的Android IllegalStateException异常：片段空必须是一个公共静态类从实例状态正确地重新创建

Question

我得到以下异常从我的Android应用：

FATAL EXCEPTION: main 
java.lang.IllegalStateException: Fragment null must be a public static class to be properly recreated from instance state. 
at android.support.v4.app.BackStackRecord.doAddOp(BackStackRecord.java:435) 
at android.support.v4.app.BackStackRecord.add(BackStackRecord.java:420) 
at android.support.v4.app.FragmentStatePagerAdapter.instantiateItem(FragmentStatePagerAdapter.java:123) 
at android.support.v4.view.ViewPager.addNewItem(ViewPager.java:1006) 
at android.support.v4.view.ViewPager.populate(ViewPager.java:1154) 
at android.support.v4.view.ViewPager.populate(ViewPager.java:1088) 
at android.support.v4.view.ViewPager.onMeasure(ViewPager.java:1614) 
at android.view.View.measure(View.java:15525) 
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:4825) 
at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1404) 
at android.widget.LinearLayout.measureVertical(LinearLayout.java:695) 
at android.widget.LinearLayout.onMeasure(LinearLayout.java:588) 
at android.view.View.measure(View.java:15525) 
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:4825) 
at android.widget.FrameLayout.onMeasure(FrameLayout.java:310) 
at android.support.v7.widget.ContentFrameLayout.onMeasure(ContentFrameLayout.java:135) 
at android.view.View.measure(View.java:15525) 
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:4825) 
at android.support.v7.widget.ActionBarOverlayLayout.onMeasure(ActionBarOverlayLayout.java:389) 
at android.view.View.measure(View.java:15525) 
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:4825) 
at android.widget.FrameLayout.onMeasure(FrameLayout.java:310) 
at android.view.View.measure(View.java:15525) 
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:4825) 
at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1404) 
at android.widget.LinearLayout.measureVertical(LinearLayout.java:695) 
at android.widget.LinearLayout.onMeasure(LinearLayout.java:588) 
at android.view.View.measure(View.java:15525) 
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:4825) 
at android.widget.FrameLayout.onMeasure(FrameLayout.java:310) 
at com.android.internal.policy.impl.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2438) 
at android.view.View.measure(View.java:15525) 
at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:1874) 
at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1089) 
at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1265) 
at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:989) 
at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:4351) 
at android.view.Choreographer$CallbackRecord.run(Choreographer.java:749) 
at android.view.Choreographer.doCallbacks(Choreographer.java:562) 
at android.view.Choreographer.doFrame(Choreographer.java:532) 
at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:735) 
at android.os.Handler.handleCallback(Handler.java:725) 
at android.os.Handler.dispatchMessage(Handler.java:92) 
at android.os.Looper.loop(Looper.java:137) 
at android.app.ActivityThread.main(ActivityThread.java:5227) 
at java.lang.reflect.Method.invokeNative(Native Method) 
at java.lang.reflect.Method.invoke(Method.java:511) 
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:795) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:562) 
at dalvik.system.NativeStart.main(Native Method) 

不幸的是，除了不具有参考到我的代码。一旦我开始一个有碎片的活动，它就会出现。我认为，以下是我的代码的相关部分：

public class MonthViewActivity extends AppCompatActivity { 

    @Override 
    protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.activity_month); 

     getSupportActionBar().setDisplayHomeAsUpEnabled(true); 

     final ViewPager viewPager = (ViewPager) findViewById(R.id.pager); 
     viewPager.setAdapter(new FragmentStatePagerAdapter(getSupportFragmentManager()) { 
      @Override 
      public Fragment getItem(final int position) { 
       return new Fragment() { 
        @Override 
        public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) { 
         View rootView = inflater.inflate(R.layout.month_view, container, false); 
         return rootView; 
        } 
       }; 
      } 

      @Override 
      public int getCount() { 
       return 12; 
      } 
     }); 
     viewPager.addOnPageChangeListener(new ViewPager.OnPageChangeListener() { 
      @Override 
      public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) { 
      } 

      @Override 
      public void onPageSelected(int position) { 
       Month month = Year.getCurrent().getMonth(position); 
       TextView month_name = (TextView) findViewById(R.id.month_name); 
       month_name.setText(month.getName()); 
      } 

      @Override 
      public void onPageScrollStateChanged(int state) { 
      } 
     }); 
     viewPager.setCurrentItem(getIntent().getExtras().getInt("month")); 

     if (getIntent().getExtras().getInt("month") == 0) { 
      // The OnPageChangeListener doesn't do it for the first one 
      Month month = Year.getCurrent().getMonth(0); 
      TextView month_name = (TextView) findViewById(R.id.month_name); 
      month_name.setText(month.getName()); 
     } 
    } 
} 

此异常不是从我的应用程序，我使用的是Android 1.5.1工作室时，将引发。它刚刚升级到Android Studio 2.1.3后才出现。

其他人似乎也有类似的问题：Fragment must be a public static class to be properly recreated from instance state 但是，我找不到解决方案。

Answer 1

不确定，但你应该使用公共静态无效onPageSelected（INT位置）。只是试一试！

Answer 2

与Android支持的lib 24.2.0及以上版本，我们可以使用 支持Android的lib 23.0.0 检查出的问题：Fragment must be a public static class to be properly recreated from instance state