应用程序更新Firebase实时数据库中的数据，但在recyclerview中不显示任何内容 [英] App updates data in firebase real-time database but doesn't show anything in recyclerview
本文介绍了应用程序更新Firebase实时数据库中的数据，但在recyclerview中不显示任何内容的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！
问题描述
我正在尝试将数据添加到firbase实时数据库中并在recyclerview上检索该数据.我能够成功地做到这一点，但是当我尝试从firebase检索数据时，即使在尝试打印我的数据时也没有发生在logacat窗口上，我能够成功做到这一点.
I am trying to add data onto firbase realtime database and retrieve that data on a recyclerview.I am successfully able to do that but when i try to retrieve data from firebase its not happening even-though when i try to print my data on logacat window i am successfully able to do that.
MainActivity.java
MainActivity.java
import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.appcompat.app.AppCompatActivity;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;
import com.google.firebase.database.ChildEventListener;
import com.google.firebase.database.DataSnapshot;
import com.google.firebase.database.DatabaseError;
import com.google.firebase.database.DatabaseReference;
import com.google.firebase.database.FirebaseDatabase;
import com.shivam.fireapp.model.User;
import java.util.ArrayList;
import java.util.List;
public class MainActivity extends AppCompatActivity {
private Button button;
private Button button2;
EditText editText;
EditText editText2;
String TAG ="MyTag";
private ChildEventListener mchildeventlistener;
private RecyclerView mRecyclerView;
private mModelAdapter modelAdapter;
private List<User> mDataList;
DatabaseReference mRootRef= FirebaseDatabase.getInstance().getReference();
DatabaseReference mRefMain =mRootRef.child("Users");
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
button = (Button) findViewById(R.id.Senddata);
button2 = (Button) findViewById((R.id.GetData));
editText = (EditText) findViewById(R.id.Firstname);
editText2 = (EditText) findViewById(R.id.Agee);
mDataList = new ArrayList<>();
mRecyclerView= findViewById(R.id.recyclerView);
mRecyclerView.setLayoutManager(new LinearLayoutManager(this));
modelAdapter = new mModelAdapter(this,mDataList);
mRecyclerView.setAdapter(modelAdapter);
mchildeventlistener = new ChildEventListener() {
@Override
public void onChildAdded(@NonNull DataSnapshot dataSnapshot, @Nullable String s) {
User user = dataSnapshot.getValue(User.class);
mDataList.add(user);
modelAdapter.notifyDataSetChanged();
Log.d(TAG,"OnChildAdded : Name "+ user.getFirst_name());
Log.d(TAG,"OnChildAdded : ageeee "+ user.getAgeeee());
}
@Override
public void onChildChanged(@NonNull DataSnapshot dataSnapshot, @Nullable String s) {
}
@Override
public void onChildRemoved(@NonNull DataSnapshot dataSnapshot) {
}
@Override
public void onChildMoved(@NonNull DataSnapshot dataSnapshot, @Nullable String s) {
}
@Override
public void onCancelled(@NonNull DatabaseError databaseError) {
}
};
mRefMain.addChildEventListener(mchildeventlistener);
}
@Override
protected void onStart(){
super.onStart();
button.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
String Name = editText.getText().toString();
String Age = editText2.getText().toString();
User user = new User(Name,Age);
String key = mRefMain.push().getKey();
mRefMain.child(key).setValue(user);
Toast.makeText(MainActivity.this,"Done",Toast.LENGTH_SHORT).show();
}
});
button2.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
}});
}
@Override
protected void onDestroy(){
super.onDestroy();
mRefMain.removeEventListener(mchildeventlistener);
}
}
activity_main.xml
activity_main.xml
<?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"
tools:context=".MainActivity">
<Button
android:id="@+id/Senddata"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginStart="32dp"
android:text="Send Data"
app:layout_constraintBottom_toBottomOf="@+id/GetData"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="@+id/GetData" />
<EditText
android:id="@+id/Firstname"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_marginStart="32dp"
android:layout_marginTop="41dp"
android:layout_marginEnd="39dp"
android:ems="10"
android:hint="Enter Name"
android:inputType="textPersonName"
app:layout_constraintEnd_toStartOf="@+id/Agee"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent" />
<Button
android:id="@+id/GetData"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginTop="160dp"
android:layout_marginEnd="40dp"
android:text="Get Data"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintTop_toTopOf="parent" />
<EditText
android:id="@+id/Agee"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_marginTop="41dp"
android:layout_marginEnd="40dp"
android:ems="10"
android:hint="Entre a Age"
android:inputType="textPersonName"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toEndOf="@+id/Firstname"
app:layout_constraintTop_toTopOf="parent" />
<androidx.recyclerview.widget.RecyclerView
android:id="@+id/recyclerView"
android:layout_width="match_parent"
android:layout_height="345dp"
android:layout_marginTop="55dp"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="@+id/Senddata" />
</androidx.constraintlayout.widget.ConstraintLayout>
mModelAdapter.java
mModelAdapter.java
import androidx.annotation.NonNull;
import androidx.recyclerview.widget.RecyclerView;
import com.shivam.fireapp.model.User;
import java.util.List;
public class mModelAdapter extends RecyclerView.Adapter<mModelAdapter.MyViewHolder> {
private Context context;
private List<User> mDataList;
public mModelAdapter(Context context, List<User> mDataList) {
this.context = context;
this.mDataList = mDataList;
}
@NonNull
@Override
public MyViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
View rootView= LayoutInflater.from(context).inflate(R.layout.recycler_view_item,parent,false);
return new MyViewHolder(rootView);
}
@Override
public void onBindViewHolder(@NonNull MyViewHolder holder, int position) {
User user = mDataList.get(position);
holder.textView.setText(user.getFirst_name()+" | "+user.getAgeeee());
}
@Override
public int getItemCount() {
return mDataList.size();
}
public class MyViewHolder extends RecyclerView.ViewHolder{
TextView textView;
public MyViewHolder(@NonNull View itemView) {
super(itemView);
textView = itemView.findViewWithTag(R.id.textView);
}
}
}
User.java
User.java
public class User {
String first_name, ageeee;
public User(String first_name, String ageeee) {
this.first_name = first_name;
this.ageeee = ageeee;
}
public User() {
}
public String getFirst_name() {
return first_name;
}
public void setFirst_name(String first_name) {
this.first_name = first_name;
}
public String getAgeeee() {
return ageeee;
}
public void setAgeeee(String ageeee) {
this.ageeee = ageeee;
}
}
recycler_view_item.xml
recycler_view_item.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="match_parent"
android:layout_height="wrap_content">
<TextView
android:id="@+id/textView"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_marginTop="8dp"
android:text="TextView"
android:textSize="24sp"
android:gravity="center"/>
</LinearLayout>
推荐答案
我遇到了同样的问题.其原因是，当firebase尚未从实时数据库中读取数据时，便制作了recyclerview.还没有任何数据为解决此问题，请在确定Firebase已读取数据时使用recyclerview.然后将使用正确的数据制作recyclerview.
I had the same problem. Its reason is that when firebase hasn't read data from realtime database yet, recyclerview has been made; and it hasn't have any data yet. For solving that you should make recyclerview when you are sure that firebase has read data. Then recyclerview will be made with correct data.
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