Android kotlin RecyclerView遍历json实现列表数据的案例

<?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="50dp">   // 这里的高度需要注意, 就是每个需要遍历的元素的高度, 千万要写成不match_parent
    <linearlayout
        android:id="@+id/item_region"
        android:layout_width="match_parent"
        android:layout_height="50dp"
        android:background="@drawable/bottom_border_white"
        android:gravity="center_vertical">
        <textview
            android:id="@+id/regionname"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_marginleft="20dp"
            android:layout_weight="2"
            android:text="china"
            android:textcolor="@color/colorprimary"
            android:textsize="16sp" />
        <linearlayout
            android:layout_width="0dp"
            android:layout_height="50dp"
            android:layout_weight="1"
            android:gravity="center_vertical"
            android:orientation="horizontal">
            <textview
                android:id="@+id/selectedbtn"
                android:layout_width="80dp"
                android:layout_height="wrap_content"
                android:text="selected"
                android:textcolor="@color/colorprimary"
                android:textsize="16sp"
                android:visibility="invisible"
                />
            <imageview
                android:layout_width="10dp"
                android:layout_height="15dp"
                android:layout_marginleft="15dp"
                android:src="@drawable/right_arrow" />
        </linearlayout>
    </linearlayout>
</linearlayout>

<?xml version="1.0" encoding="utf-8"?>
<relativelayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@color/main_bg_color"
    android:orientation="vertical"
    >
    <linearlayout
        android:id="@+id/updatearea_view"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="vertical">
        <textview
            android:layout_width="wrap_content"
            android:layout_height="50dp"
            android:layout_marginleft="20dp"
            android:layout_margintop="40dp"
            android:gravity="center_vertical"
            android:text="all regions"
            android:textcolor="@color/colorprimary"
            android:textsize="16sp"
            android:textstyle="bold" />
        <androidx.recyclerview.widget.recyclerview
            android:id="@+id/regionlistrecyclerview"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:orientation="vertical"
            />
    </linearlayout>
</relativelayout>

import kotlinx.android.synthetic.main.activity_update_area.regionlistrecyclerview
data class country(val name: string, val code: int, var selected: boolean)
/**
 * 设置页
 */
class areaupdateactivity : appcompatactivity() {
    private lateinit var adapter: simpleadapter
    override fun oncreate(savedinstancestate: bundle?) {
        super.oncreate(savedinstancestate)
        setcontentview(r.layout.activity_update_area)
        // 读取文件内容
        val jsonstring = loadjsonfromassets(this, "country.json")
        val gson = gson()
        val countryname = "china"
        val countrys: list<country> = gson.fromjson(jsonstring, type)
		// 设置默认的被选中的countryname selected 
        if (countryname != null) {
            for (item in countrys) {
                if (item.name == countryname){
                    item.selected = true
                }
            }
        }
        regionlistrecyclerview.layoutmanager = linearlayoutmanager(this)
        adapter = simpleadapter(countrys)
        regionlistrecyclerview.adapter = adapter
		// 元素的点击事件
        adapter.setonitemclicklistener(object : simpleadapter.onitemclicklistener {
            override fun onitemclick(position: int, item: country) {
                println("我点击的$item")
                adapter.notifyitemchanged(position, item) // .indexof(item)
            }
        })
    }
	// 如果json文件位于assets目录下, 这是处理非代码资源文件（如文本、json等）的方式。通过assetmanager来访问这些文件。
    fun loadjsonfromassets(context: context, filename: string): string {
        val assetmanager = context.assets
        val reader: bufferedreader
        var jsonstring: string = ""
        try {
            reader = bufferedreader(inputstreamreader(assetmanager.open(filename)))
            jsonstring = reader.use { it.readtext() }
        } catch (e: exception) {
            e.printstacktrace()
            // 处理异常情况
        }
        return jsonstring
    }
	// simpleadapter 适配器, 监听列表元素
	// 为了代码的优雅, 应该单独写在adapter里
    class simpleadapter(private val countrys: list<country>) :
        recyclerview.adapter<simpleadapter.simpleviewholder>() {
        private var selectedposition = recyclerview.no_position
        inner class simpleviewholder(itemview: view) : recyclerview.viewholder(itemview) {
            val regionname: textview = itemview.findviewbyid(r.id.regionname)
            val selectedbtn: textview = itemview.findviewbyid(r.id.selectedbtn)
            init {
                itemview.setonclicklistener {
                    // 在这里处理点击事件
                    onitemclicklistener?.let { listener ->
                        selectedposition = adapterposition
                        notifydatasetchanged()
                        if (selectedposition != recyclerview.no_position) {
                            listener.onitemclick(selectedposition, getitem(selectedposition))
                        }
                    }
                }
            }
        }
        override fun oncreateviewholder(parent: viewgroup, viewtype: int): simpleviewholder {
            val view = layoutinflater.from(parent.context)
                .inflate(r.layout.item_region, parent, false)
            return simpleviewholder(view)
        }
        interface onitemclicklistener {
            fun onitemclick(position: int, item: country)
        }
        private var onitemclicklistener: onitemclicklistener? = null
        fun setonitemclicklistener(listener: onitemclicklistener) {
            onitemclicklistener = listener
        }
        override fun onbindviewholder(holder: simpleviewholder, position: int) {
            val currentitem = getitem(position)
            holder.regionname.text = countrys[position].name
            // 点击的显示selected, 其他隐藏
            holder.selectedbtn.visibility = if (position == selectedposition) view.visible else view.invisible
            // 初始化数据 currentitem.selected为true的显示
            // 点击的时候 原currentitem.selected为true的变为false, 点击的这个元素selected显示
             if (currentitem.selected) {
                 currentitem.selected = !currentitem.selected
                holder.selectedbtn.visibility = view.visible  
                println("我显示着")
            }
            // 点击selected
            holder.selectedbtn.setonclicklistener {
                var countrystr = currentitem.name
                coroutinescope(dispatchers.io).launch {
                    updateinfo(countrystr) // 更新用户数据(自定义function)
                }
            }
        }
        override fun getitemcount(): int = countrys.size
        fun getitem(position: int): country {
            return countrys[position]
        }
    }
}

[{
		"selected": false,
		"country_id": 100006,
		"country_code": 244,
		"name": "angola",
		"country_name_cn": "安哥拉",
		"ab": "ao"
	},
	{
		"selected": false,
		"country_id": 100008,
		"country_code": 355,
		"name": "albania",
		"country_name_cn": "阿尔巴尼亚",
		"ab": "al"
	}]