android - Tab 内的 ViewPager 无法正确显示项目

Question

我有一个设置 tabhost 的 FragmentActivity。每个选项卡都是一个称为 TabFragment 的简单 fragment 。 TabFragment 有一个 ViewPager，在本例中它是一个 InfiniteViewPager by antonyt (此处讨论:ViewPager as a circular queue / wrapping)。

(主要)问题如下:

1. 我启动应用程序。我单击第二个选项卡。当我看到与第一个选项卡中相同的内容时，只有一个空白屏幕。向右滚动几次后，我确实看到了我的 TextView。

2. 在 ViewPagers 中滚动 fragment 和更改选项卡最终会导致停止，并且 FC 不会抛出明确的异常。

这是我第一次接触 Fragments，我必须承认，我不理解观察到的行为。

如有任何提示，我们将不胜感激。

整个项目是here .

代码:

带有 TabHost 的 FragmentActivity:

    package com.example.viewpagerintab;

    import java.util.HashMap;

    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.FragmentTransaction;
    import android.view.View;
    import android.widget.TabHost;
    import android.widget.TabHost.TabContentFactory;

    public class TabsFragmentActivity extends FragmentActivity implements
            TabHost.OnTabChangeListener {

        private TabHost mTabHost;
        private HashMap mapTabInfo = new HashMap();
        private TabInfo mLastTab = null;

        public TabsFragmentActivity() {

        }

        private class TabInfo {
            private String tag;
            private Class clss;
            private Bundle args;
            private Fragment fragment;

            TabInfo(String tag, Class classObject, Bundle args) {
                this.tag = tag;
                this.clss = classObject;
                this.args = args;
            }

        }

        class TabFactory implements TabContentFactory {

            private final Context mContext;

            /**
             * @param context
             */
            public TabFactory(Context context) {
                mContext = context;
            }

            /**
             * (non-Javadoc)
             * 
             * @see android.widget.TabHost.TabContentFactory#createTabContent(java.lang.String)
             */
            public View createTabContent(String tag) {
                View v = new View(mContext);
                v.setMinimumWidth(0);
                v.setMinimumHeight(0);
                return v;
            }

        }

        /**
         * (non-Javadoc)
         * 
         * @see android.support.v4.app.FragmentActivity#onCreate(android.os.Bundle)
         */
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);

            setContentView(R.layout.tabs);

            initialiseTabHost(savedInstanceState);

            if (savedInstanceState != null) {
                mTabHost.setCurrentTabByTag(savedInstanceState.getString("tab"));
            }
        }

        /**
         * (non-Javadoc)
         * 
         * @see android.support.v4.app.FragmentActivity#onSaveInstanceState(android.os.Bundle)
         */
        protected void onSaveInstanceState(Bundle outState) {
            outState.putString("tab", mTabHost.getCurrentTabTag());
            super.onSaveInstanceState(outState);
        }

        private void initialiseTabHost(Bundle args) {
            mTabHost = (TabHost) findViewById(android.R.id.tabhost);
            mTabHost.setup();
            TabInfo tabInfo = null;

            tabInfo = new TabInfo("Discover", TabFragmentD.class, args);
            TabsFragmentActivity.addTab(this, mTabHost,
                    mTabHost.newTabSpec("Discover").setIndicator("Discover"),
                    tabInfo);
            mapTabInfo.put(tabInfo.tag, tabInfo);

            tabInfo = new TabInfo("Friends", TabFragmentF.class, args);
            TabsFragmentActivity
                    .addTab(this, mTabHost, mTabHost.newTabSpec("Friends")
                            .setIndicator("Friends"), tabInfo);
            mapTabInfo.put(tabInfo.tag, tabInfo);

            onTabChanged("Discover");

            mTabHost.setOnTabChangedListener(this);
        }

        /**
         * @param activity
         * @param tabHost
         * @param tabSpec
         * @param clss
         * @param args
         */
        private static void addTab(TabsFragmentActivity activity, TabHost tabHost,
                TabHost.TabSpec tabSpec, TabInfo tabInfo) {

            // Attach a Tab view factory to the spec
            tabSpec.setContent(activity.new TabFactory(activity));
            String tag = tabSpec.getTag();

            // Check to see if we already have a fragment for this tab, probably
            // from a previously saved state. If so, deactivate it, because our
            // initial state is that a tab isn't shown.
            tabInfo.fragment = activity.getSupportFragmentManager()
                    .findFragmentByTag(tag);
            if (tabInfo.fragment != null && !tabInfo.fragment.isDetached()) {
                FragmentTransaction ft = activity.getSupportFragmentManager()
                        .beginTransaction();
                ft.detach(tabInfo.fragment);
                ft.commit();
                activity.getSupportFragmentManager().executePendingTransactions();
            }

            tabHost.addTab(tabSpec);
        }

        /**
         * (non-Javadoc)
         * 
         * @see android.widget.TabHost.OnTabChangeListener#onTabChanged(java.lang.String)
         */
        public void onTabChanged(String tag) {
            TabInfo newTab = mapTabInfo.get(tag);
            if (mLastTab != newTab) {
                FragmentTransaction ft = getSupportFragmentManager()
                        .beginTransaction();
                if (mLastTab != null) {
                    if (mLastTab.fragment != null) {
                        ft.detach(mLastTab.fragment);
                    }
                }
                if (newTab != null) {
                    if (newTab.fragment == null) {
                        newTab.fragment = Fragment.instantiate(this,
                                newTab.clss.getName(), newTab.args);
                        ft.add(R.id.realtabcontent, newTab.fragment, newTab.tag);
                    } else {
                        ft.attach(newTab.fragment);
                    }
                }

                mLastTab = newTab;
                ft.commit();
                getSupportFragmentManager().executePendingTransactions();
            }
        }

