RecyclerView上的空视图

John L. Carveth 发表于 Dev

约翰·卡维斯

在我正在开发的应用程序中，我正在使用“回收站视图”显示项目列表。我希望列表为空时显示一些视图（例如，文本视图）。我知道使用ListViews可以调用setEmptyView，但是RecyclerView没有这种方法。

我尝试将视图的可见性设置为GONE，并在RecyclerView数据集为空时使其可见，但是将任何视图添加到定义了RecyclerView的布局文件中都会导致错误：

Attempt to invoke virtual method 'boolean 
android.support.v7.widget.RecyclerView$ViewHolder.shouldIgnore()' on a null 
object reference

做我正在做的最好的方法是什么？

有关更多信息，RecyclerView被保存在一个Fragment中，并且布局在onCreateView函数中被放大。

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    View view = inflater.inflate(R.layout.fragment_grocerylist, container, false);

    rv = view.findViewById(R.id.grocery_list);

    dh = new DatabaseHandler(view.getContext());

    dataset = dh.getGroceries();

    // Set the adapter
    if (view instanceof RecyclerView) {
        Context context = view.getContext();
        RecyclerView recyclerView = (RecyclerView) view;
        recyclerView.setLayoutManager(new LinearLayoutManager(context));

        adapter = new GroceryListRecyclerViewAdapter(dataset,mListener,this);
        recyclerView.setAdapter(adapter);
    }

    ItemTouchHelper.Callback callback = new SimpleTouchHelperCallback(adapter);
    ith = new ItemTouchHelper(callback);
    ith.attachToRecyclerView(rv);

    DividerItemDecoration div = new DividerItemDecoration(rv.getContext(),
            DividerItemDecoration.VERTICAL);

    rv.addItemDecoration(div);

    return view;
}

XML：

<?xml version="1.0" encoding="utf-8"?>
<android.support.v7.widget.RecyclerView xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/grocery_list" android:name="com.github.jlcarveth.grocer.layout.fragment.GroceryListFragment"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_marginLeft="0dp"
android:layout_marginRight="0dp"
app:layoutManager="LinearLayoutManager"  tools:context="com.github.jlcarveth.grocer.layout.fragment.GroceryListFragment"   tools:listitem="@layout/grocery_item"/>

地狱战士

我更新了您的代码：

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
android:name="com.github.jlcarveth.grocer.layout.fragment.GroceryListFragment"
android:layout_width="match_parent"
tools:context="com.github.jlcarveth.grocer.layout.fragment.GroceryListFragment"
android:layout_height="match_parent">

<android.support.v7.widget.RecyclerView
    android:id="@+id/grocery_list"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:layout_marginLeft="0dp"
    android:layout_marginRight="0dp"
    app:layoutManager="LinearLayoutManager"
    tools:listitem="@layout/grocery_item" />

<TextView
    android:id="@+id/empty_view"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:gravity="center"
    android:visibility="gone"
    android:text="NO DATA AVAILABLE" />
</FrameLayout>

您的片段：

 @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {


  View view = inflater.inflate(R.layout.fragment_grocerylist, container, false);

    rv = view.findViewById(R.id.grocery_list);
    TextView emptyView = (TextView)view.findViewById(R.id.empty_view);

    dh = new DatabaseHandler(view.getContext());

    dataset = dh.getGroceries();


     Context context = view.getContext();
     RecyclerView recyclerView = (RecyclerView) rv;
     recyclerView.setLayoutManager(new LinearLayoutManager(context));

     adapter = new GroceryListRecyclerViewAdapter(dataset,mListener,this);
     recyclerView.setAdapter(adapter);


    ItemTouchHelper.Callback callback = new SimpleTouchHelperCallback(adapter);
    ith = new ItemTouchHelper(callback);
    ith.attachToRecyclerView(recyclerView);

    DividerItemDecoration div = new DividerItemDecoration(recyclerView.getContext(),
            DividerItemDecoration.VERTICAL);

    recyclerView.addItemDecoration(div);


    if (dataset.isEmpty()){
        recyclerView.setVisibility(View.GONE);
         emptyView.setVisibility(View.VISIBLE);
    } else {
         recyclerView.setVisibility(View.VISIBLE);
         emptyView.setVisibility(View.GONE);
    }



    return view;
}

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