使用带有片段的部分，NullPointerException
Posted
技术标签:
【中文标题】使用带有片段的部分，NullPointerException【英文标题】：Using sections with fragments, NullPointerException 【发布时间】：2012-11-28 02:51:36 【问题描述】：我之前通过使用 tablistener 并为每个片段设置一个类来完成带有选项卡的片段，现在我发现 Eclipse 允许您设置带有片段的选项卡或部分，所以我改用它。但现在我有一个问题。我在 mainactivity 类中创建了一个片段类。但是当我尝试更改文本视图中的数据时，我得到了一个空指针。
这里是代码
public class MainActivity extends FragmentActivity
/**
* The @link android.support.v4.view.PagerAdapter that will provide fragments for each of the
* sections. We use a @link android.support.v4.app.FragmentPagerAdapter derivative, which will
* keep every loaded fragment in memory. If this becomes too memory intensive, it may be best
* to switch to a @link android.support.v4.app.FragmentStatePagerAdapter.
*/
SectionsPagerAdapter mSectionsPagerAdapter;
/**
* The @link ViewPager that will host the section contents.
*/
ViewPager mViewPager;
@Override
public void onCreate(Bundle savedInstanceState)
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
// Create the adapter that will return a fragment for each of the three primary sections
// of the app.
mSectionsPagerAdapter = new SectionsPagerAdapter(getSupportFragmentManager());
// Set up the ViewPager with the sections adapter.
mViewPager = (ViewPager) findViewById(R.id.pager);
mViewPager.setAdapter(mSectionsPagerAdapter);
mViewPager.setCurrentItem(2);
@Override
public boolean onCreateOptionsMenu(Menu menu)
getMenuInflater().inflate(R.menu.activity_main, menu);
return true;
@SuppressWarnings("deprecation")
@Override
public boolean onOptionsItemSelected(MenuItem item)
return true;
/**
* A @link FragmentPagerAdapter that returns a fragment corresponding to one of the primary
* sections of the app.
*/
public class SectionsPagerAdapter extends FragmentPagerAdapter
public SectionsPagerAdapter(FragmentManager fm)
super(fm);
@Override
public Fragment getItem(int i)
Fragment fragment = new MainFragment();
Bundle args = new Bundle();
args.putInt(MainFragment.ARG_SECTION_NUMBER, i);
fragment.setArguments(args);
return fragment;
@Override
public int getCount()
return 4;
@Override
public CharSequence getPageTitle(int position)
switch (position)
case 0: return getString(R.string.title_section1).toUpperCase();
case 1: return getString(R.string.title_section2).toUpperCase();
case 2: return getString(R.string.title_section3).toUpperCase();
case 3: return getString(R.string.title_section4).toUpperCase();
return null;
public static class MainFragment extends Fragment
public static final String ARG_SECTION_NUMBER = "section_number";
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState)
super.onCreate(savedInstanceState);
Bundle args = getArguments();
int position = args.getInt(ARG_SECTION_NUMBER);
int tabLayout = 1;
switch(position)
case 0:
tabLayout = R.layout.tab1;
break;
case 1:
tabLayout = R.layout.tab2;
break;
case 2:
tabLayout = R.layout.tab3;
break;
case 3:
tabLayout = R.layout.tab4;
break;
View view = inflater.inflate(tabLayout, container, false);
TextView tv = (TextView) getActivity().findViewById(R.id.stats_squats);
tv.setText("DEPRSTgjhndkpgfhn");
return view;
我尝试了不同的方法来做到这一点：
TextView tv = (TextView) getActivity().findViewById(R.id.stats_squats);
tv.setText("DEPRSTgjhndkpgfhn");
TextView tv = (TextView) getView().findViewById(R.id.stats_squats);
tv.setText("DEPRSTgjhndkpgfhn");
TextView tv = (TextView) view.findViewById(R.id.stats_squats);
tv.setText("DEPRSTgjhndkpgfhn");
每次都出现同样的错误。
这里是 logcat 日志：
12-10 17:37:56.898: D/OpenGLRenderer(13574): Enabling debug mode 0
12-10 17:37:58.970: D/AndroidRuntime(13574): Shutting down VM
12-10 17:37:58.970: W/dalvikvm(13574): threadid=1: thread exiting with uncaught exception (group=0x40f82300)
12-10 17:37:58.980: E/AndroidRuntime(13574): FATAL EXCEPTION: main
12-10 17:37:58.980: E/AndroidRuntime(13574): java.lang.NullPointerException
12-10 17:37:58.980: E/AndroidRuntime(13574): at no.whg.workout.MainActivity$MainFragment.onCreateView(MainActivity.java:189)
12-10 17:37:58.980: E/AndroidRuntime(13574): at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:871)
12-10 17:37:58.980: E/AndroidRuntime(13574): at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1083)
12-10 17:37:58.980: E/AndroidRuntime(13574): at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:635)
