方向更改后更改选项卡后选项卡内容保持可见

Question

我正在使用ActionBarSherlock 在我的应用程序中实现带有标签的ActionBar。 当我启动应用程序并从选项卡切换到选项卡时，一切都很好。但是，当我从纵向模式更改为横向模式时，上次活动的选项卡的内容仍然可见。更改为另一个选项卡会导致在旧内容之上绘制新内容（见图）。

我的主要课程：

public class TreinVerkeer extends SherlockFragmentActivity {

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

    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        MenuInflater inflater = getSupportMenuInflater();
        inflater.inflate(R.menu.menu, menu);
        return true;
    }

    private void setupTabs(Bundle savedInstanceState) {
        ActionBar actionBar = getSupportActionBar();
        actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);

        Tab tab = actionBar.newTab().setText("STATIONS").setTabListener(new TabListener<StationsFragment>(this, "stations", StationsFragment.class));
        actionBar.addTab(tab);

        tab = actionBar.newTab().setText("ROUTE").setTabListener(new TabListener<RouteFragment>(this, "route", RouteFragment.class));
        actionBar.addTab(tab);

        tab = actionBar.newTab().setText("DELAYS").setTabListener(new TabListener<DelaysFragment>(this, "delays", DelaysFragment.class));
        actionBar.addTab(tab);

        if (savedInstanceState != null) {
            actionBar.setSelectedNavigationItem(savedInstanceState.getInt("tab", 0));
        }
    }

    @Override
    protected void onSaveInstanceState(Bundle outState) {
        super.onSaveInstanceState(outState);
        outState.putInt("tab", getSupportActionBar().getSelectedNavigationIndex());
    }
}

TabListener（来自"Adding Navigations Tabs" on the Android developer site，稍作改动）：

public class TabListener<T extends SherlockFragment> implements com.actionbarsherlock.app.ActionBar.TabListener {
    private SherlockFragment mFragment;
    private final Activity mActivity;
    private final String mTag;
    private final Class<T> mClass;

    /**
     * Constructor used each time a new tab is created.
     * 
     * @param activity
     *            The host Activity, used to instantiate the fragment
     * @param tag
     *            The identifier tag for the fragment
     * @param clz
     *            The fragment's Class, used to instantiate the fragment
     */
    public TabListener(Activity activity, String tag, Class<T> clz) {
        mActivity = activity;
        mTag = tag;
        mClass = clz;
    }

    /* The following are each of the ActionBar.TabListener callbacks */

    public void onTabSelected(Tab tab, FragmentTransaction ft) {
        // Check if the fragment is already initialized
        if (mFragment == null) {
            // If not, instantiate and add it to the activity
            mFragment = (SherlockFragment) SherlockFragment.instantiate(mActivity, mClass.getName());
            ft.add(android.R.id.content, mFragment, mTag);
        } else {
            // If it exists, simply attach it in order to show it
            ft.attach(mFragment);
        }
    }

    public void onTabUnselected(Tab tab, FragmentTransaction ft) {
        if (mFragment != null) {
            // Detach the fragment, because another one is being attached
            ft.detach(mFragment);
        }
    }

    public void onTabReselected(Tab tab, FragmentTransaction ft) {
        // User selected the already selected tab. Usually do nothing.
    }
}

和StationsFragment（RouteFragment和DelaysFragment是一样的，只是文字不同）

public class StationsFragment extends SherlockFragment {

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

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

有了StationsFragment的布局文件：

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

    <TextView
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:text="Stations" />

</LinearLayout>

最后是 Manifest 文件：

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.myapp"
    android:versionCode="1"
    android:versionName="1.0" >

    <uses-sdk
        android:minSdkVersion="8"
        android:targetSdkVersion="15" />

    <application
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name" >
        <activity
            android:name=".TreinVerkeer"
            android:label="@string/app_name"
            android:theme="@style/Theme.Sherlock.Light" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>

我之前在启动应用程序时遇到了同样的问题（所以甚至没有改变方向），通过在主类的onCreate 中删除setContentView(R.layout.main) 解决了这个问题。但是，我找不到解决方案。谁能帮我解决这个问题？

Answer 1

FragmentManager 将在配置更改时自动恢复当前显示的任何片段（和历史记录）。在创建和附加新实例之前调用findFragmentByTag 以查看目标片段的实例是否已存在。

Answer 2

感谢 Jake，我更新了 onTabSelected 方法，如下所示：

public void onTabSelected(Tab tab, FragmentTransaction ft) {
    SherlockFragment preInitializedFragment = (SherlockFragment) mActivity.getSupportFragmentManager().findFragmentByTag(mTag);

    // Check if the fragment is already initialized
    if (mFragment == null && preInitializedFragment == null) {
        // If not, instantiate and add it to the activity
        mFragment = (SherlockFragment) SherlockFragment.instantiate(mActivity, mClass.getName());
        ft.add(android.R.id.content, mFragment, mTag);
    } else if (mFragment != null) {
        // If it exists, simply attach it in order to show it
        ft.attach(mFragment);
    } else if (preInitializedFragment != null) {
        ft.attach(preInitializedFragment);
        mFragment = preInitializedFragment;
    }
}

此答案仅用于澄清目的，感谢 Jake :)

Answer 3

除了 Niek 发布的更改之外，您还需要进行一些微不足道的更改。主要是把Activity改成SherlockFragmentActivity。

为了其他人的利益，这是我的最终版本，似乎可以正常工作。

   public static class TabListener<T extends SherlockFragment> implements ActionBar.TabListener
   {
      private SherlockFragment mFragment;
      private final SherlockFragmentActivity mActivity;
      private final String mTag;
      private final Class<T> mClass;

      /** Constructor used each time a new tab is created.
       * @param activity  The host Activity, used to instantiate the fragment
       * @param tag  The identifier tag for the fragment
       * @param clz  The fragment's Class, used to instantiate the fragment
       */
      public TabListener(Activity activity, String tag, Class<T> clz)
      {
         mActivity = (SherlockFragmentActivity) activity;
         mTag = tag;
         mClass = clz;
      }


      public void onTabSelected(Tab tab, FragmentTransaction ft)
      {
         // Check if the fragment has already been initialised
         SherlockFragment  preInitializedFragment = (SherlockFragment) mActivity.getSupportFragmentManager().findFragmentByTag(mTag);
         if (mFragment != null)
         {
            // If it exists, simply attach it in order to show it
            ft.attach(mFragment);
         }
         else if (preInitializedFragment != null)
         {
            mFragment = preInitializedFragment;
            ft.attach(mFragment);
         }
         else
         {
            // Not found, so instantiate and add it to the activity
            mFragment = (SherlockFragment) SherlockFragment.instantiate(mActivity, mClass.getName());
            ft.add(android.R.id.content, mFragment, mTag);
         }
      }


      public void onTabUnselected(Tab tab, FragmentTransaction ft)
      {
         if (mFragment != null) {
            // Detach the fragment, because another one is being attached
            ft.detach(mFragment);
         }
      }


      public void onTabReselected(Tab tab, FragmentTransaction ft)
      {
         // User selected the already selected tab. Usually do nothing.
      }
   }