TabHost 显示一次内容 (onCreate)

Question

我在 navigationDrawer 中有一个 TabHost，我正面临这个奇怪的问题，当我从作为导航抽屉项目存在的 TabHost 转到另一个导航时，就会出现这个问题抽屉项目并返回 TabHost 它不会显示其内容，第一次它完美地工作但是当我更改项目并返回它时，它不会显示内容；换句话说，它不会加载子片段，除非我关闭应用程序并重新启动它或更改方向（重新创建片段）。

我第一次打开它时的样子（有内容）

转到另一个 navDrawer Item 和 return 到 TabHost 之后

TabHost 片段：

import android.content.Context;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentActivity;
import android.support.v4.app.FragmentPagerAdapter;
import android.support.v4.view.ViewPager;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TabHost;
import android.widget.TabWidget;

import java.util.ArrayList;

import info.fds.Emirates.R;

public  class MyFragment extends Fragment
{

    private TabHost mTabHost;
    private ViewPager mViewPager;
    private TabsAdapter mTabsAdapter;

    public MyFragment() {
    }

    @Override
    public void onCreate(Bundle instance)
    {
        super.onCreate(instance);

    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        View v = inflater.inflate(R.layout.fragment_main, container, false);

        mTabHost = (TabHost) v.findViewById(android.R.id.tabhost);
        mTabHost.setup();

        mViewPager = (ViewPager) v.findViewById(R.id.pager);
        mTabsAdapter = new TabsAdapter(getActivity(), mTabHost, mViewPager);



        return v;
    }

    @Override
    public void onResume() {
        super.onResume();
        // Here we load the content for each tab.
        mTabsAdapter.addTab(mTabHost.newTabSpec("Incident").setIndicator("Incident"), PageOneFragment.class, null);
        mTabsAdapter.addTab(mTabHost.newTabSpec("Service Request").setIndicator("Service Request"), PageTwoFragment.class, null);
    }

    public static class TabsAdapter extends FragmentPagerAdapter implements TabHost.OnTabChangeListener, ViewPager.OnPageChangeListener
    {
        private final Context mContext;
        private final TabHost mTabHost;
        private final ViewPager mViewPager;
        private final ArrayList<TabInfo> mTabs = new ArrayList<TabInfo>();

        static final class TabInfo
        {
            private final String tag;
            private final Class<?> clss;
            private final Bundle args;

            TabInfo(String _tag, Class<?> _class, Bundle _args)
            {
                tag = _tag;
                clss = _class;
                args = _args;
            }
        }

        static class DummyTabFactory implements TabHost.TabContentFactory
        {
            private final Context mContext;

            public DummyTabFactory(Context context)
            {
                mContext = context;
            }

            public View createTabContent(String tag)
            {
                View v = new View(mContext);
                v.setMinimumWidth(0);
                v.setMinimumHeight(0);
                return v;
            }
        }

        public TabsAdapter(FragmentActivity activity, TabHost tabHost, ViewPager pager)
        {
            super(activity.getSupportFragmentManager());
            mContext = activity;
            mTabHost = tabHost;
            mViewPager = pager;
            mTabHost.setOnTabChangedListener(this);
            mViewPager.setAdapter(this);
            mViewPager.setOnPageChangeListener(this);
        }

        public void addTab(TabHost.TabSpec tabSpec, Class<?> clss, Bundle args)
        {
            tabSpec.setContent(new DummyTabFactory(mContext));
            String tag = tabSpec.getTag();

            TabInfo info = new TabInfo(tag, clss, args);
            mTabs.add(info);
            mTabHost.addTab(tabSpec);
            notifyDataSetChanged();
        }

        @Override
        public int getCount()
        {
            return mTabs.size();
        }

        @Override
        public Fragment getItem(int position)
        {
            TabInfo info = mTabs.get(position);

            return Fragment.instantiate(mContext, info.clss.getName(), info.args);

