用viewpager实现图片轮播

应用中常常遇到图片轮播的需求，这时候就需要用到viewpager这个组件。viewpager是android support v4 中提供的一个组件。viewpager使用需要以下几步骤：

1.在布局文件中添加viewpager组件

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

ViewPager路径要写完整，否则会出现问题；

2.创建PagerAdapter,PagerAdapter是viewPager的内容提供者，这里我们的图片就是由PagerAdapter提供给viewpager展示的。同样PagerAdapter也在support v4包中。具体如下所示：

 public class AdvertisingAdapter extends PagerAdapter {

     private List<View> mList;

     public AdvertisingAdapter() {
         mList = new ArrayList<View>();
     }

     public void setData(List<View> list) {
         if (list != null) {
             mList.clear();
             mList.addAll(list);
             notifyDataSetChanged();
         }
     }

     @Override
     public int getCount() {
         return mList.size();
     }

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

     @Override
     public void destroyItem(ViewGroup container, int position, Object object) {
         container.removeView(mList.get(position));
     }

     @Override
     public Object instantiateItem(ViewGroup container, int position) {
         container.addView(mList.get(position), 0);
         return mList.get(position);
     }
 }

3.初始化ViewPager,PagerAdapter

     protected void setupView() {
         mPagerAdapter = new AdvertisingAdapter();
         mViewPager = (ViewPager) findViewById(R.id.vp_adv);
         mViewPager .setAdapter(mPagerAdapter );
         mAdvertising.addOnPageChangeListener(this);
     }    

待PagerAdapter填充图片数据后，ViewPager便可以将图片展示出来。

4.添加“.”。基本所有应用使用到ViewPager都会使用“.”标识当前坐标，即展示到哪一页。如下代码添加点号：

添加布局文件

 <LinearLayout
         android:id="@+id/viewGroup"
         android:layout_width="wrap_content"
         android:layout_height="wrap_content"
         android:layout_alignParentBottom="true"
         android:layout_alignParentRight="true"
         android:layout_marginBottom="20dp"
         android:layout_marginRight="20dp"
         android:orientation="horizontal"></LinearLayout>

在布局里面动态添加“点”的view

         imageViews = new ImageView[advPics.size()];
         ImageView imageView;
         for (int i = 0; i < advPics.size(); i++) {
             imageView = new ImageView(this);
             imageView.setLayoutParams(new LinearLayout.LayoutParams(50, 50));
             imageView.setPadding(15, 15, 15, 15);
             imageViews[i] = imageView;
             if (i == 0) {
                 imageViews[i].setImageResource(R.drawable.dot_focus);
             } else {
                 imageViews[i].setImageResource(R.drawable.dot_blur);
             }
             llDot.addView(imageViews[i]);
         }

拖动ViewPager时，坐标点动态改变

 　　@Override
     public void onPageSelected(int position) {
         LogUtils.d("enter onPageSelected method");

         for (int i = 0; i < advPics.size(); i++) {
             imageViews[position].setImageResource(R.drawable.dot_focus);
             if (position != i) {
                 imageViews[i].setImageResource(R.drawable.dot_blur);
             }
         }
     }

5.自动轮播。大多数时候，我们展示图片时需要其自动轮播的。

启动线程，控制轮播时间，及发出轮播请求给UI线程

 private void initAutoThread() {
         Runnable runnable = new Runnable() {
             @Override
             public void run() {
                 while (true) {
                     if (!isPlayPaused.get()) {
                         sendUiMessage(MSG_UI_CHANGE_ADV_PIC, what.get(), 0, null);
                         what.incrementAndGet();
                         if (what.get() > advPics.size() - 1) {
                             what.getAndAdd(-advPics.size());
                         }
                     }
                     if (needExit.get()) {
                         break;
                     }
                     try {
                         Thread.sleep(8000);
                     } catch (InterruptedException e) {
                         e.printStackTrace();
                     }
                 }
             }
         };
         Thread thread = new Thread(runnable);
         thread.setName("Carousel");
         thread.start();
     }

UI 线程收到请求后，对显示的图片进行更改

  mViewPager.setCurrentItem(msg.arg1);