Java 片段中的列表视图空指针异常
我试图在片段中设置滑动以刷新，该片段从解析中获取对象。但每次，我似乎都会在setadapter和list视图上得到一个空指针异常。虽然它们都已正确初始化，但它们不为null 我最近的采访：Java 片段中的列表视图空指针异常,java,android,android-fragments,android-listview,swiperefreshlayout,Java,Android,Android Fragments,Android Listview,Swiperefreshlayout,我试图在片段中设置滑动以刷新，该片段从解析中获取对象。但每次，我似乎都会在setadapter和list视图上得到一个空指针异常。虽然它们都已正确初始化，但它们不为null 我最近的采访： package com.astuetz.viewpager.extensions.sample; import android.content.Context; import android.view.LayoutInflater; import android.view.View; import andr
package com.astuetz.viewpager.extensions.sample;
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 java.util.ArrayList;
import java.util.HashMap;
public class RecentsAdapter extends BaseAdapter
{
LayoutInflater inflater;
Context context;
ArrayList<HashMap<String,String>> items = null;
public RecentsAdapter(Context context,ArrayList<HashMap<String,String>> items)
{
super();
this.context = context;
this.items = items;
inflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
}
@Override
public int getCount()
{
return items.size();
}
@Override
public Object getItem(int position)
{
return items.get(position);
}
@Override
public long getItemId(int position)
{
return position;
}
@Override
public View getView(int position, View convertView, ViewGroup parent)
{
View v = convertView;
MyHolder holder = null;
if(v == null)
{
v = inflater.inflate(R.layout.recents_list_item,parent,false);
holder = new MyHolder(v);
v.setTag(holder);
}
else
{
holder = (MyHolder) v.getTag();
}
holder.title.setText(items.get(position).get("title"));
holder.author.setText(items.get(position).get("author"));
holder.dept.setText(items.get(position).get("dept"));
holder.price.setText(items.get(position).get("price"));
// holder.place.setText(items.get(position).get("place"));
return v;
}
class MyHolder
{
TextView dept,title,author,price,place;
public MyHolder(View view)
{
title = (TextView) view.findViewById(R.id.book_title);
dept = (TextView)view.findViewById(R.id.dept_name);
author = (TextView) view.findViewById(R.id.author_name);
price = (TextView)view.findViewById(R.id.price_list);
// place = (TextView)view.findViewById(R.id.place_list);
}
}
}
package com.astuetz.viewpager.extensions.sample；
导入android.content.Context；
导入android.view.LayoutInflater；
导入android.view.view；
导入android.view.ViewGroup；
导入android.widget.BaseAdapter；
导入android.widget.TextView；
导入java.util.ArrayList；
导入java.util.HashMap；
公共类RecentsAdapter扩展BaseAdapter
{
充气机；
语境；
arraylistitems=null；
public RecentsAdapter（上下文、数组列表项）
{
超级（）；
this.context=上下文；
这个项目=项目；
充气器=（LayoutFlater）context.getSystemService（context.LAYOUT\u充气器\u服务）；
}
@凌驾
public int getCount（）
{
返回items.size（）；
}
@凌驾
公共对象getItem（int位置）
{
返回项目。获取（位置）；
}
@凌驾
公共长getItemId（int位置）
{
返回位置；
}
@凌驾
公共视图getView（int位置、视图转换视图、视图组父视图）
{
视图v=转换视图；
MyHolder=null；
如果（v==null）
{
v=充气机。充气（右布局。最近列表项目，父项，false）；
持有人=新的我的持有人（v）；
v、 setTag（支架）；
}
其他的
{
holder=（MyHolder）v.getTag（）；
}
holder.title.setText（items.get（position.get（“title”））；
holder.author.setText（items.get（position.get（“author”））；
holder.dept.setText（items.get（position.get（“dept”））；
holder.price.setText（items.get（position.get（“价格”））；
//holder.place.setText（items.get（position.get（“place”））；
返回v；
}
类别MyHolder
{
TextView部门、标题、作者、价格、地点；
公共MyHolder（视图）
{
title=（TextView）view.findViewById（R.id.book\u title）；
dept=（TextView）view.findViewById（R.id.dept\u name）；
author=（TextView）view.findViewById（R.id.author\u name）；
price=（TextView）view.findViewById（R.id.price\u列表）；
//place=（TextView）view.findViewById（R.id.place\u列表）；
}
}
}
<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:card_view="http://schemas.android.com/apk/res-auto"
android:layout_width="match_parent"
android:layout_height="match_parent">
<android.support.v4.widget.SwipeRefreshLayout
android:id="@+id/container"
android:layout_width="match_parent"
android:layout_height="match_parent">
<android.support.v7.widget.CardView
android:id="@+id/recents_card"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_margin="8dp"
card_view:cardBackgroundColor="@android:color/white"
card_view:cardCornerRadius="8dp"
android:padding="8dp">
<ListView
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:id="@+id/recents_list"
android:divider="@color/dividerColor"
android:dividerHeight="1dp"/>
</android.support.v7.widget.CardView>
</android.support.v4.widget.SwipeRefreshLayout>
</FrameLayout>
/*
* Copyright (C) 2013 Andreas Stuetz <andreas.stuetz@gmail.com>
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.astuetz.viewpager.extensions.sample;
import android.app.AlertDialog;
import android.app.ProgressDialog;
import android.content.Context;
import android.net.ConnectivityManager;
import android.net.NetworkInfo;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v4.view.ViewCompat;
import android.support.v4.widget.SwipeRefreshLayout;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Adapter;
import android.widget.ListView;