    }

包含 InfiniteViewPager 的 TabFragment:

    package com.example.viewpagerintab;

    import java.util.List;
    import java.util.Vector;

    import android.os.AsyncTask;
    import android.os.Bundle;
    import android.support.v4.app.Fragment;
    import android.support.v4.app.FragmentPagerAdapter;
    import android.support.v4.view.ViewPager;
    import android.support.v4.view.ViewPager.OnPageChangeListener;
    import android.util.Log;
    import android.view.LayoutInflater;
    import android.view.View;
    import android.view.ViewGroup;
    import android.widget.LinearLayout;

    import com.antonyt.infiniteviewpager.InfinitePagerAdapter;
    import com.example.viewpagerintab.pager.SimpleAdapter;

    public class TabFragment extends Fragment {

        private static final String TAG = TabFragment.class.getSimpleName();

        protected View mView;

        ViewPager mViewPager;

        private InfinitePagerAdapter mPagerAdapter;

        PageListener pageListener;

        public TabFragment() {

        }

        /**
         * (non-Javadoc)
         * 
         * @see android.support.v4.app.Fragment#onCreateView(android.view.LayoutInflater,
         *      android.view.ViewGroup, android.os.Bundle)
         */
        public View onCreateView(LayoutInflater inflater, ViewGroup container,
                Bundle savedInstanceState) {

            Log.d(TAG, "onCreateView - called");

            if (container == null) {
                // We have different layouts, and in one of them this
                // fragment's containing frame doesn't exist. The fragment
                // may still be created from its saved state, but there is
                // no reason to try to create its view hierarchy because it
                // won't be displayed. Note this is not needed -- we could
                // just run the code below, where we would create and return
                // the view hierarchy; it would just never be used.
                return null;
            }

            pageListener = new PageListener();

            mView = (LinearLayout) inflater.inflate(R.layout.tab, container, false);

            List fragments = new Vector();
            fragments.add(DayFragment.newInstance("one"));
            fragments.add(DayFragment.newInstance("two"));
            fragments.add(DayFragment.newInstance("three"));
            fragments.add(DayFragment.newInstance("four"));

            mPagerAdapter = new InfinitePagerAdapter(
                    new com.example.viewpagerintab.PagerAdapter(
                            getFragmentManager(), fragments));

            mViewPager = (ViewPager) mView.findViewById(R.id.viewpager);

            mViewPager.setOnPageChangeListener(pageListener);

            new setAdapterTask().execute();

            Log.d(TAG, "onCreateView - finished");

            return mView;
        }

        private class setAdapterTask extends AsyncTask {
            protected Void doInBackground(Void... params) {
                return null;
            }

            @Override
            protected void onPostExecute(Void result) {
                mViewPager.setAdapter(mPagerAdapter);
            }
        }

        class PageListener implements OnPageChangeListener {
            private final String TAG = PageListener.class.getSimpleName();

            @Override
            public void onPageScrollStateChanged(int arg0) {
                Log.d(TAG, "onPageScrollStateChanged(..) to: " + arg0);

            }

            @Override
            public void onPageScrolled(int arg0, float arg1, int arg2) {
                // Log.d(TAG, "onPageScrolled(..) - called");

            }

            @Override
            public void onPageSelected(int arg0) {
                Log.d(TAG, "onPageSelected(..) selected: " + arg0);

            }
        }
    }

TabFragmentD 和 TabFragmentF 几乎相同:

    public class TabFragmentD extends TabFragment {

        public TabFragmentD() {

        }

    }

仅包含一个 TextView 的 DayFragment:

    package com.example.viewpagerintab;

    import android.os.Bundle;
    import android.support.v4.app.Fragment;
    import android.util.Log;
    import android.view.LayoutInflater;
    import android.view.View;
    import android.view.ViewGroup;
    import android.widget.LinearLayout;
    import android.widget.TextView;

    public class DayFragment extends Fragment {

        private static final String TAG = DayFragment.class.getSimpleName();

        protected View mView;

        protected TextView tvDay;

        public DayFragment() {

        }

        /**
         * (non-Javadoc)
         * 
         * @see android.support.v4.app.Fragment#onCreateView(android.view.LayoutInflater,
         *      android.view.ViewGroup, android.os.Bundle)
         */
        public View onCreateView(LayoutInflater inflater, ViewGroup container,
                Bundle savedInstanceState) {

            if (container == null) {
                // We have different layouts, and in one of them this
                // fragment's containing frame doesn't exist. The fragment
                // may still be created from its saved state, but there is
                // no reason to try to create its view hierarchy because it
                // won't be displayed. Note this is not needed -- we could
                // just run the code below, where we would create and return
                // the view hierarchy; it would just never be used.
                return null;
            }

            mView = (LinearLayout) inflater.inflate(R.layout.day, container, false);

            tvDay = (TextView) mView.findViewById(R.id.tvText);

