Question

我希望在后台中获取最后一个片段，或者在tab b_1中显示当前的片段对我来说是一样的。如下图所示，我有一个ViewPager，另一个是内部tab b。因此，显示了四个当前片段。

问题：如何获取Fragment 2实例？

我已经看到了另一种解决方案，但没有一种适用于这种情况。

注释： ViewPager中托管的片段不是必需的。我可以在一个标签中再打开两个片段。

使用这种方法，我得到所有当前可见的片段，但不是我想要的特定片段。

public ArrayList<Fragment> getVisibleFragment() {
    List<Fragment> fragments = getSupportFragmentManager().getFragments();
    ArrayList<Fragment> visibleFragments = new ArrayList<>();
    if (fragments != null) {
        for (Fragment fragment : fragments) {
            if (fragment != null && fragment.isVisible())
                visibleFragments.add(fragment);
        }
    }
    return visibleFragments;
}

一些有趣的代码

activity_main.xml中

<android.support.design.widget.CoordinatorLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:id="@+id/activity_main"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <android.support.design.widget.AppBarLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar">

        <android.support.design.widget.TabLayout
            android:id="@+id/tabs"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            app:tabMode="fixed"
            app:tabGravity="fill"/>
    </android.support.design.widget.AppBarLayout>

    <android.support.v4.view.ViewPager
        android:id="@+id/viewpager"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        app:layout_behavior="@string/appbar_scrolling_view_behavior"/>

</android.support.design.widget.CoordinatorLayout>

MainActivity.java

public class MainActivity extends AppCompatActivity {

    private static ViewPagerAdapter adapter;
    private static ViewPager viewPager;
    private TabLayout tabLayout;

    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        viewPager = (ViewPager) findViewById(R.id.viewpager);
        setupViewPager();

        tabLayout = (TabLayout) findViewById(R.id.tabs);
        tabLayout.setupWithViewPager(viewPager);
        setupTabIcons();
    }

    private void setupViewPager() {
        adapter = new ViewPagerAdapter(getSupportFragmentManager());
        // Wrap with HostFragment to get separate tabbed nagivation.
        adapter.addFrag(HostFragment.newInstance(new Fragment1()), null);
        adapter.addFrag(HostFragment.newInstance(new RootFragment2()), null);
        adapter.addFrag(HostFragment.newInstance(new Fragment4()), null);
        viewPager.setAdapter(adapter);
        viewPager.setOffscreenPageLimit(2);
    }

    public void openNewFragment(Fragment fragment) {
        HostFragment hostFragment = (HostFragment) adapter.getItem(viewPager.getCurrentItem());
        hostFragment.replaceFragment(fragment, true);
    }
}

fragment_host.xml

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/hosted_fragment"
    android:layout_width="match_parent"
    android:layout_height="match_parent"/>

HostFragment.java

/**
 * This class implements separate navigation for a tabbed viewpager.
 *
 * Based on https://medium.com/@nilan/separate-back-navigation-for-
 * a-tabbed-view-pager-in-android-459859f607e4#.u96of4m4x
 */
public class HostFragment extends BackStackFragment {

    private Fragment fragment;

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        super.onCreateView(inflater, container, savedInstanceState);
        View view = inflater.inflate(R.layout.fragment_host, container, false);
        if (fragment != null) {
            replaceFragment(fragment, false);
        }
        return view;
    }

    public void replaceFragment(Fragment fragment, boolean addToBackstack) {
        if (addToBackstack) {
            getChildFragmentManager().beginTransaction().replace(R.id.hosted_fragment, fragment).addToBackStack(null).commit();
        } else {
            getChildFragmentManager().beginTransaction().replace(R.id.hosted_fragment, fragment).commit();
        }
    }

    public static HostFragment newInstance(Fragment fragment) {
        HostFragment hostFragment = new HostFragment();
        hostFragment.fragment = fragment;
        return hostFragment;
    }

    public Fragment getFragment() {
        return fragment;
    }
}

fragment2_root.xml

<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:id="@+id/fragment2_root"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">

    <android.support.design.widget.TabLayout
        android:id="@+id/tab2_tabs"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        app:tabMode="fixed"
        app:tabGravity="fill"/>

    <android.support.v4.view.ViewPager
        android:id="@+id/tab2_viewpager"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        app:layout_behavior="@string/appbar_scrolling_view_behavior"/>

</LinearLayout>

RootFragment2.java

public class RootFragment2 extends Fragment {

    private ViewPagerAdapter adapter;
    private ViewPager viewPager;

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        // Inflate the layout for this fragment.
        View root = inflater.inflate(R.layout.fragment2_root, container, false);

        viewPager = (ViewPager) root.findViewById(R.id.tab2_viewpager);
        setupViewPager(viewPager);

