PeriodicWorker后台运行时无法显示通知问题求助

我用PeriodicWorker实现应用数据每日备份（本地数据上传到云存储），但调用setForegroundAsync(foregroundInfo);时先出现警告：
startForegroundService() not allowed due to mAllowStartForeground false: service com.mydomain/androidx.work.impl.foreground.SystemForegroundService

备份流程结束时出现以下错误：

Unable to stop foreground service
android.app.BackgroundServiceStartNotAllowedException: Not allowed to start service Intent { act=ACTION_STOP_FOREGROUND cmp=com.mydomain/androidx.work.impl.foreground.SystemForegroundService }: app is in background uid UidRecord{dff373e u0a386 TRNB bg:+3m49s885ms idle change:procadj procs:0 seq(7594403,7591739)} caps=------
    at android.app.ContextImpl.startServiceCommon(ContextImpl.java:1945)
    at android.app.ContextImpl.startService(ContextImpl.java:1900)
    at android.content.ContextWrapper.startService(ContextWrapper.java:825)
    at androidx.work.impl.Processor.stopForegroundService(Processor.java:425)
    at androidx.work.impl.Processor.stopForeground(Processor.java:303)
    at androidx.work.impl.WorkerWrapper.resolve(WorkerWrapper.java:464)
    at androidx.work.impl.WorkerWrapper.resetPeriodicAndResolve(WorkerWrapper.java:577)
    at androidx.work.impl.WorkerWrapper.handleResult(WorkerWrapper.java:480)
    at androidx.work.impl.WorkerWrapper.onWorkFinished(WorkerWrapper.java:358)
    at androidx.work.impl.WorkerWrapper$2.run(WorkerWrapper.java:335)
    at androidx.work.impl.utils.SerialExecutorImpl$Task.run(SerialExecutorImpl.java:96)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:644)
    at java.lang.Thread.run(Thread.java:1012)

奇怪的是备份流程完全正常，所有数据都成功上传到云端，唯独通知显示不出来。请问怎么让应用在后台时也能显示这个通知？

相关代码 #

Worker实现代码 #

public class DatabaseCloudBackupWorker extends Worker {
    public static final String TAG = DatabaseCloudBackupWorker.class.getName();

    @Override
    public Result doWork() {
        Result result = Result.failure();

        Log.i(TAG, "Starting Database Backup");
        this.showProgressNotification();

        try {
            uploadData();
            result = Result.success();

        } catch (Exception e) {
            Log.e(TAG, "Error");

        }

        return result;
    }

    private void showProgressNotification() {
        Log.i(TAG, "Showing Database Backup Progress Notification");

        Notification notification = this.newProgressNotification();

        ForegroundInfo foregroundInfo;

        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.Q) {
            foregroundInfo = new ForegroundInfo(PROGRESS_NOTIFICATION_ID, notification, ServiceInfo.FOREGROUND_SERVICE_TYPE_DATA_SYNC);
        } else {
            foregroundInfo = new ForegroundInfo(PROGRESS_NOTIFICATION_ID, notification);
        }

        this.setForegroundAsync(foregroundInfo);

    }

    private Notification newProgressNotification() {
        Notification notification = new NotificationCompat.Builder(MyApp.getAppContext(), MyNotificationManager.CHANNEL_ID)
                .setSmallIcon(R.mipmap.ic_launcher)
                .setOnlyAlertOnce(true)
                .setOngoing(true)
                .setPriority(NotificationCompat.PRIORITY_HIGH)
                .setProgress(0, 0, true)
                .setForegroundServiceBehavior(NotificationCompat.FOREGROUND_SERVICE_IMMEDIATE)
                .setContentTitle("Database Backup")
                .setContentText("Database Backup in Progress")
                .build();

        return notification;
    }
}

Manifest前台服务配置 #

<service
    android:name="androidx.work.impl.foreground.SystemForegroundService"
    android:foregroundServiceType="dataSync"
    tools:node="merge" />

PeriodicWorkRequest创建代码 #

// Creating Work Request
Constraints constraints = new Constraints.Builder().setRequiredNetworkType(NetworkType.UNMETERED).build();
PeriodicWorkRequest workRequest = new PeriodicWorkRequest.Builder(DatabaseCloudBackupWorker.class, 1, TimeUnit.DAYS)
        .setInitialDelay(initialDelayInMinutes, TimeUnit.MINUTES)
        .addTag(DatabaseCloudBackupWorker.TAG_PERIODIC_WORKER)
        .setConstraints(constraints)
        .setInputData(inputData)
        .build();

