnabled(true);
                } else {
                    if (secondaryDiff > mTouchSlop) {
                        // The finger has moved enough in the vertical
                        // direction to be counted as a drag... abort
                        // any attempt to drag horizontally, to work correctly
                        // with children that have scrolling containers.
                        if (DEBUG)
                            Log.v(TAG, "Starting unable to drag!");
                        mIsUnableToDrag = true;
                    }
                }
                break;
            }

            case MotionEvent.ACTION_DOWN: {
            /*
             * Remember location of down touch. ACTION_DOWN always refers to
          * pointer index 0.
          */
                if (mOrientation == HORIZONTAL) {
                    mLastMotionX = mInitialMotion = ev.getX();
                    mLastMotionY = ev.getY();
                } else {
                    mLastMotionX = ev.getX();
                    mLastMotionY = mInitialMotion = ev.getY();
                }
                mActivePointerId = MotionEventCompat.getPointerId(ev, 0);

                if (mScrollState == SCROLL_STATE_SETTLING) {
                    // Let the user 'catch' the pager as it animates.
                    mIsBeingDragged = true;
                    mIsUnableToDrag = false;
                    setScrollState(SCROLL_STATE_DRAGGING);
                } else {
                    completeScroll();
                    mIsBeingDragged = false;
                    mIsUnableToDrag = false;
                }

                if (DEBUG)
                    Log.v(TAG, "Down at " + mLastMotionX + "," + mLastMotionY
                            + " mIsBeingDragged=" + mIsBeingDragged
                            + "mIsUnableToDrag=" + mIsUnableToDrag);
                break;
            }

            case MotionEventCompat.ACTION_POINTER_UP:
                onSecondaryPointerUp(ev);
                break;
        }

      /*
         * The only time we want to intercept motion events is if we are in the
       * drag mode.
       */
        return mIsBeingDragged;
    }

    @Override
    public boolean onTouchEvent(MotionEvent ev) {

        if (ev.getAction() == MotionEvent.ACTION_DOWN && ev.getEdgeFlags() != 0) {
            // Don't handle edge touches immediately -- they may actually belong
            // to one of our
            // descendants.
            return false;
        }

        if (mAdapter == null || mAdapter.getCount() == 0) {
            // Nothing to present or scroll; nothing to touch.
            return false;
        }

        if (mVelocityTracker == null) {
            mVelocityTracker = VelocityTracker.obtain();
        }
        mVelocityTracker.addMovement(ev);

        final int action = ev.getAction();

        switch (action & MotionEventCompat.ACTION_MASK) {
            case MotionEvent.ACTION_DOWN: {
            /*
             * If being flinged and user touches, stop the fling. isFinished
          * will be false if being flinged.
          */
                completeScroll();

                // Remember where the motion event started
                if (mOrientation == HORIZONTAL) {
                    mLastMotionX = mInitialMotion = ev.getX();
                } else {
                    mLastMotionY = mInitialMotion = ev.getY();
                }
                mActivePointerId = MotionEventCompat.getPointerId(ev, 0);
                break;
            }
            case MotionEvent.ACTION_MOVE:
                if (!mIsBeingDragged) {
                    final int pointerIndex = MotionEventCompat.findPointerIndex(ev,
                            mActivePointerId);
                    final float x = MotionEventCompat.getX(ev, pointerIndex);
                    final float y = MotionEventCompat.getY(ev, pointerIndex);
                    final float xDiff = Math.abs(x - mLastMotionX);
                    final float yDiff = Math.abs(y - mLastMotionY);
                    float primaryDiff;
                    float secondaryDiff;

                    if (mOrientation == HORIZONTAL) {
                        primaryDiff = xDiff;
                        secondaryDiff = yDiff;
                    } else {
                        primaryDiff = yDiff;
                        secondaryDiff = xDiff;
                    }

                    if (DEBUG)
                        Log.v(TAG, "Moved x to " + x + "," + y + " diff=" + xDiff
                                + "," + yDiff);
                    if (primaryDiff > mTouchSlop && primaryDiff > secondaryDiff) {
                        if (DEBUG)
                            Log.v(TAG, "Starting drag!");
                        mIsBeingDragged = true;
                        if (mOrientation == HORIZONTAL) {
                            mLastMotionX = x;
                        } else {
                            mLastMotionY = y;
                        }
                        setScrollState(SCROLL_STATE_DRAGGING);
                        setScrollingCacheEnabled(true);
                    }
                }
                if (mIsBeingDragged) {
                    // Scroll to follow the motion event
                    final int activePointerIndex = MotionEventCompat
                            .findPointerIndex(ev, mActivePointerId);
                    final float x = MotionEventCompat.getX(ev, activePointerIndex);
                    final float y = MotionEventCompat.getY(ev, activePointerIndex);

                    int size;
                    float scroll;

                    if (mOrientation == HORIZONTAL) {
                        size = getWidth();
                        scroll = getScrollX() + (mLastMotionX - x);
                        mLastMotionX = x;
                    } else {
                        size = getHeight();
                        scroll = getScrollY() + (mLastMotionY - y);
                        mLastMotionY = y;
                    }