import android.widget.Toast;
import com.parse.FindCallback;
import com.parse.GetCallback;
import com.parse.Parse;
import com.parse.ParseException;
import com.parse.ParseObject;
import com.parse.ParseQuery;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
public class RecentsCardFragment extends Fragment implements SwipeRefreshLayout.OnRefreshListener
{
ListView recentsList = (ListView)getActivity().findViewById(R.id.recents_list);
private SwipeRefreshLayout refreshBooks;
ArrayList<HashMap<String,String>> items = new ArrayList<>();
//private ProgressDialog progress;
public static RecentsCardFragment newInstance() {
RecentsCardFragment f = new RecentsCardFragment();
return f;
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.recents_card,container,false);
ViewCompat.setElevation(rootView,50);
refreshBooks = (SwipeRefreshLayout) rootView.findViewById(R.id.container);
refreshBooks.setOnRefreshListener(this);
getBooks();
RecentsAdapter adapter = new RecentsAdapter(getActivity().getApplicationContext(), items);
recentsList.setAdapter(adapter);
return rootView;
}
private ArrayList<HashMap<String,String>> getBooks(){
final ParseQuery<ParseObject> query = ParseQuery.getQuery("Posted");
query.orderByDescending("createdAt");
query.findInBackground(new FindCallback<ParseObject>() {
@Override
public void done(List<ParseObject> parseObjects, ParseException e) {
if (e == null){
Log.w("Parse","Inside getbooks()");
for (ParseObject book : parseObjects) {
HashMap<String, String> test = new HashMap<>();
String dept = book.getString("Department");
String title = book.getString("Title");
String author = book.getString("Author");
Number price_num = book.getNumber("Price");
String price = String.valueOf(price_num);
String place = book.getString("Place");
String desp = book.getString("Description");
test.put("dept", dept);
test.put("title", title);
test.put("author", author);
test.put("price", price);
test.put("place", place);
test.put("description", desp);
items.add(test);
}
} else {
Log.d("Books", "Error: " + e.getMessage());
}
}
});
return items;
}
@Override
public void onRefresh(){
refreshBooks.setRefreshing(true);
updateBooks();
}
private void updateBooks(){
Toast.makeText(getActivity(),"Refresh", Toast.LENGTH_SHORT).show();
items.addAll(getBooks());
refreshBooks.setRefreshing(false);
}
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
}
@Override
public void onActivityCreated(Bundle savedInstanceState) {
super.onActivityCreated(savedInstanceState);
}
}
/*
*版权所有（C）2013 Andreas Stuetz
*
*根据Apache许可证2.0版（以下简称“许可证”）获得许可；
*除非遵守许可证，否则不得使用此文件。
*您可以通过以下方式获得许可证副本：
*
* http://www.apache.org/licenses/LICENSE-2.0
*
*除非适用法律要求或书面同意，软件
*根据许可证进行的分发是按“原样”进行分发的，
*无任何明示或暗示的保证或条件。
*请参阅许可证以了解管理权限和权限的特定语言
*许可证下的限制。
*/
包com.astuetz.viewpager.extensions.sample；
导入android.app.AlertDialog；
导入android.app.ProgressDialog；
导入android.content.Context；
导入android.net.ConnectivityManager；
导入android.net.NetworkInfo；
导入android.os.Bundle；
导入android.support.v4.app.Fragment；
导入android.support.v4.view.ViewCompat；
导入android.support.v4.widget.swiperFreshLayout；
导入android.util.Log；
导入android.view.LayoutInflater；
导入android.view.view；
导入android.view.ViewGroup；
导入android.widget.Adapter；
导入android.widget.ListView；
导入android.widget.Toast；
导入com.parse.FindCallback；
导入com.parse.GetCallback；
导入com.parse.parse；
导入com.parse.ParseException；
导入com.parse.ParseObject；
导入com.parse.ParseQuery；
导入java.util.ArrayList；
导入java.util.HashMap；
导入java.util.List；
公共类RecentsCardFragment扩展片段实现SwiperFreshLayout.OnRefreshListener
{
ListView-recentsList=（ListView）getActivity（）.findViewById（R.id.recents\u列表）；
私家Switch书籍；
ArrayList items=新建ArrayList（）；
//私人进展对话进展；
公共静态RecentsCardFragment newInstance（）{
RecentsCardFragment f=新的RecentsCardFragment（）；
返回f；
}
@凌驾
CreateView上的公共视图（布局、充气机、视图组容器、捆绑包保存状态）{
视图根视图=充气机。充气（右布局。最近的卡，容器，假）；
ViewCompat.setElevation（根视图，50）；
refreshBooks=（SwipeRefreshLayout）rootView.findViewById（R.id.container）；
refreshBooks.setOnRefreshListener（此）；
getBooks（）；
RecentsAdapter adapter=新的RecentsAdapter（getActivity（）.getApplicationContext（），items）；
最近列表设置适配器（适配器）；
返回rootView；
}
私有ArrayList getBooks（）{
final ParseQuery=ParseQuery.getQuery（“已发布”）；
query.orderByDescending（“createdAt”）；
findInBackground（新的FindCallback（）{
@凌驾
public void done（列出parseObjects，parsee异常）{
如果（e==null）{
w（“Parse”，“Inside getbooks（）”）；
for（ParseObject手册：parseObjects）{
HashMap test=新的HashMap（）；
String dept=book.getString（“部门”）；
06-14 02:44:52.485 2373-2373/com.astuetz.viewpager.extensions.sample I/Process﹕ Sending signal. PID: 2373 SIG: 9
06-14 02:58:26.624 2502-2524/com.astuetz.viewpager.extensions.sample D/OpenGLRenderer﹕ Render dirty regions requested: true
06-14 02:58:26.644 2502-2502/com.astuetz.viewpager.extensions.sample D/﹕ HostConnection::get() New Host Connection established 0xabb86710, tid 2502
06-14 02:58:27.720 2502-2502/com.astuetz.viewpager.extensions.sample D/Atlas﹕ Validating map...
