Fragment 中带有自定义适配器的 ListView
ListView with custom adapter in Fragment
我正在尝试在 fragmnet 中将 ListView 与自定义适配器 (baseAdapter) 结合使用。
当我直接在 MainActivity 中使用此代码时，一切正常，但当我在片段中使用此代码时，它没有崩溃，但它没有显示任何内容，它只是一个空白片段。此外，当我尝试使用简单的 arrayAdapter 在片段中绑定一个 textView 时，它工作正常
所以我认为问题出在我的自定义适配器中。
为什么不显示 ListView？
我的代码：
HomeFragment.java
package com.example.alex.viewlist;
import android.app.Fragment;
import android.content.Context;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.ListView;
import android.widget.TextView;
import com.android.volley.toolbox.ImageLoader;
import com.android.volley.toolbox.NetworkImageView;
import java.util.ArrayList;
import java.util.List;
public class HomeFragment extends Fragment {
ImageLoader mImageLoader;
NetworkImageView mNetworkImageView;
public MainActivity activity = (MainActivity) getActivity();
public HomeFragment() {
// Required empty public constructor
}
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View V = inflater.inflate(R.layout.fragment_home, container, false);
CodeLearnAdapter chapterListAdapter = new CodeLearnAdapter();
ListView codeLearnLessons = (ListView) V.findViewById(R.id.listView);
codeLearnLessons.setAdapter(chapterListAdapter);
return inflater.inflate(R.layout.fragment_home, container, false);
}
@Override
public void onActivityCreated(Bundle savedInstanceState) {
super.onActivityCreated(savedInstanceState);
}
public class codeLearnChapter {
String mURL;
String mName;
}
String[] ListURL = new String[] {"http://meteo.profi-net.sk/webcams/BIELAPUT-l.jpg",
"http://meteo.profi-net.sk/webcams/Priehyba-l.jpg",
"http://meteo.profi-net.sk/webcams/JASNA_CHOPOK-l.jpg",
"http://meteo.profi-net.sk/webcams/LM_JASNA_LUKOVA-l.jpg",
"http://meteo.profi-net.sk/webcams/brhliska-l.jpg"};
String[] ListName = new String[] {"Biela púť",
"Priehyba",
"Chopok",
"Luková",
"Grand Jet"};
public List<codeLearnChapter> getDataForListView()
{
List<codeLearnChapter> codeLearnChaptersList = new ArrayList<codeLearnChapter>();
for(int i=0;i<ListURL.length;i++)
{
codeLearnChapter chapter = new codeLearnChapter();
chapter.mURL = ListURL[i];
chapter.mName = ListName[i];
codeLearnChaptersList.add(chapter);
}
return codeLearnChaptersList;
}
public class CodeLearnAdapter extends BaseAdapter {
List<codeLearnChapter> codeLearnChapterList = getDataForListView();
@Override
public int getCount() {
return codeLearnChapterList.size();
}
@Override
public codeLearnChapter getItem(int arg0) {
return codeLearnChapterList.get(arg0);
}
@Override
public long getItemId(int arg0) {
return arg0;
}
@Override
public View getView(int arg0, View arg1, ViewGroup arg2) {
if(arg1==null)
{
LayoutInflater inflater = (LayoutInflater) getActivity().getSystemService(Context.LAYOUT_INFLATER_SERVICE);
arg1 = inflater.inflate(R.layout.view_list, arg2,false);
}
TextView chapterName = (TextView)arg1.findViewById(R.id.textView1);
codeLearnChapter chapter = codeLearnChapterList.get(arg0);
String url = chapter.mURL;
chapterName.setText(chapter.mName);
mNetworkImageView = (NetworkImageView) arg1.findViewById(R.id.NetView);
// Get the ImageLoader through your singleton class.
mImageLoader = VolleySingleton.getInstance(activity).getImageLoader();
// Set the URL of the image that should be loaded into this view, and
// specify the ImageLoader that will be used to make the request.
