Android 入门程序 Kotlin版（3）--RecyclerView 瀑布流布局

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_marginRight="5dp">

    <ImageView
        android:id="@+id/fruitImage"
        android:layout_width="40dp"
        android:layout_height="40dp"
        android:layout_gravity="center_horizontal"
        android:layout_marginTop="10dp"/>

    <TextView
        android:id="@+id/fruitName"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center_horizontal"
        android:layout_marginTop="10dp"/>

</LinearLayout>

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <TextView
        android:id = "@+id/textView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center_horizontal"
        android:text = "hello_fruits"
        android:textSize = "18sp"/>
    <androidx.recyclerview.widget.RecyclerView
        android:id = "@+id/recyclerView"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_gravity="center_horizontal"/>

</LinearLayout>

package com.example.recyclerview2


import android.app.Activity
import android.content.Context
import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import android.widget.ImageView
import android.widget.TextView
import android.widget.Toast
import androidx.recyclerview.widget.LinearLayoutManager
import androidx.recyclerview.widget.RecyclerView
import androidx.recyclerview.widget.StaggeredGridLayoutManager
import kotlinx.android.synthetic.main.activity_main.*
import org.w3c.dom.Text


class Fruit(val name:String, val imageID:Int){
}
class FruitAdapter(val fruitList: List<Fruit>): RecyclerView.Adapter<FruitAdapter.ViewHolder>(){

    inner class ViewHolder(view:View):RecyclerView.ViewHolder(view){
        val image :ImageView =view.findViewById(R.id.fruitImage)
        val name:TextView = view.findViewById(R.id.fruitName)
    }

    override fun onCreateViewHolder(parent: ViewGroup, viewType:Int): ViewHolder {
        val view = LayoutInflater.from(parent.context).inflate(R.layout.fruit_item, parent, false)
        val viewHolder = ViewHolder(view)
        
        //RecyclerView 的点击事件
        viewHolder.itemView.setOnClickListener{
            val position = viewHolder.adapterPosition
            val fruit = fruitList[position]
            Toast.makeText(parent.context, fruit.name +"," + position.toString(), Toast.LENGTH_SHORT).show()

        }
        return viewHolder
    }

    override fun onBindViewHolder(holder: ViewHolder, position:Int){
        val fruit = fruitList[position]
        holder.image.setImageResource(fruit.imageID)
        holder.name.text = fruit.name
    }

    override fun getItemCount() = fruitList.size
}

class MainActivity : AppCompatActivity() {

    private val fruitList = ArrayList<Fruit>()
    
    //字典的定义
    private val nameImageMap = mapOf("Apple(苹果)" to R.drawable.apple_pic,
            "Banana(香蕉)" to R.drawable.banana_pic,
            "Cherry(樱桃)" to R.drawable.cherry_pic,
            "Grape(葡萄)" to R.drawable.grape_pic,
            "Mango(芒果)" to R.drawable.mango_pic,
            "Orange(橙子)" to R.drawable.orange_pic,
            "Pear(梨子)" to R.drawable.pear_pic,
            "Pineapple(菠萝)" to R.drawable.pineapple_pic,
            "Strawberry(草莓)" to R.drawable.strawberry_pic,
            "Watermelon(西瓜)" to R.drawable.watermelon_pic)

    //public val textView:TextView = findViewById(R.id.textView)
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        initFruits() // 初始化水果列表
        
        //实现水平滚动效果
        //val layoutManager = LinearLayoutManager(this)
        //layoutManager.orientation = LinearLayoutManager.HORIZONTAL //ViewItem 内部空间水平排列（默认竖直）
        
        //实现瀑布流效果
        val layoutManager = StaggeredGridLayoutManager(3, StaggeredGridLayoutManager.VERTICAL)
        recyclerView.layoutManager = layoutManager
        val adapter = FruitAdapter(fruitList)
        recyclerView.adapter = adapter
    }
    private fun getRandomLength(str:String):String {
        //重复字符串 随机1到5次。
        val n = (1..5).random()
        val builder = StringBuilder()
        repeat(n){
            builder.append(str)
        }
        return builder.toString()
        }

    private fun initFruits(){
        repeat(4){
            for((name, image) in nameImageMap){
                //字典键值对的循环
                fruitList.add(Fruit(getRandomLength(name), image))
            }
        }
    }
}

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.recyclerview2">

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/Theme.RecyclerView2">
        <activity android:name=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>