片段必须是在android studio中升级repo v9后出现的公共静态类崩溃错误

Question

我是Android的新手。我想创建一个活动与3个水平页面。每个页面都有一个网格视图。我使用ViewPager创建页面，并为每个页面使用GridView。下面是代码

public class CategoryActivity extends ActionBarActivity {

    static final int NUM_ITEMS = 3;

    MyAdapter mAdapter;

    ViewPager mPager;

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

        getSupportActionBar().hide();

        mAdapter = new MyAdapter(this.getSupportFragmentManager());

        mPager = (ViewPager)findViewById(R.id.pager);
        mPager.setAdapter(mAdapter);

    }

    //MyAdapter is adapter for Pager
    public class MyAdapter extends FragmentPagerAdapter {

        ArrayList<ArrayListFragment> fragments;
        public MyAdapter(FragmentManager fm) {
            super(fm);

            fragments = new ArrayList<>();

            for (int i = 0; i < NUM_ITEMS; i++) {
                ArrayListFragment f = new ArrayListFragment();

                fragments.add(f);
            }
       }

        @Override
        public int getCount() {
            return NUM_ITEMS;
        }

        @Override
        public Fragment getItem(int position) {

            //For each page -> get fragment for that page
            ArrayListFragment f = fragments.get(position);

            return f;
        }
    }

    //Adapter for each grid view in each Page
    public class ImageAdapter extends BaseAdapter {
        private Context mContext;
        private View parentView;

        public ImageAdapter(Context c) {
            mContext = c;
        }

        public ImageAdapter(Context c, View aParentView) {
            mContext = c;
            parentView = aParentView;
        }

        public int getCount() {
            return mThumbIds.length;
        }

        public Object getItem(int position) {
            return null;
        }

        public long getItemId(int position) {
            return 0;
        }

        // create a new ImageView for each item referenced by the Adapter
        public View getView(int position, View convertView, ViewGroup parent)        {
            View itemView;
            if (convertView == null) {

                //I really config view for each item in grid view....
                //The problem is not here
                //..........
            }
            return itemView;
        }

        // references to our images
        private Integer[] mThumbIds = {
                R.drawable.images, R.drawable.images,
                R.drawable.images, R.drawable.images,
                R.drawable.images, R.drawable.images,
                R.drawable.images, R.drawable.images,
                R.drawable.images, R.drawable.images,
                R.drawable.images, R.drawable.images
        };
    }

    public class ArrayListFragment extends Fragment {

        /**
         * When creating, retrieve this instance's number from its arguments.
         */
        @Override
        public void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
        }

        /**
         * The Fragment's UI is just a simple text view showing its
         * instance number.
         */
        @Override
        public View onCreateView(LayoutInflater inflater, ViewGroup container,
                                 Bundle savedInstanceState) {
            final View v = inflater.inflate(R.layout.fragment_pager_list, container, false);

            GridView gridview = (GridView) v.findViewById(R.id.categridview);

            ImageAdapter ia = new ImageAdapter(CategoryActivity.this, gridview);
            gridview.setAdapter(ia);

            return v;
        }


        @Override
        public void onActivityCreated(Bundle savedInstanceState) {
            super.onActivityCreated(savedInstanceState);

        }

    }
}

它在repo V7中工作得很好。但在我升级到repo v9后，它在以错误启动后崩溃

E/AndroidRuntime: FATAL EXCEPTION: main
                  Process: <my project process>, PID: 1901
                  java.lang.IllegalStateException: Fragment <my project package>.CategoryActivity.ArrayListFragment 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:426)
                      at android.support.v4.app.FragmentPagerAdapter.instantiateItem(FragmentPagerAdapter.java:103)
                      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:18788)
                      at android.widget.LinearLayout.measureVertical(LinearLayout.java:901)
                      at android.widget.LinearLayout.onMeasure(LinearLayout.java:630)
                      at android.view.View.measure(View.java:18788)
                      at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5951)
                      at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
                      at android.support.v7.widget.ContentFrameLayout.onMeasure(ContentFrameLayout.java:135)
                      at android.view.View.measure(View.java:18788)
                      at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5951)
                      at android.support.v7.widget.ActionBarOverlayLayout.onMeasure(ActionBarOverlayLayout.java:389)
                      at android.view.View.measure(View.java:18788)
                      at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5951)
                      at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
                      at android.view.View.measure(View.java:18788)
                      at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5951)
                      at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1465)
                      at android.widget.LinearLayout.measureVertical(LinearLayout.java:748)
                      at android.widget.LinearLayout.onMeasure(LinearLayout.java:630)
                      at android.view.View.measure(View.java:18788)
                      at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5951)
                      at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
                      at com.android.internal.policy.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2643)
                      at android.view.View.measure(View.java:18788)
                      at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:2100)
                      at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1216)
                      at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1452)
                      at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1107)
                      at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:6013)
                      at android.view.Choreographer$CallbackRecord.run(Choreographer.java:858)
                      at android.view.Choreographer.doCallbacks(Choreographer.java:670)
                      at android.view.Choreographer.doFrame(Choreographer.java:606)
                      at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:844)
                      at android.os.Handler.handleCallback(Handler.java:739)
                      at android.os.Handler.dispatchMessage(Handler.java:95)
                      at android.os.Looper.loop(Looper.java:148)
                      at android.app.ActivityThread.main(ActivityThread.java:5417)
                      at java.lang.reflect.Method.invoke(Native Method)
                      at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
                      at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
I/Process: Sending signal. PID: 1901 SIG: 9
Application terminated.

片段必须是从实例状态正确重新创建的公共静态类

为什么ArrayListFragment必须是一个公共静态类，我想每个类必须有一个单独的片段

这里有什么问题，有人能帮我弄清楚吗

Answer 1

ArrayListFragment与CategoryActivity在同一个java文件中吗？如果为真，则静态类意味着可以创建ArrayListFragment的实例，而无需创建CategoryActivity的实例。因此每个类都可以有自己的ArrayListFragment实例。