无法将可扩展ListView添加到片段中以获取错误。
我有一个导航抽屉来浏览新闻和更新片段，其中我想要一个可扩展的列表视图，但我无法添加它我不知道如何解决这个问题
fragment_news_update.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.aakash.myapp.news_update"
android:background="#d3d3d3">
<ImageView
android:layout_width="match_parent"
android:layout_height="170dp"
android:id="@+id/imageView2"
android:layout_gravity="left|top"
android:background="@drawable/news_update_top" />
<ExpandableListView
android:layout_width="wrap_content"
android:layout_height="340dp"
android:id="@+id/expListView"
android:layout_gravity="right|bottom" />
news_update.java
package com.example.aakash.myapp;
public class news_update extends Fragment{
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// Inflate the layout for this fragment
return inflater.inflate(R.layout.fragment_news_update, container, false);
}
public news_update() {
// Required empty public constructor
}
ExpandableListAdapter listAdapter;
ExpandableListView expListView;
List<String> listDataHeader;
HashMap<String, List<String>> listDataChild;
{
// get the listview
expListView = (ExpandableListView) getView().findViewById(R.id.expListView);
// Listview on child click listener
expListView.setOnChildClickListener(new ExpandableListView.OnChildClickListener() {
@Override
public boolean onChildClick(ExpandableListView parent, View v,
int groupPosition, int childPosition, long id) {
Toast.makeText(
getActivity().getApplicationContext(),
listDataHeader.get(groupPosition)
+ " : "
+ listDataChild.get(
listDataHeader.get(groupPosition)).get(
childPosition), Toast.LENGTH_SHORT)
.show();
return false;
}
});
// preparing list data
prepareListData();
listAdapter = new ExpandableListAdapter(this, listDataHeader, listDataChild);
// setting list adapter
expListView.setAdapter(listAdapter);
}
/*
* Preparing the list data
*/
private void prepareListData() {
listDataHeader = new ArrayList<String>();
listDataChild = new HashMap<String, List<String>>();
// Adding child data
listDataHeader.add("Top 250");
listDataHeader.add("Now Showing");
listDataHeader.add("Coming Soon..");
// Adding child data
List<String> top250 = new ArrayList<String>();
top250.add("The Shawshank Redemption");
top250.add("The Godfather");
top250.add("The Godfather: Part II");
top250.add("Pulp Fiction");
top250.add("The Good, the Bad and the Ugly");
top250.add("The Dark Knight");
top250.add("12 Angry Men");
List<String> nowShowing = new ArrayList<String>();
nowShowing.add("The Conjuring");
nowShowing.add("Despicable Me 2");
nowShowing.add("Turbo");
nowShowing.add("Grown Ups 2");
nowShowing.add("Red 2");
nowShowing.add("The Wolverine");
List<String> comingSoon = new ArrayList<String>();
comingSoon.add("2 Guns");
comingSoon.add("The Smurfs 2");
comingSoon.add("The Spectacular Now");
comingSoon.add("The Canyons");
comingSoon.add("Europa Report");
listDataChild.put(listDataHeader.get(0), top250); // Header, Child data
listDataChild.put(listDataHeader.get(1), nowShowing);
listDataChild.put(listDataHeader.get(2), comingSoon);
}
}
ExpandableListAdapter.java
package info.androidhive.expandablelistview;
public class ExpandableListAdapter extends BaseExpandableListAdapter {
private Context _context;
private List<String> _listDataHeader; // header titles
// child data in format of header title, child title
private HashMap<String, List<String>> _listDataChild;
public ExpandableListAdapter(Context context, List<String> listDataHeader,
HashMap<String, List<String>> listChildData) {
this._context = context;
this._listDataHeader = listDataHeader;
this._listDataChild = listChildData;
}
@Override
public Object getChild(int groupPosition, int childPosititon) {
return this._listDataChild.get(this._listDataHeader.get(groupPosition))
.get(childPosititon);
}
@Override
public long getChildId(int groupPosition, int childPosition) {
return childPosition;
}
@Override
public View getChildView(int groupPosition, final int childPosition,
boolean isLastChild, View convertView, ViewGroup parent) {
final String childText = (String) getChild(groupPosition, childPosition);
if (convertView == null) {
LayoutInflater infalInflater = (LayoutInflater) this._context
.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
convertView = infalInflater.inflate(R.layout.list_item, null);
}
TextView txtListChild = (TextView) convertView
.findViewById(R.id.lblListItem);
txtListChild.setText(childText);
return convertView;
}
@Override
public int getChildrenCount(int groupPosition) {
return this._listDataChild.get(this._listDataHeader.get(groupPosition))
.size();
}
@Override
public Object getGroup(int groupPosition) {
return this._listDataHeader.get(groupPosition);
}
@Override
public int getGroupCount() {
return this._listDataHeader.size();
}
@Override
public long getGroupId(int groupPosition) {
return groupPosition;
}
@Override
public View getGroupView(int groupPosition, boolean isExpanded,
View convertView, ViewGroup parent) {
String headerTitle = (String) getGroup(groupPosition);
if (convertView == null) {
LayoutInflater infalInflater = (LayoutInflater) this._context
.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
convertView = infalInflater.inflate(R.layout.list_group, null);
}
