Question

请让我知道为什么我的recyclerview确实没有在用户片段中显示用户列表。我正在关注此GitHub教程，但问题是他们使用了Firebase Realtime数据库，而我使用的是Firebase Firestore。我是android编程的初学者，现在我自己在you-tube上学习它，如果我的错误很愚蠢，我深表歉意。我要显示用户的数据库的屏幕快照为over here.

UserFragment.java

    package com.example.authenticatorapp.Fragments;

    import android.os.Bundle;

    import androidx.fragment.app.Fragment;
    import androidx.recyclerview.widget.LinearLayoutManager;
    import androidx.recyclerview.widget.RecyclerView;

    import android.view.LayoutInflater;
    import android.view.View;
    import android.view.ViewGroup;

    import com.example.authenticatorapp.Adapters.UserAdapter;
    import com.example.authenticatorapp.R;
    import com.firebase.ui.firestore.FirestoreRecyclerOptions;
    import com.example.authenticatorapp.User;
    import com.google.firebase.firestore.CollectionReference;
    import com.google.firebase.firestore.FirebaseFirestore;

    import java.util.ArrayList;
    import java.util.List;

    public class UsersFragment extends Fragment {
        private FirebaseFirestore db = FirebaseFirestore.getInstance();
        private CollectionReference userRef = db.collection("users");

        private UserAdapter userAdapter;
        @Override
        public View onCreateView(LayoutInflater inflater, ViewGroup container,Bundle savedInstanceState) {
            View view = inflater.inflate(R.layout.fragment_users, container, false);
            RecyclerView recyclerView1 = view.findViewById(R.id.recyclerview);
            recyclerView1.setHasFixedSize(true);
            recyclerView1.setLayoutManager(new LinearLayoutManager(getContext()));
            readUsers();
recyclerView1.setAdapter(userAdapter);


            return  view;
        }
        private void readUsers(){

            FirestoreRecyclerOptions<User> options = new FirestoreRecyclerOptions.Builder<User>()
                    .setQuery(userRef, User.class)
                    .build();
            userAdapter = new UserAdapter(options);
        }
    }

fragment_users.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="#660000"
    tools:context=".Fragments.UsersFragment">

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

</RelativeLayout>

User.java

package com.example.authenticatorapp;

public class User {

    private String fName;

    public User() {

    }

    public User(String fName) {
        this.fName = fName;
            }


        public String getfName() {
        return fName;
    }

    }

UserAdapter.java

package com.example.authenticatorapp.Adapters;

import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ImageView;
import android.widget.TextView;

import androidx.annotation.NonNull;
import androidx.recyclerview.widget.RecyclerView;
import com.example.authenticatorapp.R;
import com.example.authenticatorapp.User;
import com.firebase.ui.firestore.FirestoreRecyclerAdapter;
import com.firebase.ui.firestore.FirestoreRecyclerOptions;


public class UserAdapter extends FirestoreRecyclerAdapter<User, UserAdapter.ViewHolder> {
    public UserAdapter(@NonNull FirestoreRecyclerOptions<User> options) {
        super(options);
    }

    @Override
    protected void onBindViewHolder(@NonNull ViewHolder holder, int position, @NonNull User model) {
        holder.fName.setText(model.getfName());
        holder.profile_image.setImageResource(R.mipmap.ic_launcher);
    }

    @NonNull
    @Override
    public ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.user_item, parent, false);
        return new UserAdapter.ViewHolder(view);
    }



    class ViewHolder extends RecyclerView.ViewHolder{
        public TextView fName;
        public ImageView profile_image;

        public ViewHolder(View itemView){
            super(itemView);
            fName = itemView.findViewById(R.id.username);
            profile_image = itemView.findViewById(R.id.profile_image);
        }
    }
}

user_item.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:padding="10dp">

    <de.hdodenhof.circleimageview.CircleImageView
        android:id="@+id/profile_image"
        android:layout_width="50dp"
        android:layout_height="50dp"
        android:src="@mipmap/ic_launcher">
    </de.hdodenhof.circleimageview.CircleImageView>

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="username"
        android:id="@+id/username"
        android:layout_toRightOf="@id/profile_image"
        android:layout_toEndOf="@id/profile_image"
        android:layout_marginLeft="10dp"
        android:layout_centerVertical="true"
        android:textSize="18sp"
        android:textColor="#FFEB3B">
    </TextView>

</RelativeLayout>

Answer 1

在将readUsers()设置为adapter之前，请先呼叫recyclerView，因为您需要先初始化适配器。

public View onCreateView(LayoutInflater inflater, ViewGroup container,Bundle savedInstanceState) {
    View view = inflater.inflate(R.layout.fragment_users, container, false);
    RecyclerView recyclerView1 = view.findViewById(R.id.recyclerview);
    recyclerView1.setHasFixedSize(true);
    recyclerView1.setLayoutManager(new LinearLayoutManager(getContext()));

    /******************/
    readUsers();
    recyclerView1.setAdapter(userAdapter);
    /******************/

    return  view;
}

更新

您还需要像这样设置适配器的生命周期所有者

FirestoreRecyclerOptions<User> options = new FirestoreRecyclerOptions.Builder<User>()
                .setQuery(userRef, User.class)
                .setLifecycleOwner(this)
                .build();

为什么我的应用程序没有在我的recyclerview中显示数据库中的用户？

1 个答案: