安卓PagerAdapter在广告切换中的应用

在使用京东、淘宝客户端的时候，我们经常会看到首页的上面会有几张图片轮番的滚动，那么这个效果的背后是如何实现的，今天就来谈谈我的方式。

首先来看看程序运行的效果：

那么我们是如何实现的呢？请看下面的代码：MainActivity.java

package com.example.guanggaoqiehuan;import java.util.ArrayList;import java.util.List;import java.util.concurrent.atomic.AtomicInteger;import android.annotation.SuppressLint;import android.app.Activity;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.MotionEvent;import android.view.View;import android.view.View.OnTouchListener;import android.view.ViewGroup;import android.view.ViewGroup.LayoutParams;import android.widget.ImageView;@SuppressLint("HandlerLeak")public class MainActivity extends Activity{private ImageView[] imageViews = null;private ImageView imageView = null;private ViewPager advPager = null;//一种原子级别的线程操作private AtomicInteger what = new AtomicInteger(0);private boolean isContinue = true;@Overridepublic void onCreate(Bundle savedInstanceState){super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);initViewPager();}private void initViewPager(){advPager = (ViewPager) findViewById(R.id.adv_pager);ViewGroup group = (ViewGroup) findViewById(R.id.viewGroup);// 这里存放的是4张广告图片List<View> advPicslist = new ArrayList<View>();//四张广告图片ImageView img1 = new ImageView(this);img1.setBackgroundResource(R.drawable.image01);advPicslist.add(img1);ImageView img2 = new ImageView(this);img2.setBackgroundResource(R.drawable.image02);advPicslist.add(img2);ImageView img3 = new ImageView(this);img3.setBackgroundResource(R.drawable.image03);advPicslist.add(img3);ImageView img4 = new ImageView(this);img4.setBackgroundResource(R.drawable.image04);advPicslist.add(img4);// 对imageviews进行填充imageViews = new ImageView[advPicslist.size()];// 小图标for (int i = 0; i < advPicslist.size(); i++){imageView = new ImageView(this);imageView.setLayoutParams(new LayoutParams(20, 20));imageView.setPadding(5, 5, 5, 5);imageViews[i] = imageView;//设置初始状态时，第一张图片右下方为获得焦点的图片if (i == 0){imageViews[i].setBackgroundResource(R.drawable.banner_dian_focus);}else{imageViews[i].setBackgroundResource(R.drawable.banner_dian_blur);}group.addView(imageViews[i]);}//填充适配器数据advPager.setAdapter(new AdvAdapter(MainActivity.this, advPicslist));//注册滑动事件advPager.setOnPageChangeListener(new GuidePageChangeListener());advPager.setOnTouchListener(new OnTouchListener(){@Overridepublic boolean onTouch(View v, MotionEvent event){switch (event.getAction()){case MotionEvent.ACTION_DOWN:break;case MotionEvent.ACTION_MOVE:isContinue = false;break;case MotionEvent.ACTION_UP:isContinue = true;break;default:isContinue = true;break;}return false;}});new Thread(new Runnable(){@Overridepublic void run(){while (true){if (isContinue){//获取当前值，并发送给handler进行处理viewHandler.sendEmptyMessage(what.get());whatOption();}}}}).start();}private void whatOption(){//以原子方式将当前值加 1what.incrementAndGet();//当前值超过了图片索引的最大值，则重新开始累加值if (what.get() > imageViews.length - 1){what.getAndAdd(-4);}try{Thread.sleep(5000);}catch (InterruptedException e){e.printStackTrace();}}private final Handler viewHandler = new Handler(){@Overridepublic void handleMessage(Message msg){//设置当前屏所显示的图片，索引为消息值（0-3）advPager.setCurrentItem(msg.what);super.handleMessage(msg);}};private final class GuidePageChangeListener implements OnPageChangeListener{@Overridepublic void onPageScrollStateChanged(int arg0){}@Overridepublic void onPageScrolled(int arg0, float arg1, int arg2){}/** * 设置当前图片的右下角是否为焦点图片 *  */@Overridepublic void onPageSelected(final int arg0){what.getAndSet(arg0);for (int i = 0; i < imageViews.length; i++){imageViews[arg0].setBackgroundResource(R.drawable.banner_dian_focus);if (arg0 != i){imageViews[i].setBackgroundResource(R.drawable.banner_dian_blur);}}}}}

使用handler对图片进行轮番滚动该，从而不断的改变当前屏所显示出来的图片，其中用到了一个适配器PagerAdapter，这个类是android.support.v4包中的类，它的子类有FragmentPagerAdapter，FragmentStatePagerAdapter，这两个adapter都是Fragment的适配器，用于实现Fragment的滑动效果。我们这里使用自定义的PagerAdapter类来实现我们需要的效果。我们看下面的代码：AdvAdapter.java

package com.example.guanggaoqiehuan;import java.util.List;import android.content.Context;import android.content.Intent;import android.os.Parcelable;import android.support.v4.view.PagerAdapter;import android.support.v4.view.ViewPager;import android.view.View;import android.view.View.OnClickListener;public class AdvAdapter extends PagerAdapter{private Context context = null;//数据源，这里主要是几张图片private List<View> views = null;public AdvAdapter(Context context, List<View> views){this.context = context;this.views = views;}@Overridepublic void destroyItem(View arg0, int arg1, Object arg2){((ViewPager) arg0).removeView(views.get(arg1));}@Overridepublic void finishUpdate(View arg0){}@Overridepublic int getCount(){return views.size();}@Overridepublic Object instantiateItem(final View collection, final int position){View view = views.get(position);/** * 单击事件，跳转到第二个Activity，并将当前图片的位置传递到SecActivity中 */view.setOnClickListener(new OnClickListener() {    @Override    public void onClick(View v)     {    System.out.println("---------------- position1" + position);    Intent intent = new Intent(context, SecActivity.class);    intent.putExtra("position", position);    context.startActivity(intent);    }});((ViewPager) collection).addView(views.get(position), 0);return views.get(position);}@Overridepublic boolean isViewFromObject(View arg0, Object arg1){return arg0 == arg1;}@Overridepublic void restoreState(Parcelable arg0, ClassLoader arg1){}@Overridepublic Parcelable saveState(){return null;}@Overridepublic void startUpdate(View arg0){}}

重点我们来看看public Object instantiateItem(final View collection, final int position)；这个方法。因为在广告的轮询中，用户需要点击其中的某张图片，所以捕获用户点击的图片信息至关重要。PagerAdapter，的单击事件可以定义在instantiateItem()方法里面，它的第二个参数代表了当前屏幕
显示的图片的索引值，将该值存入intent中就可以在第二个Activity中进行获取并进行相应的处理，这里我只是将其进行简单的打印，不在说明，源码提供在下方，有需要的朋友可以免费下载，以供学习交流。

http://download.csdn.net/detail/u012191462/8641001