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使用 ViewPager 创建包含标签页的滑动视图

滑动视图允许您通过水平手指手势或滑动在同级屏幕(例如标签页)之间进行导航。此导航模式也称为“水平分页”。本主题介绍了如何创建具有滑动视图(以便在标签页之间切换)的标签页布局,以及如何显示标题条而不是标签页。

实现滑动视图

您可以使用 AndroidX 的 ViewPager 微件创建滑动视图。要使用 ViewPager 和标签页,您需要将 ViewPager材料组件的依赖项添加到项目中。

要使用 ViewPager 设置布局,请将 <ViewPager> 元素添加到 XML 布局中。例如,如果滑动视图中的每个页面都应使用整个布局,则布局应大致如下所示:

<androidx.viewpager.widget.ViewPager
        xmlns:android="http://schemas.android.com/apk/res/android"
        android:id="@+id/pager"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />
    

要插入代表各个页面的子视图,您需要将此布局挂接到 PagerAdapter。有以下两种内置适配器可供选择:

  • FragmentPagerAdapter - 适用于在固定的少量同级屏幕之间进行导航。
  • FragmentStatePagerAdapter - 适用于对未知数量的页面进行分页。 FragmentStatePagerAdapter 会在用户导航至其他位置时销毁 Fragment,从而优化内存使用情况。

以下示例展示了如何使用 FragmentStatePagerAdapter 在一系列 Fragment 对象之间滑动:

Kotlin

    class CollectionDemoFragment : Fragment() {
        // When requested, this adapter returns a DemoObjectFragment,
        // representing an object in the collection.
        private lateinit var demoCollectionPagerAdapter: DemoCollectionPagerAdapter
        private lateinit var viewPager: ViewPager

        override fun onCreateView(inflater: LayoutInflater,
                container: ViewGroup?,
                savedInstanceState: Bundle?): View? {
           return inflater.inflate(R.layout.collection_demo, container, false)
        }

        override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
            demoCollectionPagerAdapter = DemoCollectionPagerAdapter(childFragmentManager)
            viewPager = view.findViewById(R.id.pager)
            viewPager.adapter = demoCollectionPagerAdapter
        }
    }

    // Since this is an object collection, use a FragmentStatePagerAdapter,
    // and NOT a FragmentPagerAdapter.
    class DemoCollectionPagerAdapter(fm: FragmentManager) : FragmentStatePagerAdapter(fm) {

        override fun getCount(): Int  = 100

        override fun getItem(i: Int): Fragment {
            val fragment = DemoObjectFragment()
            fragment.arguments = Bundle().apply {
                // Our object is just an integer :-P
                putInt(ARG_OBJECT, i + 1)
            }
            return fragment
        }

        override fun getPageTitle(position: Int): CharSequence {
            return "OBJECT ${(position + 1)}"
        }
    }

    private const val ARG_OBJECT = "object"

    // Instances of this class are fragments representing a single
    // object in our collection.
    class DemoObjectFragment : Fragment() {

       override fun onCreateView(inflater: LayoutInflater,
               container: ViewGroup?,
               savedInstanceState: Bundle?): View {
           return inflater.inflate(R.layout.fragment_collection_object, container, false)
       }

        override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
            arguments?.takeIf { it.containsKey(ARG_OBJECT) }?.apply {
                val textView: TextView = view.findViewById(android.R.id.text1)
                textView.text = getInt(ARG_OBJECT).toString()
            }
        }
    }
    

Java

    public class CollectionDemoFragment extends Fragment {
        // When requested, this adapter returns a DemoObjectFragment,
        // representing an object in the collection.
        DemoCollectionPagerAdapter demoCollectionPagerAdapter;
        ViewPager viewPager;

        @Nullable
        @Override
        public View onCreateView(@NonNull LayoutInflater inflater,
                @Nullable ViewGroup container,
                @Nullable Bundle savedInstanceState) {
            return inflater.inflate(R.layout.collection_demo, container, false);
        }

