Android RecyclerView轮播图实现 支持放大动画

android studio的模拟器录屏会黑屏，也不知道是什么bug

效果演示

主要用到了PagerSnapHelper（使RecyclerView滑动表现和viewpager一致）和滑动监听器

样式

activity_main.xml

<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">

    <com.example.gallery.GalleryRecyclerView
        android:id="@+id/recycler_view"
        android:layout_width="match_parent"
        android:layout_height="200dp"
        app:layout_constraintTop_toTopOf="parent" />

androidx.constraintlayout.widget.ConstraintLayout>

item.xml

<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <ImageView
        android:id="@+id/image_view"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:scaleType="centerCrop" />

androidx.constraintlayout.widget.ConstraintLayout>

代码

MainActivity

package com.example.gallery

import android.os.Bundle
import androidx.appcompat.app.AppCompatActivity
import com.example.gallery.databinding.ActivityMainBinding
import java.util.*

class MainActivity : AppCompatActivity() {
     
    private lateinit var binding: ActivityMainBinding
    private var timer: Timer = Timer()
    override fun onCreate(savedInstanceState: Bundle?) {
     
        super.onCreate(savedInstanceState)

		// 使用viewBinding
        binding = ActivityMainBinding.inflate(layoutInflater)
        setContentView(binding.root)

        val galleryAdapter = GalleryAdapter(arrayListOf(
                "https://ss0.bdstatic.com/70cFuHSh_Q1YnxGkpoWK1HF6hhy/it/u=3801171559,43130079&fm=26&gp=0.jpg",
                "https://img.zcool.cn/community/01936a58be7362a801219c77fe8358.jpg@1280w_1l_2o_100sh.jpg",
                "https://th.bing.com/th/id/R5d175f44c74fe609a7e7904c1581ba9e?rik=x36FeBN9WfmLcg&riu=http%3a%2f%2fwww.benbenla.cn%2fimages%2f20150626%2fbenbenla-03c.jpg&ehk=HdoV02a0Y%2bAbwlolGa0M%2fdZ073aXMUqidwkvB%2fLo1ZM%3d&risl=&pid=ImgRaw"
        ))
        binding.recyclerView.adapter = galleryAdapter

        binding.recyclerView.scrollToPosition(galleryAdapter.start)
        val paddingHorizon = 100
        val paddingVertical = 50
        binding.recyclerView.setPadding(paddingHorizon, paddingVertical, paddingHorizon, paddingVertical)
        binding.recyclerView.clipToPadding = false
    }

    override fun onResume() {
     
        super.onResume()
        timer.schedule(object : TimerTask() {
     
            override fun run() {
     
                binding.recyclerView.next()
            }
        }, 5000, 5000)
    }

    override fun onPause() {
     
        super.onPause()
        timer.cancel()
    }

}

GalleryRecyclerView

package com.example.gallery

import android.content.Context
import android.util.AttributeSet
import androidx.recyclerview.widget.LinearLayoutManager
import androidx.recyclerview.widget.PagerSnapHelper
import androidx.recyclerview.widget.RecyclerView
import kotlin.math.abs
import kotlin.math.min

class GalleryRecyclerView : RecyclerView {
     
    constructor(context: Context) : super(context)
    constructor(context: Context, attrs: AttributeSet?) : super(context, attrs)
    constructor(context: Context, attrs: AttributeSet?, defStyleAttr: Int) : super(
        context,
        attrs,
        defStyleAttr
    )

    var minScale: Float = 0.9f
    var maxScale: Float = 1.1f
    val linearLayoutManager = LinearLayoutManager(context, HORIZONTAL, false)

    var position: Int = 0

    init {
     

        layoutManager = linearLayoutManager
        val pagerSnapHelper = PagerSnapHelper()
        pagerSnapHelper.attachToRecyclerView(this)
        // 添加滑动监听
        addOnScrollListener(object : RecyclerView.OnScrollListener() {
     
            override fun onScrolled(recyclerView: RecyclerView, dx: Int, dy: Int) {
     
                val first = linearLayoutManager.findFirstVisibleItemPosition()
                val last = linearLayoutManager.findLastVisibleItemPosition()
                val snapView = pagerSnapHelper.findSnapView(linearLayoutManager) ?: return
                val snap = linearLayoutManager.getPosition(snapView)
                position = snap

                if (snap <= 100 || snap >= Int.MAX_VALUE - 100) {
     
                    scrollToPosition(adapter!!.itemCount / 2)
                }

                // 避免当前展示图被遮挡
                snapView.z = Float.MAX_VALUE
                // 放大程度
                val scaleSpan: Float = maxScale - minScale

				// 前一张图片
                linearLayoutManager.findViewByPosition(first)?.apply {
     
                    pagerSnapHelper
                        .calculateDistanceToFinalSnap(linearLayoutManager, this)
                        ?.get(0)
                        ?.let {
      distance ->
                        	// 滑动时，系数ratio值为[0,1]
                            val ratio: Float = min((width - abs(distance)).toFloat() / 800, 1f)
                            scaleX = ratio * scaleSpan + minScale
                            scaleY = scaleX
                        }
                }
                // 后一张图片
                linearLayoutManager.findViewByPosition(last)?.apply {
     
                    pagerSnapHelper
                        .calculateDistanceToFinalSnap(linearLayoutManager, this)
                        ?.get(0)
                        ?.let {
      distance ->
                            val ratio: Float = min((width - abs(distance)).toFloat() / 800, 1f)
                            scaleX = ratio * scaleSpan + minScale
                            scaleY = scaleX
                        }
                }
            }
        })
    }

    fun next() {
     
        smoothScrollToPosition(position + 1)
    }

}

GalleryAdapter

package com.example.gallery

import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import android.widget.ImageView
import androidx.recyclerview.widget.RecyclerView
import com.squareup.picasso.Picasso

class GalleryAdapter(var urls: List<String>) : RecyclerView.Adapter<GalleryAdapter.ViewHolder>() {
     


    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ViewHolder {
     
        // Create a new view, which defines the UI of the list item
        val view = LayoutInflater.from(parent.context)
            .inflate(R.layout.item, parent, false)
        return ViewHolder(view)
    }

    override fun onBindViewHolder(holder: ViewHolder, position: Int) {
     
        val index = position % urls.size
        Picasso
            .get()
            .load(urls[index])
            .placeholder(R.drawable.place_holder)
            .into(holder.imageView)
    }

    override fun getItemCount(): Int {
     
        return Int.MAX_VALUE
    }

    val start: Int
        get() {
     
            val temp = itemCount / 2
            return temp - temp % urls.size
        }


    class ViewHolder(itemView: View) : RecyclerView.ViewHolder(itemView) {
     
        val imageView: ImageView = itemView.findViewById(R.id.image_view)

    }

}