mNetworkImageView.setImageUrl(url, mImageLoader);
return arg1;
}
}
}
fragment_home.xml
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent"
android:layout_height="match_parent" tools:context="com.example.alex.viewlist.HomeFragment">
<ListView
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:id="@+id/listView"
android:layout_alignParentTop="true"
android:layout_centerHorizontal="true" />
viewList.xml
<view
android:layout_width="fill_parent"
android:layout_height="wrap_content"
class="android.support.v7.widget.CardView"
android:id="@+id/view"
android:layout_alignParentTop="true"
android:layout_centerHorizontal="true"
xmlns:android="http://schemas.android.com/apk/res/android"
android:paddingLeft="4dp"
android:paddingTop="4dp"
android:paddingRight="4dp"
android:paddingBottom="4dp">
<RelativeLayout
android:layout_width="fill_parent" android:layout_height="fill_parent"
android:orientation="vertical">
<view
android:layout_width="fill_parent"
android:layout_height="wrap_content"
class="com.android.volley.toolbox.NetworkImageView"
android:id="@+id/NetView"
android:layout_alignParentLeft="true"
android:layout_alignParentTop="true" />
<TextView
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:id="@+id/textView1"
android:layout_gravity="left|bottom"
android:textSize="22dp"
android:layout_below="@+id/NetView"
android:layout_alignParentLeft="true"
android:layout_alignParentStart="true"
android:background="#ffd4d4d4"
android:textColor="#ff272727"
android:paddingTop="10dp"
android:paddingBottom="10dp"
android:paddingLeft="20dp"
android:layout_marginTop="2dp"
android:layout_marginBottom="2dp"
android:layout_marginLeft="2dp"
android:layout_marginRight="2dp"/>
</RelativeLayout>
编辑：
如果我将 OnCreateView 方法替换为 return: return V;我收到 NPE 错误：
02-27 20:52:15.955 28063-28063/com.example.alex.viewlist E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: com.example.alex.viewlist, PID: 28063
java.lang.NullPointerException
at com.android.volley.toolbox.Volley.newRequestQueue(Volley.java:43)
at com.android.volley.toolbox.Volley.newRequestQueue(Volley.java:78)
at com.example.alex.viewlist.VolleySingleton.<init>(VolleySingleton.java:18)
at com.example.alex.viewlist.VolleySingleton.getInstance(VolleySingleton.java:39)
at com.example.alex.viewlist.HomeFragment$CodeLearnAdapter.getView(HomeFragment.java:133)
at android.widget.AbsListView.obtainView(AbsListView.java:2263)
at android.widget.ListView.makeAndAddView(ListView.java:1790)
at android.widget.ListView.fillDown(ListView.java:691)
at android.widget.ListView.fillFromTop(ListView.java:752)
at android.widget.ListView.layoutChildren(ListView.java:1630)
at android.widget.AbsListView.onLayout(AbsListView.java:2091)
at android.view.View.layout(View.java:14817)
at android.view.ViewGroup.layout(ViewGroup.java:4631)
at android.widget.FrameLayout.layoutChildren(FrameLayout.java:453)
at android.widget.FrameLayout.onLayout(FrameLayout.java:388)
at android.view.View.layout(View.java:14817)
at android.view.ViewGroup.layout(ViewGroup.java:4631)
at android.widget.RelativeLayout.onLayout(RelativeLayout.java:1055)
at android.view.View.layout(View.java:14817)
at android.view.ViewGroup.layout(ViewGroup.java:4631)
at android.widget.FrameLayout.layoutChildren(FrameLayout.java:453)
at android.widget.FrameLayout.onLayout(FrameLayout.java:388)
at android.view.View.layout(View.java:14817)
at android.view.ViewGroup.layout(ViewGroup.java:4631)
at android.support.v7.internal.widget.ActionBarOverlayLayout.onLayout(ActionBarOverlayLayout.java:502)
at android.view.View.layout(View.java:14817)
at android.view.ViewGroup.layout(ViewGroup.java:4631)
at android.widget.FrameLayout.layoutChildren(FrameLayout.java:453)
at android.widget.FrameLayout.onLayout(FrameLayout.java:388)
at android.view.View.layout(View.java:14817)
at android.view.ViewGroup.layout(ViewGroup.java:4631)
at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1671)
at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1525)
at android.widget.LinearLayout.onLayout(LinearLayout.java:1434)
