Android 如何在FragmentTabHost中获取当前选定的片段

还有一些问题与这个问题有关。例如但它不起作用

让我展示一下我在代码中做了什么

活动\u main.xml

<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools" android:id="@+id/container"
    android:layout_width="match_parent" android:layout_height="match_parent"
    tools:context=".MainActivity" tools:ignore="MergeRootFrame" >

    <fragment
        android:id="@+id/my_fragment"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:name="com.example.zhouhao.test.MyFragment"
        tools:layout="@layout/fragment_my" />

</FrameLayout>

公共类MyFragment扩展片段实现了TabHost.OnTabChangeListener{

FragmentTabHost mFragmentTabHost;


public MyFragment() {
}

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    View rootView = inflater.inflate(R.layout.fragment_my, container, false);
    if (rootView != null) {
        mFragmentTabHost = (FragmentTabHost) rootView.findViewById(android.R.id.tabhost);
        mFragmentTabHost.setup(getActivity(), getActivity().getSupportFragmentManager(), R.id.panel_content);
        TabFragment1 tab1Fragment = new TabFragment1();
        TabFragment2 tab2Fragment = new TabFragment2();
        TabFragment3 tab3Fragment = new TabFragment3();
        TabHost.TabSpec spec1 = mFragmentTabHost.newTabSpec("1").setIndicator("");
        TabHost.TabSpec spec2 = mFragmentTabHost.newTabSpec("2").setIndicator("");
        TabHost.TabSpec spec3 = mFragmentTabHost.newTabSpec("3").setIndicator("");
        mFragmentTabHost.addTab(spec1,tab1Fragment.getClass(), null);
        mFragmentTabHost.addTab(spec2,tab2Fragment.getClass(), null);
        mFragmentTabHost.addTab(spec3,tab3Fragment.getClass(), null);
        mFragmentTabHost.setOnTabChangedListener(this);
        return rootView;
    } else {
        return super.onCreateView(inflater, container, savedInstanceState);
    }
}

@Override
public void onTabChanged(String tabId) {

    BaseFragment f = (BaseFragment)getActivity().getSupportFragmentManager().findFragmentByTag(tabId);
    Log.d("Log",tabId);
}

}

---

我的问题是BaseFragment在我的onTabChanged中总是空的。有人能帮忙吗？谢谢。

如果所选片段从未实例化，则无法立即获取该片段

@Override
public void onTabChanged(final String tabId) {
    Fragment fg = getSupportFragmentManager().findFragmentByTag(tabId);
    Log.d(TAG, "onTabChanged(): " + tabId + ", fragment " + fg);

    if (fg == null) {
        new Handler().postDelayed(new Runnable() {            
            @Override
            public void run() {
                Fragment fg = getSupportFragmentManager().findFragmentByTag(tabId);
                Log.d(TAG, "onTabChanged() delay 50ms: " + tabId + ", fragment " + fg);              
            }
        }, 50);
    }
}

输出：

// cannot get the selected fragment immediately if the fragment has never been instantiated.
onTabChanged(): 1, fragment null
onTabChanged() delay 50ms: 1, fragment HistoryFragment{6f7a9d5 #2 id=0x7f09006e 1}
onTabChanged(): 2, fragment null
onTabChanged() delay 50ms: 2, fragment HistoryFragment{10c59e72 #3 id=0x7f09006e 2}

// can get the selected fragment immediately if the fragment already instantiated.
onTabChanged(): 1, fragment HistoryFragment{6f7a9d5 #2 id=0x7f09006e 1}
onTabChanged(): 2, fragment HistoryFragment{10c59e72 #3 id=0x7f09006e 2}

---

我想我找到了解决这个问题的正确方法，下面是我的答案

创建一个TabBean

然后，获得三个包含三个片段的TabBean实例

第四，这是最重要的一步，我没有像这样使用findFragmentByTag（）获取片段实例

相反，我的答案是这样的：

tabs.get(0).getFragment().newInstance();

然后投下它

---

我终于得到了这个片段。

请看下面的文章。这与我在文章中提到的url完全相同。但它不适合我。我可以在添加Tab时使用HashMap来存储片段。但是该选项卡被添加到FragmentTabHost中，可能有办法将其检索回来。我说的对吗？在活动中添加

mMyFragment

的地方也张贴代码，以获取TabFragment1,2,3，。。。首先需要获取

mMyFragment

，然后获取TabFragment1,2,3，。。。碎片

@Override
public void onTabChanged(final String tabId) {
    Fragment fg = getSupportFragmentManager().findFragmentByTag(tabId);
    Log.d(TAG, "onTabChanged(): " + tabId + ", fragment " + fg);

    if (fg == null) {
        new Handler().postDelayed(new Runnable() {            
            @Override
            public void run() {
                Fragment fg = getSupportFragmentManager().findFragmentByTag(tabId);
                Log.d(TAG, "onTabChanged() delay 50ms: " + tabId + ", fragment " + fg);              
            }
        }, 50);
    }
}

// cannot get the selected fragment immediately if the fragment has never been instantiated.
onTabChanged(): 1, fragment null
onTabChanged() delay 50ms: 1, fragment HistoryFragment{6f7a9d5 #2 id=0x7f09006e 1}
onTabChanged(): 2, fragment null
onTabChanged() delay 50ms: 2, fragment HistoryFragment{10c59e72 #3 id=0x7f09006e 2}

// can get the selected fragment immediately if the fragment already instantiated.
onTabChanged(): 1, fragment HistoryFragment{6f7a9d5 #2 id=0x7f09006e 1}
onTabChanged(): 2, fragment HistoryFragment{10c59e72 #3 id=0x7f09006e 2}

private int imgId;    
private int textId;    
private Class fragment;   
public MainTabBean(int textId, int imgId, Class fragment) {    
    this.textId = textId;    
    this.imgId = imgId;    
    this.fragment = fragment;    
}

public int getTextId() {
    return textId;
}

public void setTextId(int textId) {
    this.textId = textId;
}

public int getImgId() {
    return imgId;
}

public void setImgId(int imgId) {
    this.imgId = imgId;
}

public Class getFragment() {
    return fragment;
}

public void setFragment(Class fragment) {
    this.fragment = fragment;
}

List<MainTabBean> tabs = new ArrayList<>();
// three TabBean instances
TabBean homeTab = new MainTabBean(R.string.home, R.drawable.tab_home, HomepageFragment.class);
TabBean postcardTab = new MainTabBean(R.string.postcard, R.drawable.tab_postcard, PostcardFragment.class);
Bean notificationTab = new MainTabBean(R.string.notification, R.drawable.tab_notification, NotificationFragment.class);
// put tabs into a list
tabs.add(homeTab);
tabs.add(postcardTab);
tabs.add(notificationTab);

// Obtain FragmentTabHost
tabHost = findViewById(android.R.id.tabhost);
// Associate fragmentManager with container
tabHost.setup(this, getSupportFragmentManager(), R.id.main_content);
// Create TabSpecs with TabBean and add it on TabHost
for(MainTabBean tab : tabs) {
    TabHost.TabSpec spec = tabHost.newTabSpec(String.valueOf(tab.getTextId()))// set a tag
                                .setIndicator(getTabIndicator(tab));// set an indicator
    tabHost.addTab(spec, tab.getFragment(), null);// add a tab
}

getSupportFragmentManager()
                .findFragmentByTag(String.valueOf(tabs.get(1).getTextId()));

tabs.get(0).getFragment().newInstance();