尝试按照本教程操作： https://www.airpair.com/android/list-fragment-android-studio 并得到错误，
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.user.fragmentlistexample/com.example.user.fragmentlistexample.MainActivity}: java.lang.IllegalArgumentException: No view found for id 0x7f080002 (com.example.user.fragmentlistexample:id/container) for fragment ExampleItemFragment{2f05586b #1 id=0x7f080002}
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2325)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2390)
at android.app.ActivityThread.access$800(ActivityThread.java:151)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1303)
ExampleItemFragment.java：
package com.example.user.fragmentlistexample;
import android.app.Activity;
import android.os.Bundle;
import android.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AbsListView;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.ListAdapter;
import android.widget.TextView;
import android.widget.Toast;
import com.example.user.fragmentlistexample.dummy.DummyContent;
import java.util.ArrayList;
import java.util.List;
/**
* A fragment representing a list of Items.
* <p/>
* Large screen devices (such as tablets) are supported by replacing the ListView
* with a GridView.
* <p/>
* Activities containing this fragment MUST implement the {@link OnFragmentInteractionListener}
* interface.
*/
public class ExampleItemFragment extends Fragment implements AbsListView.OnItemClickListener {
// TODO: Rename parameter arguments, choose names that match
// the fragment initialization parameters, e.g. ARG_ITEM_NUMBER
private static final String ARG_PARAM1 = "param1";
private static final String ARG_PARAM2 = "param2";
// TODO: Rename and change types of parameters
private String mParam1;
private String mParam2;
private List exampleListItemList;
private OnFragmentInteractionListener mListener;
/**
* The fragment's ListView/GridView.
*/
private AbsListView mListView;
/**
* The Adapter which will be used to populate the ListView/GridView with
* Views.
*/
private ListAdapter mAdapter;
// TODO: Rename and change types of parameters
public static ExampleItemFragment newInstance(String param1, String param2) {
ExampleItemFragment fragment = new ExampleItemFragment();
Bundle args = new Bundle();
args.putString(ARG_PARAM1, param1);
args.putString(ARG_PARAM2, param2);
fragment.setArguments(args);
return fragment;
}
/**
* Mandatory empty constructor for the fragment manager to instantiate the
* fragment (e.g. upon screen orientation changes).
*/
public ExampleItemFragment() {
}
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
exampleListItemList = new ArrayList();
exampleListItemList.add(new ExampleListItem("Example 1"));
exampleListItemList.add(new ExampleListItem("Example 2"));
exampleListItemList.add(new ExampleListItem("Example 3"));
mAdapter = new ExampleListAdapter(getActivity(), exampleListItemList);
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.fragment_example_item_list, container, false);
// Set the adapter
mListView = (AbsListView) view.findViewById(android.R.id.list);
((AdapterView<ListAdapter>) mListView).setAdapter(mAdapter);
// Set OnItemClickListener so we can be notified on item clicks
mListView.setOnItemClickListener(this);
return view;
}
@Override
public void onAttach(Activity activity) {
super.onAttach(activity);
try {
mListener = (OnFragmentInteractionListener) activity;
} catch (ClassCastException e) {
throw new ClassCastException(activity.toString()
+ " must implement OnFragmentInteractionListener");
}
}
@Override
public void onDetach() {
super.onDetach();
mListener = null;
}
@Override
public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
ExampleListItem item = (ExampleListItem)this.exampleListItemList.get(position);
Toast.makeText(getActivity(), item.getItemTitle() + " Clicked!"
, Toast.LENGTH_SHORT).show();
}
/**
* The default content for this Fragment has a TextView that is shown when
* the list is empty. If you would like to change the text, call this method
* to supply the text it should use.
*/
public void setEmptyText(CharSequence emptyText) {
View emptyView = mListView.getEmptyView();
if (emptyView instanceof TextView) {
((TextView) emptyView).setText(emptyText);
}
}
/**
* This interface must be implemented by activities that contain this
* fragment to allow an interaction in this fragment to be communicated
* to the activity and potentially other fragments contained in that
* activity.
* <p/>
* See the Android Training lesson <a href=
* "http://developer.android.com/training/basics/fragments/communicating.html"
* >Communicating with Other Fragments</a> for more information.
*/
public interface OnFragmentInteractionListener {
// TODO: Update argument type and name
public void onFragmentInteraction(String id);
}
}
MainActivity.java
package com.example.user.fragmentlistexample;
import android.app.Activity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
public class MainActivity extends Activity implements ExampleItemFragment.OnFragmentInteractionListener{
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
if (savedInstanceState == null) {
getFragmentManager().beginTransaction()
.add(R.id.container, new ExampleItemFragment())
.commit();
}
}
@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);
}
public void onFragmentInteraction(String id){
}
}
MainActivityFragment.java
package com.example.user.fragmentlistexample;
import android.app.Fragment;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
/**
* A placeholder fragment containing a simple view.
*/
public class MainActivityFragment extends Fragment {
public MainActivityFragment() {
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
return inflater.inflate(R.layout.fragment_main, container, false);
}
}
ActivityMain.xml
<fragment
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/fragment"
android:name="com.example.user.fragmentlistexample.MainActivityFragment"
tools:layout="@layout/fragment_main"
android:layout_width="match_parent"
android:layout_height="match_parent"
/>
fragment_example_item_list.xml
<ListView android:id="@android:id/list" android:layout_width="match_parent"
android:layout_height="match_parent" />
<TextView android:id="@android:id/empty" android:layout_width="match_parent"
android:layout_height="match_parent" android:gravity="center" />
FragmentMain.xml
<RelativeLayout 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"
android:id="@+id/container"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
android:paddingBottom="@dimen/activity_vertical_margin" tools:context=".MainActivityFragment">
</RelativeLayout>
答案 0 :(得分：0)
在MainActivity中使用setContentView(R.layout.activity_main);，然后使用
getFragmentManager().beginTransaction()
.add(R.id.container, new ExampleItemFragment())
.commit();
您正在使用的R.id.container基本上不在您的activity_main.xml中，而是在fragment_main.xml中。这就是showin NullPointerException的原因。
如果您想从MainActivity访问容器，请在activity_main.xml