Question

我试图绑定服务和活动，以便我可以设置服务来获取时间并将其呈现在活动上。但该计划报告的错误为：

public void startTimeService(View v){
    startService(intent);
    Log.d(tag,"--startTimeService--");
      bindService(intent, con, Service.BIND_AUTO_CREATE);
        Log.d(tag,"post--startTimeService")**;
        tv.setText("current time is：/n"+mBinder.getService().getTime());

运行该程序可以获取日志： - startTimeService--并post-startTimeService，但仍然报告错误：

07-13 08：23：19.832：E / AndroidRuntime（3217）：引起：java.lang。 NullPointerException ：尝试调用虚方法＆＃39; com.himanmin .xu.servicedemo.TimeService com.himanmin.xu.servicedemo.TimeService $ MyBinder.getService（）＆＃39;在空对象引用上

代码TimeService.java如下：

 public class TimeService extends Service {
    private final String tag = "TimeService";
    private int state;
    private int count;
    private boolean quit;

    public class MyBinder extends Binder{
        public TimeService getService(){
            Log.d(tag,"--getService()");
            return TimeService.this;
        }
    }

    private MyBinder mBinder = new MyBinder();

    public int getState(){
        //get the state of service
        Log.d(tag,"--getState()");
        return state;
    }

    public String getTime(){
        Log.d(tag,"--getTime()");
        SimpleDateFormat dateFormat24 = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");  
        //12 format 
        //SimpleDateFormat dateFormat12 = new SimpleDateFormat("yyyy-MM-dd hh:mm:ss");  
        return dateFormat24.format(Calendar.getInstance().getTime());
    }

    public int getCount(){
        Log.d(tag,"--getCount()");
        return count;
    }
    @Override
    public IBinder onBind(Intent intent) {
        // TODO Auto-generated method stub
        Log.d(tag,"--onBind");
        System.out.println("Service is Binded");
        return mBinder;
    }

    @Override
    public void onCreate(){
        super.onCreate();
        Log.d(tag,"--onCreate");**
        System.out.println("Service for time is created");
        count = (int) System.currentTimeMillis();
    }
    @Override
    public boolean onUnbind(Intent intent){
        Log.d(tag,"--onUnbind");
        System.out.println("Serveice is unbinded");
        count = (int) (System.currentTimeMillis() - count);
        return true;
    }

    @Override
    public void onDestroy(){
        super.onDestroy();
        Log.d(tag,"--onDestroy");
        this.quit = true;
        System.out.println("Service for time is destoryed");
        count = (int) (System.currentTimeMillis() - count);
    }
}

运行bindService（）后，将调用onCreate（）类的方法TimeService，它应该是logcat --onCreate，但是没有这样的日志，taht意味着 bindService(intent, con, Service.BIND_AUTO_CREATE)没有跑。我无法弄清楚原因。 intent和mainfest.xml如下：

private final String serviceAction = "com.himanmin.xu.servicedemo.TIME_SERVICE";

intent = new Intent();
intent.setAction(serviceAction);

<service android:name = "com.himanmin.xu.servicedemo.TimeService">
            <intent-filter>
                <action android:name="com.himanmin.xu.servicedemo.TIME_SERVICE"/>
            </intent-filter>
        </service>

你能帮助我解决问题吗？

Answer 1

问题似乎是服务需要时间才能启动。当你打电话：

bindService(intent, con, Service.BIND_AUTO_CREATE);

该方法将触发一个intent并立即返回。然后Android系统将在最短的可用时间启动您的服务。因此，当您致电：

tv.setText("current time is：/n"+mBinder.getService().getTime());

您的服务尚未启动，这就是您获得空指针异常的原因。

要解决此问题，您必须按照Android Bound Services doc page中的说明实现服务连接（稍微修改以适合您的情况）：

/** Defines callbacks for service binding, passed to bindService() */
private ServiceConnection mConnection = new ServiceConnection() {

    @Override
    public void onServiceConnected(ComponentName className,
            IBinder service) {
        // We've bound to LocalService, cast the IBinder and get LocalService instance
        mBinder = (MyBinder) service;
        tv.setText("current time is：/n"+mBinder.getService().getTime());
        mBound = true;
    }

    @Override
    public void onServiceDisconnected(ComponentName arg0) {
        mBound = false;
    }
};

只有在调用onServiceConnected方法并且mBound设置为true后才能使用mBinder对象。

bindService（）使用NullPointerException

1 个答案: