无法更改视图的大小取决于列表的大小

Question

我的问题是在我的RecycleView上布局上的更改视图。我有列表梦想。这个视图包含两个状态myDreamEmptyLayout witch show Text“现在你没有梦想了。\ n添加梦想！”当myDreamList为空并且大小为等于0.但是，当myDreamList大于1时显示列表梦。 问题是什么时候myDream列表中，并删除所有不能显示我的看法myDreamEmptyLayout。 什么是问题？

这是我fragment_my_dream.xml

<?xml version="1.0" encoding="utf-8"?> 
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android" 
      android:layout_width="match_parent" 
      android:layout_height="match_parent" 
      android:background="@color/colorBackground" 
    > 

    <LinearLayout 
     android:id="@+id/myDreamEmptyLayout" 
     android:layout_width="match_parent" 
     android:layout_height="match_parent" 
     android:orientation="vertical"> 

     <TextView 
      android:layout_width="match_parent" 
      android:layout_height="match_parent" 
      android:gravity="center" 
      android:text="@string/for_now_you_don_t_have_dream_n_add_dream" 
      android:textColor="@color/colorWhite"/> 

    </LinearLayout> 


    <android.support.v7.widget.RecyclerView 
     android:id="@+id/myDreamRecyclerView" 
     android:layout_width="match_parent" 
     android:layout_height="match_parent" 
     android:visibility="gone"/> 
</FrameLayout> 

这是我的片段类

public class MyDreamFragment extends Fragment { 

     public static final int REQUEST_CODE_CREATE = 1; 


     @BindView(R.id.myDreamRecyclerView) 
     RecyclerView myDreamRecyclerView; 
     @BindView(R.id.myDreamEmptyLayout) 
     LinearLayout myDreamEmptyLayout; 

     private MyDreamAdapter myDreamAdapter; 
     private List<MyDream> myDreamList; 
     String idUserString; 
     private DbHelper dbHelper; 
     private Unbinder unbinder; 
     private Dao<MyDream, Integer> myDreamDao; 
     private Dao<User, Integer> myUserDao; 

     @Override 

     public void onCreate(@Nullable Bundle savedInstanceState) { 
      super.onCreate(savedInstanceState); 
      setHasOptionsMenu(true); 
     } 

     @Nullable 
     @Override 
     public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) { 
      View rootView = inflater.inflate(R.layout.fragment_my_dream, container, false); 
      unbinder = ButterKnife.bind(this, rootView); 
      TextView title = (TextView) getActivity().findViewById(R.id.toolbarTextView); 
      title.setText(R.string.title_my_dreams); 
      return rootView; 
     } 

     @Override 
     public void onViewCreated(View view, @Nullable Bundle savedInstanceState) { 
      super.onViewCreated(view, savedInstanceState); 

      Application application = (Application) getApplicationContext(); 
      idUserString = application.getFirebaseId(); 

      dbHelper = new DbHelper(getActivity()); 

      try { 
       myDreamDao = dbHelper.getDao(MyDream.class); 
      } catch (SQLException e) { 
       e.printStackTrace(); 
      } 

      try { 
       myUserDao = dbHelper.getDao(User.class); 
      } catch (SQLException e) { 
       e.printStackTrace(); 
      } 

      QueryBuilder<User, Integer> userQa = myUserDao.queryBuilder(); 

      try { 
       userQa.where().eq(User.Columns.FIREBASE_ID, idUserString); 
      } catch (SQLException e) { 
       e.printStackTrace(); 
      } 

      QueryBuilder<MyDream, Integer> myDreamQa = myDreamDao.queryBuilder(); 


      try { 
       myDreamList = myDreamQa.join(userQa).query(); 
      } catch (SQLException e) { 
       e.printStackTrace(); 
      } 

      if (myDreamList != null && myDreamList.size() > 0) { 
       myDreamRecyclerView.setLayoutManager(new LinearLayoutManager(getActivity())); 
       myDreamAdapter = new MyDreamAdapter(myDreamList, getActivity()); 
       myDreamRecyclerView.setAdapter(myDreamAdapter); 
      } 

     } 

     @Override 
     public void onCreateOptionsMenu(Menu menu, MenuInflater inflater) { 
      super.onCreateOptionsMenu(menu, inflater); 
      inflater.inflate(R.menu.menu_add, menu); 
     } 

     @Override 
     public void onResume() { 
      super.onResume(); 

      if (myDreamList.size() == 0) { 

       myDreamEmptyLayout.setVisibility(View.VISIBLE); 
       myDreamRecyclerView.setVisibility(View.GONE); 

      } else { 

       myDreamEmptyLayout.setVisibility(View.GONE); 
       myDreamRecyclerView.setVisibility(View.VISIBLE); 

      } 
     } 

     @Override 
     public boolean onOptionsItemSelected(MenuItem item) { 

      switch (item.getItemId()) { 
       case R.id.action_addream: 
        Intent intent = new Intent(getActivity(), AddEditDreamActivity.class); 
        startActivityForResult(intent, REQUEST_CODE_CREATE); 
        return true; 
      } 

      return super.onOptionsItemSelected(item); 
     } 


     @Override 
     public void onActivityResult(int requestCode, int resultCode, Intent data) { 
      super.onActivityResult(requestCode, resultCode, data); 

      if (resultCode == AddEditDreamActivity.RESULT_OK) { 
       if (requestCode == REQUEST_CODE_CREATE) { 
        if (data != null) { 
         MyDream myDream = data.getParcelableExtra("dream"); 
         myDreamAdapter.addMyDream(myDream); 
         Toast.makeText(getActivity(), "Dream was added", Toast.LENGTH_SHORT).show(); 
        } 
       } 
      } 

     } 

     @Override 
     public void onDestroyView() { 
      super.onDestroyView(); 
      unbinder.unbind(); 
     } 
    } 

Answer 1

你myDreamList不会反应到待更改，因此myDreamEmptyLayout不会得到通知的新的信息（如尺寸达到零）可用。为了对抗这种看this ObservableArrayList和它的OnListChangedCallback。将myDreamList更改为ObservableArrayList将onResume代码（当然没有super）更改为OnListChangedCallback，并通过addOnListChangedCallback添加此回调。这样，对列表所做的更改将根据您的需求反映在布局上。

代码：

//this goes to onCreate. DISCLAIMER : code written without testing, please confirm that it works. 
myDreamList.addOnListChangedCallback(new ObservableList.OnListChangedCallback() { 

/*snipped useless methods*/ 

    @Override 
    public void onChanged(ObservableList<T> sender) { 
      if (sender.size() == 0) { 

       myDreamEmptyLayout.setVisibility(View.VISIBLE); 
       myDreamRecyclerView.setVisibility(View.GONE); 

      } else { 

       myDreamEmptyLayout.setVisibility(View.GONE); 
       myDreamRecyclerView.setVisibility(View.VISIBLE); 

      } 
     } 
}