1.我们经常打开一个App会看到有广告图片轮播的效果，首先上效果图
1.我们经常打开一个App会看到有广告图片轮播的效果，首先上效果图
2.实现的过程
1.轮播页面他是一个ViewPager
2.然后我们使用RelativeLayout来把小圆点放置在图片上，然后滑动时动态修改小圆点的背景，就产生了滑动
的效果
3.自动滑动的效果，我们可以利用ScheduledExecutorService这个类来实现，他可以周期性的执行任务，这样就可以自动滑动了
3.要点说明
1.public void onPageScrollStateChanged(int arg0) {}
通过网上查找发现当ViewPager页面滑动时，arg0有三种不同的参数
1.当arg0 =1使表示手势滑动
2.当arg0 =2时表示页面自动滑动
3.当arg0 =3,表示滑动到最后一页
1.通过这些参数，我们就可以然手动滑动的时候关闭自动滑动功能
2.当滑动到最后一面时，把ViewPager当前项设置到第一页
2.在写这个功能的时候，把高分辨率的图片放在了自定义的drawable文件夹下，这样如果图片一些，就会引发
内存溢出异常，当图片一大，这样程序就会需要很多的内存来加载，这在android中是不行，所以我们应该把图片
放在对应的drawable文件下，就可避免这种情况，系统应该在后台自动处理了
4.下面填出实现的源代码，在最后会有完整源码的下载链接
1.主Activity
package com.example.demo_image_scroll;import java.util.ArrayList;import java.util.List;import java.util.Map;import java.util.concurrent.Executors;import java.util.concurrent.ScheduledExecutorService;import java.util.concurrent.TimeUnit;import android.app.ActionBar.LayoutParams;import android.app.Activity;import android.content.Context;import android.graphics.BitmapFactory;import android.os.Bundle;import android.os.Handler;import android.os.Message;import android.support.v4.view.ViewPager;import android.support.v4.view.ViewPager.OnPageChangeListener;import android.view.LayoutInflater;import android.view.View;import android.widget.ImageView;import android.widget.LinearLayout;import android.widget.RelativeLayout;public class MainActivity extends Activity {private LayoutInflater inflater;private ViewPager mviewPager;/**用于小圆点图片*/private List<ImageView> dotViewList;/**用于存放轮播效果图片*/private List<ImageView> list;LinearLayout dotLayout;private int currentItem = 0;//当前页面boolean isAutoPlay = true;//是否自动轮播private ScheduledExecutorService scheduledExecutorService;private Handler handler = new Handler(){@Overridepublic void handleMessage(Message msg) {// TODO Auto-generated method stubsuper.handleMessage(msg);if(msg.what == 100){mviewPager.setCurrentItem(currentItem);}}};@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);inflater = LayoutInflater.from(MainActivity.this);mviewPager = (ViewPager) findViewById(R.id.myviewPager);dotLayout = (LinearLayout)findViewById(R.id.dotLayout);dotLayout.removeAllViews();initView();if(isAutoPlay){startPlay();}}public void initView(){dotViewList = new ArrayList<ImageView>();list = new ArrayList<ImageView>();for (int i = 0; i < 4; i++) {ImageView dotView = new ImageView(MainActivity.this);LinearLayout.LayoutParams params = new LinearLayout.LayoutParams(new LayoutParams(LayoutParams.WRAP_CONTENT, android.view.ViewGroup.LayoutParams.WRAP_CONTENT));params.leftMargin = 15;//设置小圆点的外边距params.rightMargin = 15;params.height = 40;//设置小圆点的大小params.width = 40;if(i == 0){dotView.setBackgroundResource(R.drawable.point_pressed);}else{dotView.setBackgroundResource(R.drawable.point_unpressed);}dotLayout.addView(dotView, params);dotViewList.add(dotView);//上面是动态添加了四个小圆点}ImageView img1 = (ImageView) inflater.inflate(R.layout.scroll_vew_item, null);ImageView img2 = (ImageView) inflater.inflate(R.layout.scroll_vew_item, null);ImageView img3 = (ImageView) inflater.inflate(R.layout.scroll_vew_item, null);ImageView img4 = (ImageView) inflater.inflate(R.layout.scroll_vew_item, null);img1.setBackgroundResource(R.drawable.main_img1);img2.setBackgroundResource(R.drawable.main_img2);img3.setBackgroundResource(R.drawable.main_img3);img4.setBackgroundResource(R.drawable.main_img4);list.add(img1);list.add(img2);list.add(img3);list.add(img4);ImagePaperAdapter