当我尝试通知某事时出现空错误

Question

大家好，我刚开始使用 Android，我正在尝试从与我的主要活动不同的类发出通知。但是 e.printStackTrace() 说“null”并停在以下行：“NotificationManager notificationManager = (NotificationManager) getSystemService(NOTIFICATION_SERVICE);”如果我从 mainActivity 发出相同的通知，一切顺利。你能帮我吗？

if(giorni_di_differenza <= 15)
{

    try{
        PendingIntent pi = PendingIntent.getActivity(context, 0, new Intent(android.provider.Settings.ACTION_LOCATION_SOURCE_SETTINGS), 0);
        NotificationCompat.Builder n = new NotificationCompat.Builder(context)
            .setContentTitle(nome_evento)
            .setContentText(descrizione_evento)
            .setContentIntent(pi)
            .setAutoCancel(true)
            .setLights(Color.GREEN, 1000, 1000)
            .setSmallIcon(R.drawable.ic_launcher);

        NotificationManager notificationManager = (NotificationManager) getSystemService(NOTIFICATION_SERVICE);

        notificationManager.notify(0, n.build());

    }catch(Exception e){
        e.printStackTrace();
    }
}

如果您需要更多代码，我可以发给您。

LogCat:http://pastebin.com/W4hKbf6W（Pause GC错误是三星库存ROM的错误）

Answer 1

您需要Context 才能从外部Activity 访问NotificationManager

    NotificationManager notificationManager = (NotificationManager) context.getSystemService(NOTIFICATION_SERVICE);

而且你的logcat也清楚地说

java.lang.IllegalStateException：系统服务不可用于 onCreate()之前的活动

只有在onCreate() 或Activity 之后才能访问NotificationManager

Answer 2

是的，因为它在您的课程中找不到上下文：

NotificationManager nm = (NotificationManager) context.getSystemService(Context.NOTIFICATION_SERVICE);

这样做：

或

//pass different id for different notifications
private void showNotification(Context con, int notificationID) {
    if(giorni_di_differenza <= 15)
    {

        try{
            PendingIntent pi = PendingIntent.getActivity(con, 0, new Intent(android.provider.Settings.ACTION_LOCATION_SOURCE_SETTINGS), 0);
            NotificationCompat.Builder n = new NotificationCompat.Builder(con)
                .setContentTitle(nome_evento)
                .setContentText(descrizione_evento)
                .setContentIntent(pi)
                .setAutoCancel(true)
                .setLights(Color.GREEN, 1000, 1000)
                .setSmallIcon(R.drawable.ic_launcher);
        NotificationManager notificationManager = (NotificationManager) con.getSystemService(NOTIFICATION_SERVICE);

        notificationManager.notify(notificationID, n.build());

    }catch(Exception e){
        e.printStackTrace();
    }
}
}