使用后退按钮时,碎片并不总是被替换

Question

我正在使用操作栏标签,因为我需要在每个页面上都有导航元素.我正在使用ActionBarSherlock来实现向后兼容性(最低API 8,目标API 17).我的MainActivity扩展了SherlockFragmentActivity.在我onCreate()身上,我有

ActionBar actionBar = getSupportActionBar();
actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);

actionBar.setDisplayShowTitleEnabled(true);

Tab tab1 = actionBar.newTab().setText("My Pages")
    .setTabListener(new MyPagesFragment());

Tab tab2 = actionBar.newTab().setText("Search")
    .setTabListener(new SearchFragment());

Tab tab3 = actionBar.newTab().setText("About")
    .setTabListener(new AboutFragment());

// Start with the second tab selected.
actionBar.addTab(tab1, 0, false);
actionBar.addTab(tab2, 1, true);
actionBar.addTab(tab3, 2, false);

所有选项卡片段都是实现的SherlockListFragmentsActionBar.TabListener,并执行此操作

@Override
public void onTabSelected(Tab tab, FragmentTransaction ft) {
    ft.replace(android.R.id.content, this, "mypages");
}

@Override
public void onTabUnselected(Tab tab, FragmentTransaction ft) {
    ft.remove(this);
}

@Override
public void onTabReselected(Tab tab, FragmentTransaction ft) {
    // Force a complete reload.
    onTabSelected(tab, ft);
}

搜索页面有一个EditText,并在调用之前使用其值在AsyncTask中从API获取数据并将其添加到SQLite数据库中

((MainActivity) getActivity()).showDetailView(responseCode);

以显示细节,这是我的MainActivity的方法如下:

protected void showDetailView(long codeID) {
    SherlockFragment detailFragment = new DetailFragment();
    Bundle args = new Bundle();
    args.putLong("codeID", codeID);
    detailFragment.setArguments(args);

    FragmentManager manager = getSupportFragmentManager();
    FragmentTransaction ft = manager.beginTransaction();
    ft.replace(android.R.id.content, detailFragment);
    ft.addToBackStack(null);
    ft.commit();
}

DetailFragment是一个SherlockFragment,用于getArguments()检索codeID--

Bundle args = getArguments();
if (null != args) {
  codeRowID = args.getLong("codeID");
}

- 并从数据库中读取匹配数据以显示它.所述数据通常包含指向更多细节的链接,单击这些链接会导致使用新的codeID再次调用showDetailView.

MyPages是所有缓存详细信息页面的列表,它也调用showDetailView:

@Override
public void onItemClick(AdapterView<?> parent, View v, int position, long id) {
  ((MainActivity) getActivity()).showDetailView(pages[position].codeId);
}

展望未来,这似乎工作正常.但是,当我使用后退按钮时,有时碎片会粘在一起,因此它们仍然可以在恢复的碎片后面看到.我该如何阻止这种情况发生？

---

我认为问题可能是标签没有被添加到后台？但是当我尝试这样做时,他们会抛出异常,告诉我他们无法添加到后台,所以我不明白你应该如何处理这个问题.我不明白为什么这个东西,它似乎应该是一个令人难以置信的基本导航的东西,很多人都想做 - 后面的键已经在我见过的每个Android手机和桌子,物理或软件! - 显然没有已知的解决方案.我是否从根本上误解了他们的使用？片段是不是应该在这种情况下使用？你怎么做持久导航元素而不在每个页面上重复相同的代码？

---

记录 - 启动应用程序 -

07-20 23:33:49.521: D/NAVIGATION_TRACE(7425): MAIN - onCreate
07-20 23:33:50.013: D/NAVIGATION_TRACE(7425): SEARCH - onTabSelected
07-20 23:33:50.021: D/NAVIGATION_TRACE(7425): SEARCH - onCreateView
07-20 23:33:50.060: D/NAVIGATION_TRACE(7425): SEARCH - onActivityCreated
07-20 23:33:50.060: D/NAVIGATION_TRACE(7425): MAIN - onResume

现在搜索可见.搜索项目以显示详细信息视图 -

07-20 23:34:52.123: D/NAVIGATION_TRACE(7425): SEARCH - handleResponseCode
07-20 23:34:52.123: D/NAVIGATION_TRACE(7425): MAIN - showDetailView - 31

