Android ViewPager实现智能无限循环滚动回绕效果

android系统提供的ViewPager标准方式是左右可以自由滑动，但是滑动到最左边的极限位置是第一个page，滑动到最右边的位置是最后一个page，当滑动到最左或者最右时候，就不能再滑动/滚动了，这是Android系统默认的ViewPager实现方式。 

但是有些情况下开发者可能希望ViewPager能够智能的无限循环滚动回绕，比如现在总共有编号1, 2, 3, 4, 5的5个Page。 

（1）当用户手指从右往左滚动到最右边/最后面的页面5时候，如果此时用户继续拖住ViewPager往左边滑动，那么ViewPager将回绕、循环到第一个Page -> 1，接着就是2,3,4,5；

（2）反过来，如果当用户手指从左往右，滑到最左边的第一个Page：1时候，如果此时继续拖住ViewPager继续从左往右滑动，那么将回绕到5，接着就是4,3,2,1.

我们把这种ViewPager称之谓“无限循环滚动回绕”的ViewPager。 

这种类型的ViewPager网上有较多实现方式，现在给出一个流程较广的代码实现。 

写一个测试的MainActivity.Java:

package zhangphil.demo;

import java.util.Random;

import android.app.Activity;
import android.graphics.Color;
import android.os.Bundle;
import android.support.v4.view.PagerAdapter;
import android.view.Gravity;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;

public class MainActivity extends Activity {

 @Override
 protected void onCreate(Bundle savedInstanceState) {
 super.onCreate(savedInstanceState);
 setContentView(R.layout.activity_main);
 LoopViewPager viewpager = (LoopViewPager) findViewById(R.id.viewpager);
 viewpager.setAdapter(new SamplePagerAdapter());
 }

 public class SamplePagerAdapter extends PagerAdapter {
 private final Random random = new Random();
 private int mSize;

 public SamplePagerAdapter() {
 mSize = 5;
 }

 public SamplePagerAdapter(int count) {
 mSize = count;
 }

 @Override
 public int getCount() {
 return mSize;
 }

 @Override
 public boolean isViewFromObject(View view, Object object) {
 return view == object;
 }

 @Override
 public void destroyItem(ViewGroup view, int position, Object object) {
 view.removeView((View) object);
 }

 @Override
 public Object instantiateItem(ViewGroup view, int position) {
 TextView textView = new TextView(view.getContext());

 textView.setText(position + 1 + "");
 textView.setBackgroundColor(0xff000000 | random.nextInt(0x00ffffff));
 textView.setGravity(Gravity.CENTER);
 textView.setTextColor(Color.WHITE);
 textView.setTextSize(50);
 view.addView(textView, ViewGroup.LayoutParams.MATCH_PARENT, ViewGroup.LayoutParams.MATCH_PARENT);

 return textView;
 }

 // 增加item
 public void addItem() {
 mSize++;
 notifyDataSetChanged();
 }

 // 删除item
 public void removeItem() {
 mSize--;
 mSize = mSize < 0 ? 0 : mSize;

 notifyDataSetChanged();
 }
 }
}

MainActivity.java需要的布局文件activity_main.xml：

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
 xmlns:tools="http://schemas.android.com/tools"
 android:layout_width="match_parent"
 android:layout_height="match_parent"
 tools:context="zhangphil.demo.MainActivity" >

 <zhangphil.demo.LoopViewPager
  android:id="@+id/viewpager"
  android:layout_width="match_parent"
  android:layout_height="match_parent"/>
</RelativeLayout> 

核心关键代码LoopViewPager.java类和LoopViewPager.java依赖的LoopPagerAdapterWrapper.java！ 

LoopViewPager.java：

package zhangphil.demo;

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;

public class LoopViewPager extends ViewPager {
 private static final boolean DEFAULT_BOUNDARY_CASHING = false;
 private static final boolean DEFAULT_BOUNDARY_LOOPING = true;

 private LoopPagerAdapterWrapper mAdapter;
 private boolean mBoundaryCaching = DEFAULT_BOUNDARY_CASHING;
 private boolean mBoundaryLooping = DEFAULT_BOUNDARY_LOOPING;
 private List<OnPageChangeListener> mOnPageChangeListeners;

 /**
 * helper function which may be used when implementing FragmentPagerAdapter
 *
 * @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
 */
 public void setBoundaryCaching(boolean flag) {
 mBoundaryCaching = flag;
 if (mAdapter != null) {
 mAdapter.setBoundaryCaching(flag);
 }
 }

 public void setBoundaryLooping(boolean flag) {
 mBoundaryLooping = flag;
 if (mAdapter != null) {
 mAdapter.setBoundaryLooping(flag);
 }
 }

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

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

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

 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 setOnPageChangeListener(OnPageChangeListener listener) {
 addOnPageChangeListener(listener);
 }

 @Override
 public void addOnPageChangeListener(OnPageChangeListener listener) {
 if (mOnPageChangeListeners == null) {
 mOnPageChangeListeners = new ArrayList<>();
 }
 mOnPageChangeListeners.add(listener);
 }

