java - 当它被服务调用时，在 AsycTask 中的 Handler 中的 Toast 上获取 NullPointerException

Question

当我使用应用程序时，我开始知道在 AsycTask 中我不能直接使用 Toast，除非它是一个处理程序。所以对于处理程序，到目前为止它工作正常。 Toast 作为处理程序如下

private void threadMsg(String msg) {

        if (!msg.equals(null) && !msg.equals("")) {
            Message msgObj = handler.obtainMessage();
            Bundle b = new Bundle();
            b.putString("message", msg);
            msgObj.setData(b);
            handler.sendMessage(msgObj);
        }
}

private final Handler handler = new Handler() {

        public void handleMessage(Message msg) {

            String aResponse = msg.getData().getString("message");

            if ((null != aResponse)) {
                // ALERT MESSAGE
                Toast.makeText(
                        getBaseContext(),
                        "Server Response: " + aResponse,
                        Toast.LENGTH_SHORT).show();
                progressBarHolder.setVisibility(View.INVISIBLE);
            }
            else
            {

                // ALERT MESSAGE
                Toast.makeText(
                        getBaseContext(),
                        "Not Got Response From Server.",
                        Toast.LENGTH_SHORT).show();
            }
        }
};

我只是在我的 AsycTask 中调用 threadMsg("Message"); 并且它工作正常。但是在我的新要求中，我碰巧从服务中调用了 AsycTask。当我执行它时，我在 Toast 上遇到空指针异常。
我不明白在这种情况下发生了什么。请帮我解决这个问题。

编辑:我正在执行 AsycTask 的服务代码

public class FirstService extends Service {

   TayKitDatabaseOpenHelper db = new TayKitDatabaseOpenHelper(this);
   private MyApplication app;
   /** indicates how to behave if the service is killed */
   int mStartMode;

   /** interface for clients that bind */
   IBinder mBinder;

   /** indicates whether onRebind should be used */
   boolean mAllowRebind;

   /** Called when the service is being created. */
   @Override
   public void onCreate() {
     app = (MyApplication) getApplication();
     AsycInvokerActivity.OrderDeliveryAsyTask sm=new  
     AsycInvokerActivity().new OrderDeliveryAsyTask(orderDelivered);
     sm.execute();
   }
   public void onStart(Intent intent, int startId) {
      System.out.println("insuide service omstart");

   }

   /** The service is starting, due to a call to startService() */
   @Override
   public int onStartCommand(Intent intent, int flags, int startId) {
      System.out.println("inside FirstServece's onStartCommand");
      List<OrderDeliveryModel> deliveredOrders =   
      db.getAllDeliveredOrdersByUserId(app.getPudoType());
      System.err.println("Total Number or orders which has to be synced: 
      "+deliveredOrders.size());

      return mStartMode;
   }

   /** A client is binding to the service with bindService() */
   @Override
   public IBinder onBind(Intent intent) {
     return mBinder;
   }

   /** Called when all clients have unbound with unbindService() */
   @Override
   public boolean onUnbind(Intent intent) {
     return mAllowRebind;
   }

   /** Called when a client is binding to the service with bindService()*/
   @Override
   public void onRebind(Intent intent) {

   }

   /** Called when The service is no longer used and is being destroyed */
   @Override
   public void onDestroy() {

   }
 }

编辑:堆栈跟踪

java.lang.NullPointerException
        at android.widget.Toast.<init>(Toast.java:92)
        at android.widget.Toast.makeText(Toast.java:233)
        at com.example.databaseUtils.offlineDataUtils.AsycInvokerActivity$OrderDeliveryAsyTask$1.run(AsycInvokerActivity.java:174)
        at android.os.Handler.handleCallback(Handler.java:605)
        at android.os.Handler.dispatchMessage(Handler.java:92)
        at android.os.Looper.loop(Looper.java:137)
        at android.app.ActivityThread.main(ActivityThread.java:4441)
        at java.lang.reflect.Method.invokeNative(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:511)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:823)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:590)
        at dalvik.system.NativeStart.main(Native Method)

Answer 1

问题是服务没有运行 n UI 线程。您可以通过 Activity 显示 Toast:

@Override
public void onCreate() {
    super.onCreate();
    mHandler = new Handler();
}
@Override
protected void onHandleIntent(Intent intent) {
    mHandler.post(new Runnable() {            
        @Override
        public void run() {
            Toast.makeText(MyIntentService.this, 
                "Hello Toast!", Toast.LENGTH_LONG).show();                
        }
    });
}