TextView lblListHeader = (TextView) convertView
.findViewById(R.id.lblListHeader);
lblListHeader.setTypeface(null, Typeface.BOLD);
lblListHeader.setText(headerTitle);
return convertView;
}
@Override
public boolean hasStableIds() {
return false;
}
@Override
public boolean isChildSelectable(int groupPosition, int childPosition) {
return true;
}
}
MainActivity.java
package com.example.aakash.myapp;
public class MainActivity extends AppCompatActivity
implements NavigationView.OnNavigationItemSelectedListener {
NavigationView navigationView = null;
Toolbar toolbar=null;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
//set an initial fragment
home fragment = new home();
android.support.v4.app.FragmentTransaction fragmentTransaction = getSupportFragmentManager().beginTransaction();
fragmentTransaction.replace(R.id.fragment_container,fragment);
fragmentTransaction.commit();
toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
fab.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
Snackbar.make(view, "Not Available Right Now !!", Snackbar.LENGTH_SHORT)
.setAction("Action", null).show();
}
});
DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(
this, drawer, toolbar, R.string.navigation_drawer_open, R.string.navigation_drawer_close);
drawer.setDrawerListener(toggle);
toggle.syncState();
navigationView = (NavigationView) findViewById(R.id.nav_view);
navigationView.setNavigationItemSelectedListener(this);
}
@Override
public void onBackPressed() {
DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
if (drawer.isDrawerOpen(GravityCompat.START)) {
drawer.closeDrawer(GravityCompat.START);
} else {
super.onBackPressed();
}
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.main, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
//noinspection SimplifiableIfStatement
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
@SuppressWarnings("StatementWithEmptyBody")
@Override
public boolean onNavigationItemSelected(MenuItem item) {
// Handle navigation view item clicks here.
int id = item.getItemId();
if (id == R.id.nav_home) {
home fragment = new home();
android.support.v4.app.FragmentTransaction fragmentTransaction = getSupportFragmentManager().beginTransaction();
fragmentTransaction.replace(R.id.fragment_container,fragment);
fragmentTransaction.commit();
// Handle the camera action
}
if (id == R.id.nav_news_updates) {
news_update fragment = new news_update();
android.support.v4.app.FragmentTransaction fragmentTransaction = getSupportFragmentManager().beginTransaction();
fragmentTransaction.replace(R.id.fragment_container,fragment);
fragmentTransaction.commit();
// Handle the camera action
} else if (id == R.id.nav_admission) {
Gallery_Fragment fragment = new Gallery_Fragment();
android.support.v4.app.FragmentTransaction fragmentTransaction = getSupportFragmentManager().beginTransaction();
fragmentTransaction.replace(R.id.fragment_container,fragment);
fragmentTransaction.commit();
} else if (id == R.id.nav_results) {
} else if (id == R.id.nav_l_o_h) {
} else if (id == R.id.nav_contact_us) {
}
DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
drawer.closeDrawer(GravityCompat.START);
return true;
}
}
的AndroidManifest.xml
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.aakash.myapp" >
<application
android:allowBackup="true"
android:icon="@mipmap/ic_launcher"
android:label="@string/app_name"
android:supportsRtl="true"
android:theme="@style/AppTheme" >
<activity
android:name=".MainActivity"
android:label="@string/app_name"
android:theme="@style/AppTheme.NoActionBar" >
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
</application>
error_log中
06-03 22:20:05.587 3547-3547/com.example.aakash.myapp E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.aakash.myapp, PID: 3547
java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.View android.app.Activity.findViewById(int)' on a null object reference
at com.example.aakash.myapp.news_update.<init>(news_update.java:46)
at com.example.aakash.myapp.MainActivity.onNavigationItemSelected(MainActivity.java:111)
at android.support.design.widget.NavigationView$1.onMenuItemSelected(NavigationView.java:151)
at android.support.v7.view.menu.MenuBuilder.dispatchMenuItemSelected(MenuBuilder.java:811)
at android.support.v7.view.menu.MenuItemImpl.invoke(MenuItemImpl.java:152)
at android.support.v7.view.menu.MenuBuilder.performItemAction(MenuBuilder.java:958)
at android.support.design.internal.NavigationMenuPresenter$1.onClick(NavigationMenuPresenter.java:318)
at android.view.View.performClick(View.java:5198)
at android.view.View$PerformClick.run(View.java:21147)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5417)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
答案 0 :(得分：0)
为什么要将news_update扩展到FragmentActivity。只是用Fragment扩展。 FragmentActivity不是一个片段，它是Activity的子类，因此您收到错误news_update cannot be converted to Fragment
import android.support.v4.app.Fragment;
public class news_update extends Fragment{}
答案 1 :(得分：0)
Fragment没有setContentView()方法，您无法直接在findViewById()中使用Fragment方法。您可以参考阅读this。而不是setContentView()，您必须在链接中提及资源文件，并将膨胀的ViewGroup收集到本地ViewGroup中。一旦你拥有了那个膨胀的ViewGroup，你就可以在那个特定的ViewGroup中找到任何视图。
首先执行所有这些操作，阅读链接并尝试运行该应用程序。您的问题将得到解决