我对Android编程非常陌生，我正试图在instantiateItem类上创建SlidingTabsBasicFragment，以返回ConversationsFragment的片段。
根据我的理解，我的类ConversationsFragment返回一个片段，它将被实例化。但相反，第二页上没有显示任何内容。
我正在使用SlidingTabsBasic示例进行此操作：
主要活动onCreate：
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Log.v("Logs", "first");
if (savedInstanceState == null) {
FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();
SlidingTabsBasicFragment fragment = new SlidingTabsBasicFragment();
transaction.replace(R.id.sample_content_fragment, fragment);
//ConversationsFragment fragment = new ConversationsFragment();
//transaction.replace(R.id.sample_content_fragment, new ConversationsFragment());
transaction.commit();
}
}
SlidingTabsBasicFragment：
package com.example.android.slidingtabsbasic;
import com.example.android.common.logger.Log;
import com.example.android.common.view.SlidingTabLayout;
import android.content.Context;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentPagerAdapter;
import android.support.v4.app.FragmentTransaction;
import android.support.v4.view.PagerAdapter;
import android.support.v4.view.ViewPager;
import android.util.SparseArray;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AbsListView;
import android.widget.AdapterView;
import android.widget.ListAdapter;
import android.widget.TextView;
/**
* A basic sample which shows how to use {@link com.example.android.common.view.SlidingTabLayout}
* to display a custom {@link ViewPager} title strip which gives continuous feedback to the user
* when scrolling.
*/
public class SlidingTabsBasicFragment extends Fragment {
static final String LOG_TAG = "SlidingTabsBasicFragment";
/**
* A custom {@link ViewPager} title strip which looks much like Tabs present in Android v4.0 and
* above, but is designed to give continuous feedback to the user when scrolling.
*/
private SlidingTabLayout mSlidingTabLayout;
/**
* A {@link ViewPager} which will be used in conjunction with the {@link SlidingTabLayout} above.
*/
private ViewPager mViewPager;
/**
* Inflates the {@link View} which will be displayed by this {@link Fragment}, from the app's
* resources.
*/
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
return inflater.inflate(R.layout.fragment_sample, container, false);
}
// BEGIN_INCLUDE (fragment_onviewcreated)
/**
* This is called after the {@link #onCreateView(LayoutInflater, ViewGroup, Bundle)} has finished.
* Here we can pick out the {@link View}s we need to configure from the content view.
*
* We set the {@link ViewPager}'s adapter to be an instance of {@link SamplePagerAdapter}. The
* {@link SlidingTabLayout} is then given the {@link ViewPager} so that it can populate itself.
*
* @param view View created in {@link #onCreateView(LayoutInflater, ViewGroup, Bundle)}
*/
@Override
public void onViewCreated(View view, Bundle savedInstanceState) {
// BEGIN_INCLUDE (setup_viewpager)
// Get the ViewPager and set it's PagerAdapter so that it can display items
mViewPager = (ViewPager) view.findViewById(R.id.viewpager);
mViewPager.setAdapter(new CustomPagerAdapter(getFragmentManager(),getActivity()));
// END_INCLUDE (setup_viewpager)
// BEGIN_INCLUDE (setup_slidingtablayout)
// Give the SlidingTabLayout the ViewPager, this must be done AFTER the ViewPager has had
// it's PagerAdapter set.
mSlidingTabLayout = (SlidingTabLayout) view.findViewById(R.id.sliding_tabs);
mSlidingTabLayout.setViewPager(mViewPager);
// END_INCLUDE (setup_slidingtablayout)
}
// END_INCLUDE (fragment_onviewcreated)
public class CustomPagerAdapter extends FragmentPagerAdapter {
protected Context mContext;
public CustomPagerAdapter(FragmentManager fm, Context context) {
super(fm);
mContext = context;
}
@Override
public CharSequence getPageTitle(int position) {
return "Item " + (position + 1);
}
@Override
public Fragment getItem(int position) {
if(position==0){
// return fragment
}else{
ConversationsFragment fragment = new ConversationsFragment();
return fragment;
}
return null;
}
@Override
public int getCount() {
return 3;
}
}
}
这是我的ConversationsFragment：
public class ConversationsFragment 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 OnFragmentInteractionListener mListener;
/**
* The fragment's ListView/GridView.
*/
private AbsListView mListView;
/**
* The Adapter which will be used to populate the ListView/GridView with
* Views.
*/
private List conversationsListItemList; // at the top of your fragment listW
private ListAdapter mAdapter;
// TODO: Rename and change types of parameters
public static ConversationsFragment newInstance(String param1, String param2) {
ConversationsFragment fragment = new ConversationsFragment();
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 ConversationsFragment() {
}
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
if (getArguments() != null) {
mParam1 = getArguments().getString(ARG_PARAM1);
mParam2 = getArguments().getString(ARG_PARAM2);
}
// TODO: Change Adapter to display your content
conversationsListItemList = new ArrayList();
conversationsListItemList.add(new ConversationsListItem("Example 1","conversa"));
conversationsListItemList.add(new ConversationsListItem("Example 2","conversa"));
conversationsListItemList.add(new ConversationsListItem("Example 3","conversa"));
mAdapter = new ConversationsListAdapter(getActivity(), conversationsListItemList);
/* mAdapter = new ArrayAdapter<DummyContent.DummyItem>(getActivity(),
android.R.layout.simple_list_item_1, android.R.id.text1, DummyContent.ITEMS);*/
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.fragment_conversations, 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) {
if (null != mListener) {
// Notify the active callbacks interface (the activity, if the
// fragment is attached to one) that an item has been selected.
mListener.onFragmentInteraction(DummyContent.ITEMS.get(position).id);
}
}
public void setEmptyText(CharSequence emptyText) {
View emptyView = mListView.getEmptyView();
if (emptyView instanceof TextView) {
((TextView) emptyView).setText(emptyText);
}
}
public interface OnFragmentInteractionListener {
public void onFragmentInteraction(String id);
}
}
截图：
第一个屏幕：
https://goo.gl/photos/Ze5ThZgevGaALDj47
第二屏：
https://goo.gl/photos/x7JPnESAtZsBT5DC8
现在出现这个错误：
06-16 12:32:58.946 12228-12228/com.example.android.slidingtabsbasic E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: com.example.android.slidingtabsbasic, PID: 12228
java.lang.NullPointerException
at android.support.v4.app.BackStackRecord.doAddOp(BackStackRecord.java:417)
at android.support.v4.app.BackStackRecord.add(BackStackRecord.java:412)
at android.support.v4.app.FragmentPagerAdapter.instantiateItem(FragmentPagerAdapter.java:99)
答案 0 :(得分：0)
我认为您的代码问题是返回View和Fragment
以下代码为我工作
public class CustomPagerAdapter extends FragmentPagerAdapter {
protected Context mContext;
public CustomPagerAdapter(FragmentManager fm, Context context) {
super(fm);
mContext = context;
}
@Override
public CharSequence getPageTitle(int position) {
return "" + tabsTitle[position];
}
@Override
public Fragment getItem(int position) {
if(position==0){
// return fragment
}else{
ConversationsFragment fragment = new ConversationsFragment();
return fragment;
}
return null;
}
@Override
public int getCount() {
return 3;
}
}