在我的应用程序中，我有MainActivity（扩展Fragment活动），topButtons独立于mPagerView（例如：AddButton），内部有碎片的PagerView。我想做的是：
1）下载一些内容（新活动开始，然后在activityResult上完成获取信息）
2）创建新对象并将其添加到ViewPager中Fragment内的listView。
3）在向列表添加新元素后，在PagerView中的Fragment内刷新listView。
我得到了什么：
1）成功下载文件并创建对象并将其添加到列表
问题：
1）当我想刷新listview时，我得到的错误如下：......中的NullPointerException
代码在这里：
在PagerView中找到我的目标片段：
Fragment frag = mAdapter.getItem(position);
if(position == 1)
{
((KwejkFragment) frag).notifyNewInsertedData();
}
尝试在目标片段（我的方法）中使用此方法刷新lisview：
public void notifyNewInsertedData()
{
this.adapter.notifyDataSetChanged(); //App crashes here telling me that I have a null pointerException. List is created on activityStarted and is not null.
}
在这里我得到了一个错误：
02-15 15:02:27.833: E/AndroidRuntime(31310): Caused by: java.lang.NullPointerException
02-15 15:02:27.833: E/AndroidRuntime(31310): at pl.app.fragments.KwejkFragment.notifyNewInsertedData(KwejkFragment.java:340)
02-15 15:02:27.833: E/AndroidRuntime(31310): at pl.engine.main.MainActivity.onActivityResult(MainActivity.java:630)
02-15 15:02:27.833: E/AndroidRuntime(31310): at android.app.Activity.dispatchActivityResult(Activity.java:3908)
02-15 15:02:27.833: E/AndroidRuntime(31310): at android.app.ActivityThread.deliverResults(ActivityThread.java:2549)
02-15 15:02:27.833: E/AndroidRuntime(31310): ... 11 more
有什么问题？如何解决这个问题？我究竟做错了什么？所有列表都存储在GlobalApplication类中。我在创建片段时指向它们并获取此列表。
更新：
public class KwejkFragment extends Fragment{
private static ArrayList<GifModel> list = null; //BASIC PROGRAM LIST
private static ListView listView;
private static List<GifModel> sortingList;
private AlertDialog.Builder dialog;
private DataBaseManager dataBaseManager;
private Handler handler;
private ListAdapter adapter;
private String sprawdzenie;
///////// VARIABLES HERE////////
private boolean useAnimations = false;
private int animationSpinnerPosition;
private String fragmentTag;
public KwejkFragment(String tagName,String sprawdzenie)
{
this.fragmentTag = tagName;
this.sprawdzenie = sprawdzenie;
}
public String sprawdzenie()
{
return sprawdzenie;
}
public String getTagName()
{
return this.fragmentTag;
}
public void refresh(){};
@Override
public void onActivityCreated(Bundle savedInstanceState) {
// TODO Auto-generated method stub
super.onActivityCreated(savedInstanceState);
getSharedPreferences();
//setHandler();
GlobalApplication globalApp = (GlobalApplication) getActivity().getApplication();
list = globalApp.getKwejkList();
adapter = new ListAdapter(getActivity(), R.id.list_item, list, useAnimations, animationSpinnerPosition);
}
@Override
public String toString() {
// TODO Auto-generated method stub
return fragmentTag;
}
@Override
public void onDestroy() {
// TODO Auto-generated method stub
super.onDestroy();
//dataBaseManager.close();
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.kwejkpl_layout, container, false);
listView = (ListView) view.findViewById(R.id.listViewKwejk);
// list = new ArrayList<GifModel>();
// list.add(new GifModel());
// adapter = new ListAdapter(getActivity(), R.id.list_item,list, useAnimations, animationSpinnerPosition);
// if(adapter == null)
// System.out.println("ADAPTER YEST NULL");
listView.setAdapter(adapter);
// TODO Auto-generated method stubl
//prepareDataBase();
//list = dataBaseManager.getAllGifs();
//Log.i("!!!!!!!",""+ list.size());
setUpView();
//adapter.notifyDataSetChanged();
return view;
}
public void createNewItems(String name,int rating)
{
GifModel gif = new GifModel();
gif.setNameOfItem(name);
gif.setRating(rating);
list.add(gif);
System.out.println(list.size());
//System.out.println("Is adapter null:"+ adapter.isEmpty());
adapter = new ListAdapter(getActivity(), R.id.list_item, list, useAnimations, animationSpinnerPosition);
listView.setAdapter(adapter);
adapter.notifyDataSetChanged();
}
@Override
public void onResume() {
// TODO Auto-generated method stub
// Thread a = new Thread(new Runnable() {
//
// @Override
