Android 入门程序 Kotlin版（2）

ListView的用法介绍。

2个组件， TextView，ListView依次纵向线性布局。

ViewItem的布局，左边图片，右边文字水平排列：

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<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="60dp">

    <ImageView
        android:id="@ id/fruitImage"
        android:layout_width="80dp"
        android:layout_height="80dp"
        android:layout_gravity="center_vertical"
        android:layout_marginLeft="10dp"/>

    <TextView
        android:id="@ id/fruitName"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center_vertical"
        android:layout_marginLeft="10dp"/>

</LinearLayout>

Activity的布局

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<?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_vertical"
        android:text = "Hello, fruits"
        android:textSize = "20sp"/>
    <ListView
        android:id = "@ id/listView"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_gravity="right"/>

</LinearLayout>

Kotlin 代码：

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package com.example.listviewtest

import android.app.Activity
import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import android.widget.ArrayAdapter
import android.widget.ImageView
import android.widget.TextView
import android.widget.Toast
import kotlinx.android.synthetic.main.activity_main.*


class Fruit(val name:String, val imageID:Int){
}
class FruitAdapter(activity: Activity, val resourceId:Int, data :List<Fruit>): ArrayAdapter<Fruit>(activity, resourceId, data){

    inner class ViewHolder(val fruitImage:ImageView, val fruitName:TextView)  //inner calss 表示内部类
    override fun getView(position:Int, convertView: View?, parent: ViewGroup):View {
        val view:View
        val viewHolder:ViewHolder
        if (convertView == null){
            view = LayoutInflater.from(context).inflate(resourceId, parent, false)
            val fruitImage: ImageView = view.findViewById(R.id.fruitImage)
            val fruitName: TextView = view.findViewById(R.id.fruitName)
            viewHolder = ViewHolder(fruitImage, fruitName)
            view.tag = viewHolder
        }
        else {
            view = convertView
            viewHolder = view.tag as ViewHolder
        }

        val fruit = getItem(position)// 获取当前项的Fruit实例
        if(fruit != null){
            viewHolder.fruitImage.setImageResource(fruit.imageID)
            viewHolder.fruitName.text = fruit.name
        }
        return view
    }
}
class MainActivity : AppCompatActivity() {
    //private val data = listOf("Apple", "Banana","Orange","Watermelon", "Pear","Grape", "Pineapple",
    //"Strawberry","Cherry","Mango")
    private val fruitList = ArrayList<Fruit>()

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        initFruits() // 初始化水果列表
        val adapter = FruitAdapter(this, R.layout.fruit_item, fruitList)
        listView.adapter = adapter
        listView.setOnItemClickListener { parent, view, position, id ->
            val fruit = fruitList[position]
            textView.setText("选中了第"  (position 1).toString() "个水果-->"   fruit.name)
            //Toast.makeText(this, fruit.name  ","   position.toString(), Toast.LENGTH_SHORT).show()
        }
    }

    private fun initFruits(){
        repeat(2){
            fruitList.add(Fruit("Apple(苹果)", R.drawable.apple_pic))
            fruitList.add(Fruit("Banana(香蕉)", R.drawable.banana_pic))
            fruitList.add(Fruit("Cherry(樱桃)", R.drawable.cherry_pic))
            fruitList.add(Fruit("Grape(葡萄)", R.drawable.grape_pic))
            fruitList.add(Fruit("Mango(芒果)", R.drawable.mango_pic))
            fruitList.add(Fruit("Orange(橘子)", R.drawable.orange_pic))
            fruitList.add(Fruit("Pear(梨子)", R.drawable.pear_pic))
            fruitList.add(Fruit("Pineapple(菠萝)", R.drawable.pineapple_pic))
            fruitList.add(Fruit("Strawberry(草莓)", R.drawable.strawberry_pic))
            fruitList.add(Fruit("Watermelon(西瓜)", R.drawable.watermelon_pic))

        }
    }
}

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AndroidManifest

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

    <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.ListViewTest">
        <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>

listview android

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