Java tutorial
/* * Copyright (C) 2013 Leszek Mzyk * * 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 com.baiiu.zhihudaily.view.widget.loopvp; import android.content.Context; import android.support.v4.view.PagerAdapter; import android.support.v4.view.ViewPager; import android.util.AttributeSet; import com.baiiu.zhihudaily.view.widget.loopvp._interface.ILoopViewPager; import java.util.ArrayList; import java.util.List; /** * A ViewPager subclass enabling infinte scrolling of the viewPager elements * <p> * When used for paginating views (in opposite to fragments), no code changes * should be needed only change xml's from <android.support.v4.view.ViewPager> * to <com.imbryk.viewPager.LoopViewPager> * <p> * If "blinking" can be seen when paginating to first or last view, simply call * seBoundaryCaching( true ), or change DEFAULT_BOUNDARY_CASHING to true * <p> * When using a FragmentPagerAdapter or FragmentStatePagerAdapter, * additional changes in the adapter must be done. * The adapter must be prepared to create 2 extra items e.g.: * <p> * The original adapter creates 4 items: [0,1,2,3] * The modified adapter will have to create 6 items [0,1,2,3,4,5] * with mapping realPosition=(position-1)%count * [0->3, 1->0, 2->1, 3->2, 4->3, 5->0] * <p> * ???. */ public class LoopingViewPager extends AutoScrollViewPager implements ILoopViewPager { private static final boolean DEFAULT_BOUNDARY_CASHING = false; private List<OnPageChangeListener> mIndicatorPageChangeListeners; private LoopingAdapterWrapper mAdapter; private boolean mBoundaryCaching = DEFAULT_BOUNDARY_CASHING; public LoopingViewPager(Context context) { this(context, null); } public LoopingViewPager(Context context, AttributeSet attrs) { super(context, attrs); addOnPageChangeListener(onPageChangeListener); } @Override public int getRealCount() { return mAdapter != null ? mAdapter.getRealCount() : 0; } @Override public int getRealCurrentItem() { return getCurrentItem(); } @Override public int getFakeCurrentItem() { return super.getCurrentItem(); } @Override public void setFakeCurrentItem(int item) { setCurrentItem(item); } @Override public void setAdapter(PagerAdapter adapter) { mAdapter = new LoopingAdapterWrapper(adapter); mAdapter.setBoundaryCaching(mBoundaryCaching); super.setAdapter(mAdapter); // setOffscreenPageLimit(mAdapter.getCount());//(viewPager.items)??,notifyDataSetChanged?. setCurrentItem(0, false); } @Override public PagerAdapter getAdapter() { return mAdapter;//?AutoScrollViewPager // return mAdapter != null ? mAdapter.getRealAdapter() : mAdapter; } @Override public int getCurrentItem() { return mAdapter != null ? mAdapter.toRealPosition(super.getCurrentItem()) : 0; } @Override public void setCurrentItem(int item, boolean smoothScroll) { int realItem = mAdapter.toInnerPosition(item); super.setCurrentItem(realItem, smoothScroll); } @Override public void setCurrentItem(int item) { if (getCurrentItem() != item) { setCurrentItem(item, true); } } @Override public void addOnIndicatorPageChangeListener(OnPageChangeListener listener) { if (listener == null) { return; } if (mIndicatorPageChangeListeners == null) { mIndicatorPageChangeListeners = new ArrayList<>(); } mIndicatorPageChangeListeners.add(listener); } 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; if (mIndicatorPageChangeListeners != null) { for (OnPageChangeListener listener : mIndicatorPageChangeListeners) { if (listener != null) { listener.onPageSelected(realPosition); } } } } } @Override public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) { int realPosition = position; if (mAdapter != null) { realPosition = mAdapter.toRealPosition(position); if (positionOffset == 0 && mPreviousOffset == 0 && (position == 0 || position == mAdapter.getCount() - 1)) { setCurrentItem(realPosition, false); } } mPreviousOffset = positionOffset; if (mIndicatorPageChangeListeners != null) { for (OnPageChangeListener listener : mIndicatorPageChangeListeners) { if (listener != null) { 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 = LoopingViewPager.super.getCurrentItem(); int realPosition = mAdapter.toRealPosition(position); if (state == ViewPager.SCROLL_STATE_IDLE && (position == 0 || position == mAdapter.getCount() - 1)) { setCurrentItem(realPosition, false); } } if (mIndicatorPageChangeListeners != null) { for (OnPageChangeListener listener : mIndicatorPageChangeListeners) { if (listener != null) { listener.onPageScrollStateChanged(state); } } } } }; /** * 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); } } }