Question

我正在开发一个Android应用程序，其中我在一个片段活动中有许多片段。我现在有一个新的片段，里面有一个对fragmentpageradapter的调用。但是，这会抛出空指针异常。有可能这样做吗？

在onPostExecute（AsyncTask）中的片段内： -

DailyForecastPageAdapter adapter = new DailyForecastPageAdapter(Integer.parseInt(forecastDaysNum),getActivity().getChildFragmentManager(), forecastWeather);

我面临问题的天气碎片。

public class WeatherFrag extends Fragment{


private TextView cityText;
private TextView condDescr;
private TextView temp;
//private TextView press;
//private TextView windSpeed;
//private TextView windDeg;
private TextView unitTemp;

//private TextView hum;
private ImageView imgView;

private static String forecastDaysNum = "5";
private ViewPager pager;

public View onCreateView(LayoutInflater inflater, ViewGroup container,
        Bundle savedInstanceState) {

    View rootView = inflater.inflate(R.layout.weather_main, container, false);
    String city = "London, UK";
    String lang = "en";

    cityText = (TextView) getActivity().findViewById(R.id.cityText);
    temp = (TextView) getActivity().findViewById(R.id.temp);
    unitTemp = (TextView) getActivity().findViewById(R.id.unittemp);
    //unitTemp.setText("°C");
    condDescr = (TextView) getActivity().findViewById(R.id.skydesc);

    pager = (ViewPager) getActivity().findViewById(R.id.pager);
    imgView = (ImageView) getActivity().findViewById(R.id.condIcon);
    JSONWeatherTask task = new JSONWeatherTask();
    task.execute(new String[]{city,lang});

    JSONForecastWeatherTask task1 = new JSONForecastWeatherTask();
    task1.execute(new String[]{city,lang, forecastDaysNum});
    return rootView;
}

私有类JSONWeatherTask扩展了AsyncTask {

    @Override
    protected Weather doInBackground(String... params) {
        Weather weather = new Weather();
        String data = ( (new WeatherHttpClient()).getWeatherData(params[0], params[1]));

        try {
            weather = JSONWeatherParser.getWeather(data);
            System.out.println("Weather ["+weather+"]");
            // Let's retrieve the icon
            weather.iconData = ( (new WeatherHttpClient()).getImage(weather.currentCondition.getIcon()));

        } catch (JSONException e) {             
            e.printStackTrace();
        }
        return weather;

}


@Override
protected void onPostExecute(Weather weather) {         
        super.onPostExecute(weather);
        Log.d("Err","Inside Post Exe");
        if (weather.iconData != null && weather.iconData.length > 0) {
            Log.d("Err","Inside Post Exe-if");
            Bitmap img = BitmapFactory.decodeByteArray(weather.iconData, 0, weather.iconData.length); 
            imgView.setImageBitmap(img);

        }

        Log.d("Err","Inside On Post Exe-Out");
        cityText.setText(weather.location.getCity() + "," + weather.location.getCountry());
        temp.setText("" + Math.round((weather.temperature.getTemp() - 275.15)));
        condDescr.setText(weather.currentCondition.getCondition() + "(" + weather.currentCondition.getDescr() + ")");

        /*

        temp.setText("" + Math.round((weather.temperature.getTemp() - 275.15)) + "°C");
        hum.setText("" + weather.currentCondition.getHumidity() + "%");
        press.setText("" + weather.currentCondition.getPressure() + " hPa");
        windSpeed.setText("" + weather.wind.getSpeed() + " mps");
        windDeg.setText("" + weather.wind.getDeg() + "°");
        */  
    }

}

私有类JSONForecastWeatherTask扩展了AsyncTask {

    @Override
    protected WeatherForecast doInBackground(String... params) {

        String data = ( (new WeatherHttpClient()).getForecastWeatherData(params[0], params[1], params[2]));
        WeatherForecast forecast = new WeatherForecast();
        try {
            forecast = JSONWeatherParser.getForecastWeather(data);
            System.out.println("Weather ["+forecast+"]");

            //weather.iconData = ( (new WeatherHttpClient()).getImage(weather.currentCondition.getIcon()));

        } catch (JSONException e) {             
            e.printStackTrace();
        }
        return forecast;

}





@Override
    protected void onPostExecute(WeatherForecast forecastWeather) {         
        super.onPostExecute(forecastWeather);
        Log.d("Err","Reached onpostexe");
        DailyForecastPageAdapter adapter = new DailyForecastPageAdapter(Integer.parseInt(forecastDaysNum),getChildFragmentManager(), forecastWeather);
        Log.d("Err","error before");
        pager.setAdapter(adapter);
    }



  }
}

logcat的

02-20 20:25:51.847: E/AndroidRuntime(5241): FATAL EXCEPTION: main
02-20 20:25:51.847: E/AndroidRuntime(5241): Process: com.akisoft.slidingmenu, PID: 5241
02-20 20:25:51.847: E/AndroidRuntime(5241): java.lang.NullPointerException
02-20 20:25:51.847: E/AndroidRuntime(5241):     at com.akisoft.weather.main.WeatherFrag$JSONWeatherTask.onPostExecute(WeatherFrag.java:94)
02-20 20:25:51.847: E/AndroidRuntime(5241):     at com.akisoft.weather.main.WeatherFrag$JSONWeatherTask.onPostExecute(WeatherFrag.java:1)
02-20 20:25:51.847: E/AndroidRuntime(5241):     at android.os.AsyncTask.finish(AsyncTask.java:632)
02-20 20:25:51.847: E/AndroidRuntime(5241):     at android.os.AsyncTask.access$600(AsyncTask.java:177)
02-20 20:25:51.847: E/AndroidRuntime(5241):     at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:645)
02-20 20:25:51.847: E/AndroidRuntime(5241):     at android.os.Handler.dispatchMessage(Handler.java:102)
02-20 20:25:51.847: E/AndroidRuntime(5241):     at android.os.Looper.loop(Looper.java:136)
02-20 20:25:51.847: E/AndroidRuntime(5241):     at android.app.ActivityThread.main(ActivityThread.java:5017)
02-20 20:25:51.847: E/AndroidRuntime(5241):     at java.lang.reflect.Method.invokeNative(Native Method)
02-20 20:25:51.847: E/AndroidRuntime(5241):     at java.lang.reflect.Method.invoke(Method.java:515)
02-20 20:25:51.847: E/AndroidRuntime(5241):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
02-20 20:25:51.847: E/AndroidRuntime(5241):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
02-20 20:25:51.847: E/AndroidRuntime(5241):     at dalvik.system.NativeStart.main(Native Method)

任何人都可以帮我解决/理解为什么我会获得NPE？我真的只需要它作为片段。

Answer 1

我找到了解决方案。问题是由于我在引用所有textViews时使用了getActivity（），而getChildFragmentManager（）足以创建FragmentPagerAdapter的对象。

而不是getActivity（），我使用了我的视图，即rootView（在我的情况下），这解决了问题。：）

Answer 2

将以下代码移至：

JSONWeatherTask task = new JSONWeatherTask();
task.execute(new String[]{city,lang});

JSONForecastWeatherTask task1 = new JSONForecastWeatherTask();
task1.execute(new String[]{city,lang, forecastDaysNum});

到onActivityCreated或onAtach

可能在Fragment里面有一个FragmentPagerAdapter，它是FragmentActivity的一部分吗？

2 个答案: