Android 控件 - ViewPager 的适配器（PagerAdapter、FragmentPagerAdapter、FragmentStatePagerAdapter）
ViewPager 概述
ViewPager 是 Android 中实现页面滑动切换的经典组件
ViewPager 有如下适配器
| 适配器 | 说明 |
|---|---|
| PagerAdapter | 用于将任意类型的视图与 ViewPager 绑定，自由度最高 |
| FragmentPagerAdapter | 当页面数量较少，且所有 Fragment 都希望常驻内存、不会被销毁时使用 |
| FragmentStatePagerAdapter | 当页面数量很多，，或者 Fragment 可能动态增删时使用 |
- ViewPager2 是 ViewPager 升级版
一、PagerAdapter
1、Adapter
- view_pager_item_image.xml
<?xml version="1.0" encoding="utf-8"?><androidx.constraintlayout.widget.ConstraintLayoutxmlns:android="http://schemas.android.com/apk/res/android"xmlns:app="http://schemas.android.com/apk/res-auto"android:layout_width="match_parent"android:layout_height="match_parent"><ImageViewandroid:id="@+id/iv_image"android:layout_width="200dp"android:layout_height="200dp"app:layout_constraintBottom_toBottomOf="parent"app:layout_constraintEnd_toEndOf="parent"app:layout_constraintStart_toStartOf="parent"app:layout_constraintTop_toTopOf="parent"/></androidx.constraintlayout.widget.ConstraintLayout>- ImagePagerAdapter.kt
classImagePagerAdapter(privatevalcontext:Context,privatevalimages:List<Int>):PagerAdapter(){privatevalinflater:LayoutInflater=LayoutInflater.from(context)overridefungetCount():Int{returnimages.size}overridefunisViewFromObject(view:View,`object`:Any):Boolean{returnview===`object`}overridefuninstantiateItem(container:ViewGroup,position:Int):Any{valview=inflater.inflate(R.layout.view_pager_item_image,container,false)valivImage=view.findViewById<ImageView>(R.id.iv_image)ivImage.setImageResource(images[position])container.addView(view)returnview}overridefundestroyItem(container:ViewGroup,position:Int,`object`:Any){super.destroyItem(container,position,`object`)container.removeView(`object`asView)}}2、Activity
- activity_view_pager_test.xml
<?xml version="1.0" encoding="utf-8"?><androidx.constraintlayout.widget.ConstraintLayoutxmlns:android="http://schemas.android.com/apk/res/android"xmlns:app="http://schemas.android.com/apk/res-auto"xmlns:tools="http://schemas.android.com/tools"android:id="@+id/main"android:layout_width="match_parent"android:layout_height="match_parent"tools:context=".ViewPagerTestActivity"><androidx.viewpager.widget.ViewPagerandroid:id="@+id/vp_content"android:layout_width="match_parent"android:layout_height="370dp"android:background="#f5f5f5"app:layout_constraintBottom_toBottomOf="parent"app:layout_constraintEnd_toEndOf="parent"app:layout_constraintStart_toStartOf="parent"app:layout_constraintTop_toTopOf="parent"/></androidx.constraintlayout.widget.ConstraintLayout>- ViewPagerTestActivity.kt
classViewPagerTestActivity:AppCompatActivity(){overridefunonCreate(savedInstanceState:Bundle?){super.onCreate(savedInstanceState)enableEdgeToEdge()setContentView(R.layout.activity_view_pager_test)ViewCompat.setOnApplyWindowInsetsListener(findViewById(R.id.main)){v,insets->valsystemBars=insets.getInsets(WindowInsetsCompat.Type.systemBars())v.setPadding(systemBars.left,systemBars.top,systemBars.right,systemBars.bottom)insets}valvpContent=findViewById<ViewPager>(R.id.vp_content)vpContent.adapter=ImagePagerAdapter(this,listOf(R.drawable.image1,R.drawable.image2))}}二、FragmentPagerAdapter
1、Adapter
- MyFragmentPagerAdapter.kt
classMyFragmentPagerAdapter(fm:FragmentManager,privatevalfragments:List<Fragment>,privatevaltitles:List<String>):FragmentPagerAdapter(fm){overridefungetCount():Int{returnfragments.size}overridefungetItem(position:Int):Fragment{returnfragments[position]}overridefungetPageTitle(position:Int):CharSequence?{returntitles[position]}}2、Fragment
- fragment_home.xml
<?xml version="1.0" encoding="utf-8"?><LinearLayoutxmlns:android="http://schemas.android.com/apk/res/android"android:layout_width="match_parent"android:layout_height="match_parent"android:gravity="center"android:orientation="vertical"><TextViewandroid:layout_width="wrap_content"android:layout_height="wrap_content"android:text="首页页面"android:textSize="24sp"/><Buttonandroid:id="@+id/btn_open"android:layout_width="wrap_content"android:layout_height="wrap_content"android:layout_marginTop="20dp"android:text="打开"/></LinearLayout>- HomeFragment.kt
publicclassHomeFragment extends Fragment{@OverridepublicViewonCreateView(LayoutInflater inflater,ViewGroup container,Bundle savedInstanceState){returninflater.inflate(R.layout.fragment_home,container,false);}@OverridepublicvoidonViewCreated(@NonNullView view,@NullableBundle savedInstanceState){super.onViewCreated(view,savedInstanceState);Button btnOpen=view.findViewById(R.id.btn_open);btnOpen.setOnClickListener(v->{Toast.makeText(getActivity(),"test content",Toast.LENGTH_LONG).show();});}}- fragment_discover.xml