        TabLayout tabLayout = (TabLayout) root.findViewById(R.id.tab2_tabs);
        tabLayout.setupWithViewPager(viewPager);

        return root;
    }

    private void setupViewPager(ViewPager viewPager) {
        adapter = new ViewPagerAdapter(getActivity().getSupportFragmentManager());
        // Wrap with HostFragment to get separate tabbed nagivation.
        adapter.addFrag(HostFragment.newInstance(new Fragment2()), null);
        adapter.addFrag(HostFragment.newInstance(new Fragment3()), null);
        viewPager.setAdapter(adapter);
        viewPager.setOffscreenPageLimit(1);
    }

    public ViewPagerAdapter getAdapter() {
        return adapter;
    }

    public ViewPager getViewPager() {
        return viewPager;
    }
}

Answer 1

首先在SparseArray＆＃39;中定义ViewPagers。适配器如下。在这个数组中，我们将保留片段的实例。

SparseArray<Fragment> registeredFragments = new SparseArray<>();

并覆盖您的适配器＆＃39; instantiateItem方法。

@Override
public Object instantiateItem(ViewGroup container, int position) {
    Fragment fragment = (Fragment) super.instantiateItem(container, position);
    registeredFragments.put(position, fragment);
    return fragment;
}

同时覆盖destroyItem

的ViewPagers方法

@Override
public void destroyItem(ViewGroup container, int position, Object object) {
    registeredFragments.remove(position);
    super.destroyItem(container, position, object);
}

定义一种新方法来获取ViewPager Fragments个实例。

public Fragment getRegisteredFragment(int position) {
    return registeredFragments.get(position);
}

最后设置为PageChangeListener添加ViewPagers：

viewPager.addOnPageChangeListener(new ViewPager.OnPageChangeListener() {

    @Override
    public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {

    }

    @Override
    public void onPageSelected(int position) {
        // Here's your instance
        YourFragment fragment =(YourFragment)yourPagerAdapter.getRegisteredFragment(position);

    }

    @Override
    public void onPageScrollStateChanged(int state) {

    }
});

我希望这会帮助你。祝你好运。

编辑：对不起，我无法准确理解您计划做什么，但如果您需要保留子片段（b_1，b_2）实例，您可以为您的活动定义一种方法，例如

public void setCurrentFragment(Fragment fragment){
      this.currentFragment = fragment;
}

在您的子视图寻呼机适配器中，您可以调用此方法，如下所示：

subViewPager.addOnPageChangeListener(new ViewPager.OnPageChangeListener() {

    @Override
    public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {

    }

    @Override
    public void onPageSelected(int position) {
        // Here's your instance
        YourFragment fragment =(YourFragment)yourSubPagerAdapter.getRegisteredFragment(position);
        ((MyActivity)getActivity).setCurrentFragment(fragment);
    }

    @Override
    public void onPageScrollStateChanged(int state) {

    }
});

通过这种方式，您可以保留一个实例和顶部片段。

Answer 2

在对DEADMC发表评论之后，我决定用额外的内存来实现它，在列表中保存开放的片段。

我解释我的解决方案。我有两种类型的特殊片段，主机和 root 。主机片段是选项卡的init。 Root Fragments是那些持有ViewPager的片段。在这种情况下，tab_b有一个带有内部ViewPager的Root Fragment。

对于每个标签，对于每个 HostFragment ，我添加了一个列表fragments以保存在此标签中打开的片段。还有一个方法getCurrentFragment，可以在此选项卡中显示最后一个。

public class HostFragment extends BackStackFragment {

    private ArrayList<Fragment> fragments = new ArrayList<>();

    public Fragment getCurrentFragment() {
        return fragments.get(fragments.size() - 1);
    }

还需要一种删除此选项卡中显示的最后一个片段的方法，以保持真实状态。后退按钮需要重定向到此方法。

    public void removeCurrentFragment() {
        getChildFragmentManager().popBackStack();
        fragments.remove(fragments.size() - 1);
    }

还需要更改以前的方法，以插入打开到列表中的新片段。

    public void replaceFragment(Fragment fragment, boolean addToBackstack) {
        // NEW: Add new fragment to the list.
        fragments.add(fragment);
        if (addToBackstack) {
            getChildFragmentManager().beginTransaction().replace(R.id.hosted_fragment, fragment).addToBackStack(null).commit();
        } else {
            getChildFragmentManager().beginTransaction().replace(R.id.hosted_fragment, fragment).commit();
        }
    }

    public static HostFragment newInstance(Fragment fragment) {
        HostFragment hostFragment = new HostFragment();
        // NEW: Add first fragment to the list.
        hostFragment.fragments.add(fragment);
        return hostFragment;
    }
} // HostFragment.

RootFragment 是由拥有ViewPager的片段实现的接口。

public interface RootFragment {

    /**
     * Opens a new Fragment in the current page of the ViewPager held by this Fragment.
     *
     * @param fragment - new Fragment to be opened.
     */
    void openNewFragment(Fragment fragment);

    /**
     * Returns the fragment displayed in the current tab of the ViewPager held by this Fragment.
     */
    Fragment getCurrentFragment();
}

然后，实施将是：

MainActivity 不是片段，但我实现了 RootFragment 界面。

public class MainActivity extends AppCompatActivity implements RootFragment {

    private void setupViewPager() {
        adapter = new ViewPagerAdapter(getSupportFragmentManager());
        // Wrap with HostFragment to get separate tabbed nagivation.
        adapter.addFrag(HostFragment.newInstance(new Fragment1()), null);
        adapter.addFrag(new RootFragment2(), null); // This is a Root, not a Host.
        adapter.addFrag(HostFragment.newInstance(new Fragment4()), null);
        viewPager.setAdapter(adapter);
        // 2 because TabLayout has 3 tabs.
        viewPager.setOffscreenPageLimit(2);
    }

    @Override
    public void openNewFragment(Fragment fragment) {
        Fragment hosted = adapter.getItem(viewPager.getCurrentItem());
        // Replace the fragment of current tab to [fragment].
        if (hosted instanceof HostFragment) {
            ((HostFragment) hosted).replaceFragment(fragment, true);
        // Spread action to next ViewPager.
        } else {
            ((RootFragment) hosted).openNewFragment(fragment);
        }
    }

    @Override
    public Fragment getCurrentFragment() {
        Fragment hosted = adapter.getItem(viewPager.getCurrentItem());
        // Return current tab's fragment.
        if (hosted instanceof HostFragment) {
            return ((HostFragment) hosted).getCurrentFragment();
        // Spread action to next ViewPager.
        } else {
            return ((RootFragment) hosted).getCurrentFragment();
        }
    }
}

和 RootFragment2

public class RootFragment2 extends Fragment implements RootFragment {

    private void setupViewPager(ViewPager viewPager) {
        adapter = new ViewPagerAdapter(getActivity().getSupportFragmentManager());
        // Wrap with HostFragment to get separate tabbed nagivation.
        adapter.addFrag(HostFragment.newInstance(new Fragment2()), null);
        adapter.addFrag(HostFragment.newInstance(new Fragment3()), null);
        viewPager.setAdapter(adapter);
        // 1 because TabLayout has 2 tabs.
        viewPager.setOffscreenPageLimit(1);
    }

    @Override
    public void openNewFragment(Fragment fragment) {
        ((HostFragment) adapter.getItem(viewPager.getCurrentItem())).replaceFragment(fragment, true);
    }

    @Override
    public Fragment getCurrentFragment() {
        return ((HostFragment) adapter.getItem(viewPager.getCurrentItem())).getCurrentFragment();
    }
}

然后，我只需要打电话：

（（MainActivity）getActivity（））。getCurrentFragment（）;

Answer 3

您可以创建包含// in app.js file, remove module name : define(["angular", "angularRoute","angularAnimate"], function(angular) { var WalletHubApp = angular.module('WalletHubApp', ['ui.router','ngAnimate']); WalletHubApp.config(function($stateProvider, $urlRouterProvider) { $urlRouterProvider.otherwise('/walletHub/1/'); $stateProvider .state('test', { url: '/walletHub/:id/{folderPath:[a-zA-Z0-9/]*}', templateUrl: function ($stateParams){ return "templates/"+$stateParams.id + '.html'; }, controllerProvider: function($stateParams) { console.log($stateParams) var ctrlName = $stateParams.id + "Controller"; return ctrlName; } }); }); return WalletHubApp; }); // in controller file change WalletHubApp to app define(['app'], function(WalletHubApp) { WalletHubApp.controller('1Controller', function ($scope,$stateParams,$stateParams,$state,$http) { $http.get('sample.json') .then(function(res){ $scope.persons = res.data }); var parts = $stateParams.folderPath.split('/') $scope.params = false; if(parts[0] != "") { $scope.parts = parts; $scope.params = true; } }) return; });方法的CustomFragment类，并从getClassName类扩展。然后从Fragment类而不是RootFragment2扩展所有片段，例如CustomFragment。

所以你可以得到这样的片段：

Fragment

Answer 4

我会做那样的事情：

<强> 1 即可。创建这样的界面。

public interface ReturnMyself {
    Fragment returnMyself();
}

<强> 2 即可。 ViewPagers中的所有片段都应该实现这一个。

第3 即可。将OnPageChangeListener添加到主VP。所以你总会知道当前的位置。

<强> 4 即可。添加OnPageChangeListener您的内部VP，以便您知道屏幕上有哪一个。

<强> 5 即可。向您的适配器（主要和内部）添加方法，该方法从传递给它的列表中返回您的片段。

public ReturnMyself getReturnMyselfAtPosition()

<强> 6 即可。所有片段都应在returnMyself()

中返回

<强> 7 即可。具有内部片段的片段应该返回给自己类似的东西。

Fragment returnMyself() {
    return this.myInnerFragmentAdapter.getReturnMyselfAtPosition().returnMyself(); 
}

<强> 8 即可。从您刚刚调用的主要片段/活动开始。

this.adapter.getReturnMyselfAtPosition().returnMyself();

你得到了你现在的片段。

如何在viewpager的特定选项卡中显示当前片段？

4 个答案: