如何让我的 android 应用程序连接到实时 firebase 数据库以在实时数据库中创建更新 toast？

Question

这是我的 fireabase 数据库 View Database

我想要的只是在我的 android 应用程序中生成一个 toast 或一个通知，说明在 faces 或 movement 目录下添加了哪些更改或哪些新条目。我正在尝试使用 addValueEventListener() 方法，但我无法让它工作。下面是我的 android 应用程序中的 onCreate() 方法。我试图通过遵循这个https://www.youtube.com/watch?v=vxCDS6DaFSQ youtube 教程来实现这一点。我已经将我的应用程序连接到了 Firebase。另外，我正在尝试通过不使用 firebase 云功能来完成此操作。

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    Toast.makeText(this, "Firebase Successful", Toast.LENGTH_SHORT).show();

    FirebaseDatabase database = FirebaseDatabase.getInstance();
    DatabaseReference myRef = database.getReference("message");
    myRef.child("App")
            .addValueEventListener(new ValueEventListener() {
                @Override
                public void onDataChange(@NonNull DataSnapshot snapshot) {
                    Iterable<DataSnapshot> children = snapshot.getChildren();

                    for (DataSnapshot child: children)
                    {
                        String value = child.getValue(String.class);
                        Toast.makeText(MainActivity.this, "Data" + value, Toast.LENGTH_SHORT).show();
                    }
                }

                @Override
                public void onCancelled(@NonNull DatabaseError error) {

                }
            });
}

如果这不能通过使用 addValueEventListener() 方法来实现，还有其他相对简单的替代方法吗？

这是我的 MainActivity.java（有两个按钮）

package com.example.notification_test;

import androidx.annotation.NonNull;
import androidx.appcompat.app.AppCompatActivity;
import androidx.core.app.NotificationCompat;
import androidx.core.app.NotificationManagerCompat;

import android.app.NotificationChannel;
import android.app.NotificationManager;
import android.os.Build;
import android.os.Bundle;
import android.view.View;
import android.widget.Toast;

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.google.firebase.database.ValueEventListener;

public class MainActivity extends AppCompatActivity {
    private final String CHANNEL_ID = "personal_notifications";
    private final int NOTIFICATION_ID = 001;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Toast.makeText(this, "Firebase Successful", Toast.LENGTH_SHORT).show();

        DatabaseReference myRef = FirebaseDatabase.getInstance().getReference();
        myRef.child("App").addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(@NonNull DataSnapshot snapshot) {
                Iterable<DataSnapshot> children = snapshot.getChildren();

                for (DataSnapshot child: children)
                {
                    String value = child.getValue(String.class);
                    Toast.makeText(MainActivity.this, "Data" + value, Toast.LENGTH_SHORT).show();
                }
            }

            @Override
            public void onCancelled(@NonNull DatabaseError error) {

            }
        });
    }

    public void testFirebase(View view)
    {
        FirebaseDatabase database = FirebaseDatabase.getInstance();
        DatabaseReference myRef = database.getReference("message");
        myRef.setValue("Hello");
    }

    public void displayNotification(View view)
    {
        createNotificationChannel();
        NotificationCompat.Builder builder = (NotificationCompat.Builder) new NotificationCompat.Builder(getApplicationContext(), CHANNEL_ID);
        builder.setSmallIcon(R.drawable.ic_sms);
        builder.setContentTitle("Simple Notification");
        builder.setContentText("This is a simple notification..");
        builder.setPriority(NotificationCompat.PRIORITY_DEFAULT);

        NotificationManagerCompat notificationManagerCompat = NotificationManagerCompat.from(this);
        notificationManagerCompat.notify(NOTIFICATION_ID, builder.build());

    }

    private void createNotificationChannel()
    {
        if(Build.VERSION.SDK_INT>=Build.VERSION_CODES.O)
        {
            CharSequence name = "Personal Notifications";
            String description = "Include all the personal notifications";
            int importance = NotificationManager.IMPORTANCE_DEFAULT;

            NotificationChannel notificationChannel = new NotificationChannel(CHANNEL_ID, name, importance);

            notificationChannel.setDescription(description);

            NotificationManager notificationManager = (NotificationManager) getSystemService(NOTIFICATION_SERVICE);
            notificationManager.createNotificationChannel(notificationChannel);

        }

    }

}```

Answer 1

我假设您的问题在这一行

 DatabaseReference myRef = database.getReference("message");

根据Firebase Docs 您不应该将 "message" 传递给数据库引用。

Answer 2

这应该适合你：

 DatabaseReference myRef = FirebaseDatabase.getInstance().getReference();
 myRef.child("App").addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(@NonNull DataSnapshot snapshot) {
                Iterable<DataSnapshot> children = snapshot.getChildren();

                for (DataSnapshot child: children)
                {
                    String value = child.getValue(String.class);
                    Toast.makeText(MainActivity.this, "Data" + value, Toast.LENGTH_SHORT).show();
                }
            }

            @Override
            public void onCancelled(@NonNull DatabaseError error) {

            }
        });
}