        @Override
        public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
            demoCollectionPagerAdapter = new DemoCollectionPagerAdapter(getChildFragmentManager());
            viewPager = view.findViewById(R.id.pager);
            viewPager.setAdapter(demoCollectionPagerAdapter);
       }
    }

    // Since this is an object collection, use a FragmentStatePagerAdapter,
    // and NOT a FragmentPagerAdapter.
    public class DemoCollectionPagerAdapter extends FragmentStatePagerAdapter {
        public DemoCollectionPagerAdapter(FragmentManager fm) {
            super(fm);
        }

        @Override
        public Fragment getItem(int i) {
            Fragment fragment = new DemoObjectFragment();
            Bundle args = new Bundle();
            // Our object is just an integer :-P
            args.putInt(DemoObjectFragment.ARG_OBJECT, i + 1);
            fragment.setArguments(args);
            return fragment;
        }

        @Override
        public int getCount() {
            return 100;
        }

        @Override
        public CharSequence getPageTitle(int position) {
            return "OBJECT " + (position + 1);
        }
    }

    // Instances of this class are fragments representing a single
    // object in our collection.
    public class DemoObjectFragment extends Fragment {
        public static final String ARG_OBJECT = "object";

        @Override
        public View onCreateView(LayoutInflater inflater,
                ViewGroup container, Bundle savedInstanceState) {
           return inflater.inflate(R.layout.fragment_collection_object, container, false);
        }

        @Override
        public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
            Bundle args = getArguments();
            ((TextView) view.findViewById(android.R.id.text1))
                    .setText(Integer.toString(args.getInt(ARG_OBJECT)));
        }
    }
    

下面几部分将介绍如何添加标签页,以帮助简化页面之间的导航。

使用 TabLayout 添加标签页

TabLayout 提供了一种横向显示标签页的方式。当与 ViewPager 结合使用时,TabLayout 可以提供一种熟悉的界面,让用户在滑动视图中浏览各个页面。

图 1:具有四个标签页的 TabLayout

要在 ViewPager 中包含 TabLayout,请在 <ViewPager> 元素内添加 <TabLayout> 元素,如下所示:

<androidx.viewpager.widget.ViewPager
        xmlns:android="http://schemas.android.com/apk/res/android"
        android:id="@+id/pager"
        android:layout_width="match_parent"
        android:layout_height="match_parent">

        <com.google.android.material.tabs.TabLayout
            android:id="@+id/tab_layout"
            android:layout_width="match_parent"
            android:layout_height="wrap_content" />

    </androidx.viewpager.widget.ViewPager>
    

接下来,使用 setupWithViewPager()TabLayoutViewPager 相关联。TabLayout 中的各个标签页会自动填充 PagerAdapter 中的页面标题:

Kotlin

    class CollectionDemoFragment : Fragment() {
        ...
        override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
            val tabLayout = view.findViewById(R.id.tab_layout)
            tabLayout.setupWithViewPager(viewPager)
        }
        ...
    }

    class DemoCollectionPagerAdapter(fm: FragmentManager) : FragmentStatePagerAdapter(fm) {

        override fun getCount(): Int  = 4

        override fun getPageTitle(position: Int): CharSequence {
            return "OBJECT ${(position + 1)}"
        }
        ...
    }
    

Java

    public class CollectionDemoFragment extends Fragment {
        ...
        @Override
        public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
            TabLayout tabLayout = view.findViewById(R.id.tab_layout);
            tabLayout.setupWithViewPager(viewPager);
        }
        ...
    }

    public class DemoCollectionPagerAdapter extends FragmentStatePagerAdapter {
        ...
        @Override
        public int getCount() {
            return 4;
        }

        @Override
        public CharSequence getPageTitle(int position) {
            return "OBJECT " + (position + 1);
        }

        ...
    }
    

有关标签页布局的其他设计准则,请参阅适用于标签页的 Material Design 文档