Question

我在firebase中从数据库中检索信息时遇到问题，并将其列在recyclerView中。应用程序在我启动时运行，但信息和列表不会显示它应该在何处显示。我一直坚持这个问题已经有一段时间了，并且会对任何帮助都有所帮助！

  public class UsersActivity extends AppCompatActivity {

    private RecyclerView mUsersList;
    private FirebaseAuth mAuth;
    private DrawerLayout mDrawerLayout;
    private ActionBarDrawerToggle mToggle;
    private RecyclerView mUserList;
    private DatabaseReference mUsersDatabase;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_users);

        mUserList = (RecyclerView) findViewById(R.id.user_list);
        mUserList.setHasFixedSize(true);
        mUserList.setLayoutManager(new LinearLayoutManager(this));

        mUsersDatabase = FirebaseDatabase.getInstance().getReference().child("users");

        //Toolbar modifications
        Toolbar my_toolbar = findViewById(R.id.mCustomToolbar);
        setSupportActionBar(my_toolbar);
        getSupportActionBar().setTitle("Kontakter");
        getSupportActionBar().setLogo(R.drawable.log);

        //Toogle modifications
        mDrawerLayout = findViewById(R.id.drawerLayout);
        mToggle = new ActionBarDrawerToggle(this, mDrawerLayout, R.string.open, R.string.close);
        mDrawerLayout.addDrawerListener(mToggle);
        mToggle.syncState();
        getSupportActionBar().setDisplayHomeAsUpEnabled(true);

        //Setting Navigation View Item Selected Listener to handle the item click of the navigation menu
        NavigationView nv = findViewById(R.id.nav_menu);
        nv.setNavigationItemSelectedListener(new NavigationView.OnNavigationItemSelectedListener() {
            // This method will trigger on item Click of navigation menu
            @Override
            public boolean onNavigationItemSelected(@NonNull MenuItem menuItem){
                //Switch send you to the activity that you click on by comparing ItemId med R.id.....
                switch(menuItem.getItemId()){
                    case(R.id.nav_mainmenu):
                        Intent sendToMainMenu = new Intent(getApplicationContext(),menuActivity.class);
                        startActivity(sendToMainMenu);
                        break;
                    case(R.id.nav_logout):
                        Intent sendToLoginPage = new Intent(getApplicationContext(), LoginActivity.class);
                        startActivity(sendToLoginPage);
                        break;
                    case(R.id.nav_settings):
                        Intent sendToSettingsPage = new Intent(getApplicationContext(), SettingsActivity.class);
                        startActivity(sendToSettingsPage);
                        break;
                    case(R.id.nav_allusers):
                        Intent sendToAllUsersPage = new Intent(getApplicationContext(), UsersActivity.class);
                        startActivity(sendToAllUsersPage);
                        break;
                }
                return true;
            }
        });

    }

    //Handle action bar item clicks here. The action bar will automatically handle clicks on the Home/Up button
    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        if(mToggle.onOptionsItemSelected(item)){
            return true;
        }
        return super.onOptionsItemSelected(item);
    }

    @Override
    protected void onStart() {
        super.onStart();
        Query query = FirebaseDatabase.getInstance().getReference().child("users");
        final FirebaseRecyclerOptions<Users> options = new FirebaseRecyclerOptions.Builder<Users>().setQuery(query, Users.class).build();
        FirebaseRecyclerAdapter adapter = new FirebaseRecyclerAdapter<Users, UsersViewHolder>(options){

            @NonNull
            @Override
            public UsersViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
                View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.single_user_layout, parent, false);

                return new UsersViewHolder(view);
            }

            @Override
            protected void onBindViewHolder(@NonNull UsersViewHolder holder, int position, @NonNull Users model) {
                holder.setDisplayName(model.getName());
            }
        };

        mUserList.setAdapter(adapter);

    }

    public static class UsersViewHolder extends RecyclerView.ViewHolder{

        View mView;

        public  UsersViewHolder(View itemView){
            super(itemView);

            mView=itemView;
        }

        public void setDisplayName(String name){
            TextView userNameView = mView.findViewById(R.id.contact_name);
            userNameView.setText(name);
        }


    }

上述活动的xml：

    <?xml version="1.0" encoding="utf-8"?>
<android.support.v4.widget.DrawerLayout 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/drawerLayout"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="com.example.rebeckagerdtham.skane18.activities.menuActivity">

    <android.support.constraint.ConstraintLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent">

        <include
            android:id="@+id/mCustomToolbar"
            layout="@layout/toolbar"></include>

        <android.support.v7.widget.RecyclerView
            android:id="@+id/user_list"
            android:layout_width="369dp"
            android:layout_height="294dp"
            android:layout_marginBottom="8dp"
            android:layout_marginEnd="8dp"
            android:layout_marginStart="8dp"
            android:layout_marginTop="8dp"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintHorizontal_bias="1.0"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toBottomOf="@+id/mCustomToolbar"
            app:layout_constraintVertical_bias="0.0"></android.support.v7.widget.RecyclerView>

    </android.support.constraint.ConstraintLayout>

    <android.support.design.widget.NavigationView
        android:id="@+id/nav_menu"
        android:layout_width="wrap_content"
        android:layout_height="match_parent"
        android:layout_gravity="start"
        app:headerLayout="@layout/navigation_header"
        app:menu="@menu/navigationmenu"></android.support.design.widget.NavigationView>

</android.support.v4.widget.DrawerLayout>

第一项活动中使用的类用户：

public class Users {

  public String name;

  public Users(){

  }

  public Users(String name) {
    this.name = name;
  }

  public String getName() {
    return name;
  }

  public void setName(String name) {
    this.name = name;
  }

Answer 1

为了使您的代码有效，请考虑使用以下步骤。

移动onCreate（）方法内的onStart()方法中的所有代码，但以下代码行除外：
```
super.onStart();
```

制作adapter可变全球：

private FirebaseRecyclerAdapter<Users, UsersViewHolder> adapter;

从onCreate（）方法中删除FirebaseRecyclerAdapter。

在onStart()和onStop()方法中添加以下代码行。

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

@Override
protected void onStop() {
    super.onStop();
    if(adapter != null) {
        adapter.stopListening();
    }
}

不要忘记在你的模型类priviate中设置你的文件：
```
private String name;
```

FirebaseRecycleradapter / RecyclerView无法正常工作

1 个答案: