Android AlarmManager 通知無聲音解決：設置 Notification.defaults

問題

自定義 BroadcastReceiver 發送通知，彈出提示但**無鈴聲、無震動**。

原因

未設置 Notification.defaults，系統不知道使用默認鈴聲/震動/燈光模式。

修正代碼

Notification notification = new NotificationCompat.Builder(context, CHANNEL_ID)
        .setSmallIcon(R.drawable.icon)
        .setContentTitle("ALERT!!!!")
        .setContentText("Time Over")
        .setContentIntent(contentIntent)
        .setDefaults(NotificationCompat.DEFAULT_SOUND | NotificationCompat.DEFAULT_VIBRATE) // 關鍵
        .setPriority(NotificationCompat.PRIORITY_HIGH)
        .build();

可選常量

Android 8.0+ (Oreo) 必須創建 NotificationChannel

if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
    NotificationChannel channel = new NotificationChannel(CHANNEL_ID, "Alarms", NotificationManager.IMPORTANCE_HIGH);
    channel.setDescription("Alarm notifications");
    NotificationManager manager = context.getSystemService(NotificationManager.class);
    manager.createNotificationChannel(channel);
}