码：

WebRequest wRequest;
wRequest = WebRequest.Create("https://fcm.googleapis.com/fcm/send");
wRequest.Method = "post";
wRequest.ContentType = " application/json;charset=UTF-8";
wRequest.Headers.Add(string.Format("Authorization: key={0}",AppId));

wRequest.Headers.Add(string.Format("Sender: id={0}",SenderId));

string postData = "{\"registration_ids\":[\"" + regIds + "\"],\"data\": "+ value +"}";

Byte[] bytes = Encoding.UTF8.GetBytes(postData);
wRequest.ContentLength = bytes.Length;

Stream stream = wRequest.GetRequestStream();
stream.Write(bytes,bytes.Length);
stream.Close();

WebResponse wResponse = wRequest.GetResponse();

消息服务 –

public class MessagingService extends FirebaseMessagingService {
    @Override
    public void onMessageReceived(RemoteMessage remoteMessage) {
        Map<String,String>  data = remoteMessage.getData();
        sendNotification(data);
    }

    public void showMessage(Map<String,String>  serverData) {
        Intent i = new Intent(this,MainActivity.class);
        i.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);

        PendingIntent pendingIntent = PendingIntent.getActivity(this,i,PendingIntent.FLAG_UPDATE_CURRENT);

        NotificationCompat.Builder builder = new NotificationCompat.Builder(this)
                .setAutoCancel(true)
                .setContentTitle(serverData.get("Title"))
                .setContentText(serverData.get("Message"))
                .setSmallIcon(R.drawable.common_google_signin_btn_icon_dark)
                .setContentIntent(pendingIntent);

        NotificationManager manager = (NotificationManager) getSystemService(Context.NOTIFICATION_SERVICE);

        manager.notify(Integer.parseInt(serverData.get("ItemId")),builder.build());
    }

    private void sendNotification(Map<String,String>  serverData) {
        Intent intent = new Intent(this,MainActivity.class);
        intent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
        PendingIntent pendingIntent = PendingIntent.getActivity(this,0 /* request code */,intent,PendingIntent.FLAG_UPDATE_CURRENT);

        long[] pattern = {500,500,500};

        Uri defaultSoundUri= RingtoneManager.getDefaultUri(RingtoneManager.TYPE_NOTIFICATION);

        NotificationCompat.Builder notificationBuilder = (NotificationCompat.Builder) new NotificationCompat.Builder(this)
                .setSmallIcon(R.drawable.common_google_signin_btn_icon_dark)
                .setContentTitle(serverData.get("Title"))
                .setContentText(serverData.get("Message"))
                .setAutoCancel(true)
                .setVibrate(pattern)
                .setLights(Color.BLUE,1,1)
                .setSound(defaultSoundUri)
                .setContentIntent(pendingIntent);

        NotificationManager notificationManager = (NotificationManager) getSystemService(Context.NOTIFICATION_SERVICE);
        notificationManager.notify(Integer.parseInt(serverData.get("ItemId")),notificationBuilder.build());
    }

}

主要活动-

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
       FirebaseMessaging.getInstance().subscribeToTopic("test");
        FirebaseInstanceId.getInstance().getToken();
    }
}

表现-

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="test.com.firebasenotify">
    <uses-permission android:name="android.permission.INTERNET"/>
    <uses-permission android:name="android.permission.READ_PHONE_STATE" />
    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">
        <activity android:name=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>

        <service android:name=".MessagingService">
            <intent-filter>
                <action android:name="com.google.firebase.MESSAGING_EVENT" />
            </intent-filter>
        </service>
        <service android:name=".InstanceIDService">
            <intent-filter>
                <action android:name="com.google.firebase.INSTANCE_ID_EVENT" />
            </intent-filter>
        </service>

    </application>

</manifest>