Android在加载Fragment时无法显示ProgressBar [重复]

Question

所以我有可以从底部导航菜单访问的3 片段。当我选择“主页”时，它会打开一个 fragment，其中包含一个填充有来自 Firebase 数据库的数据的 RecyclerView。如何在recyclerview 从firebase 获取数据时显示progressbar？花了大约 1-2 秒，我想要一个 progressbar。

编辑：我创建了一个progressbar，但如果我在创建片段后将其可见性设置为 GONE，则 progressbar 根本不会出现。

XML 文件：

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout
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">

<ProgressBar
    android:id="@+id/progressBarHome"
    android:layout_width="100dp"
    android:layout_height="39dp"
    android:elevation="7dp"
    android:visibility="visible"
    android:indeterminateTint="@android:color/black"
    app:layout_constraintBottom_toBottomOf="parent"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toTopOf="parent" />

<androidx.recyclerview.widget.RecyclerView
    android:id="@+id/recycler1"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@color/blue"/>

</androidx.constraintlayout.widget.ConstraintLayout>

Java 文件：

public class HomeFragment extends Fragment {
private RecyclerView recyclerView;
carAdapter adapter; // Create Object of the Adapter class
DatabaseReference mbase;
private ProgressBar progressBar; 
@Nullable
@Override
public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {

    View view = inflater.inflate(R.layout.fragment_home,container,false);
    mbase = FirebaseDatabase.getInstance().getReference("Cars");
    recyclerView = view.findViewById(R.id.recycler1);


    // To display the Recycler view linearly
    recyclerView.setLayoutManager(new LinearLayoutManager(getActivity()));

    // It is a class provide by the FirebaseUI to make a
    // query in the database to fetch appropriate data
    FirebaseRecyclerOptions<car> options = new FirebaseRecyclerOptions.Builder<car>()
            .setQuery(mbase, car.class)
            .build();
    // Connecting object of required Adapter class to
    // the Adapter class itself
    adapter = new carAdapter(options);
    // Connecting Adapter class with the Recycler view*/
    recyclerView.setAdapter(adapter);
    return view;
}

@Override
public void onViewCreated(View view, Bundle savedInstanceState) {
    super.onViewCreated(view, savedInstanceState);
    progressBar = view.findViewById(R.id.progressBarHome);
    progressBar.setVisibility(View.GONE);
}


@Override public void onStart()
{
    super.onStart();
    adapter.startListening();

}

// Function to tell the app to stop getting
// data from database on stoping of the activity
@Override public void onStop()
{
    super.onStop();
    adapter.stopListening();
}
}

Answer 1

我认为您不想在创建Fragment 后立即将其设为GONE，要显示ProgressBar，您应该改为在onViewCreated 中将其设为VISIBLE。然后，在获取您的 firebase 数据后，将其设为 GONE 以隐藏它。

@Override
public void onViewCreated(View view, Bundle savedInstanceState) {
    super.onViewCreated(view, savedInstanceState);
    progressBar = view.findViewById(R.id.progressBarHome);
    progressBar.setVisibility(View.VISIBLE);
}