<?xml version="1.0" encoding="utf-8"?><LinearLayoutxmlns:android="http://schemas.android.com/apk/res/android"android:layout_width="match_parent"android:layout_height="match_parent"android:gravity="center"android:orientation="vertical"><TextViewandroid:layout_width="wrap_content"android:layout_height="wrap_content"android:text="发现页面"android:textSize="24sp"/></LinearLayout>- DiscoverFragment.kt
publicclassDiscoverFragment extends Fragment{@OverridepublicViewonCreateView(LayoutInflater inflater,ViewGroup container,Bundle savedInstanceState){returninflater.inflate(R.layout.fragment_discover,container,false);}}- fragment_profile.xml
<?xml version="1.0" encoding="utf-8"?><LinearLayoutxmlns:android="http://schemas.android.com/apk/res/android"android:layout_width="match_parent"android:layout_height="match_parent"android:gravity="center"android:orientation="vertical"><TextViewandroid:layout_width="wrap_content"android:layout_height="wrap_content"android:text="个人页面"android:textSize="24sp"/></LinearLayout>- ProfileFragment.kt
publicclassProfileFragment extends Fragment{@OverridepublicViewonCreateView(LayoutInflater inflater,ViewGroup container,Bundle savedInstanceState){returninflater.inflate(R.layout.fragment_profile,container,false);}}3、Activity
- activity_view_pager_test.xml
<?xml version="1.0" encoding="utf-8"?><androidx.constraintlayout.widget.ConstraintLayoutxmlns:android="http://schemas.android.com/apk/res/android"xmlns:app="http://schemas.android.com/apk/res-auto"xmlns:tools="http://schemas.android.com/tools"android:id="@+id/main"android:layout_width="match_parent"android:layout_height="match_parent"tools:context=".ViewPagerTestActivity"><androidx.viewpager.widget.ViewPagerandroid:id="@+id/vp_content"android:layout_width="match_parent"android:layout_height="370dp"android:background="#f5f5f5"app:layout_constraintBottom_toBottomOf="parent"app:layout_constraintEnd_toEndOf="parent"app:layout_constraintStart_toStartOf="parent"app:layout_constraintTop_toTopOf="parent"/></androidx.constraintlayout.widget.ConstraintLayout>- ViewPagerTestActivity.kt
classViewPagerTestActivity:AppCompatActivity(){overridefunonCreate(savedInstanceState:Bundle?){super.onCreate(savedInstanceState)enableEdgeToEdge()setContentView(R.layout.activity_view_pager_test)ViewCompat.setOnApplyWindowInsetsListener(findViewById(R.id.main)){v,insets->valsystemBars=insets.getInsets(WindowInsetsCompat.Type.systemBars())v.setPadding(systemBars.left,systemBars.top,systemBars.right,systemBars.bottom)insets}valvpContent=findViewById<ViewPager>(R.id.vp_content)vpContent.adapter=MyFragmentPagerAdapter(supportFragmentManager,listOf(HomeFragment(),DiscoverFragment(),ProfileFragment()),listOf("Home","Discover","Profile"))}}三、FragmentStatePagerAdapter
1、Adapter
- NewsStatePagerAdapter.kt
classNewsStatePagerAdapter(fm:FragmentManager,privatevalcategories:List<String>):FragmentStatePagerAdapter(fm){overridefungetCount():Int{returncategories.size}overridefungetItem(position:Int):Fragment{returnNewsFragment.newInstance(categories[position])}overridefungetPageTitle(position:Int):CharSequence?{returncategories[position]}}2、Fragment
- NewsFragment.kt
class NewsFragment : Fragment() { companion object { fun newInstance(category: String): NewsFragment { return NewsFragment().apply { arguments = Bundle().apply { putString("category", category) } } } } override fun onCreateView( inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle? ): View? { return TextView(requireContext()).apply { text = arguments?.getString("category") ?: "无" textSize = 24f gravity = Gravity.CENTER } } }3、Activity
- activity_view_pager_test.xml
<?xml version="1.0" encoding="utf-8"?><androidx.constraintlayout.widget.ConstraintLayoutxmlns:android="http://schemas.android.com/apk/res/android"xmlns:app="http://schemas.android.com/apk/res-auto"xmlns:tools="http://schemas.android.com/tools"android:id="@+id/main"android:layout_width="match_parent"android:layout_height="match_parent"tools:context=".ViewPagerTestActivity"><androidx.viewpager.widget.ViewPagerandroid:id="@+id/vp_content"android:layout_width="match_parent"android:layout_height="370dp"android:background="#f5f5f5"app:layout_constraintBottom_toBottomOf="parent"app:layout_constraintEnd_toEndOf="parent"app:layout_constraintStart_toStartOf="parent"app:layout_constraintTop_toTopOf="parent"/></androidx.constraintlayout.widget.ConstraintLayout>- ViewPagerTestActivity.kt
classViewPagerTestActivity:AppCompatActivity(){overridefunonCreate(savedInstanceState:Bundle?){super.onCreate(savedInstanceState)enableEdgeToEdge()setContentView(R.layout.activity_view_pager_test)ViewCompat.setOnApplyWindowInsetsListener(findViewById(R.id.main)){v,insets->valsystemBars=insets.getInsets(WindowInsetsCompat.Type.systemBars())v.setPadding(systemBars.left,systemBars.top,systemBars.right,systemBars.bottom)insets}valvpContent=findViewById<ViewPager>(R.id.vp_content)vpContent.adapter=NewsStatePagerAdapter(supportFragmentManager,listOf("推荐","热点","科技","体育","娱乐"))}}