Android借助Handler,实现ViewPager中页面的自动切换

jopen 6年前

在很多电商网页及app上都有自动切换的商品的推广快,感觉体验挺不错的,正好今天学习使用ViewPager,因此也实现了一个功能类似的demo。

下面是其中的两个截图:

Android借助Handler,实现ViewPager中页面的自动切换         Android借助Handler,实现ViewPager中页面的自动切换

实现一个自动播放功能的ViewPager,要做的主要有以下的几个部分:



  • 实现一个ViewPagerAdapter,用于为ViewPager提供展示内容(例如上面的两张小猫图片
public class ViewPagerAdapter extends PagerAdapter {    private List<View> mData;    public ViewPagerAdapter(List<View> mData) {     this.mData = mData;    }      @Override    public int getCount() {     return mData.size();    }      @Override    public boolean isViewFromObject(View arg0, Object arg1) {     return arg0 == arg1;    }        @Override    public Object instantiateItem(ViewGroup container, int position) {     View v = mData.get(position);     container.addView(v);     return v;    }        @Override    public void destroyItem(ViewGroup container, int position, Object object) {  //   super.destroyItem(container, position, object);     container.removeView(mData.get(position));    }       }


  • 实现一个OnPageChangeListener,这样在页面切换后可以提示当前页面所在的位置(例如上图中,左下角的3个圆点,红色表示当前页面
private class ViewPageChangeListener implements OnPageChangeListener {      @Override    public void onPageScrollStateChanged(int arg0) {    }      @Override    public void onPageScrolled(int arg0, float arg1, int arg2) {    }      //监听页面改变事件来改变viewIndicator中的指示图片    @Override    public void onPageSelected(int arg0) {     int len = viewIndicator.getChildCount();     for(int i = 0; i < len; ++i)      viewIndicator.getChildAt(i).setBackgroundResource(R.drawable.tip_normal);     viewIndicator.getChildAt(arg0).setBackgroundResource(R.drawable.tip_select);    }       }


  • 实现一个Handler,用于在一定的时间间隔后修改UI(将当前显示的图片切换到下一个)

private Handler mHandler = new Handler() {    public void handleMessage(android.os.Message msg) {     switch(msg.what) {     case 1:      int totalcount = pagers.size();//autoChangeViewPager.getChildCount();      int currentItem = autoChangeViewPager.getCurrentItem();            int toItem = currentItem + 1 == totalcount ? 0 : currentItem + 1;            Log.i(TAG, "totalcount: " + totalcount + "   currentItem: " + currentItem + "   toItem: " + toItem);            autoChangeViewPager.setCurrentItem(toItem, true);            //每两秒钟发送一个message,用于切换viewPager中的图片      this.sendEmptyMessageDelayed(1, 2000);     }    }   };



上面这3段就是主要的代码,除此之外,还需要在onResume()中发送一个起始message以及在onStop()中停止ViewPager页面的自动切换等内容。

完整的代码如下:

