Fragment 中的 ViewPager 返回时会丢失内容

Question

我正在使用FragmentActivity 实现tabhost，在第一个选项卡下我加载了一个包含Viewpager 和CirclePageIndIcator 的欢迎片段，我需要在该WelcomeFragment 中加载4 个视图

这是我的 WelcomeFragment

public class WelcomeFragment extends Fragment
{
     PageAdapter mAdapter;
        ViewPager mPager;
        CirclePageIndicator mIndicator;
        List<Fragment> fragments;
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.frag_welcome_layout,null);
        mPager=(ViewPager)view.findViewById(R.id.myViewPager);
        mIndicator=(CirclePageIndicator)view.findViewById(R.id.circlePageIndicator1);
        fragments=new ArrayList<Fragment>();
        return view;
    }
    @Override
    public void onActivityCreated(Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);
        Fragment fragment;
        for(int i=0;i<4;i++)
        {
            fragment= Fragment.instantiate(getActivity(), TipsFragment.class.getName());
            fragments.add(fragment);
        }
            mAdapter = new PageAdapter(getFragmentManager(),fragments);
            mPager.setAdapter(mAdapter);
        mIndicator.setViewPager(mPager);
    }
}

这是我的页面适配器

public class PageAdapter extends FragmentPagerAdapter implements Serializable{

    List<Fragment> fragments;
    public PageAdapter(FragmentManager fm,List<Fragment> frags) {
        super(fm);
        fragments = frags;

    }

    @Override
    public Fragment getItem(int arg0) {
        // TODO Auto-generated method stub
        return TipsFragment.newInstance(0, 0);
    }

    @Override
    public int getCount() {
        // TODO Auto-generated method stub
        return 4;
    }

    @Override
    public void destroyItem(ViewGroup container, int position, Object object) {
        FragmentManager manager = ((Fragment) object).getFragmentManager();
        FragmentTransaction trans = manager.beginTransaction();
        trans.remove((Fragment) object);
        trans.commit();

        super.destroyItem(container, position, object);
    }

}

当我首先加载应用程序时，tabFragmentActivity 加载成功并且 welcomeFragment 中的 viewpager 工作正常，但是当我移动到第二个选项卡并再次返回到第一个选项卡时，ViewPager 没有成功加载。

我该如何解决？

根据我使用 getChildFragmentManager 的建议，但应用程序崩溃了 logcat 中的错误

09-09 13:28:39.412: E/AndroidRuntime(3100): FATAL EXCEPTION: main
09-09 13:28:39.412: E/AndroidRuntime(3100): java.lang.IllegalStateException: No activity
09-09 13:28:39.412: E/AndroidRuntime(3100):     at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1091)
09-09 13:28:39.412: E/AndroidRuntime(3100):     at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1086)
09-09 13:28:39.412: E/AndroidRuntime(3100):     at android.support.v4.app.FragmentManagerImpl.dispatchActivityCreated(FragmentManager.java:1877)
09-09 13:28:39.412: E/AndroidRuntime(3100):     at android.support.v4.app.Fragment.performActivityCreated(Fragment.java:1492)
09-09 13:28:39.412: E/AndroidRuntime(3100):     at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:947)
09-09 13:28:39.412: E/AndroidRuntime(3100):     at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1104)
09-09 13:28:39.412: E/AndroidRuntime(3100):     at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:682)
09-09 13:28:39.412: E/AndroidRuntime(3100):     at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1460)
09-09 13:28:39.412: E/AndroidRuntime(3100):     at android.support.v4.app.FragmentManagerImpl$1.run(FragmentManager.java:440)
09-09 13:28:39.412: E/AndroidRuntime(3100):     at android.os.Handler.handleCallback(Handler.java:725)
09-09 13:28:39.412: E/AndroidRuntime(3100):     at android.os.Handler.dispatchMessage(Handler.java:92)
09-09 13:28:39.412: E/AndroidRuntime(3100):     at android.os.Looper.loop(Looper.java:137)
09-09 13:28:39.412: E/AndroidRuntime(3100):     at android.app.ActivityThread.main(ActivityThread.java:5041)
09-09 13:28:39.412: E/AndroidRuntime(3100):     at java.lang.reflect.Method.invokeNative(Native Method)
09-09 13:28:39.412: E/AndroidRuntime(3100):     at java.lang.reflect.Method.invoke(Method.java:511)
09-09 13:28:39.412: E/AndroidRuntime(3100):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
09-09 13:28:39.412: E/AndroidRuntime(3100):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
09-09 13:28:39.412: E/AndroidRuntime(3100):     at dalvik.system.NativeStart.main(Native Method

)

Answer 1

如果您在Fragment 中使用ViewPager，则在创建新适配器时，您应该使用ChildFragmentManager：

getChildFragmentManager()

Answer 2

试试这个：

    ViewPager pager = [your viewPAger]
    pager.setOffscreenPageLimit([quantity of tabs that you are going to use]);

使用这句话 (pager.setOffscreenPageLimit)，您可以指定标签在被 ViewPager 擦除之前可以站立多远！

干杯！

Answer 3

使用 AsyncTask 设置 ViewPagerAdapter：

private class SetAdapterTask extends AsyncTask<Void, Void, Void> {
        protected Void doInBackground(Void... params) {
            return null;
        }

        @Override
        protected void onPostExecute(Void result) {

            if(mPagerAdapter != null) mViewPager.setAdapter(mPagerAdapter);
        }
    }   

这样称呼它：

mAdapter = new PageAdapter(getChildFragmentManager(), fragments);
new SetAdapterTask().execute();

而不是调用：

mViewPager.setAdapter(mPagerAdapter);

并且将适配器设置在 onCreateView(...) 方法中，不是 onActivityCreated(...).

另外，使用 getChildFragmentManager() 而不是 getFragmentManager()。