片段内的自定义列表不起作用
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【中文标题】片段内的自定义列表不起作用【英文标题】：Custom list inside Fragment not working 【发布时间】：2017-04-11 02:19:06 【问题描述】：我只是在片段中使用了一个自定义列表。我使用 volley 从 api 检索了这些数据。它显示以下错误。我想解决这个问题，有人可以帮助我。
java.lang.NullPointerException: Attempt to invoke virtual method 'com.android.volley.toolbox.ImageLoader com.example.user.ekta.AppController.getImageLoader()' on a null object reference
at com.example.user.ekta.MyBookAdapter.<init>(MyBookAdapter.java:25)
at com.example.user.ekta.FullInfoTabFragment.onCreateView(FullInfoTabFragment.java:85).
这是我的片段类
package com.example.user.ekta;
import android.app.ProgressDialog;
import android.content.Context;
import android.content.Intent;
import android.content.res.TypedArray;
import android.graphics.Canvas;
import android.graphics.drawable.Drawable;
import android.os.Bundle;
import android.support.annotation.Nullable;
import android.support.v4.app.Fragment;
import android.support.v4.content.ContextCompat;
import android.support.v7.widget.DefaultItemAnimator;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;
import android.support.v7.widget.Toolbar;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.MotionEvent;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AdapterView;
import android.widget.ImageView;
import android.widget.ListView;
import android.widget.Toast;
import com.android.volley.Response;
import com.android.volley.VolleyError;
import com.android.volley.VolleyLog;
import com.android.volley.toolbox.JsonArrayRequest;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import java.util.ArrayList;
import java.util.List;
public class FullInfoTabFragment extends Fragment
private static final String EXTRA_SRORT_CARD_MODEL = "EXTRA_SRORT_CARD_MODEL";
// String transitionTag;
private SportCardModel sportCardModel;
private Toolbar toolbar;
private ImageView ivPhoto;
private static final String TAG = FullInfoTabFragment.class.getSimpleName();
private static final String url = "http://myeducationhunt.com/public/schools";
private ProgressDialog pDialog;
private List<MyBook> ourBooksListItems = new ArrayList<MyBook>();
private ListView listView;
private MyBookAdapter adapter;
public static FullInfoTabFragment newInstance(SportCardModel sportCardModel)
FullInfoTabFragment fragment = new FullInfoTabFragment();
Bundle args = new Bundle();
args.putParcelable(EXTRA_SRORT_CARD_MODEL, sportCardModel);
fragment.setArguments(args);
return fragment;
@Override
public void onCreate(Bundle savedInstanceState)
super.onCreate(savedInstanceState);
if (getArguments() != null)
sportCardModel = getArguments().getParcelable(EXTRA_SRORT_CARD_MODEL);
if (savedInstanceState != null)
sportCardModel = savedInstanceState.getParcelable(EXTRA_SRORT_CARD_MODEL);
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState)
View view = inflater.inflate(R.layout.fragment_full_info, container, false);
toolbar = (Toolbar) view.findViewById(R.id.toolbar);
ivPhoto = (ImageView) view.findViewById(R.id.ivPhoto);
listView = (ListView) view.findViewById(R.id.list);
adapter = new MyBookAdapter(getActivity(), ourBooksListItems);
listView.setAdapter(adapter);
listView.setTextFilterEnabled(true);
listView.setOnItemClickListener(new AdapterView.OnItemClickListener()
@Override
public void onItemClick(AdapterView<?> parent, View view, int position, long id)
// OurSchool ourSchool = new OurSchool();
// Intent i = new Intent(getContext(), SchoolDetails.class);
// i.putExtra("id", ourSchoolsListItems.get(position).schoolId);
// i.putExtra("name", ourSchoolsListItems.get(position).schoolName);
// i.putExtra("location", ourSchoolsListItems.get(position).schoolLocation);
// i.putExtra("logo", ourSchoolsListItems.get(position).schoolLogo);
// i.putExtra("email", ourSchoolsListItems.get(position).schoolEmail);
// i.putExtra("website", ourSchoolsListItems.get(position).schoolWebsite);
// i.putExtra("created_at", ourSchoolsListItems.get(position).createdAt);
// i.putExtra("updated_at", ourSchoolsListItems.get(position).updatedAt);
// startActivity(i);
);
pDialog = new ProgressDialog(getActivity());
// Showing progress dialog before making http request
pDialog.setMessage("Loading…");
pDialog.show();
// Creating volley request obj
JsonArrayRequest schoolRequest = new JsonArrayRequest(url,
new Response.Listener<JSONArray>()
@Override
public void onResponse(JSONArray response)
Log.d(TAG, response.toString());
pDialog.hide();
// Parsing json
