Android ViewPager无限循环实现底部小圆点动态滑动

页面拖动到最后一页 再向下滑动回复到 第一页，第一页向前滑动回到 最后一页

同时，底部红色小圆点随着页面的滑动距离比例随时改变位置

布局：

<?xml version="1.0" encoding="utf-8"?>
<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"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
tools:context="com.lian.viewpagertest.MainActivity">

<android.support.v4.view.ViewPager
 android:id="@+id/viewpager"
 android:layout_width="match_parent"
 android:layout_height="match_parent" >
</android.support.v4.view.ViewPager>

<TextView
 android:id="@+id/tv"
 android:layout_width="wrap_content"
 android:layout_height="wrap_content"
 android:text="内容"
 android:textSize="25sp"
 android:layout_alignParentBottom="true"
 android:layout_centerHorizontal="true"
 />

<RelativeLayout
 android:id="@+id/rl_bottom"
 android:layout_width="wrap_content"
 android:layout_height="wrap_content"
 android:layout_alignParentBottom="true"
 android:layout_centerHorizontal="true"
 android:layout_marginBottom="45dip" >

<LinearLayout
  android:id="@+id/ll_points"
  android:layout_width="wrap_content"
  android:layout_height="wrap_content"
  android:orientation="horizontal" >
 </LinearLayout>

<View
  android:id="@+id/v_redpoint"
  android:layout_width="10dip"
  android:layout_height="10dip"
  android:background="@drawable/red_circle" />
</RelativeLayout>
</RelativeLayout>

其中red_circle是用shape绘制的红色小圆点

最后的LinearLayout实际上是灰色小圆点的容器，在代码中根据数据的长度动态确定数目

代码：

package com.lian.viewpagertest;

import android.os.Bundle;
import android.support.v4.view.PagerAdapter;
import android.support.v4.view.ViewPager;
import android.support.v7.app.AppCompatActivity;
import android.util.Log;
import android.view.View;
import android.view.ViewGroup;
import android.view.ViewTreeObserver;
import android.widget.ImageView;
import android.widget.LinearLayout;
import android.widget.RelativeLayout;
import android.widget.TextView;

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

public class MainActivity extends AppCompatActivity {

private ViewPager mViewPager;
private TextView mTextView;
private LinearLayout mLinearLayout;
private View mView;
private List<ImageView> mDataList;
private int diatance;

@Override
protected void onCreate(Bundle savedInstanceState) {
 super.onCreate(savedInstanceState);
 initView();
 initData();
 initEvent();
}

/**
 * 初始化数据
 */

private void initData() {
 int[] sorce = new int[]{R.drawable.a,R.drawable.b,R.drawable.c,R.drawable.d,R.drawable.e};

mDataList = new ArrayList<ImageView>();

for (int i = 0;i < sorce.length;i ++){
  ImageView img = new ImageView(getApplicationContext());
  img.setImageResource(sorce[i]);
  mDataList.add(img);

//添加底部灰点
  View v = new View(getApplicationContext());
  v.setBackgroundResource(R.drawable.gray_circle);
  //指定其大小
  LinearLayout.LayoutParams params = new LinearLayout.LayoutParams(20,20);
  if (i != 0)
   params.leftMargin = 20;
  v.setLayoutParams(params);
  mLinearLayout.addView(v);
 }

mViewPager.setAdapter(new MyAdapter());

//设置每次加载时第一页在MAX_VALUE / 2 - Extra 页，造成用户无限轮播的错觉
 int startPage = Integer.MAX_VALUE / 2;
 int extra = startPage ％ mDataList.size();
 startPage = startPage - extra;
 mViewPager.setCurrentItem(startPage);
}

/**
 * ViewPager的容器
 */

public class MyAdapter extends PagerAdapter{

@Override
 public int getCount() {
  //告诉容器我们的数据长度为Integer.MAX_VALUE，这样就可以一直滚动
  return Integer.MAX_VALUE;
 }

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

@Override
 public Object instantiateItem(ViewGroup container, int position) {
  //若position超过mDataList.size()，会发生越界异常，所以这里每次超过size又从0开始计算位置
  position = position ％ mDataList.size();

ImageView img = mDataList.get(position);
  container.addView(img);

return img;
 }

@Override
 public void destroyItem(ViewGroup container, int position, Object object) {

position = position ％ mDataList.size();

container.removeView((View)object);

// super.destroyItem(container, position, object);
 }
}

private void initEvent() {

/**
  * 当底部红色小圆点加载完成时测出两个小灰点的距离，便于计算后面小红点动态移动的距离
  */
 mView.getViewTreeObserver().addOnGlobalLayoutListener(new ViewTreeObserver.OnGlobalLayoutListener() {
  @Override
  public void onGlobalLayout() {
   diatance = mLinearLayout.getChildAt(1).getLeft() - mLinearLayout.getChildAt(0).getLeft();
   Log.d("两点间距",diatance + "测出来了");
  }
 });

mViewPager.setOnPageChangeListener(new ViewPager.OnPageChangeListener() {
  @Override
  public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {

//测出页面滚动时小红点移动的距离，并通过setLayoutParams(params)不断更新其位置
   position = position ％ mDataList.size();
   float leftMargin = diatance * (position + positionOffset);
   RelativeLayout.LayoutParams params = (RelativeLayout.LayoutParams) mView.getLayoutParams();
   params.leftMargin = Math.round(leftMargin);
   mView.setLayoutParams(params);
   Log.d("红点在这",leftMargin + "");
  }

@Override
  public void onPageSelected(int position) {

}

@Override
  public void onPageScrollStateChanged(int state) {

}
 });
}

private void initView() {

setContentView(R.layout.activity_main);

mViewPager = (ViewPager) findViewById(R.id.viewpager);

mTextView = (TextView) findViewById(R.id.tv);

mLinearLayout = (LinearLayout) findViewById(R.id.ll_points);

mView = findViewById(R.id.v_redpoint);
}
}