public class MainActivity extends Activity {   private static final String TAG = MainActivity.class.getSimpleName();   private ViewPager autoChangeViewPager;      //用来指示当前显示图片所在位置   private LinearLayout viewIndicator;      //包含要在ViewPager中显示的图片   private List<View> pagers;   @Override   protected void onCreate(Bundle savedInstanceState) {    super.onCreate(savedInstanceState);    setContentView(R.layout.activity_main);        autoChangeViewPager = (ViewPager) findViewById(R.id.autoVP);    viewIndicator = (LinearLayout) findViewById(R.id.vpindicator);        initAdapter();        //监听页面改变事件来改变viewIndicator中的指示图片    autoChangeViewPager.setOnPageChangeListener(new ViewPageChangeListener());       }      private void initAdapter() {    //即将在viewPager中展示的图片资源    int[] imgs = {R.drawable.i1, R.drawable.i2, R.drawable.i3};        //init pagers;    pagers = new ArrayList<View>();    LinearLayout.LayoutParams img_params = new LayoutParams(      LayoutParams.MATCH_PARENT, LayoutParams.MATCH_PARENT      );    for(int i = 0; i < imgs.length; ++i) {     ImageView iv = new ImageView(this);     iv.setBackgroundResource(imgs[i]);     iv.setLayoutParams(img_params);     final int index = i;     iv.setOnClickListener(new OnClickListener() {      //当viewPager中的图片被点击后,跳转到新的activity      @Override      public void onClick(View v) {       Intent i = new Intent(MainActivity.this, InvokedActivity.class);       i.putExtra("name", "cat " + index);       MainActivity.this.startActivity(i);      }     });     pagers.add(iv);    }    autoChangeViewPager.setAdapter(new ViewPagerAdapter(pagers));        //init indicator    LinearLayout.LayoutParams ind_params = new LayoutParams(      LayoutParams.WRAP_CONTENT, LayoutParams.WRAP_CONTENT      );    for(int i = 0; i < imgs.length; ++i) {     ImageView iv = new ImageView(this);     if(i == 0)      iv.setBackgroundResource(R.drawable.tip_select);     else      iv.setBackgroundResource(R.drawable.tip_normal);     iv.setLayoutParams(ind_params);     viewIndicator.addView(iv);    }   }      @Override   protected void onResume() {    super.onResume();    //activity启动两秒钟后,发送一个message,用来将viewPager中的图片切换到下一个    mHandler.sendEmptyMessageDelayed(1, 2000);   }      @Override   protected void onStop() {    super.onStop();    //停止viewPager中图片的自动切换    mHandler.removeMessages(1);   }     public class ViewPagerAdapter extends PagerAdapter {    private List<View> mData;    public ViewPagerAdapter(List<View> mData) {     this.mData = mData;    }      @Override    public int getCount() {     return mData.size();    }      @Override    public boolean isViewFromObject(View arg0, Object arg1) {     return arg0 == arg1;    }        @Override    public Object instantiateItem(ViewGroup container, int position) {     View v = mData.get(position);     container.addView(v);     return v;    }        @Override    public void destroyItem(ViewGroup container, int position, Object object) {  //   super.destroyItem(container, position, object);     container.removeView(mData.get(position));    }       }      private class ViewPageChangeListener implements OnPageChangeListener {      @Override    public void onPageScrollStateChanged(int arg0) {    }      @Override    public void onPageScrolled(int arg0, float arg1, int arg2) {    }      //监听页面改变事件来改变viewIndicator中的指示图片    @Override    public void onPageSelected(int arg0) {     int len = viewIndicator.getChildCount();     for(int i = 0; i < len; ++i)      viewIndicator.getChildAt(i).setBackgroundResource(R.drawable.tip_normal);     viewIndicator.getChildAt(arg0).setBackgroundResource(R.drawable.tip_select);    }       }      private Handler mHandler = new Handler() {    public void handleMessage(android.os.Message msg) {     switch(msg.what) {     case 1:      int totalcount = pagers.size();//autoChangeViewPager.getChildCount();      int currentItem = autoChangeViewPager.getCurrentItem();            int toItem = currentItem + 1 == totalcount ? 0 : currentItem + 1;            Log.i(TAG, "totalcount: " + totalcount + "   currentItem: " + currentItem + "   toItem: " + toItem);            autoChangeViewPager.setCurrentItem(toItem, true);            //每两秒钟发送一个message,用于切换viewPager中的图片      this.sendEmptyMessageDelayed(1, 2000);     }    }   };  }




布局文件如下:(上面代码中的InvokedActivity非常简单,此处就省略了)

<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"      android:layout_width="match_parent"      android:layout_height="match_parent" >        <android.support.v4.view.ViewPager          android:id="@+id/autoVP"          android:layout_width="match_parent"          android:layout_height="match_parent" />        <LinearLayout          android:id="@+id/vpindicator"          android:layout_width="match_parent"          android:layout_height="wrap_content"          android:layout_gravity="bottom"          android:orientation="horizontal" />    </FrameLayout>