细节现在可见; 搜索消失了.单击mypages选项卡 -

07-20 23:35:37.787: D/NAVIGATION_TRACE(7425): SEARCH - onTabUnselected
07-20 23:35:37.787: D/NAVIGATION_TRACE(7425): MYPAGES - onTabSelected
07-20 23:35:37.826: D/NAVIGATION_TRACE(7425): MYPAGES - onCreateView
07-20 23:35:37.873: D/NAVIGATION_TRACE(7425): MYPAGES - onActivityCreated

MyPages现在可见; 细节不见了.点击后退按钮 -

07-20 23:36:12.130: D/NAVIGATION_TRACE(7425): SEARCH - onCreateView
07-20 23:36:12.201: D/NAVIGATION_TRACE(7425): SEARCH - onActivityCreated

搜索和 MyPages现在都显示.

---

主要活动:

public class MainActivity extends SherlockFragmentActivity 
{

    @Override
    protected void onCreate(Bundle savedInstanceState)
    {   
        super.onCreate(savedInstanceState);
        Log.d("NAVIGATION_TRACE", "MAIN - onCreate");

        ActionBar actionBar = getSupportActionBar();
        actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);

        actionBar.setDisplayShowTitleEnabled(true);

        Tab tab1 = actionBar.newTab().setText("My Pages")
            .setTabListener(new TabListener<MyPagesFragment>(
            this, "mypages", MyPagesFragment.class));

        Tab tab2 = actionBar.newTab().setText("Search")
            .setTabListener(new TabListener<SearchFragment>(
            this, "search", SearchFragment.class));

        Tab tab3 = actionBar.newTab().setText("About")
            .setTabListener(new TabListener<AboutFragment>(
            this, "about", AboutFragment.class));

        // Start with the second tab selected.
        actionBar.addTab(tab1, 0, false);
        actionBar.addTab(tab2, 1, true);
        actionBar.addTab(tab3, 2, false);
    }

    @Override
    public void onBackPressed()
    {
        FragmentManager fm = getSupportFragmentManager();
        if (0 < fm.getBackStackEntryCount())
        {
            super.onBackPressed();
        } else {
            // prompt to quit
            AlertDialog.Builder alertErrorResponse = new AlertDialog.Builder(this);
            alertErrorResponse.setMessage("Close app?");
            alertErrorResponse.setNegativeButton("Cancel", null);
            alertErrorResponse.setPositiveButton("OK", new DialogInterface.OnClickListener()
            {
            @Override
            public void onClick(DialogInterface dialog, int which)
            {
                finish();
            }
            });
            alertErrorResponse.show();
        }
    }

    public void showDetailView(long codeID) {
        Log.d("NAVIGATION_TRACE", "MAIN - showDetailView - "+String.valueOf(codeID));
        lastShownCode = codeID;
        FragmentManager manager = getSupportFragmentManager();
        FragmentTransaction ft = manager.beginTransaction();
        SherlockFragment detailFragment = new DetailFragment();
        Bundle args = new Bundle();
        args.putLong("codeID", codeID);
        detailFragment.setArguments(args);
        ft.replace(android.R.id.content, detailFragment, "details");
        ft.addToBackStack(null);
        ft.commit();
    }

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

        public TabListener (SherlockFragmentActivity activity, String tag, Class<T> clz) 
        {
            Log.d("NAVIGATION_TRACE", "TabListener - "+tag+" - "+clz.getCanonicalName());
            mActivity = activity;
            mTag = tag;
            mClass = clz;

            FragmentTransaction ft = mActivity.getSupportFragmentManager().beginTransaction();
            mFragment = (SherlockListFragment) mActivity.getSupportFragmentManager().findFragmentByTag(mTag);
            if (mFragment != null && !mFragment.isDetached()) 
            {
                Log.d("NAVIGATION_TRACE", "DETACH - "+mTag);
                removeDetail(ft);
                ft.detach(mFragment);
            }
            ft.commit();
        }

        public void clearBackStack()
        {
            Log.d("NAVIGATION_TRACE", "clearBackStack - "+mTag);
            FragmentManager fm = mActivity.getSupportFragmentManager();
            if (null != fm && 0 < fm.getBackStackEntryCount())
            {
            fm.popBackStack(null, FragmentManager.POP_BACK_STACK_INCLUSIVE);
            }
        }

