fragment中通过getActivity()获取Context空指针

试了好多方法不行；
在onCreateView()中可以获取，然后在onCreateView()中获取，并设置为全局变量，然后在其它方法中使用，可是郁闷的是还报空指针

java.lang.NullPointerException
 at com.weather.weather.activity.WeatherFragment.jointURL(WeatherFragment.java:390)
 at com.weather.weather.activity.MyAsyncTask.onPostExecute(MyAsyncTask.java:99)
 at com.weather.weather.activity.MyAsyncTask.onPostExecute(MyAsyncTask.java:25)
 at android.os.AsyncTask.finish(AsyncTask.java:631)
 at android.os.AsyncTask.access$600(AsyncTask.java:177)
 at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:644)
 at android.os.Handler.dispatchMessage(Handler.java:99)
 at android.os.Looper.loop(Looper.java:137)
 at android.app.ActivityThread.main(ActivityThread.java:5457)
 at java.lang.reflect.Method.invokeNative(Native Method)
 at java.lang.reflect.Method.invoke(Method.java:525)
 at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:879)
 at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:695)
 at dalvik.system.NativeStart.main(Native Method)