java ActionBar选项卡空指针异常
我正在尝试使用这个tutorial来实现actionbar标签，这些标签是片段，但我一直遇到这个错误：
LogCat：
06-16 17:00:46.778: E/AndroidRuntime(25789): FATAL EXCEPTION: main
06-16 17:00:46.778: E/AndroidRuntime(25789): java.lang.NullPointerException
06-16 17:00:46.778: E/AndroidRuntime(25789): at com.myapp.Main.initWidgets(Main.java:115)
06-16 17:00:46.778: E/AndroidRuntime(25789): at com.myapp.Main.onCreateView(Main.java:52)
06-16 17:00:46.778: E/AndroidRuntime(25789): at 安卓.support.v4.app.Fragment.performCreateView(Fragment.java:1500)
06-16 17:00:46.778: E/AndroidRuntime(25789): at 安卓.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:938)
06-16 17:00:46.778: E/AndroidRuntime(25789): at 安卓.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1115)
06-16 17:00:46.778: E/AndroidRuntime(25789): at 安卓.support.v4.app.BackStackRecord.run(BackStackRecord.java:682)
06-16 17:00:46.778: E/AndroidRuntime(25789): at 安卓.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1478)
06-16 17:00:46.778: E/AndroidRuntime(25789): at 安卓.support.v4.app.FragmentManagerImpl.executePendingTransactions(FragmentManager.java:478)
06-16 17:00:46.778: E/AndroidRuntime(25789): at 安卓.support.v4.app.FragmentPagerAdapter.finishUpdate(FragmentPagerAdapter.java:141)
06-16 17:00:46.778: E/AndroidRuntime(25789): at 安卓.support.v4.view.ViewPager.populate(ViewPager.java:1068)
06-16 17:00:46.778: E/AndroidRuntime(25789): at 安卓.support.v4.view.ViewPager.populate(ViewPager.java:914)
06-16 17:00:46.778: E/AndroidRuntime(25789): at 安卓.support.v4.view.ViewPager$3.run(ViewPager.java:244)
06-16 17:00:46.778: E/AndroidRuntime(25789): at 安卓.os.Handler.handleCallback(Handler.java:605)
06-16 17:00:46.778: E/AndroidRuntime(25789): at 安卓.os.Handler.dispatchMessage(Handler.java:92)
06-16 17:00:46.778: E/AndroidRuntime(25789): at 安卓.os.Looper.loop(Looper.java:137)
06-16 17:00:46.778: E/AndroidRuntime(25789): at 安卓.app.ActivityThread.main(ActivityThread.java:4441)
06-16 17:00:46.778: E/AndroidRuntime(25789): at java.lang.reflect.Method.invokeNative(Native Method)
06-16 17:00:46.778: E/AndroidRuntime(25789): at java.lang.reflect.Method.invoke(Method.java:511)
06-16 17:00:46.778: E/AndroidRuntime(25789): at com.安卓.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
06-16 17:00:46.778: E/AndroidRuntime(25789): at com.安卓.internal.os.ZygoteInit.main(ZygoteInit.java:551)
06-16 17:00:46.778: E/AndroidRuntime(25789): at dalvik.system.NativeStart.main(Native Method)
我是碎片新手，有人能帮我解决这个问题吗？以下是导致错误的片段的代码：
public class Main extends Fragment {
private SharedPreferences prefs;
private Latest latest;
private ArrayList<ActivityItems> activities;
private MainAdapter adapter;
private ListView list;
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.main_activity, container,
false);
prefs = getActivity().getSharedPreferences(
getActivity().getPackageName(), getActivity().MODE_PRIVATE);
Log.v("--", prefs.getString(Constants.TOKEN, "") + " TNK");
initWidgets();
return rootView;
}
private void initWidgets() {
activities = new ArrayList<ActivityItems>();
list = (ListView) getActivity().findViewById(R.id.main_activity_list);
// initActionBar();
new AsyncTask<Void, Void, Void>() {
@Override
protected Void doInBackground(Void... params) {
getActivityData();
try {
JSONObject jObj = new JSONObject(getLatest());
for (int i = 0; i < jObj.getJSONArray("items").length(); i++) {
JSONObject j = jObj.getJSONArray("items")
.getJSONObject(i);
JSONObject userJson = j.getJSONObject("user");
JSONObject me = userJson.getJSONObject("me");
boolean following = me.getBoolean("following");
User user = new User(userJson.getInt("id"),
userJson.getString("username"),
userJson.getString("name"),
userJson.getString("location"),
userJson.getString("avatar_url"), following);
JSONObject meLiked = j.getJSONObject("me");
activities.add(new ActivityItems(j.getInt("id"), j
.getInt("views_count"),
j.getInt("likes_count"), j
.getInt("comments_count"), j
.getString("title"), j
.getString("image_url"), j
.getString("image_url_large"), j
.getString("image_url_small"), j
.getString("created_at"), meLiked
.getBoolean("liked"), user));
}
latest = new Latest(jObj.getInt("page_count"),
jObj.getInt("total_count"), activities);
} catch (JSONException e) {
e.printStackTrace();
}
return null;
}
protected void onPostExecute(Void result) {
Log.v("--", activities.size() + " activities");
adapter = new MainAdapter(getActivity(), activities);
list.setAdapter(adapter);
};
}.execute();
list.setOnItemClickListener(new OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> parent, View view,
int position, long id) {
try {
Intent intent = new Intent(getActivity(), ItemDetails.class);
intent.putExtra(Constants.ITEM_DETAILS,
activities.get(position));
startActivity(intent);
} catch (Exception e) {
e.printStackTrace();
}
}
});
}
private String getLatest() {
HttpClient httpclient = new DefaultHttpClient();
String result = null;
// Prepare a request object
HttpGet httpget = new HttpGet(
"http://api.staging.server.com/v1/shots/latest?access_token="
+ prefs.getString(Constants.TOKEN, ""));
// Execute the request
HttpResponse response;
try {
response = httpclient.execute(httpget);