//
WorkManager workManager = WorkManager.getInstance(MyApp.getAppContext());

Log.i(TAG, "Enqueuing DatabaseCloudBackupWorker");
Operation operation = workManager.enqueueUniquePeriodicWork(DatabaseCloudBackupWorker.NAME_PERIODIC, ExistingPeriodicWorkPolicy.UPDATE, workRequest);

解决方案 #

1. 替换为同步的setForeground方法 #

异步的setForegroundAsync可能导致Worker执行完成后前台服务还未初始化，改用同步方法确保状态生效：

private void showProgressNotification() {
    Log.i(TAG, "Showing Database Backup Progress Notification");

    Notification notification = this.newProgressNotification();

    ForegroundInfo foregroundInfo;

    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.Q) {
        foregroundInfo = new ForegroundInfo(PROGRESS_NOTIFICATION_ID, notification, ServiceInfo.FOREGROUND_SERVICE_TYPE_DATA_SYNC);
    } else {
        foregroundInfo = new ForegroundInfo(PROGRESS_NOTIFICATION_ID, notification);
    }

    try {
        setForeground(foregroundInfo);
    } catch (Exception e) {
        Log.e(TAG, "Failed to set foreground state", e);
    }
}

2. 确保通知渠道与权限配置正确 #

• 备份通知的渠道必须设置为高优先级，避免被系统隐藏：

NotificationChannel channel = new NotificationChannel(CHANNEL_ID, "备份通知", NotificationManager.IMPORTANCE_HIGH);
channel.setDescription("应用数据备份进度通知");
NotificationManager notificationManager = getSystemService(NotificationManager.class);
notificationManager.createNotificationChannel(channel);

• Android 13及以上版本，需动态申请POST_NOTIFICATIONS权限：

if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.TIRAMISU) {
    if (ContextCompat.checkSelfPermission(this, Manifest.permission.POST_NOTIFICATIONS) != PackageManager.PERMISSION_GRANTED) {
        registerForActivityResult(new ActivityResultContracts.RequestPermission(), isGranted -> {
            // 处理权限申请结果
        }).launch(Manifest.permission.POST_NOTIFICATIONS);
    }
}

3. 提前启动前台服务 #

在doWork()方法最开始就调用通知启动逻辑，确保在系统规定的10秒窗口内完成前台服务初始化：

@Override
public Result doWork() {
    Result result = Result.failure();
    try {
        // 优先启动前台通知
        this.showProgressNotification();
        Log.i(TAG, "Starting Database Backup");
        
        uploadData();
        result = Result.success();

        // 备份成功后更新通知
        Notification successNotification = new NotificationCompat.Builder(MyApp.getAppContext(), MyNotificationManager.CHANNEL_ID)
                .setSmallIcon(R.mipmap.ic_launcher)
                .setContentTitle("备份完成")
                .setContentText("数据已成功上传至云端")
                .setPriority(NotificationCompat.PRIORITY_HIGH)
                .setOngoing(false)
                .build();
        setForeground(new ForegroundInfo(PROGRESS_NOTIFICATION_ID, successNotification));
        // 延迟5秒自动取消通知
        new Handler(Looper.getMainLooper()).postDelayed(() -> {
            NotificationManager notificationManager = MyApp.getAppContext().getSystemService(NotificationManager.class);
            notificationManager.cancel(PROGRESS_NOTIFICATION_ID);
        }, 5000);

    } catch (Exception e) {
        Log.e(TAG, "Backup failed", e);
        // 备份失败时更新通知
        Notification failNotification = new NotificationCompat.Builder(MyApp.getAppContext(), MyNotificationManager.CHANNEL_ID)
                .setSmallIcon(R.mipmap.ic_launcher)
                .setContentTitle("备份失败")
                .setContentText("数据上传出错，请稍后重试")
                .setPriority(NotificationCompat.PRIORITY_HIGH)
                .setOngoing(false)
                .build();
        try {
            setForeground(new ForegroundInfo(PROGRESS_NOTIFICATION_ID, failNotification));
        } catch (Exception ex) {
            Log.e(TAG, "Failed to update fail notification", ex);
        }
    }

    return result;
}

4. 更新WorkManager依赖版本 #

使用最新稳定版WorkManager，修复旧版本的后台兼容问题：

// Module级build.gradle
dependencies {
    implementation "androidx.work:work-runtime:2.8.1" // 或更高版本
}

内容的提问来源于stack exchange，提问作者FranKs