LoopViewPager.java

package me.qixingchen.mdbilibili.widget;

import android.content.Context;
import android.support.v4.view.PagerAdapter;
import android.support.v4.view.ViewPager;
import android.util.AttributeSet;

import java.util.ArrayList;
import java.util.List;

/**
 * Created by qixingchen on 15/12/4.
 * pager无限循环
 */
public class LoopViewPager extends ViewPager {

    private static final boolean DEFAULT_BOUNDARY_CASHING = false;

    private List<OnPageChangeListener> mOnPageChangeListeners = new ArrayList<>();
    private LoopPagerAdapter mAdapter;
    private boolean mBoundaryCaching = DEFAULT_BOUNDARY_CASHING;
    private OnPageChangeListener onPageChangeListener = new OnPageChangeListener() {
        private float mPreviousOffset = -1;
        private float mPreviousPosition = -1;

        @Override
        public void onPageSelected(int position) {

            int realPosition = mAdapter.toRealPosition(position);
            if (mPreviousPosition != realPosition) {
                mPreviousPosition = realPosition;
                for (OnPageChangeListener listener : mOnPageChangeListeners) {
                    listener.onPageSelected(realPosition);
                }
            }
        }

        @Override
        public void onPageScrolled(int position, float positionOffset,
                                   int positionOffsetPixels) {
            int realPosition = position;
            if (mAdapter == null) {
                return;
            }
            if (mAdapter != null) {
                realPosition = mAdapter.toRealPosition(position);

                if (positionOffset == 0
                        && mPreviousOffset == 0
                        && (position == 0 || position == mAdapter.getCount() - 1)) {
                    setCurrentItem(realPosition, false);
                }
            }

            mPreviousOffset = positionOffset;

            for (OnPageChangeListener listener : mOnPageChangeListeners) {
                if (realPosition != mAdapter.getRealCount() - 1) {
                    listener.onPageScrolled(realPosition,
                            positionOffset, positionOffsetPixels);
                } else {
                    if (positionOffset > .5) {
                        listener.onPageScrolled(0, 0, 0);
                    } else {
                        listener.onPageScrolled(realPosition,
                                0, 0);
                    }
                }
            }
        }

        @Override
        public void onPageScrollStateChanged(int state) {
            if (mAdapter != null) {
                int position = LoopViewPager.super.getCurrentItem();
                int realPosition = mAdapter.toRealPosition(position);
                if (state == ViewPager.SCROLL_STATE_IDLE
                        && (position == 0 || position == mAdapter.getCount() - 1)) {
                    setCurrentItem(realPosition, false);
                }
            }
            for (OnPageChangeListener listener : mOnPageChangeListeners) {
                listener.onPageScrollStateChanged(state);
            }
        }
    };

    public LoopViewPager(Context context) {
        super(context);
        init();
    }

    public LoopViewPager(Context context, AttributeSet attrs) {
        super(context, attrs);
        init();
    }

    /**
     * helper function which may be used when implementing FragmentPagerAdapter
     *
     * @param position
     * @param count
     *
     * @return (position-1)%count
     */
    public static int toRealPosition(int position, int count) {
        position = position - 1;
        if (position < 0) {
            position += count;
        } else {
            position = position % count;
        }
        return position;
    }

    /**
     * If set to true, the boundary views (i.e. first and last) will never be destroyed
     * This may help to prevent "blinking" of some views
     *
     * @param flag
     */
    public void setBoundaryCaching(boolean flag) {
        mBoundaryCaching = flag;
        if (mAdapter != null) {
            mAdapter.setBoundaryCaching(flag);
        }
    }

    @Override
    public PagerAdapter getAdapter() {
        return mAdapter != null ? mAdapter.getRealAdapter() : mAdapter;
    }

    @Override
    public void setAdapter(PagerAdapter adapter) {
        mAdapter = new LoopPagerAdapter(adapter);
        mAdapter.setBoundaryCaching(mBoundaryCaching);
        super.setAdapter(mAdapter);
        setCurrentItem(0, false);
    }

    @Override
    public int getCurrentItem() {
        return mAdapter != null ? mAdapter.toRealPosition(super.getCurrentItem()) : 0;
    }

    ;

    @Override
    public void setCurrentItem(int item) {
        if (getCurrentItem() != item) {
            setCurrentItem(item, true);
        }
    }

    public void setCurrentItem(int item, boolean smoothScroll) {
        int realItem = mAdapter.toInnerPosition(item);
        super.setCurrentItem(realItem, smoothScroll);
    }

    @Override
    public void addOnPageChangeListener(OnPageChangeListener listener) {
        mOnPageChangeListeners.add(listener);
    }

    private void init() {
        super.addOnPageChangeListener(onPageChangeListener);
    }

}