动态创建Fragment

在项目的开发过程中，动态创建fragment是没必要的，而且不太现实的，因为fragment要显示UI加载数据。因为我们的项目使用的跨平台的开发框架React Native，安卓的activity、fragment的只是用来显示js页面的容器，所有的业务都是js来实现的，包括底部的Tabbar切换都是js实现的，原生安卓只是显示出来。现在的需求是，根据底部的tabbar 创建fragment然后加载相应js的页面，默认只有一个fragment显示默认的js页面，比如默认首页，创建一个首页的fragment，切换到订单标签的时候再去创建订单的fragment,依次类推。

1、一般我们创建fragment的时候都是先一次性创建，然后往容器里面添加,像这样

private void initFragment() {    //实例化fragment    indexFragment = new IndexFragment();    newsFragment = new NewsFragment();    myFragment = new MyFragment();    originFragment = new OriginFragment();    //添加到数组    fragments = new Fragment[]{indexFragment, newsFragment, myFragment, originFragment};    //添加到容器并显示默认    getSupportFragmentManager().beginTransaction().add(R.id.fl_container, indexFragment)            .add(R.id.fl_container, newsFragment).add(R.id.fl_container, myFragment)            .add(R.id.fl_container, originFragment).hide(originFragment)            .hide(newsFragment).hide(myFragment).show(indexFragment).commit();}

下标签切换的时候

switch (tab) {    case "job":        index = 0;        break;    case "news":        index = 1;        break;    case "my":        index = 2;        break;    case "origin":        index = 3;        break;}if (currentIndex != index) {    FragmentTransaction ft = getSupportFragmentManager().beginTransaction();    ft.hide(fragments[currentIndex]);    if (!fragments[index].isAdded()) {        ft.add(R.id.fl_container, fragments[index]);    }    ft.show(fragments[index]).commit();}currentIndex = index;
像这样的写法是通过下标来切换。

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2、项目需求的写法，通过Map集合来存储Fragment，在切换底部Tabbar的时候先判断Map集合里面是否包含该标签的fragment，

如果没有创建并添加到Map集合里面去

private Map<String, Fragment> mapFragments = new HashMap<>();//初始化默认显示的页面private void init() {    indexFragment = new IndexFragment();    //fragment按标签添加到Map集合    mapFragments.put("job", indexFragment);    //提交事务    getSupportFragmentManager().beginTransaction().add(R.id.fl_container, indexFragment, "job")            .show(indexFragment).commit();}
底部TabBar切换的时候所做的处理
//默认显示标签的fragmentprivate String currentFragment = "job";private void changeTab(String tab) {    if (currentFragment.equals(tab))        return;    FragmentTransaction ft = getSupportFragmentManager().beginTransaction();    //把上个页面先隐藏    if (!currentFragment.equals(tab)) {        ft.hide(mapFragments.get(currentFragment));    }    //判断Map集合里面是否有该标签的fragment,如果没有创建并添加到集合    if (!mapFragments.containsKey(tab)) {        newsFragment = new NewsFragment();        Bundle bundle = new Bundle();        bundle.putString("type", tab);        newsFragment.setArguments(bundle);        mapFragments.put(tab, newsFragment);        ft.add(R.id.fl_container, newsFragment, tab);    }    ft.show(mapFragments.get(tab)).commit();    currentFragment = tab;    }
3、公用的fragment
public class NewsFragment extends Fragment {    private String tag = "news";    @Override    public void onCreate(@Nullable Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        Bundle bundle = getArguments();        if (bundle != null)            tag = bundle.getString("type");    }    @Nullable    @Override    public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {        View view = inflater.inflate(R.layout.layout_news, container, false);        FrameLayout layout = (FrameLayout) view.findViewById(R.id.fl_news);        Bundle bundle = new Bundle();        bundle.putString("type", tag);        // 缓存中不存在RootView,直接创建        ReactRootView mReactRootView = new ReactRootView(getActivity());        ReactInstanceManager reactInstanceManager = MainApplication.createReactInstanceManager(CodePushConstants.MAIN1_JS_BUNDLE_NAME);        mReactRootView.startReactApplication(                reactInstanceManager,                "init_project",                bundle);        layout.addView(mReactRootView);        return view;    }}
4、总结：
创建两个fragment，一个用于默认显示第一个页面，一个用来做公共的fragment，创建的时候通过tag标签标记该fragment并存储