我正在尝试以下代码,其中一个服务正在实现我的监听器：

public class MyListenerClass extends Service implements MyListenerInterface {

public void onCurrencyRecieved(MyEventClass event) {

System.out.println("Coins Recieved - Listener Successful");

stopSelf();

Toast toast = Toast.makeText(getApplicationContext(),"Service Stopped",Toast.LENGTH_LONG);

toast.show();

}

@Override

public void onCreate() {

Toast toast = Toast.makeText(getApplicationContext(),"Service started",Toast.LENGTH_LONG);

toast.show();

super.onCreate();

}

现在,onCreate()内部的toast工作正常,但是在重写方法内部抛出以下异常：

01-03 18:52:35.740: ERROR/AndroidRuntime(2388): java.lang.NullPointerException

01-03 18:52:35.740: ERROR/AndroidRuntime(2388): at android.content.ContextWrapper.getApplicationContext(ContextWrapper.java:100)

01-03 18:52:35.740: ERROR/AndroidRuntime(2388): at com.test.listenertest1.MyListenerClass.onCurrencyRecieved(MyListenerClass.java:28)

01-03 18:52:35.740: ERROR/AndroidRuntime(2388): at com.test.listenertest1.MyEventGenerator.generateEvent(MyEventGenerator.java:34)

01-03 18:52:35.740: ERROR/AndroidRuntime(2388): at com.test.listenertest1.MyEventGenerator.(MyEventGenerator.java:16)

01-03 18:52:35.740: ERROR/AndroidRuntime(2388): at com.test.listenertest1.NewActivity.onKeyDown(NewActivity.java:33)

01-03 18:52:35.740: ERROR/AndroidRuntime(2388): at android.view.KeyEvent.dispatch(KeyEvent.java:1037)

01-03 18:52:35.740: ERROR/AndroidRuntime(2388): at android.app.Activity.dispatchKeyEvent(Activity.java:2046)

01-03 18:52:35.740: ERROR/AndroidRuntime(2388): at com.android.internal.policy.impl.PhoneWindow$DecorView.dispatchKeyEvent(PhoneWindow.java:1631)

01-03 18:52:35.740: ERROR/AndroidRuntime(2388): at android.view.ViewRoot.deliverKeyEventToViewHierarchy(ViewRoot.java:2368)

01-03 18:52:35.740: ERROR/AndroidRuntime(2388): at android.view.ViewRoot.handleFinishedEvent(ViewRoot.java:2338)

01-03 18:52:35.740: ERROR/AndroidRuntime(2388): at android.view.ViewRoot.handleMessage(ViewRoot.java:1641)

01-03 18:52:35.740: ERROR/AndroidRuntime(2388): at android.os.Handler.dispatchMessage(Handler.java:99)

我想我错过了一些重要的java概念.我们不能在重写方法中使用getApplicationContext()吗？