在水平視圖中的列表視圖尋呼機不更新

Question

我有一個水平視圖尋呼機通過3個ListViews頁面。三個列表視圖是從三個不同的數據庫表中填充的。問題是，當我滑過頁面，listview不加載，而是顯示一個白色的屏幕。

@Override 
protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
      setContentView(R.layout.viewp); 
    MyPagerAdapter adapter = new MyPagerAdapter(); 
    ViewPager myPager = (ViewPager) findViewById(R.id.threepageviewer); 
    myPager.setAdapter(adapter); 
    myPager.setCurrentItem(1); 
} 

private class MyPagerAdapter extends PagerAdapter { 

    public int getCount() { 
     return 3; 
    } 

    public Object instantiateItem(View collection, int position) { 

     LayoutInflater inflater = (LayoutInflater) collection.getContext() 
       .getSystemService(Context.LAYOUT_INFLATER_SERVICE); 

     int resId = 0; 
     switch (position) { 
     case 0: 
      resId = R.layout.left; 
      ListView list = new ListView(Listing.this); 
      helper = new DbHelper(Listing.this); 
      dataset_cursor1 = helper.getAll1(); 
      startManagingCursor(dataset_cursor1); 
      adapter1 = new NoteAdapter(dataset_cursor1); 
      list.setAdapter(adapter1); 
      adapter1.notifyDataSetChanged(); 

      break; 
     case 1: 
      resId = R.layout.middle; 
      ListView list1 = new ListView(Listing.this); 
      helper = new DbHelper(Listing.this); 
      dataset_cursor2 = helper.getAll(); 
      startManagingCursor(dataset_cursor2); 
      adapter2 = new NoteAdapter(dataset_cursor2); 
      list1.setAdapter(adapter2); 
      adapter2.notifyDataSetChanged(); 
      break; 
     case 2: 
      resId = R.layout.right; 
      ListView list2 = new ListView(Listing.this); 
      helper = new DbHelper(Listing.this); 
      dataset_cursor3 = helper.getAll2(); 
      startManagingCursor(dataset_cursor3); 
      adapter3 = new NoteAdapter(dataset_cursor3); 
      list2.setAdapter(adapter3); 
      adapter3.notifyDataSetChanged(); 

      break; 
     } 

     View view = inflater.inflate(resId, null); 

     ((ViewPager) collection).addView(view, 0); 

     return view; 
    } 

    @Override 
    public void destroyItem(View arg0, int arg1, Object arg2) { 
     ((ViewPager) arg0).removeView((View) arg2); 

    } 

    @Override 
    public void finishUpdate(View arg0) { 

    } 

    @Override 
    public boolean isViewFromObject(View arg0, Object arg1) { 
     return arg0 == ((View) arg1); 

    } 

    @Override 
    public void restoreState(Parcelable arg0, ClassLoader arg1) { 

    } 

    @Override 
    public Parcelable saveState() { 
     return null; 
    } 

    @Override 
    public void startUpdate(View arg0) { 

    } 

    public int getItemPosition(Object object) { 
     return POSITION_NONE; 
    } 
} 

這裏有什麼問題。

Answer 1

您正在膨脹佈局，但您沒有添加任何視圖。你應該這樣做：

public Object instantiateItem(View collection, int position) { 

     LayoutInflater inflater = (LayoutInflater) collection.getContext() 
       .getSystemService(Context.LAYOUT_INFLATER_SERVICE); 
     View view; 
     switch (position) { 
     case 0: 
      view = = inflater.inflate(R.layout.left, null); 
      ListView list = (ListView) view.findViewById(R.id.listviewleft); //id of your listview 
      helper = new DbHelper(Listing.this); 
      dataset_cursor1 = helper.getAll1(); 
      startManagingCursor(dataset_cursor1); 
      adapter1 = new NoteAdapter(dataset_cursor1); 
      list.setAdapter(adapter1); 
      adapter1.notifyDataSetChanged(); 

      break; 
      (...) 
     } 


    ((ViewPager) collection).addView(view); 

    return view; 
}