IntentService调用AsyncTask的问题

我创造了IntentService课堂和表演asyncTask但出现异常时onPreExecute()在此代码行调用pDialog.show();

AsyncHandlerService类---

public class AsyncHandlerService extends IntentService{
ProgressDialog pDialog;
HttpPost post;
HttpResponse response;
Context ctx;

public AsyncHandlerService() {
    super("AsyncHandlerService");
    ctx = this;
}

@Override
protected void onHandleIntent(Intent intent) {
    new LoadDeviceInfo().execute();   
}


class LoadDeviceInfo extends AsyncTask<String, String, String> {

@Override
protected void onPreExecute() {
    super.onPreExecute();
    pDialog = new ProgressDialog(ctx);
    pDialog.setMessage("Updating device info...");
    pDialog.setIndeterminate(false);
    pDialog.setCancelable(false);
    pDialog.show(); //Exception here..
}

protected String doInBackground(String... args) {
}

protected void onPostExecute(String file_url) {
    pDialog.dismiss();
}

UPDATE:

我正在打电话IntentService在具有意图过滤器的广播接收器中android.intent.action.PACKAGE_REPLACED在 android 清单中定义。代码 - -

public class OnUpgradeBroadcastReceiver extends BroadcastReceiver {
Context activity;
@Override
    public void onReceive(final Context context, final Intent intent) {
         activity = context;
         Intent msgIntent = new Intent(activity, AsyncHandlerService.class);
            activity.startService(msgIntent);
    }
}

错误日志：

com.testapp.main fatal error : Unable to add window -- 
token null is not for an application
android.view.WindowManager$BadTokenException: Unable to add window -- 
token null is not for an application
at android.view.ViewRootImpl.setView(ViewRootImpl.java:588)
at android.view.WindowManagerImpl.addView(WindowManagerImpl.java:326)
at android.view.WindowManagerImpl.addView(WindowManagerImpl.java:224)
at android.view.WindowManagerImpl$CompatModeWrapper.
addView(WindowManagerImpl.java:149)
at android.app.Dialog.show(Dialog.java:277)
at com.testapp.main.AsyncHandlerService$LoadDeviceInfo.
onPreExecute(AsyncHandlerService.java:62)
at android.os.AsyncTask.executeOnExecutor(AsyncTask.java:586)
at android.os.AsyncTask.execute(AsyncTask.java:534)

First, IntentService已经使用后台线程。你不需要another后台线程。做需要在后台完成的工作onHandleIntent().

Second, a Service无法显示Dialog。相反，让应用程序的 UI 层知道工作是通过事件总线上的消息完成的（例如，LocalBroadcastManager、greenrobot 的 EventBus、Square 的 Otto）。如果 UI 层不处理该事件，您的服务可以引发Notification或者以其他方式让用户了解已完成的工作（如果需要）。