Duplicata Possível:
O Android Toast iniciado a partir do Serviço é exibido apenas uma vez

Estou usando o serviço Android definido em android.app.Service.

Eu chamo este serviço (myService) de uma atividade.

O MyService é:

public class myService extends Service{

 public IBinder onBind(Intent intent){
    return null;
}

public void onCreate(){
    super.onCreate();
    TimerTask task = new TimerTask(){
        public void run(){
            Log.i("test","service running");
            checkDate();            
        }           
    };
    timer = new Timer();
    timer.schedule(task, 0, 20000);
}

 public void checkDate(){
    Toast toast = Toast.makeText(this, "SIMPLE MESSAGE!", Toast.LENGTH_LONG);
    toast.show();
}

}

O método checkDate () reside na classe myService.

O erro produzido é:

 09-19 15:41:35.267: E/AndroidRuntime(2026): FATAL EXCEPTION: Timer-0
 09-19 15:41:35.267: E/AndroidRuntime(2026): java.lang.RuntimeException: Can't create handler inside thread that has not called Looper.prepare()
 09-19 15:41:35.267: E/AndroidRuntime(2026):    at android.os.Handler.<init>(Handler.java:121)
 09-19 15:41:35.267: E/AndroidRuntime(2026):    at android.widget.Toast$TN.<init>(Toast.java:310)
 09-19 15:41:35.267: E/AndroidRuntime(2026):    at android.widget.Toast.<init>(Toast.java:84)
 09-19 15:41:35.267: E/AndroidRuntime(2026):    at android.widget.Toast.makeText(Toast.java:226)