        }

        public void onTabChanged(String tabId)
        {
            int position = mTabHost.getCurrentTab();
            mViewPager.setCurrentItem(position);
        }

        public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels)
        {
        }

        public void onPageSelected(int position)
        {
            // Unfortunately when TabHost changes the current tab, it kindly
            // also takes care of putting focus on it when not in touch mode.
            // The jerk.
            // This hack tries to prevent this from pulling focus out of our
            // ViewPager.
            TabWidget widget = mTabHost.getTabWidget();
            int oldFocusability = widget.getDescendantFocusability();
            widget.setDescendantFocusability(ViewGroup.FOCUS_BLOCK_DESCENDANTS);
            mTabHost.setCurrentTab(position);
            widget.setDescendantFocusability(oldFocusability);
        }

        public void onPageScrollStateChanged(int state)
        {
        }
    }
}

PageOneFragment:

public class PageOneFragment extends Fragment
{
    @Override
    public void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)
    {
        return inflater.inflate(R.layout.pageone_fragment, container, false);
    }

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

    @Override
    public void onAttach(Activity activity)
    {
        super.onAttach(activity);
    }

    @Override
    public void onStart()
    {
        super.onStart();
    }

    @Override
    public void onResume()
    {
        super.onResume();
    }
}

PageTwoFragment

public class PageTwoFragment extends Fragment
{
    @Override
    public void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)
    {
        return inflater.inflate(R.layout.pagetwo_fragment, container, false);
    }

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

    @Override
    public void onAttach(Activity activity)
    {
        super.onAttach(activity);
    }

    @Override
    public void onStart()
    {
        super.onStart();
    }

    @Override
    public void onResume()
    {
        super.onResume();
    }
}

注意： 调试后我注意到 onCreateView() 在 PageOneFragment 和 PageTwoFragment 未执行。

这是怎么回事，为什么 tabHost 在导航到另一个项目后没有加载它的内容？

编辑： 经过数小时的痛苦调试，我发现我的代码在第二次调用时从未执行过休假方法：

@Override
        public Fragment getItem(int position)//never get executed after the second call
        {
            TabInfo info = mTabs.get(position);

            return Fragment.instantiate(mContext, info.clss.getName(), info.args);

        }

我该如何解决这个问题？

非常感谢任何帮助。

提前致谢。

Answer 1

这个荒谬的错误浪费了我很多时间，而解决方案其实很简单，问题是我用 FragmentPagerAdapter 而不是 FragmentStatePagerAdapter 替换后，一切正常，希望这能帮助其他有类似问题的人。

Answer 2

在您的代码中，FragmentPageAdapter 将使用 activity 的 FragmentManager，但是当 instantiateItem 在 FragmentPageAdapter 中时，它会在activity 的 FragmentManager。不幸的是，PageOneFragment和PageTwoFragment已经在activity的FragmentManager中，所以没有新创建PageOneFragment和PageTwoFragment , FragmentPageAdapter 将使用 Fragment backstack 中的 PageOneFragment。但是在最后的FragmentPageAdapter中添加了PageOneFragment，然后就没有内容了。

使用 FragmentPageStateAdapter 替换 FragmentPageAdapter 是一个简单的选择。如果你想在某些时候使用比FragmentPageStateAdapter更好的FragmentPageAdapter，你可以这样使用：

    public TabsAdapter(Fragment fragment, TabHost tabHost, ViewPager pager)
    {
        super(fragment.getChildFragmentManager());


        mContext = fragment.getActivity();
        mTabHost = tabHost;
        mViewPager = pager;
        mTabHost.setOnTabChangedListener(this);
        mViewPager.setAdapter(this);
        mViewPager.setOnPageChangeListener(this);
        Log.i("Test", "TabsAdapter super");
    }

使用 ChildFragmentManager.

我觉得把activity的FragmentManager里面的PageOneFragment和PageTwoFragment去掉也是可以的。

TabHost 显示一次内容 (onCreate)

TabHost displays content once (onCreate)

java

android

fragment

android-tabhost

navigation-drawer