at android.view.View.layout(View.java:14817)
at android.view.ViewGroup.layout(ViewGroup.java:4631)
at android.widget.FrameLayout.layoutChildren(FrameLayout.java:453)
at android.widget.FrameLayout.onLayout(FrameLayout.java:388)
at android.view.View.layout(View.java:14817)
at android.view.ViewGroup.layout(ViewGroup.java:4631)
at android.view.ViewRootImpl.performLayout(ViewRootImpl.java:2066)
at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1823)
at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1079)
at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:5784)
at android.view.Choreographer$CallbackRecord.run(Choreographer.java:774)
at android.view.Choreographer.doCallbacks(Choreographer.java:587)
at android.view.Choreographer.doFrame(Choreographer.java:550)
at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:760)
at android.os.Handler.handleCallback(Handler.java:733)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:136)
at android.app.ActivityThread.main(ActivityThread.java:5017)
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)
因为 List<codeLearnChapter> codeLearnChapterList = getDataForListView(); 这一行 getDataForListView() 不会填充列表数据，所以你必须在构造函数初始化时调用它。
只需将构造函数添加到您的自定义适配器 CodeLearnAdapter
喜欢
List<codeLearnChapter> codeLearnChapterList ;
public CodeLearnAdapter () {
codeLearnChapterList = getDataForListView();
}
并且在 onCreateView 中你必须 return View V，因为它总是膨胀新创建的视图所以没有任何列表。
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View V = inflater.inflate(R.layout.fragment_home, container, false);
CodeLearnAdapter chapterListAdapter = new CodeLearnAdapter();
ListView codeLearnLessons = (ListView) V.findViewById(R.id.listView);
codeLearnLessons.setAdapter(chapterListAdapter);
return V;
}
从堆栈跟踪中，我怀疑 mImageLoader 可以为 null，因为 activity 没有获取 Context 的引用，所以替换
// 通过你的单例获取ImageLoader class.
mImageLoader = VolleySingleton.getInstance(activity).getImageLoader();
和
// 通过你的单例获取ImageLoader class.
mImageLoader = VolleySingleton.getInstance(getActivity()).getImageLoader();
我看到两个问题：
- 首先，您的
onCreateView() 方法有问题。您将布局 (R.layout.fragment_home) 膨胀两次。该方法的最后一行应该是 return v; 而不是 return inflater.inflate(R.layout.fragment_home, container, false);
其次，在 class 初始化时调用适配器 List<codeLearnChapter> codeLearnChapterList = getDataForListView(); 中的第一行。通常的做法是在适配器的构造函数中发送数据：
public CodeLearnAdapter () {
this.codeLearnChapterList = getDataForListView();
}
我正在尝试在 fragmnet 中将 ListView 与自定义适配器 (baseAdapter) 结合使用。
当我直接在 MainActivity 中使用此代码时，一切正常，但当我在片段中使用此代码时，它没有崩溃，但它没有显示任何内容，它只是一个空白片段。此外，当我尝试使用简单的 arrayAdapter 在片段中绑定一个 textView 时，它工作正常 所以我认为问题出在我的自定义适配器中。
为什么不显示 ListView？
我的代码： HomeFragment.java
package com.example.alex.viewlist;
import android.app.Fragment;
import android.content.Context;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.ListView;
import android.widget.TextView;
import com.android.volley.toolbox.ImageLoader;
import com.android.volley.toolbox.NetworkImageView;
import java.util.ArrayList;
import java.util.List;
public class HomeFragment extends Fragment {
ImageLoader mImageLoader;
NetworkImageView mNetworkImageView;
public MainActivity activity = (MainActivity) getActivity();
public HomeFragment() {
// Required empty public constructor
}
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View V = inflater.inflate(R.layout.fragment_home, container, false);
CodeLearnAdapter chapterListAdapter = new CodeLearnAdapter();
ListView codeLearnLessons = (ListView) V.findViewById(R.id.listView);
codeLearnLessons.setAdapter(chapterListAdapter);
return inflater.inflate(R.layout.fragment_home, container, false);
}
@Override
public void onActivityCreated(Bundle savedInstanceState) {
super.onActivityCreated(savedInstanceState);
}
public class codeLearnChapter {
String mURL;
String mName;
}
String[] ListURL = new String[] {"http://meteo.profi-net.sk/webcams/BIELAPUT-l.jpg",
"http://meteo.profi-net.sk/webcams/Priehyba-l.jpg",
"http://meteo.profi-net.sk/webcams/JASNA_CHOPOK-l.jpg",
"http://meteo.profi-net.sk/webcams/LM_JASNA_LUKOVA-l.jpg",
"http://meteo.profi-net.sk/webcams/brhliska-l.jpg"};
String[] ListName = new String[] {"Biela púť",