for (int i = 0; i < response.length(); i++)
try
JSONObject obj = response.getJSONObject(i);
MyBook myBook = new MyBook();
myBook.bookName = obj.getString("name");
myBook.bookAuthor = obj.getString("location");
myBook.bookCover= obj.getString("logo");
// adding schools to ourSchool list
ourBooksListItems.add(myBook);
catch (JSONException e)
e.printStackTrace();
adapter.notifyDataSetChanged();
, new Response.ErrorListener()
@Override
public void onErrorResponse(VolleyError error)
VolleyLog.d(TAG, "Error: " + error.getMessage());
pDialog.hide();
);
// Adding request to request queue
AppController.getInstance().addToRequestQueue(schoolRequest);
return view;
@Override
public void onViewCreated(View view, @Nullable Bundle savedInstanceState)
super.onViewCreated(view, savedInstanceState);
toolbar.setTitle(sportCardModel.getSportTitle());
toolbar.setNavigationIcon(R.drawable.ic_back);
toolbar.setNavigationOnClickListener(new View.OnClickListener()
@Override
public void onClick(View view)
getActivity().onBackPressed();
);
toolbar.setBackgroundColor(ContextCompat.getColor(getContext(), sportCardModel.getBackgroundColorResId()));
ivPhoto.setImageResource(sportCardModel.getImageResId());
@Override
public void onSaveInstanceState(Bundle outState)
outState.putParcelable(EXTRA_SRORT_CARD_MODEL, sportCardModel);
super.onSaveInstanceState(outState);
static class DividerItemDecoration extends RecyclerView.ItemDecoration
private static final int[] ATTRS = new int[]android.R.attr.listDivider;
private Drawable mDivider;
/**
* Default divider will be used
*/
public DividerItemDecoration(Context context)
final TypedArray styledAttributes = context.obtainStyledAttributes(ATTRS);
mDivider = styledAttributes.getDrawable(0);
styledAttributes.recycle();
/**
* Custom divider will be used
*/
public DividerItemDecoration(Context context, int resId)
mDivider = ContextCompat.getDrawable(context, resId);
@Override
public void onDraw(Canvas c, RecyclerView parent, RecyclerView.State state)
int left = parent.getPaddingLeft();
int right = parent.getWidth() - parent.getPaddingRight();
int childCount = parent.getChildCount();
for (int i = 0; i < childCount; i++)
View child = parent.getChildAt(i);
RecyclerView.LayoutParams params = (RecyclerView.LayoutParams) child.getLayoutParams();
int top = child.getBottom() + params.bottomMargin;
int bottom = top + mDivider.getIntrinsicHeight();
mDivider.setBounds(left, top, right, bottom);
mDivider.draw(c);
这是我的适配器类
package com.example.user.ekta;
import android.app.Activity;
import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.TextView;
import com.android.volley.toolbox.ImageLoader;
import com.android.volley.toolbox.NetworkImageView;
import java.util.List;
/**
* Created by user on 11/27/2016.
*/
public class MyBookAdapter extends BaseAdapter
private Activity activity;
private LayoutInflater inflater;
private List<MyBook> ourbooksList;
ImageLoader imageLoader = AppController.getInstance().getImageLoader();
public MyBookAdapter(Activity activity, List<MyBook> ourbooksListsList)
this.activity = activity;
this.ourbooksList = ourbooksListsList;
@Override
public int getCount()
return ourbooksList.size();
@Override
public Object getItem(int location)
return ourbooksList.get(location);
@Override
public long getItemId(int position)
return position;
@Override
public View getView(int position, View convertView, ViewGroup parent)
if (inflater == null)
inflater = (LayoutInflater) activity
.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
if (convertView == null)
convertView = inflater.inflate(R.layout.list_books, null);
if (imageLoader == null)
imageLoader = AppController.getInstance().getImageLoader();
NetworkImageView bookCover = (NetworkImageView) convertView
.findViewById(R.id.bookCover);
TextView bookName = (TextView) convertView.findViewById(R.id.bookName);
TextView boookAuthor = (TextView) convertView.findViewById(R.id.bookAuthor);
MyBook m = ourbooksList.get(position);
bookCover.setImageUrl(m.getBookCover(), imageLoader);
bookName.setText("Name: " + m.getBookName());
boookAuthor.setText("Address: " + String.valueOf(m.getBookAuthor()));
return convertView;
【问题讨论】：
显示你的 AppController 代码 根据错误，您的单例正在引起问题。它为空，您在 AppController.getInstance() 上调用 getImageLoader() 时会崩溃 谢谢 rahul。我的错误已修复 【参考方案1】：AppController.getInstance() 返回 null，你还没有初始化你的 Appcontroller。
如果 AppController 扩展了您的应用程序，那么您必须更改清单
android:name=“appController 的路径”在应用部分。
【讨论】：
哦我忘了。我犯了一个愚蠢的错误。非常感谢你提醒我以上是关于片段内的自定义列表不起作用的主要内容，如果未能解决你的问题，请参考以下文章