06-14 02:58:28.692 2502-2502/com.astuetz.viewpager.extensions.sample I/Choreographer﹕ Skipped 57 frames! The application may be doing too much work on its main thread.
06-14 02:58:28.716 2502-2502/com.astuetz.viewpager.extensions.sample D/AndroidRuntime﹕ Shutting down VM
06-14 02:58:28.720 2502-2502/com.astuetz.viewpager.extensions.sample E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: com.astuetz.viewpager.extensions.sample, PID: 2502
java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.View android.support.v4.app.FragmentActivity.findViewById(int)' on a null object reference
at com.astuetz.viewpager.extensions.sample.RecentsCardFragment.<init>(RecentsCardFragment.java:54)
at com.astuetz.viewpager.extensions.sample.RecentsCardFragment.newInstance(RecentsCardFragment.java:68)
at com.astuetz.viewpager.extensions.sample.MainActivity$MyPagerAdapter.getItem(MainActivity.java:133)
at android.support.v4.app.FragmentPagerAdapter.instantiateItem(FragmentPagerAdapter.java:97)
at android.support.v4.view.ViewPager.addNewItem(ViewPager.java:837)
at android.support.v4.view.ViewPager.populate(ViewPager.java:987)
at android.support.v4.view.ViewPager.populate(ViewPager.java:919)
at android.support.v4.view.ViewPager.onMeasure(ViewPager.java:1441)
at android.view.View.measure(View.java:17430)
at android.widget.LinearLayout.measureVertical(LinearLayout.java:875)
at android.widget.LinearLayout.onMeasure(LinearLayout.java:613)
at android.view.View.measure(View.java:17430)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5463)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:430)
at android.view.View.measure(View.java:17430)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5463)
at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1436)
at android.widget.LinearLayout.measureVertical(LinearLayout.java:722)
at android.widget.LinearLayout.onMeasure(LinearLayout.java:613)
at android.view.View.measure(View.java:17430)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5463)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:430)
at android.view.View.measure(View.java:17430)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5463)
at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1436)
at android.widget.LinearLayout.measureVertical(LinearLayout.java:722)
at android.widget.LinearLayout.onMeasure(LinearLayout.java:613)
at android.view.View.measure(View.java:17430)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5463)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:430)
at com.android.internal.policy.impl.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2560)
at android.view.View.measure(View.java:17430)
at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:2001)
at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1166)
at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1372)
at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1054)
at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:5779)
at android.view.Choreographer$CallbackRecord.run(Choreographer.java:767)
at android.view.Choreographer.doCallbacks(Choreographer.java:580)
at android.view.Choreographer.doFrame(Choreographer.java:550)
at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:753)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5221)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
06-14 02:58:32.992 2502-2502/com.astuetz.viewpager.extensions.sample I/Process﹕ Sending signal. PID: 2502 SIG: 9
public class RecentsCardFragment extends Fragment implements SwipeRefreshLayout.OnRefreshListener
{
ListView recentsList;
private SwipeRefreshLayout refreshBooks;
ArrayList<HashMap<String,String>> items = new ArrayList<>();
//private ProgressDialog progress;
public static RecentsCardFragment newInstance() {
RecentsCardFragment f = new RecentsCardFragment();
return f;
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.recents_card,container,false);
recentsList = (ListView)rootView.findViewById(R.id.recents_list);
ViewCompat.setElevation(rootView,50);
refreshBooks = (SwipeRefreshLayout) rootView.findViewById(R.id.container);
refreshBooks.setOnRefreshListener(this);
getBooks();
RecentsAdapter adapter = new RecentsAdapter(getActivity().getApplicationContext(), items);
recentsList.setAdapter(adapter);
return rootView;
}