"Priehyba",
"Chopok",
"Luková",
"Grand Jet"};
public List<codeLearnChapter> getDataForListView()
{
List<codeLearnChapter> codeLearnChaptersList = new ArrayList<codeLearnChapter>();
for(int i=0;i<ListURL.length;i++)
{
codeLearnChapter chapter = new codeLearnChapter();
chapter.mURL = ListURL[i];
chapter.mName = ListName[i];
codeLearnChaptersList.add(chapter);
}
return codeLearnChaptersList;
}
public class CodeLearnAdapter extends BaseAdapter {
List<codeLearnChapter> codeLearnChapterList = getDataForListView();
@Override
public int getCount() {
return codeLearnChapterList.size();
}
@Override
public codeLearnChapter getItem(int arg0) {
return codeLearnChapterList.get(arg0);
}
@Override
public long getItemId(int arg0) {
return arg0;
}
@Override
public View getView(int arg0, View arg1, ViewGroup arg2) {
if(arg1==null)
{
LayoutInflater inflater = (LayoutInflater) getActivity().getSystemService(Context.LAYOUT_INFLATER_SERVICE);
arg1 = inflater.inflate(R.layout.view_list, arg2,false);
}
TextView chapterName = (TextView)arg1.findViewById(R.id.textView1);
codeLearnChapter chapter = codeLearnChapterList.get(arg0);
String url = chapter.mURL;
chapterName.setText(chapter.mName);
mNetworkImageView = (NetworkImageView) arg1.findViewById(R.id.NetView);
// Get the ImageLoader through your singleton class.
mImageLoader = VolleySingleton.getInstance(activity).getImageLoader();
// Set the URL of the image that should be loaded into this view, and
// specify the ImageLoader that will be used to make the request.
mNetworkImageView.setImageUrl(url, mImageLoader);
return arg1;
}
}
}
fragment_home.xml
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent"
android:layout_height="match_parent" tools:context="com.example.alex.viewlist.HomeFragment">
<ListView
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:id="@+id/listView"
android:layout_alignParentTop="true"
android:layout_centerHorizontal="true" />
viewList.xml
<view
android:layout_width="fill_parent"
android:layout_height="wrap_content"
class="android.support.v7.widget.CardView"
android:id="@+id/view"
android:layout_alignParentTop="true"
android:layout_centerHorizontal="true"
xmlns:android="http://schemas.android.com/apk/res/android"
android:paddingLeft="4dp"
android:paddingTop="4dp"
android:paddingRight="4dp"
android:paddingBottom="4dp">
<RelativeLayout
android:layout_width="fill_parent" android:layout_height="fill_parent"
android:orientation="vertical">
<view
android:layout_width="fill_parent"
android:layout_height="wrap_content"
class="com.android.volley.toolbox.NetworkImageView"
android:id="@+id/NetView"
android:layout_alignParentLeft="true"
android:layout_alignParentTop="true" />
<TextView
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:id="@+id/textView1"
android:layout_gravity="left|bottom"
android:textSize="22dp"
android:layout_below="@+id/NetView"
android:layout_alignParentLeft="true"
android:layout_alignParentStart="true"
android:background="#ffd4d4d4"
android:textColor="#ff272727"
android:paddingTop="10dp"
android:paddingBottom="10dp"
android:paddingLeft="20dp"
android:layout_marginTop="2dp"
android:layout_marginBottom="2dp"
android:layout_marginLeft="2dp"
android:layout_marginRight="2dp"/>
</RelativeLayout>
编辑：
如果我将 OnCreateView 方法替换为 return: return V;我收到 NPE 错误：
02-27 20:52:15.955 28063-28063/com.example.alex.viewlist E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: com.example.alex.viewlist, PID: 28063
java.lang.NullPointerException
at com.android.volley.toolbox.Volley.newRequestQueue(Volley.java:43)
at com.android.volley.toolbox.Volley.newRequestQueue(Volley.java:78)
at com.example.alex.viewlist.VolleySingleton.<init>(VolleySingleton.java:18)
at com.example.alex.viewlist.VolleySingleton.getInstance(VolleySingleton.java:39)
at com.example.alex.viewlist.HomeFragment$CodeLearnAdapter.getView(HomeFragment.java:133)
at android.widget.AbsListView.obtainView(AbsListView.java:2263)
at android.widget.ListView.makeAndAddView(ListView.java:1790)
at android.widget.ListView.fillDown(ListView.java:691)
