滑动视图可让您通过水平手指手势(即滑动)在同级屏幕(例如选项卡)之间导航。这种导航模式也称为水平分页。本文将教您如何创建带有滑动视图以在选项卡之间切换的选项卡布局,以及如何显示标题栏而非选项卡。
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
和选项卡,您需要将 ViewPager
和 Material Components 的依赖项添加到您的项目中。
要使用 ViewPager
设置布局,请将 <ViewPager>
元素添加到您的 XML 布局中。例如,如果滑动视图中的每个页面都使用整个布局,则您的布局看起来像这样
<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" />
要插入代表每个页面的子视图,您需要将此布局连接到 PagerAdapter
。您可以选择以下两种内置适配器:
FragmentPagerAdapter
:在少量固定数量的同级屏幕之间导航时使用此适配器。FragmentStatePagerAdapter
:当需要分页处理未知数量的页面时使用此适配器。FragmentStatePagerAdapter
通过在用户离开页面时销毁片段来优化内存使用。
例如,您可以使用 FragmentStatePagerAdapter
滑动浏览一系列 Fragment
对象,如下所示:
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, // 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 the 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, // 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 the 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))); } }
以下部分展示了如何添加选项卡以方便在页面之间导航。
使用 TabLayout 添加选项卡
TabLayout
提供了一种水平显示选项卡的方式。与 ViewPager
一起使用时,TabLayout
提供了一个熟悉的界面,用于在滑动视图中的页面之间导航。
图 1. 具有四个选项卡的 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()
将 TabLayout
连接到 ViewPager
。TabLayout
中的各个选项卡将自动使用 PagerAdapter
中的页面标题填充。
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); } ... }
有关选项卡布局的其他设计指导,请参阅 Material Design 选项卡文档。