            String text = getArguments().getString("text");
            Log.d(TAG, "creating view with text: " + text);

            tvDay.setText(text);

            return mView;
        }

        public static DayFragment newInstance(String text) {
            Log.d(TAG, "newInstance with text: " + text);
            DayFragment f = new DayFragment();

            // Supply text input as an argument.
            Bundle args = new Bundle();
            args.putString("text", text);
            f.setArguments(args);

            return f;
        }

    }

寻呼机适配器:

    package com.example.viewpagerintab;

    import java.util.List;

    import android.support.v4.app.Fragment;
    import android.support.v4.app.FragmentManager;
    import android.support.v4.app.FragmentPagerAdapter;

    public class PagerAdapter extends FragmentPagerAdapter {

        private List fragments;

        public PagerAdapter(FragmentManager fm, List fragments) {
            super(fm);
            this.fragments = fragments;
        }

        /*
         * (non-Javadoc)
         * 
         * @see android.support.v4.app.FragmentPagerAdapter#getItem(int)
         */
        @Override
        public Fragment getItem(int position) {
            return fragments.get(position);
        }

        /*
         * (non-Javadoc)
         * 
         * @see android.support.v4.view.PagerAdapter#getCount()
         */
        @Override
        public int getCount() {
            return this.fragments.size();
        }
    }

InfiniteViewPager 和 InfinitePageAdapter 在 antonyt's github 上.

tabs.xml:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical" >

<TabHost
    android:id="@android:id/tabhost"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent" >

    <LinearLayout
        android:layout_width="fill_parent"
        android:layout_height="fill_parent"
        android:orientation="vertical" >

        <TabWidget
            android:id="@android:id/tabs"
            android:layout_width="fill_parent"
            android:layout_height="wrap_content"
            android:layout_weight="0"
            android:orientation="horizontal" />

        <FrameLayout
            android:id="@android:id/tabcontent"
            android:layout_width="0dp"
            android:layout_height="0dp"
            android:layout_weight="0" />

        <FrameLayout
            android:id="@+android:id/realtabcontent"
            android:layout_width="fill_parent"
            android:layout_height="0dp"
            android:layout_weight="1" />
    </LinearLayout>
</TabHost>
</LinearLayout>

tab.xml:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:background="@android:color/black" >

<com.antonyt.infiniteviewpager.InfiniteViewPager
    android:id="@+android:id/viewpager"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent" />

</LinearLayout>

day.xml:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:background="@android:color/black"
android:gravity="center" >

<TextView
    android:id="@+id/tvText"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:textColor="@android:color/white" />

</LinearLayout>

更新

正如 CommonsWare 所指出的，Android 存在 fragment 中的 fragment 问题。

我将 tabs.xml 修改为:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:orientation="vertical" >

    <TabHost
        android:id="@android:id/tabhost"
        android:layout_width="fill_parent"
        android:layout_height="fill_parent" >

        <LinearLayout
            android:layout_width="fill_parent"
            android:layout_height="fill_parent"
            android:orientation="vertical" >

            <TabWidget
                android:id="@android:id/tabs"
                android:layout_width="fill_parent"
                android:layout_height="wrap_content"
                android:layout_weight="0"
                android:orientation="horizontal" />

            <FrameLayout
                android:id="@android:id/tabcontent"
                android:layout_width="0dp"
                android:layout_height="0dp"
                android:layout_weight="0" />

            <FrameLayout
                android:id="@+android:id/realtabcontent"
                android:layout_width="fill_parent"
                android:layout_height="0dp"
                android:layout_weight="0" />

            <com.antonyt.infiniteviewpager.InfiniteViewPager
                android:id="@+android:id/viewpager"
                android:layout_width="fill_parent"
                android:layout_height="0dp"
                android:layout_weight="1" />
        </LinearLayout>
    </TabHost>

</LinearLayout>

并创建了空的 TabFragments (tab.xml):

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="0dp"
    android:layout_height="0dp" >

</LinearLayout>

因此，现在切换标签几乎与滑动无关。

唯一的缺点是，在更改选项卡后尝试将 ViewPager 的当前位置设置为 0 时会出现一个非常烦人的问题(应用程序无一异常(exception)地崩溃了)。

Answer 1

不支持 fragment 内的 fragment ，according to the author of the fragments framework .

据我所知，您有一个 fragment 保存在您的 ViewPager 上，它又使用返回 fragment 的 PagerAdapter。这将无法可靠地工作。

要么将 ViewPager 移出 fragment (因此它直接由 Activity 持有)，要么切换到不使用 fragment 的 PagerAdapter 实现。