Question

我正在尝试将 jsr-179 APi 实现到诺基亚 Symbian 手机中，以便通过 J2me 使用 setLocationListener 进行定期位置更新。在模拟器中它工作正常。当我在诺基亚 5230 设备上安装 Midlet 时，出现 NullPointerException 并且应用程序自动终止。可能的原因有哪些？

下面是我的类，我正在 netbeans 的表单上实例化该类的对象

class MovementTracker implements LocationListener {

        LocationProvider provider;
        Location lastValidLocation;
        UpdateHandler handler;
        boolean done;

    public MovementTracker() throws LocationException
    {

    done = false;
    handler = new UpdateHandler();
    new Thread(handler).start();

        //Defining Criteria for Location Provider
       /*
        Criteria cr = new Criteria();
        cr.setHorizontalAccuracy(500);
       */


        //you can place cr inside getInstance
    provider = LocationProvider.getInstance(null);

        //listener,interval,timeout,int maxAge
        //Passing -1 selects default interval
       // provider.setLocationListener(MovementTracker.this, -1, -1, -1);
         provider.setLocationListener(MovementTracker.this, -1, 30000, 30000);

    }

    public void locationUpdated(LocationProvider provider, Location location)
    {
    handler.handleUpdate(location);
        batteryLevel = System.getProperty("com.nokia.mid.batterylevel");
        sn = System.getProperty("com.nokia.mid.networksignal");
        localTime =  System.currentTimeMillis();

        Send_Location();
    }

    public void providerStateChanged(LocationProvider provider, int newState)
    {
    }

    class UpdateHandler implements Runnable
    {
    private Location updatedLocation = null;

    // The run method performs the actual processing of the location

    public void run()
        {
        Location locationToBeHandled = null;
        while (!done)
            {
        synchronized(this)
                {
            if (updatedLocation == null)
                    {
            try
                        {
                wait();
            }
                        catch (Exception e)
                        {
                // Handle interruption
            }
            }
            locationToBeHandled = updatedLocation;
            updatedLocation = null;
        }

        // The benefit of the MessageListener is here.
        // This thread could via similar triggers be
        // handling other kind of events as well in
        // addition to just receiving the location updates.
        if (locationToBeHandled != null)
            processUpdate(locationToBeHandled);
        }
                try
                {
                    Thread.sleep(10000); //Sleeps for 10 sec & then sends the data
                }
                catch (InterruptedException ex)
                {
                }


    }

    public synchronized void handleUpdate(Location update)
        {
        updatedLocation = update;
        notify();
    }

    private void processUpdate(Location update)
        {
        latitude = update.getQualifiedCoordinates().getLatitude();
            longitude = update.getQualifiedCoordinates().getLongitude();
            altitude = update.getQualifiedCoordinates().getAltitude();

    }
    }
} 

Answer 1

public MovementTracker() 抛出 LocationException

...
我没有编写任何处理 LocationException 的代码。

没有代码是非常危险的做法，只需在网络上搜索“java咽下异常”之类的内容即可。

由于实现细节，诺基亚很可能会抛出 LocationException，而模拟器不会抛出它。由于您不处理异常，这确实可能会使您在诺基亚的 midlet 崩溃 - 并且您不会知道其原因，因为您没有编写任何代码来处理它。

如何捕获该异常？

您可以做的最简单的事情是显示带有异常消息的警报，并在用户阅读并消除警报后退出 midlet