// Examine the response status
Log.i("Praeda", response.getStatusLine().toString());
// Get hold of the response entity
HttpEntity entity = response.getEntity();
// If the response does not enclose an entity, there is no need
// to worry about connection release
if (entity != null) {
// A Simple JSON Response Read
InputStream instream = entity.getContent();
result = convertStreamToString(instream);
// now you have the string representation of the HTML request
instream.close();
}
} catch (Exception e) {
}
return result;
}
private String getActivityData() {
HttpClient httpclient = new DefaultHttpClient();
String result = null;
// Prepare a request object
HttpGet httpget = new HttpGet(
"http://api.staging.server.com/v1/session/activity?access_token="
+ prefs.getString(Constants.TOKEN, ""));
// Execute the request
HttpResponse response;
try {
response = httpclient.execute(httpget);
// Examine the response status
Log.i("Praeda", response.getStatusLine().toString());
// Get hold of the response entity
HttpEntity entity = response.getEntity();
// If the response does not enclose an entity, there is no need
// to worry about connection release
if (entity != null) {
// A Simple JSON Response Read
InputStream instream = entity.getContent();
result = convertStreamToString(instream);
// now you have the string representation of the HTML request
instream.close();
}
} catch (Exception e) {
}
return result;
}
public static String convertStreamToString(InputStream is) {
/*
* To convert the InputStream to String we use the
* BufferedReader.readLine() method. We iterate until the BufferedReader
* return null which means there's no more data to read. Each line will
* appended to a StringBuilder and returned as String.
*/
BufferedReader reader = new BufferedReader(new InputStreamReader(is));
StringBuilder sb = new StringBuilder();
String line = null;
try {
while ((line = reader.readLine()) != null) {
sb.append(line + "\n");
}
} catch (IOException e) {
e.printStackTrace();
} finally {
try {
is.close();
} catch (IOException e) {
e.printStackTrace();
}
}
return sb.toString();
}
}
下面是包含选项卡片段的片段活动：
public class ActivityExample extends FragmentActivity implements
ActionBar.TabListener {
private ViewPager viewPager;
private TabsPagerAdapter mAdapter;
private ActionBar actionBar;
// Tab titles
private String[] tabs = { "Following", "Popular", "Latest" };
@SuppressLint("NewApi")
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.tabbed_activity);
// Initilization
initActionBar();
viewPager = (ViewPager) findViewById(R.id.pager);
actionBar = getActionBar();
mAdapter = new TabsPagerAdapter(getSupportFragmentManager());
viewPager.setAdapter(mAdapter);
actionBar.setHomeButtonEnabled(false);
actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);
// Adding Tabs
for (String tab_name : tabs) {
actionBar.addTab(actionBar.newTab().setText(tab_name)
.setTabListener(this));
}
/**
* on swiping the viewpager make respective tab selected
* */
viewPager.setOnPageChangeListener(new ViewPager.OnPageChangeListener() {
@Override
public void onPageSelected(int position) {
// on changing the page
// make respected tab selected
actionBar.setSelectedNavigationItem(position);
}
@Override
public void onPageScrolled(int arg0, float arg1, int arg2) {
}
@Override
public void onPageScrollStateChanged(int arg0) {
}
});
}
@Override
public void onTabReselected(Tab tab, FragmentTransaction ft) {
}
@Override
public void onTabSelected(Tab tab, FragmentTransaction ft) {
// on tab selected
// show respected fragment view
viewPager.setCurrentItem(tab.getPosition());
}
@Override
public void onTabUnselected(Tab tab, FragmentTransaction ft) {
}
private void initActionBar() {
// title bar init
final ViewGroup actionBarLayout = (ViewGroup) getLayoutInflater()
.inflate(R.layout.activity_actionbar, null);
// Set up your ActionBar
final ActionBar actionBar = getActionBar();
actionBar.setDisplayShowCustomEnabled(true);
actionBar.setCustomView(actionBarLayout);
Typeface mTypeface = Typeface.createFromAsset(getAssets(),
"rockwell.ttf");
TextView title = (TextView) findViewById(R.id.activity_action_title);
// ImageButton back = (ImageButton) findViewById(R.id.signup_back);
// Button signUp = (Button) findViewById(R.id.signup_signup);
actionBar.setDisplayShowHomeEnabled(false);
actionBar.setDisplayHomeAsUpEnabled(false);
getActionBar().setDisplayHomeAsUpEnabled(false);
title.setText("Home");
title.setGravity(Gravity.CENTER);
title.setTypeface(mTypeface);
title.setTextSize(20);
}
}
这是我的标签
public class TabsPagerAdapter extends FragmentPagerAdapter {
public TabsPagerAdapter(FragmentManager fm) {
super(fm);
}
@Override
public Fragment getItem(int index) {
switch (index) {
case 0:
// Top Rated fragment activity
return new FollowingTab();
case 1:
// Games fragment activity
return new PopularTab();
case 2:
// Movies fragment activity
return new Main();
}
return null;
}
@Override
public int getCount() {
// get item count - equal to number of tabs
return 3;
}
}
# 1 楼答案
您的listview可能位于fragment layout中，您正在调用：
您应该通过调用initWidgets（rootView）和initWidgets put将rootView传递给initWidgets（）：