                    final float lowerBound = Math.max(0, (mCurItem - 1) * size);
                    final float upperBound = Math.min(mCurItem + 1,
                            mAdapter.getCount() - 1)
                            * size;
                    if (scroll < lowerBound) {
                        scroll = lowerBound;
                    } else if (scroll > upperBound) {
                        scroll = upperBound;
                    }
                    if (mOrientation == HORIZONTAL) {
                        // Don't lose the rounded component
                        mLastMotionX += scroll - (int) scroll;
                        scrollTo((int) scroll, getScrollY());
                    } else {
                        // Don't lose the rounded component
                        mLastMotionY += scroll - (int) scroll;
                        scrollTo(getScrollX(), (int) scroll);
                    }
                    if (mOnPageChangeListener != null) {
                        final int position = (int) scroll / size;
                        final int positionOffsetPixels = (int) scroll % size;
                        final float positionOffset = (float) positionOffsetPixels
                                / size;
                        mOnPageChangeListener.onPageScrolled(position,
                                positionOffset, positionOffsetPixels);
                    }
                }
                break;
            case MotionEvent.ACTION_UP:
                if (mIsBeingDragged) {
                    final VelocityTracker velocityTracker = mVelocityTracker;
                    velocityTracker.computeCurrentVelocity(1000, mMaximumVelocity);
                    int initialVelocity;
                    float lastMotion;
                    int sizeOverThree;

                    if (mOrientation == HORIZONTAL) {
                        initialVelocity = (int) VelocityTrackerCompat.getXVelocity(
                                velocityTracker, mActivePointerId);
                        lastMotion = mLastMotionX;
                        sizeOverThree = getWidth() / 3;
                    } else {
                        initialVelocity = (int) VelocityTrackerCompat.getYVelocity(
                                velocityTracker, mActivePointerId);
                        lastMotion = mLastMotionY;
                        sizeOverThree = getHeight() / 3;
                    }

                    mPopulatePending = true;
                    if ((Math.abs(initialVelocity) > mMinimumVelocity)
                            || Math.abs(mInitialMotion - lastMotion) >= sizeOverThree) {
                        if (lastMotion > mInitialMotion) {
                            setCurrentItemInternal(mCurItem - 1, true, true);
                        } else {
                            setCurrentItemInternal(mCurItem + 1, true, true);
                        }
                    } else {
                        setCurrentItemInternal(mCurItem, true, true);
                    }

                    mActivePointerId = INVALID_POINTER;
                    endDrag();
                }
                break;
            case MotionEvent.ACTION_CANCEL:
                if (mIsBeingDragged) {
                    setCurrentItemInternal(mCurItem, true, true);
                    mActivePointerId = INVALID_POINTER;
                    endDrag();
                }
                break;
            case MotionEventCompat.ACTION_POINTER_DOWN: {
                final int index = MotionEventCompat.getActionIndex(ev);
                if (mOrientation == HORIZONTAL) {
                    mLastMotionX = MotionEventCompat.getX(ev, index);
                } else {
                    mLastMotionY = MotionEventCompat.getY(ev, index);
                }
                mActivePointerId = MotionEventCompat.getPointerId(ev, index);
                break;
            }
            case MotionEventCompat.ACTION_POINTER_UP:
                onSecondaryPointerUp(ev);
                final int index = MotionEventCompat.findPointerIndex(ev,
                        mActivePointerId);
                if (mOrientation == HORIZONTAL) {
                    mLastMotionX = MotionEventCompat.getX(ev, index);
                } else {
                    mLastMotionY = MotionEventCompat.getY(ev, index);
                }
                break;
        }
        return true;
    }

    private void onSecondaryPointerUp(MotionEvent ev) {
        final int pointerIndex = MotionEventCompat.getActionIndex(ev);
        final int pointerId = MotionEventCompat.getPointerId(ev, 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;
            if (mOrientation == HORIZONTAL) {
                mLastMotionX = MotionEventCompat.getX(ev, newPointerIndex);
            } else {
                mLastMotionY = MotionEventCompat.getY(ev, newPointerIndex);
            }
            mActivePointerId = MotionEventCompat.getPointerId(ev,
                    newPointerIndex);
            if (mVelocityTracker != null) {
                mVelocityTracker.clear();
            }
        }
    }

    private void endDrag() {
        mIsBeingDragged = false;
        mIsUnableToDrag = false;

        if (mVelocityTracker != null) {
            mVelocityTracker.recycle();
            mVelocityTracker = null;
        }
    }

    private void setScrollingCacheEnabled(boolean enabled) {
        if (mScrollingCacheEnabled != enabled) {
            mScrollingCacheEnabled = enabled;
            if (USE_CACHE) {
                final int size = getChildCount();
                for (int i = 0; i < size; ++i) {
                    final View child = getChildAt(i);
                    if (child.getVisibility() != GONE) {
                        child.setDrawingCacheEnabled(enabled);
                    }
                }
            }
        }
    }

}