 @Override
 public void removeOnPageChangeListener(OnPageChangeListener listener) {
 if (mOnPageChangeListeners != null) {
 mOnPageChangeListeners.remove(listener);
 }
 }

 @Override
 public void clearOnPageChangeListeners() {
 if (mOnPageChangeListeners != null) {
 mOnPageChangeListeners.clear();
 }
 }

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

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

 private void init(Context context) {
 if (onPageChangeListener != null) {
 super.removeOnPageChangeListener(onPageChangeListener);
 }
 super.addOnPageChangeListener(onPageChangeListener);
 }

 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 (mOnPageChangeListeners != null) {
  for (int i = 0; i < mOnPageChangeListeners.size(); i++) {
  OnPageChangeListener listener = mOnPageChangeListeners.get(i);
  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 (mOnPageChangeListeners != null) {
 for (int i = 0; i < mOnPageChangeListeners.size(); i++) {
  OnPageChangeListener listener = mOnPageChangeListeners.get(i);
  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 = LoopViewPager.super.getCurrentItem();
 int realPosition = mAdapter.toRealPosition(position);
 if (state == ViewPager.SCROLL_STATE_IDLE && (position == 0 || position == mAdapter.getCount() - 1)) {
  setCurrentItem(realPosition, false);
 }
 }

 if (mOnPageChangeListeners != null) {
 for (int i = 0; i < mOnPageChangeListeners.size(); i++) {
  OnPageChangeListener listener = mOnPageChangeListeners.get(i);
  if (listener != null) {
  listener.onPageScrollStateChanged(state);
  }
 }
 }
 }
 };
}

LoopPagerAdapterWrapper.java：

package zhangphil.demo;

import android.os.Parcelable;
import android.support.v4.app.FragmentPagerAdapter;
import android.support.v4.app.FragmentStatePagerAdapter;
import android.support.v4.view.PagerAdapter;
import android.util.SparseArray;
import android.view.View;
import android.view.ViewGroup;

public class LoopPagerAdapterWrapper extends PagerAdapter {

 private PagerAdapter mAdapter;

 private SparseArray<ToDestroy> mToDestroy = new SparseArray<>();

 private static final boolean DEFAULT_BOUNDARY_CASHING = true;
 private static final boolean DEFAULT_BOUNDARY_LOOPING = true;

 private boolean mBoundaryCaching = DEFAULT_BOUNDARY_CASHING;
 private boolean mBoundaryLooping = DEFAULT_BOUNDARY_LOOPING;

 void setBoundaryCaching(boolean flag) {
 mBoundaryCaching = flag;
 }

 void setBoundaryLooping(boolean flag) {
 mBoundaryLooping = flag;
 }

 LoopPagerAdapterWrapper(PagerAdapter adapter) {
 this.mAdapter = adapter;
 }

 @Override
 public void notifyDataSetChanged() {
 mToDestroy = new SparseArray<>();
 super.notifyDataSetChanged();
 }

 int toRealPosition(int position) {
 int realPosition = position;
 int realCount = getRealCount();
 if (realCount == 0)
 return 0;
 if (mBoundaryLooping) {
 realPosition = (position - 1) % realCount;
 if (realPosition < 0)
 realPosition += realCount;
 }

 return realPosition;
 }

 public int toInnerPosition(int realPosition) {
 int position = (realPosition + 1);
 return mBoundaryLooping ? position : realPosition;
 }

 private int getRealFirstPosition() {
 return mBoundaryLooping ? 1 : 0;
 }

 private int getRealLastPosition() {
 return getRealFirstPosition() + getRealCount() - 1;
 }

 @Override
 public int getCount() {
 int count = getRealCount();
 return mBoundaryLooping ? count + 2 : count;
 }

 public int getRealCount() {
 return mAdapter.getCount();
 }

 public PagerAdapter getRealAdapter() {
 return mAdapter;
 }

 @Override
 public Object instantiateItem(ViewGroup container, int position) {
 int realPosition = (mAdapter instanceof FragmentPagerAdapter || mAdapter instanceof FragmentStatePagerAdapter)
 ? position : toRealPosition(position);

 if (mBoundaryCaching) {
 ToDestroy toDestroy = mToDestroy.get(position);
 if (toDestroy != null) {
 mToDestroy.remove(position);
 return toDestroy.object;
 }
 }
 return mAdapter.instantiateItem(container, realPosition);
 }

 @Override
 public void destroyItem(ViewGroup container, int position, Object object) {
 int realFirst = getRealFirstPosition();
 int realLast = getRealLastPosition();
 int realPosition = (mAdapter instanceof FragmentPagerAdapter || mAdapter instanceof FragmentStatePagerAdapter)
 ? position : toRealPosition(position);

 if (mBoundaryCaching && (position == realFirst || position == realLast)) {
 mToDestroy.put(position, new ToDestroy(container, realPosition, object));
 } else {
 mAdapter.destroyItem(container, realPosition, object);
 }
 }

 /*
 * Delegate rest of methods directly to the inner adapter.
 */

 @Override
 public void finishUpdate(ViewGroup container) {
 mAdapter.finishUpdate(container);
 }