at android.widget.ListView.fillFromTop(ListView.java:752)
at android.widget.ListView.layoutChildren(ListView.java:1630)
at android.widget.AbsListView.onLayout(AbsListView.java:2091)
at android.view.View.layout(View.java:14817)
at android.view.ViewGroup.layout(ViewGroup.java:4631)
at android.widget.FrameLayout.layoutChildren(FrameLayout.java:453)
at android.widget.FrameLayout.onLayout(FrameLayout.java:388)
at android.view.View.layout(View.java:14817)
at android.view.ViewGroup.layout(ViewGroup.java:4631)
at android.widget.RelativeLayout.onLayout(RelativeLayout.java:1055)
at android.view.View.layout(View.java:14817)
at android.view.ViewGroup.layout(ViewGroup.java:4631)
at android.widget.FrameLayout.layoutChildren(FrameLayout.java:453)
at android.widget.FrameLayout.onLayout(FrameLayout.java:388)
at android.view.View.layout(View.java:14817)
at android.view.ViewGroup.layout(ViewGroup.java:4631)
at android.support.v7.internal.widget.ActionBarOverlayLayout.onLayout(ActionBarOverlayLayout.java:502)
at android.view.View.layout(View.java:14817)
at android.view.ViewGroup.layout(ViewGroup.java:4631)
at android.widget.FrameLayout.layoutChildren(FrameLayout.java:453)
at android.widget.FrameLayout.onLayout(FrameLayout.java:388)
at android.view.View.layout(View.java:14817)
at android.view.ViewGroup.layout(ViewGroup.java:4631)
at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1671)
at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1525)
at android.widget.LinearLayout.onLayout(LinearLayout.java:1434)
at android.view.View.layout(View.java:14817)
at android.view.ViewGroup.layout(ViewGroup.java:4631)
at android.widget.FrameLayout.layoutChildren(FrameLayout.java:453)
at android.widget.FrameLayout.onLayout(FrameLayout.java:388)
at android.view.View.layout(View.java:14817)
at android.view.ViewGroup.layout(ViewGroup.java:4631)
at android.view.ViewRootImpl.performLayout(ViewRootImpl.java:2066)
at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1823)
at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1079)
at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:5784)
at android.view.Choreographer$CallbackRecord.run(Choreographer.java:774)
at android.view.Choreographer.doCallbacks(Choreographer.java:587)
at android.view.Choreographer.doFrame(Choreographer.java:550)
at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:760)
at android.os.Handler.handleCallback(Handler.java:733)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:136)
at android.app.ActivityThread.main(ActivityThread.java:5017)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:515)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:785)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:601)
at dalvik.system.NativeStart.main(Native Method)
因为 List<codeLearnChapter> codeLearnChapterList = getDataForListView(); 这一行 getDataForListView() 不会填充列表数据，所以你必须在构造函数初始化时调用它。
只需将构造函数添加到您的自定义适配器 CodeLearnAdapter
喜欢
List<codeLearnChapter> codeLearnChapterList ;
public CodeLearnAdapter () {
codeLearnChapterList = getDataForListView();
}
并且在 onCreateView 中你必须 return View V，因为它总是膨胀新创建的视图所以没有任何列表。
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View V = inflater.inflate(R.layout.fragment_home, container, false);
CodeLearnAdapter chapterListAdapter = new CodeLearnAdapter();
ListView codeLearnLessons = (ListView) V.findViewById(R.id.listView);
codeLearnLessons.setAdapter(chapterListAdapter);
return V;
}
从堆栈跟踪中，我怀疑 mImageLoader 可以为 null，因为 activity 没有获取 Context 的引用，所以替换
// 通过你的单例获取ImageLoader class.
mImageLoader = VolleySingleton.getInstance(activity).getImageLoader();
和
// 通过你的单例获取ImageLoader class.
mImageLoader = VolleySingleton.getInstance(getActivity()).getImageLoader();
我看到两个问题：
- 首先，您的
onCreateView()方法有问题。您将布局 (R.layout.fragment_home) 膨胀两次。该方法的最后一行应该是return v;而不是return inflater.inflate(R.layout.fragment_home, container, false); 其次，在 class 初始化时调用适配器
List<codeLearnChapter> codeLearnChapterList = getDataForListView();中的第一行。通常的做法是在适配器的构造函数中发送数据：public CodeLearnAdapter () { this.codeLearnChapterList = getDataForListView(); }