adapter = new ImagePaperAdapter((ArrayList)list);mviewPager.setAdapter(adapter);mviewPager.setCurrentItem(0);mviewPager.setOnPageChangeListener(new MyPageChangeListener());}/*** 开始轮播图切换*/private void startPlay(){scheduledExecutorService = Executors.newSingleThreadScheduledExecutor();scheduledExecutorService.scheduleAtFixedRate(new SlideShowTask(), 1, 4, TimeUnit.SECONDS);//根据他的参数说明，第一个参数是执行的任务，第二个参数是第一次执行的间隔，第三个参数是执行任务的周期；}/***执行轮播图切换任务**/private class SlideShowTask implements Runnable{@Overridepublic void run() {// TODO Auto-generated method stubsynchronized (mviewPager) {currentItem = (currentItem+1)%list.size();handler.sendEmptyMessage(100);}}}/*** ViewPager的监听器* 当ViewPager中页面的状态发生改变时调用**/private class MyPageChangeListener implements OnPageChangeListener{boolean isAutoPlay = false;@Overridepublic void onPageScrollStateChanged(int arg0) {// TODO Auto-generated method stubswitch (arg0) {case 1:// 手势滑动，空闲中isAutoPlay = false;System.out.println(" 手势滑动，空闲中");break;case 2:// 界面切换中isAutoPlay = true;System.out.println(" 界面切换中");break;case 0:// 滑动结束，即切换完毕或者加载完毕// 当前为最后一张，此时从右向左滑，则切换到第一张if (mviewPager.getCurrentItem() == mviewPager.getAdapter().getCount() – 1 && !isAutoPlay) {mviewPager.setCurrentItem(0);System.out.println(" 滑动到最后一张");}// 当前为第一张，此时从左向右滑，则切换到最后一张else if (mviewPager.getCurrentItem() == 0 && !isAutoPlay) {mviewPager.setCurrentItem(mviewPager.getAdapter().getCount() – 1);System.out.println(" 滑动到第一张");}break;}}@Overridepublic void onPageScrolled(int arg0, float arg1, int arg2) {// TODO Auto-generated method stub}@Overridepublic void onPageSelected(int pos) {// TODO Auto-generated method stub//这里面动态改变小圆点的被背景，来实现效果currentItem = pos;for(int i=0;i < dotViewList.size();i++){if(i == pos){((View)dotViewList.get(pos)).setBackgroundResource(R.drawable.point_pressed);}else {((View)dotViewList.get(i)).setBackgroundResource(R.drawable.point_unpressed);}}}}}2.然后是ImagerPaperAdapterpackage com.example.demo_image_scroll;import java.util.ArrayList;import android.support.v4.view.PagerAdapter;import android.support.v4.view.ViewPager;import android.view.View;import android.view.ViewGroup;import android.view.ViewParent;import android.widget.ImageView;public class ImagePaperAdapter extends PagerAdapter {private ArrayList<ImageView>list;public ImagePaperAdapter(ArrayList<ImageView> list) {// TODO Auto-generated constructor stubthis.list = list;}@Overridepublic int getCount() {// TODO Auto-generated method stubreturn list.size();}@Overridepublic boolean isViewFromObject(View arg0, Object arg1) {// TODO Auto-generated method stubreturn arg0 == arg1;}@Overridepublic void destroyItem(ViewGroup container, int position,Object object) {//Warning：不要在这里调用removeView}@Overridepublic Object instantiateItem(ViewGroup container, int position) {// TODO Auto-generated method stubImageView view = list.get(position) ;ViewParent vp = view.getParent();if(vp != null){ViewGroup parent = (ViewGroup)vp;parent.removeView(view);}//上面这些语句必须加上，如果不加的话，就会产生则当用户滑到第四个的时候就会触发这个异常//原因是我们试图把一个有父组件的View添加到另一个组件。((ViewPager)container).addView(list.get(position));System.out.println("————");return list.get(position);}}
补充一点
谁的指间滑过了千年时光；谁在反反复复中追问可曾遗忘；
