android - 即使 fragment 被隐藏，FragmentTabHost 也会触发 onCreateView

Question

我在 fragment 中有一个 FragmentTabHost。我有 4 个标签。当我点击标签时，即使我使用 fragment 事务隐藏它，标签的 onCreateView 也会被触发？

我调试发现，当我从home选项卡中点击create选项卡时

CreateFragment createFragment = (CreateFragment) fm.findFragmentByTag(CREATE_TAG);

即使我在 tabHost.addTab 中添加了它，它还是 null？

如何在选项卡之间移动而不调用每个 fragment 的 onCreateView？

谢谢

这是 fragment 类

public class TabFragment extends Fragment {

public static final String HOME_TAG = "home";
public static final String CREATE_TAG = "create";
public static final String SEARCH_TAG = "search";
public static final String PROFILE_TAG = "profile";


private MyFragmentTabHost tabHost;
private MyFragmentTabHost.TabInfo tabInfo;

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup viewGroup, Bundle savedInstanceState){
    View view = inflater.inflate(R.layout.fragment_tab, viewGroup, false);

    tabHost = (MyFragmentTabHost) view.findViewById(android.R.id.tabhost);
    tabHost.setup(getActivity(), getChildFragmentManager(), android.R.id.tabcontent);
    tabHost.addTab(tabHost.newTabSpec(HOME_TAG).setIndicator(getString(R.string.tab_home)), HomeFragment.class, null);
    tabHost.addTab(tabHost.newTabSpec(CREATE_TAG).setIndicator(getString(R.string.tab_create)), CreateFragment.class, null);
    tabHost.addTab(tabHost.newTabSpec(SEARCH_TAG).setIndicator(getString(R.string.tab_search)), CreateFragment.class, null);
    tabHost.addTab(tabHost.newTabSpec(PROFILE_TAG).setIndicator(getString(R.string.tab_profile)), CreateFragment.class, null);

    MyFragmentTabHost.OnTabChangeListener tabListener = new MyFragmentTabHost.OnTabChangeListener() {
        @Override
        public void onTabChanged(String s) {
            FragmentManager fm = getChildFragmentManager();
            HomeFragment homeFragment = (HomeFragment) fm.findFragmentByTag(HOME_TAG);
            CreateFragment createFragment = (CreateFragment) fm.findFragmentByTag(CREATE_TAG);

            FragmentTransaction ft = fm.beginTransaction();

            if(s.equalsIgnoreCase(HOME_TAG)){
                if(homeFragment == null)
                    ft.add(R.id.tabcontent, new HomeFragment(), HOME_TAG);
                else{
                    if(createFragment != null)
                        ft.hide(createFragment);
                    ft.show(homeFragment);
                }
            }
            else if(s.equalsIgnoreCase(CREATE_TAG)){
                if(createFragment == null)
                    ft.add(R.id.tabcontent, new CreateFragment(), CREATE_TAG);
                else{
                    if(homeFragment != null)
                        ft.hide(homeFragment);
                    ft.show(createFragment);
                }
            }

            ft.commit();
        }
    };

    tabHost.setOnTabChangedListener(tabListener);

    return view;
}
}

Answer 1

在 FragmentTabHost 中:

private FragmentTransaction doTabChanged(String tabId, FragmentTransaction ft) {
    TabInfo newTab = null;
    for (int i=0; i<mTabs.size(); i++) {
        TabInfo tab = mTabs.get(i);
        if (tab.tag.equals(tabId)) {
            newTab = tab;
        }
    }
    if (newTab == null) {
        throw new IllegalStateException("No tab known for tag " + tabId);
    }
    if (mLastTab != newTab) {
        if (ft == null) {
            ft = mFragmentManager.beginTransaction();
        }
        if (mLastTab != null) {
            if (mLastTab.fragment != null) {
                ft.detach(mLastTab.fragment);
            }
        }
        if (newTab != null) {
            if (newTab.fragment == null) {
                newTab.fragment = Fragment.instantiate(mContext,
                        newTab.clss.getName(), newTab.args);
                ft.add(mContainerId, newTab.fragment, newTab.tag);
            } else {
                ft.attach(newTab.fragment);
            }
        }

        mLastTab = newTab;
    }
    return ft;
}

Transaction.attach(Fragment) 将重新创建 View ，请参阅源代码中的详细信息。所以，你可以在你的 fragment 中添加这样的代码:

public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
    if (!isCreated || mRootView == null) {
        isCreated = true;
        mRootView = inflater.inflate(R.layout.fragment_home_task, container, false);
        ButterKnife.bind(this,mRootView);
        onViewInitialized();
    }
    return mRootView;
}