 @Override
 public boolean isViewFromObject(View view, Object object) {
 return mAdapter.isViewFromObject(view, object);
 }

 @Override
 public void restoreState(Parcelable bundle, ClassLoader classLoader) {
 mAdapter.restoreState(bundle, classLoader);
 }

 @Override
 public Parcelable saveState() {
 return mAdapter.saveState();
 }

 @Override
 public void startUpdate(ViewGroup container) {
 mAdapter.startUpdate(container);
 }

 @Override
 public void setPrimaryItem(ViewGroup container, int position, Object object) {
 mAdapter.setPrimaryItem(container, position, object);
 }

 /*
 * End delegation
 */

 /**
 * Container class for caching the boundary views
 */
 static class ToDestroy {
 ViewGroup container;
 int position;
 Object object;

 public ToDestroy(ViewGroup container, int position, Object object) {
 this.container = container;
 this.position = position;
 this.object = object;
 }
 }
}

如果读者有兴趣使用，直接将上面两个核心关键代码放入到自己的项目代码包中，当作自己写的类直接使用即可，写布局时候不要再写ViewPager，而是直接像我上面写的那个布局文件一样用LoopViewPager。

以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持。

# Android  # ViewPager循环滚动回绕  # ViewPager无限循环滚动  # ViewPager无限循环滚动回绕  # Android ListView实现无限循环滚动  # Android可自定义垂直循环滚动布局  # Android ViewPager无限循环滑动并可自动滚动完整实例  # android水平循环滚动控件使用详解  # Android使用Recyclerview实现图片水平自动循环滚动效果  # Android自定义可循环的滚动选择器CycleWheelView  # Android高仿京东垂直循环滚动新闻栏  # Android 使用ViewPager自动滚动循环轮播效果  # Android实现无限循环滚动  # 第一个  # 自己的  # 往右  # 往左  # 这是  # 就不  # 有兴趣  # 较多  # 动了  # 像我  # 能再  # 到第  # 大家多多  # 总共有  # 滑到  # 再写  # 包中  # 之谓  # 较广  # 情况下 

相关文章： 如何快速配置高效服务器建站软件？  制作证书网站有哪些,全国城建培训中心证书查询官网？  ,sp开头的版面叫什么？  寿县云建站：智能SEO优化与多行业模板快速上线指南  如何用手机制作网站和网页,手机移动端的网站能制作成中英双语的吗？  网站插件制作软件免费下载,网页视频怎么下到本地插件？  如何在云虚拟主机上快速搭建个人网站？  建站之星后台密码如何安全设置与找回？  制作网站哪家好,cc、.co、.cm哪个域名更适合做网站？  专业商城网站制作公司有哪些,pi商城官网是哪个？  弹幕视频网站制作教程下载,弹幕视频网站是什么意思？  零基础网站服务器架设实战：轻量应用与域名解析配置指南  个人摄影网站制作流程,摄影爱好者都去什么网站？  微信小程序制作网站有哪些,微信小程序需要做网站吗？  如何在西部数码注册域名并快速搭建网站？  制作农业网站的软件,比较好的农业网站推荐一下？  网站制作需要会哪些技术,建立一个网站要花费多少？  公司网站的制作公司,企业网站制作基本流程有哪些？  如何在阿里云完成域名注册与建站？  建站VPS推荐：2025年高性能服务器配置指南  如何用VPS主机快速搭建个人网站？  如何选择域名并搭建高效网站？  如何快速查询网址的建站时间与历史轨迹？  表情包在线制作网站免费,表情包怎么弄？  如何用好域名打造高点击率的自主建站？  完全自定义免费建站平台：主题模板在线生成一站式服务  ,有什么在线背英语单词效率比较高的网站？  内网网站制作软件,内网的网站如何发布到外网？  简易网站制作视频教程,使用记事本编写一个简单的网页html文件？  建站之星Pro快速搭建教程：模板选择与功能配置指南  如何选择PHP开源工具快速搭建网站？  潮流网站制作头像软件下载,适合母子的网名有哪些？  建站主机CVM配置优化、SEO策略与性能提升指南  建站主机SSH密钥生成步骤及常见问题解答？  建站之星如何取消后台验证码生成？  网站制作知乎推荐,想做自己的网站用什么工具比较好？  如何在阿里云ECS服务器部署织梦CMS网站？  实例解析Array和String方法  岳西云建站教程与模板下载_一站式快速建站系统操作指南  电商网站制作公司有哪些,1688网是什么意思？  JS中使用new Date(str)创建时间对象不兼容firefox和ie的解决方法(两种)  如何高效配置香港服务器实现快速建站？  网站制作的软件有哪些,制作微信公众号除了秀米还有哪些比较好用的平台？  教学论文网站制作软件有哪些,写论文用什么软件 ？  详解免费开源的.NET多类型文件解压缩组件SharpZipLib（.NET组件介绍之七）  建站之星2.7模板快速切换与批量管理功能操作指南  如何破解联通资金短缺导致的基站建设难题？  电视网站制作tvbox接口,云海电视怎样自定义添加电视源？  网站制作软件有哪些,制图软件有哪些？  重庆网站制作公司哪家好,重庆中考招生办官方网站？