为什么第一次进入我的活动时它没有数据组成viewpager + fragment？

Question

我的活动构成了viewpager和fragment，但是当我第一次输入它时没有数据，如果我将寻呼机从一个滚动到四个，然后将四个滚动到两个，这一刻它将显示数据，然后你继续滚动，所有数据都会显示。我不知道为什么会这样，你能帮助我吗？以下是我的代码：

public class WatchVideosActivity extends FragmentActivity {

private TabPageIndicator mTabIndicator;
private ViewPager mViewPager;
private int mWidth;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_watch_videos);

    getScreenWidth();
    initView();
}

/**
 * 获取屏幕的宽度
 */
private void getScreenWidth(){
    DisplayMetrics dm = new DisplayMetrics();
    getWindowManager().getDefaultDisplay().getMetrics(dm);
    mWidth = dm.widthPixels;
}

/**
 * 初始化View
 */
private void initView(){
    mTabIndicator = (TabPageIndicator)findViewById(R.id.tab_pager_indicator);
    mViewPager = (ViewPager)findViewById(R.id.watch_video_viewpager);
    mViewPager.setAdapter(new WatchVideoPagerAdapter(WatchVideosActivity.this,getSupportFragmentManager(),mWidth));
    mTabIndicator.setViewPager(mViewPager);
}

}

public class WatchVideoPagerAdapter extends FragmentPagerAdapter{

public static final String[] title = new String[]{"期指在线","和讯座谈会","中国经济学人","中国分析师访谈"};
private Context mContext;
private int mWidth;

public WatchVideoPagerAdapter(Context context,FragmentManager fm,int width) {
    super(fm);
    this.mContext = context;
    this.mWidth = width;
}

@Override
public int getCount() {
    return title.length;
}

@Override
public Fragment getItem(int position) {
    return new FragmentFactory(mContext,position,mWidth);   //创建fragment
}

@Override
public CharSequence getPageTitle(int position) {
    return title[position];
}

}

public class FragmentFactory extends Fragment {

private int position;
private ListView mWatchVideoList;
private Context mContext;
private int mWidth;
private Integer mPagerIndex = 1;
private Integer[] titleId = new Integer[] { 123817825, 180524655, 168567237, 182001231 };
private List<VideoEntity> newsPagerList = new ArrayList<VideoEntity>();
private VideoAdapter videoAdapter; 

public FragmentFactory(Context context, int position, int width) {
    super();
    this.position = position;
    this.mContext = context;
    this.mWidth = width;
}

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
    View view = inflater.inflate(R.layout.watchvideo_fragment_view, container, false);
    mWatchVideoList = (ListView) view.findViewById(R.id.watchvideo_list);
    getData();
    mWatchVideoList.setAdapter(videoAdapter);
    return view;
}

private Handler mHandler = new Handler() {
    @SuppressWarnings("unchecked")
    public void handleMessage(android.os.Message msg) {
        newsPagerList = (List<VideoEntity>) msg.obj;
        videoAdapter = new VideoAdapter(mContext, mWatchVideoList, newsPagerList, mWidth);
        videoAdapter.notifyDataSetChanged();
    };
};

private void getData() {
    OkHttpUtils.getInputStream("http://wapi.hexun.com/Api_videoList.cc?pid=" + titleId[position] + "&pc=20&pn=1",
            mHandler, 0);
}

}

Answer 1

不要在handleMessage（）中实例化VideoAdapter，而是在onCreteView中将其实例化一次

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,  Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.watchvideo_fragment_view, container, false);
 mWatchVideoList = (ListView) view.findViewById(R.id.watchvideo_list);
 newsPagerList=new ArrayList<VideoEntity>();
videoAdapter = new VideoAdapter(mContext, mWatchVideoList, newsPagerList, mWidth); ///Send empty list for the first time
mWatchVideoList.setAdapter(videoAdapter);
getData();
return view;

}

在VideoAdapter中创建一个方法

VideoAdapter{


public void addItems(ArrayList<VideoEntity> list){
 newsPageList.addAll(list); ///newsPageList is your list used in Adapter
 notifyDataSetChanged();
}  

当您从服务器获取数据时，请调用适配器的addItems（）方法，该方法将通知您的列表，您将显示您的数据。

private Handler mHandler = new Handler() {
@SuppressWarnings("unchecked")
public void handleMessage(android.os.Message msg) {
    newsPagerList = (List<VideoEntity>) msg.obj;
    videoAdapter.addItems(newsPagerList);
};

};

希望这会对你有所帮助。

Answer 2

您的列表的适配器在mHandler中不相同。