使用Kotlin编写RecyclerView

一：project-build.gradle代码

apply plugin: 'com.android.application'

apply plugin: 'kotlin-android'

apply plugin: 'kotlin-android-extensions'

android {
    compileSdkVersion 28
    defaultConfig {
        applicationId "com.hexl.mykotlin1"
        minSdkVersion 21
        targetSdkVersion 28
        versionCode 1
        versionName "1.0"
        testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }
    }
}

dependencies {
    implementation fileTree(include: ['*.jar'], dir: 'libs')
    implementation "org.jetbrains.kotlin:kotlin-stdlib-jre7:$kotlin_version"
    implementation 'com.android.support:appcompat-v7:28.0.0'
    implementation 'com.android.support.constraint:constraint-layout:1.1.3'
    testImplementation 'junit:junit:4.12'
    androidTestImplementation 'com.android.support.test:runner:1.0.2'
    androidTestImplementation 'com.android.support.test.espresso:espresso-core:3.0.2'
    implementation 'com.android.support:design:28.0.0'
    implementation 'com.android.support:recyclerview-v7:28.0.0'
}

二：app-builde.gralde

// Top-level build file where you can add configuration options common to all sub-projects/modules.

buildscript {
    ext.kotlin_version = '1.2.30'
    repositories {
        google()
        jcenter()
    }
    dependencies {
        classpath 'com.android.tools.build:gradle:3.1.3'
        classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"

        // NOTE: Do not place your application dependencies here; they belong
        // in the individual module build.gradle files
    }
}

allprojects {
    repositories {
        google()
        jcenter()
    }
}

task clean(type: Delete) {
    delete rootProject.buildDir
}

三：实现代码

package com.hexl.mykotlin1

import android.content.Context
import android.support.v7.app.AppCompatActivity
import android.os.Bundle
import android.support.v7.widget.LinearLayoutManager
import android.support.v7.widget.RecyclerView
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import android.widget.TextView
import android.widget.Toast

class MainActivity : AppCompatActivity() {
    //初始化数据源
    val data = listOf("hexl", "Dongl", "Dongl", "Dongl", "Dongl", "Dongl", "Dongl", "Dongl",
            "Dongl", "Dongl", "Dongl", "Dongl", "Dongl", "Dongl", "Dongl", "Dongl", "Dongl",
            "Dongl", "Dongl", "Dongl", "Dongl")

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        //设置布局
        setContentView(R.layout.activity_main)
        //绑定id，这里的泛型需要指定view，kotlin会自动推断类型。
        val recyclerView = findViewById(R.id.rv)
        //设置布局管理器
        recyclerView.layoutManager = LinearLayoutManager(this)
        //初始化适配器
        val adapter = MyAdapter(this, data)
        //设置适配器
        recyclerView.adapter = adapter
        //item点击事件
        adapter.setOnItemClickListener(listener = object : MyAdapter.OnItemClickListener {
            override fun setOnItemClickListener(view: View, int: Int) {
                //kotlin 不能使用 MainActivity.this 这种方式获取 Context 对象
                // this@MainActivity、MainActivity@this，通过这两种方式获取
                Toast.makeText(this@MainActivity, int.toString(), Toast.LENGTH_LONG).show()
            }
        })
    }
}

/**
 * 适配器
 * 通过构造函数将 上下文 和 数据源 传到适配器里
 * 也可以采用次构造函数constructor（）
 */
class MyAdapter(private val context: Context, private val data: List) : RecyclerView.Adapter() {
    private var listener: OnItemClickListener? = null
//    private var context1: Context? = null
//    private var data1: ArrayList? = null

//    constructor(context1: Context, data1: ArrayList) {
//        this.context1 = context1
//        this.data1 = data1
//    }

    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): MyVH {
        return MyVH(LayoutInflater.from(context).inflate(R.layout.item_rv, parent, false))
    }

    override fun getItemCount(): Int {
        return data.size
    }

    override fun onBindViewHolder(viewholder: MyVH, position: Int) {
        viewholder.textView.text = data[position]
        viewholder.itemView.setOnClickListener {
            //!! 等价于 ？ 检测是否为null
            listener!!.setOnItemClickListener(view = viewholder.itemView, int = position)
        }
    }

    fun setOnItemClickListener(listener: OnItemClickListener) {
        this.listener = listener
    }

    class MyVH(itemView: View) : RecyclerView.ViewHolder(itemView) {
        var textView: TextView = itemView.findViewById(R.id.tv_text)
    }

    interface OnItemClickListener {
        fun setOnItemClickListener(view: View, int: Int)
    }
}

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