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"
	}]