Java 从单独的类更新Listview（SharedReferences->；ArrayList）

我想在onPostExecute（）单独类中的fragmen中更新我的Listview

Listview的第一次初始化工作正常，但当我再次调用createList（）时，应用程序崩溃（NullPointerException）

有什么想法吗

主要片段：

  public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState){
            View fragmentView = inflater.inflate(R.layout.main_fragment, container, false);

            StartSocketService = (Button) fragmentView.findViewById(R.id.start_socketservice);
            StartSocketService.setOnClickListener(this);
            StopSocketService = (Button) fragmentView.findViewById(R.id.stop_socketservice);
            StopSocketService.setOnClickListener(this);

            listview = (ListView) fragmentView.findViewById(R.id.listView1);
            createList();

            return fragmentView;
        }

        public void createList(){

            //Reading Server IPs from SharedPreferences and put them to ListView
            SharedPreferences settings = getActivity().getSharedPreferences("Found_Devices", 0);

            for (int i = 0; i < 255; i++) {
                if ((settings.getString("Server"+i,null)) != null) {
                    serverList.add(settings.getString("Server"+i, null));
                    Log.v("Reading IP: " +settings.getString("Server"+i, null), " from SraredPreferrences at pos.: "+i );
                }
            }
            //Initializing listView

            final StableArrayAdapter adapter = new StableArrayAdapter(getActivity(),android.R.layout.simple_list_item_1, serverList);
            listview.setAdapter(adapter);

            listview.setOnItemClickListener(new AdapterView.OnItemClickListener() {

                @TargetApi(Build.VERSION_CODES.JELLY_BEAN)
                @Override
                public void onItemClick(AdapterView<?> parent, final View view, int position, long id) {
                    final String item = (String) parent.getItemAtPosition(position);
                    view.animate().setDuration(2000).alpha(0).withEndAction(new Runnable() {
                        @Override
                        public void run() {
                            serverList.remove(item);
                            adapter.notifyDataSetChanged();
                            view.setAlpha(1);
                        }
                    });
                }

            });
        }

线路：

56 : SharedPreferences settings = getActivity().getSharedPreferences("Found_Devices", 0);
94 : cList.createList();
57: async_cient = new AsyncTask<Void, Void, Void>() {

56:SharedReferences设置=getActivity（）.GetSharedReferences（“找到的设备”，0）；
94:cList.createList（）；
57:async\u cient=新的AsyncTask（）{

您正在创建一个新的片段实例，但没有上下文（活动）可在其中运行 线路

---

尝试获取他的活动，但片段所在的活动不存在；）

您不能在片段的onCreateView（）中使用getActivity（）方法。此时尚未创建活动。请将代码移动到onActivityCreated（）中谢谢。我以为主要活动仍然存在，我不会关闭它。我还不明白…：）从活动中获取片段的实例，然后调用你的方法。谢谢，我还无法解决此问题。你能向我详细解释一下吗？

07-29 14:42:46.428    3382-3382/de.liquidbeam.LED.control D/AndroidRuntime﹕ Shutting down VM
07-29 14:42:46.428    3382-3382/de.liquidbeam.LED.control W/dalvikvm﹕ threadid=1: thread exiting with uncaught exception (group=0x41549ba8)
07-29 14:42:46.438    3382-3382/de.liquidbeam.LED.control E/AndroidRuntime﹕ FATAL EXCEPTION: main
    Process: de.liquidbeam.LED.control, PID: 3382
    java.lang.NullPointerException
            at de.liquidbeam.LED.control.fragments.Main_Fragment.createList(Main_Fragment.java:56)
            at de.liquidbeam.LED.control.background.UDP_Discover$1.onPostExecute(UDP_Discover.java:94)
            at de.liquidbeam.LED.control.background.UDP_Discover$1.onPostExecute(UDP_Discover.java:57)
            at android.os.AsyncTask.finish(AsyncTask.java:632)
            at android.os.AsyncTask.access$600(AsyncTask.java:177)
            at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:645)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:136)
            at android.app.ActivityThread.main(ActivityThread.java:5001)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:515)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:785)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:601)
            at dalvik.system.NativeStart.main(Native Method)
07-29 14:47:46.591    3382-3382/de.liquidbeam.LED.control I/Process﹕ Sending signal. PID: 3382 SIG: 9

56 : SharedPreferences settings = getActivity().getSharedPreferences("Found_Devices", 0);
94 : cList.createList();
57: async_cient = new AsyncTask<Void, Void, Void>() {

SharedPreferences settings = getActivity().getSharedPreferences("Found_Devices", 0);