【Android开发】ViewPager

应用场景

1. 引导界面、相册多图片预览
2. 多Tab页面、App导航
3. 广告播放展示

使用步骤

1. 添加依赖
2. xml布局中引用viewPager
3. 声明数组，将图片存入
4. 创建适配器，完成资源配置
5. 为viewpager设置适配器

1.添加依赖

build.grandle

dependencies {
    implementation 'androidx.viewpager2:viewpager2:1.0.0-alpha02'
}

2. xml布局中引用viewPager

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns: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:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <androidx.viewpager2.widget.ViewPager2
        android:id="@+id/pagers"
        android:layout_width="match_parent"
        android:layout_height="180dp"
        android:orientation="horizontal"
        app:layout_constraintTop_toTopOf="parent"/>

	    <LinearLayout
        android:id="@+id/dots"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:orientation="horizontal"
        android:gravity="center_horizontal"
        app:layout_constraintTop_toTopOf="parent"
        android:layout_marginTop="160dp">
        <ImageView
            android:layout_width="10dp"
            android:layout_height="10dp"
            android:background="@drawable/dot_selected"/>
        <ImageView
            android:layout_width="10dp"
            android:layout_height="10dp"
            android:background="@drawable/dot_unselected"/>
        <ImageView
            android:layout_width="10dp"
            android:layout_height="10dp"
            android:background="@drawable/dot_unselected"/>
        <ImageView
            android:layout_width="10dp"
            android:layout_height="10dp"
            android:background="@drawable/dot_unselected"/>
    </LinearLayout>

</androidx.constraintlayout.widget.ConstraintLayout>

class MainActivity : AppCompatActivity() {
    
    
    var pics: MutableList<Int> = ArrayList()
    var dots: LinearLayout? = null

    override fun onCreate(savedInstanceState: Bundle?) {
    
    
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
		
		//3. 声明数组，将图片存入
        pics.add(R.mipmap.bg1)
        pics.add(R.mipmap.bg2)
        pics.add(R.mipmap.bg3)
        pics.add(R.mipmap.bg4)
		
		//4. 创建适配器，完成资源配置
        //实例化适配器(RecyclerView.Adapter)
        val adapter: RecyclerView.Adapter<*> = object : RecyclerView.Adapter<RecyclerView.ViewHolder>() {
    
    
            //创建
            override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): RecyclerView.ViewHolder {
    
    
                //此时用的布局是ViewPager每一页中用来乘放图片的布局
                //该布局不设置任何控件，因为会直接将图片作为根布局的背景
                val v = LayoutInflater.from(this@MainActivity).inflate(R.layout.item, parent, false)
                return ViewHolder(v)
            }

            //绑定(为ViewHolder里面的控件设置显示内容)
            override fun onBindViewHolder(holder: RecyclerView.ViewHolder, position: Int) {
    
    
                val h = holder as MainActivity.ViewHolder
                h.container.setBackgroundResource(pics[position])
            }

            //数量
            override fun getItemCount(): Int {
    
    
                return pics.size
            }
        }
	
		//5. 为viewpager设置适配器
        val pagers = findViewById<ViewPager2>(R.id.pagers)
        pagers.adapter = adapter
        
        var myDots = dots
        myDots = findViewById(R.id.dots)
        pagers.registerOnPageChangeCallback(object : ViewPager2.OnPageChangeCallback() {
    
    
            override fun onPageSelected(position: Int) {
    
    
                super.onPageSelected(position)
                for (i in 0 until myDots.childCount) {
    
    
                    (myDots.getChildAt(i) as ImageView).setBackgroundResource(R.drawable.dot_unselected)
                }
                (myDots.getChildAt(position) as ImageView).setBackgroundResource(R.drawable.dot_selected)
            }
        })
    }

    inner class ViewHolder(itemView: View) : RecyclerView.ViewHolder(itemView) {
    
    
        var container: LinearLayout = itemView.findViewById(R.id.container)

    }
}