12-10 17:37:58.980: E/AndroidRuntime(13574): at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1431)
12-10 17:37:58.980: E/AndroidRuntime(13574): at android.support.v4.app.FragmentManagerImpl.executePendingTransactions(FragmentManager.java:431)
12-10 17:37:58.980: E/AndroidRuntime(13574): at android.support.v4.app.FragmentPagerAdapter.finishUpdate(FragmentPagerAdapter.java:141)
12-10 17:37:58.980: E/AndroidRuntime(13574): at android.support.v4.view.ViewPager.populate(ViewPager.java:895)
12-10 17:37:58.980: E/AndroidRuntime(13574): at android.support.v4.view.ViewPager.populate(ViewPager.java:772)
12-10 17:37:58.980: E/AndroidRuntime(13574): at android.support.v4.view.ViewPager.onMeasure(ViewPager.java:1234)
12-10 17:37:58.980: E/AndroidRuntime(13574): at android.view.View.measure(View.java:15172)
12-10 17:37:58.980: E/AndroidRuntime(13574): at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:4816)
12-10 17:37:58.980: E/AndroidRuntime(13574): at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
12-10 17:37:58.980: E/AndroidRuntime(13574): at android.view.View.measure(View.java:15172)
12-10 17:37:58.980: E/AndroidRuntime(13574): at android.widget.LinearLayout.measureVertical(LinearLayout.java:833)
12-10 17:37:58.980: E/AndroidRuntime(13574): at android.widget.LinearLayout.onMeasure(LinearLayout.java:574)
12-10 17:37:58.980: E/AndroidRuntime(13574): at android.view.View.measure(View.java:15172)
12-10 17:37:58.980: E/AndroidRuntime(13574): at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:4816)
12-10 17:37:58.980: E/AndroidRuntime(13574): at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
12-10 17:37:58.980: E/AndroidRuntime(13574): at com.android.internal.policy.impl.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2435)
12-10 17:37:58.980: E/AndroidRuntime(13574): at android.view.View.measure(View.java:15172)
12-10 17:37:58.980: E/AndroidRuntime(13574): at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:1850)
12-10 17:37:58.980: E/AndroidRuntime(13574): at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1102)
12-10 17:37:58.980: E/AndroidRuntime(13574): at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1275)
12-10 17:37:58.980: E/AndroidRuntime(13574): at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1000)
12-10 17:37:58.980: E/AndroidRuntime(13574): at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:4214)
12-10 17:37:58.980: E/AndroidRuntime(13574): at android.view.Choreographer$CallbackRecord.run(Choreographer.java:725)
12-10 17:37:58.980: E/AndroidRuntime(13574): at android.view.Choreographer.doCallbacks(Choreographer.java:555)
12-10 17:37:58.980: E/AndroidRuntime(13574): at android.view.Choreographer.doFrame(Choreographer.java:525)
12-10 17:37:58.980: E/AndroidRuntime(13574): at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:711)
12-10 17:37:58.980: E/AndroidRuntime(13574): at android.os.Handler.handleCallback(Handler.java:615)
12-10 17:37:58.980: E/AndroidRuntime(13574): at android.os.Handler.dispatchMessage(Handler.java:92)
12-10 17:37:58.980: E/AndroidRuntime(13574): at android.os.Looper.loop(Looper.java:137)
12-10 17:37:58.980: E/AndroidRuntime(13574): at android.app.ActivityThread.main(ActivityThread.java:4931)
12-10 17:37:58.980: E/AndroidRuntime(13574): at java.lang.reflect.Method.invokeNative(Native Method)
12-10 17:37:58.980: E/AndroidRuntime(13574): at java.lang.reflect.Method.invoke(Method.java:511)
12-10 17:37:58.980: E/AndroidRuntime(13574): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:791)
12-10 17:37:58.980: E/AndroidRuntime(13574): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:558)
12-10 17:37:58.980: E/AndroidRuntime(13574): at dalvik.system.NativeStart.main(Native Method)
【问题讨论】：
尝试只输入 TextView tv = (TextView) findViewById(R.id.stats_squats);在 findView 方法之前没有任何方法。告诉我会发生什么。TextView 定义在哪个布局文件中？
由于这个TextView是在一个fragment类里面而不是一个activity里面，所以这行不通，我们得到的消息是Cannot make a static reference to the non-static method findViewById(int) from the type Activity
【参考方案1】：
如果您查看Fragment documentation，您会发现onCreateView() 在onCreateActivity() 之前运行。 getActivity() 将在 onCreateView() 中返回 null。您需要将该部分移出onCreateView() 并覆盖onActivityCreated()..
【讨论】：
谢谢。如果我不是无神论者，我会认为你是上帝。 Err... 好的哈哈。这里没有上帝，之前偶然发现了这个:)以上是关于使用带有片段的部分，NullPointerException的主要内容，如果未能解决你的问题，请参考以下文章