        @Override
        public void onTabSelected(Tab tab, FragmentTransaction ft) 
        {
            Log.d("NAVIGATION_TRACE", "onTabSelected - "+mTag);

            clearBackStack();

            ft = mActivity.getSupportFragmentManager().beginTransaction();

            if (mFragment == null) 
            {
                Log.d("NAVIGATION_TRACE", "ADD/SHOW - "+mClass.getName());
                removeDetail(ft);
                mFragment = (SherlockListFragment) SherlockListFragment.instantiate(mActivity, mClass.getName());
                ft.add(android.R.id.content, mFragment, mTag);
                ft.commit();
            } 
            else 
            {
                Log.d("NAVIGATION_TRACE", "ATTACH/SHOW - "+mClass.getName());
                removeDetail(ft);
                ft.attach(mFragment);
                ft.show(mFragment);
                ft.commit();
            }

        }

        @Override
        public void onTabUnselected(Tab tab, FragmentTransaction ft) 
        {        
            Log.d("NAVIGATION_TRACE", "onTabUnselected - "+mTag);
            ft = mActivity.getSupportFragmentManager().beginTransaction();

            if (null != mFragment) 
            {
                Log.d("NAVIGATION_TRACE", "HIDE/DETACH - "+mTag);
                removeDetail(ft);
                ft.hide(mFragment);
                ft.detach(mFragment);
                ft.commitAllowingStateLoss();
            }
        }

        @Override
        public void onTabReselected(Tab tab, FragmentTransaction ft) {
        }

        public void removeDetail(FragmentTransaction ft) {
            SherlockFragment detailFragment = (SherlockFragment) mActivity.getSupportFragmentManager().findFragmentByTag("details");
            if (null != detailFragment && !detailFragment.isDetached()) {
            Log.d("NAVIGATION_TRACE", "DETACH - details");
            ft.detach(detailFragment);
            }
        }
    }   
}

示例片段 - MyPagesFragment:

public class MyPagesFragment extends SherlockListFragment implements
        OnItemClickListener
    {

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
        Bundle savedInstanceState)
    {
        Log.d("NAVIGATION_TRACE", "MYPAGES - onCreateView");
        View view = inflater.inflate(R.layout.mypages, null);

        // code to set up list adapter here
    }

    @Override
    public void onActivityCreated(Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);
        Log.d("NAVIGATION_TRACE", "MYPAGES - onActivityCreated");
        getListView().setOnItemClickListener(this);
    }

    @Override
    public void onItemClick(AdapterView<?> parent, View v, int position, long id)
    {
        Log.d("NAVIGATION_TRACE", "MYPAGES - onItemClick");
        ((MainActivity) getActivity()).showDetailView(pages[position].codeId);
    }
}

DetailFragment

public class DetailFragment extends SherlockFragment implements
        OnItemClickListener
{

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
        Bundle savedInstanceState)
    {       
        View view = inflater.inflate(R.layout.detail, null);

        // bunch of display / list set up code goes here

        return view;
    }

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

    @Override
    public void onItemClick(AdapterView<?> parent, View view, int position, long id)
    {
        // Details page can open other details pages:
        ((MainActivity) getActivity()).showDetailView(pages[position].id);
    }

}

---

注意:添加的更改是在Sheldon的回答之后做出的(他似乎已经烦恼地删除了他们的答案和注释),这就是TabListener代码在原始部分和后来发布的代码之间发生变化的原因.

我目前通过在每个选项卡选项上清空backstack来攻击解决方案,并将顶部选项卡作为退出应用程序请求进行处理,这是好的,我猜,但我真的希望用户能够保留如果可能的话,通过标签进行备份(因为这样,例如,如果我是五个详细信息页面,我停下来快速搜索某些内容,结果发现,不存在,我可以回到那些详细信息页面并且仍然会上升一个或多个以跟随不同的细节链接.)

Answer 1

尝试这个..

    FragmentManager manager = getSupportFragmentManager();
    if (manager.getBackStackEntryCount() > 0)
        getSupportFragmentManager().popBackStack();
    else
        finish();