RecyclerView 在布局中不显示任何项目

Question

I have a navigation drawer activity that contains a fragment that contains a RecyclerView. This RecyclerView works perfectly if it is the only component in this fragment, but I want to add a button above the RecyclerView and therefore insert the RecyclerView and the button in a LinearLayout. But then the RecyclerView has disappeared or no longer shows any elements.

How can I embed this RecyclerView in a layout?

RecyclerView works with this one:

<?xml version="1.0" encoding="utf-8"?>
<androidx.recyclerview.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/list"
  android:layout_width="match_parent"
  android:layout_height="match_parent"
  android:layout_marginLeft="16dp"
  android:layout_marginRight="16dp"
  android:name="com.company.myapp.ui.ItemFragment"
  app:layoutManager="LinearLayoutManager"
  tools:context=".ui.home.HomeFragment"
  tools:listitem="@layout/fragment_item" />

RecyclerView has disappeared in this one:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout 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:layout_width="match_parent"
  android:layout_height="match_parent"
  android:orientation="vertical">

  <Button
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="Delete Item" />

  <androidx.recyclerview.widget.RecyclerView
    android:id="@+id/list"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:layout_marginLeft="16dp"
    android:layout_marginRight="16dp"
    android:name="com.company.myapp.ui.ItemFragment"
    app:layoutManager="LinearLayoutManager"
    tools:context=".ui.home.HomeFragment"
    tools:listitem="@layout/fragment_item" />

</LinearLayout>

See complete project here: https://github.com/jriegraf/MyApp

Answer 1

You have this code in HomeFragment :

// Set the adapter
if (view instanceof RecyclerView) {
  Context context = view.getContext();
  RecyclerView recyclerView = (RecyclerView) view;
  if (mColumnCount <= 1) {
    recyclerView.setLayoutManager(new LinearLayoutManager(context));
  } else {
    recyclerView.setLayoutManager(new GridLayoutManager(context, mColumnCount));
  }
  recyclerView.setAdapter(new MyItemRecyclerViewAdapter(DummyContent.ITEMS, mListener));
}

This is your problem. Once you wrap RecyclerView into LinearLayout , this

if (view instanceof RecyclerView)

isn't true any more, because now, view 's type is LinearLayout .

If the view doesn't remove the recyclerView, you can ommit the if statement, and change this line:

RecyclerView recyclerView = (RecyclerView) view;

into:

RecyclerView recyclerView = (RecyclerView) view.findViewById(R.id.list);