// public void run() {
// list = dataBaseManager.getAllGifs();
// handler.sendEmptyMessage(1);
// //System.out.println(list.size());
// }
// });
// a.start();
super.onResume();
adapter.notifyDataSetChanged();
}
@Override
public void onDestroyView() {
// TODO Auto-generated method stub
//dataBaseManager.close();
super.onDestroyView();
}
public void prepareDataBase()
{
// if(ifAppWorks)
// {
// dataBaseManager.close();
// }
dataBaseManager = new DataBaseManager(getActivity());
dataBaseManager.open();
System.out.println("has connection?:" + dataBaseManager.isOpen());
}
private void setHandler()
{
handler = new Handler() {
@Override
public void handleMessage(Message msg) {
if(msg.what == 1)
{
adapter = new ListAdapter(getActivity(), R.layout.list_item, list, useAnimations, animationSpinnerPosition);
listView.setAdapter(adapter);
adapter.notifyDataSetChanged();
}
}
};
}
private void getSharedPreferences()
{
SharedPreferences preferences = getActivity().getSharedPreferences(Tools.PREFS_NAME,Activity.MODE_PRIVATE);
useAnimations = preferences.getBoolean("animation", false);
animationSpinnerPosition = preferences.getInt("animationPosition", 0);
}
private void setUpView(){
dialog = new AlertDialog.Builder(getActivity());
listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> parent, final View view, int position, long id) {
System.out.println(list.get(position).getCoverUrl());
System.out.println("link pozycji");
//GlobalApplication app = (GlobalApplication) getApplication();
if(list.get(position).getCoverUrl().contains("http://i1.ytimg") || list.get(position).getCoverUrl().contains("http://www.youtube.com/embed"))
{
Intent intent = new Intent(getActivity(), MovieShow.class);
//System.out.println(list.get(position).getUrl());
intent.putExtra("youtubeLink", list.get(position).getUrl());
System.out.println(list.get(position).getUrl());
intent.putExtra("header", list.get(position).getNameOfIteme());
intent.putExtra("contentlink", list.get(position).getMainLinkToTheContent());
System.out.println(list.get(position).getUrl());
//overridePendingTransition(R.anim.trans_left_in,R.anim.trans_left_out);
System.out.println(list.get(position).getUrl());
startActivity(intent);
// if(app.getIfAnimationsOrNot())
// overridePendingTransition(R.anim.trans_left_in,R.anim.trans_left_out);
}
else if((list.get(position).getCoverUrl().contains("jpg")) || (list.get(position).getCoverUrl().contains("png")) ||
(list.get(position).getCoverUrl().contains("jpeg")))
{
Intent intent = new Intent(getActivity(), ImageShow.class);
intent.putExtra("imageUrl", list.get(position).getUrl());
intent.putExtra("header", list.get(position).getNameOfIteme());
intent.putExtra("contentlink", list.get(position).getMainLinkToTheContent());
startActivity(intent);
// if(app.getIfAnimationsOrNot())
// overridePendingTransition(R.anim.trans_left_in,R.anim.trans_left_out);
}
else
{
// Intent intent = new Intent(MainActivity.this, GifAnimationClass.class);
// intent.putExtra("gifAdress", list.get(position).getUrl());
// System.out.println(list.get(position).getUrl());
// startActivity(intent);
Intent intent = new Intent(getActivity(), GifPlay.class);
intent.putExtra("webUrl", list.get(position).getUrl());
intent.putExtra("header", list.get(position).getNameOfIteme());
intent.putExtra("contentlink", list.get(position).getMainLinkToTheContent());
//overridePendingTransition(R.anim.trans_left_in,R.anim.trans_left_out);
startActivity(intent);
// if(app.getIfAnimationsOrNot())
// overridePendingTransition(R.anim.trans_left_in,R.anim.trans_left_out);
// //overridePendingTransition(R.anim.trans_left_in,R.anim.trans_left_out);
}
}
});
}
public void notifyNewInsertedData()
{
this.adapter.notifyDataSetChanged();
}
}
答案 0 :(得分：1)
我认为您的适配器为null。尝试在片段的onStart方法中初始化它。
@Override
public void onStart() {
adapter = new ListAdapter(getActivity(), R.id.list_item, list, useAnimations, animationSpinnerPosition);
}