如何使用 Kotlin 从 RecyclerView (ArrayList) 中保存数据？答案

【问题标题】：How to save data from RecyclerView (ArrayList) with Kotlin?如何使用 Kotlin 从 RecyclerView (ArrayList) 中保存数据？
【发布时间】：2021-12-31 02:37:22
【问题描述】：

我在 Kotlin 中创建了一个 RecyclerView，并希望使用 GSON 库保存来自 RecyclerView（ArrayList）的数据。我已经搜索了很多，但找不到有效的解决方案。这是我当前的代码：（没有保存功能）

MainActivity.kt：

class MainActivity : AppCompatActivity(), ExampleAdapter.OnItemClickListener {
    private val exampleList = generateDummyList(500)
    private val adapter = ExampleAdapter(exampleList, this)

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        recycler_view.adapter = adapter
        recycler_view.layoutManager = LinearLayoutManager(this)
        recycler_view.setHasFixedSize(true)
    }
    fun insertItem(view: View) {
        val index = Random.nextInt(8)

        val newItem = ExampleItem(
            R.drawable.ic_android,
            "New item at position $index",
            "Line 2"
        )
        exampleList.add(index, newItem)
        adapter.notifyItemInserted(index)
    }
    fun removeItem(view: View) {
        val index = Random.nextInt(8)
        exampleList.removeAt(index)
        adapter.notifyItemRemoved(index)
    }
    override fun onItemClick(position: Int) {
        Toast.makeText(this, "Item $position clicked", Toast.LENGTH_SHORT).show()
        val clickedItem = exampleList[position]
        clickedItem.text1 = "Clicked"
        adapter.notifyItemChanged(position)
    }
    private fun generateDummyList(size: Int): ArrayList<ExampleItem> {
        val list = ArrayList<ExampleItem>()
        for (i in 0 until size) {
            val drawable = when (i % 3) {
                0 -> R.drawable.ic_android
                1 -> R.drawable.ic_audio
                else -> R.drawable.ic_sun
            }
            val item = ExampleItem(drawable, "Item $i", "Line 2")
            list += item
        }
        return list
    }
}

ExampleItem.kt：

data class ExampleItem(val imageResource: Int, var text1: String, var text2: String)

ExampleAdapter.kt：

class ExampleAdapter(
    private val exampleList: List<ExampleItem>,
    private val listener: OnItemClickListener) :
    RecyclerView.Adapter<ExampleAdapter.ExampleViewHolder>() {
    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ExampleViewHolder {
        val itemView = LayoutInflater.from(parent.context).inflate(R.layout.example_item,
            parent, false)
        return ExampleViewHolder(itemView)
    }
    override fun onBindViewHolder(holder: ExampleViewHolder, position: Int) {
        val currentItem = exampleList[position]
        holder.imageView.setImageResource(currentItem.imageResource)
        holder.textView1.text = currentItem.text1
        holder.textView2.text = currentItem.text2
    }
    override fun getItemCount() = exampleList.size
    inner class ExampleViewHolder(itemView: View) : RecyclerView.ViewHolder(itemView),
        View.OnClickListener {
        val imageView: ImageView = itemView.image_view
        val textView1: TextView = itemView.text_view_1
        val textView2: TextView = itemView.text_view_2
        init {
            itemView.setOnClickListener(this)
        }
        override fun onClick(v: View?) {
            val position = adapterPosition
            if (position != RecyclerView.NO_POSITION) {
                listener.onItemClick(position)
            }
        }
    }
    interface OnItemClickListener {
        fun onItemClick(position: Int)
    }
}

【问题讨论】：

您要将数据保存在哪里？本地数据库，例如房间数据库或共享首选项？

标签： java android kotlin android-recyclerview gson

【解决方案1】：

首先，您需要使用 onBindViewHolder 中的 json 对象将数据转换为 json

String json = {"phonetype":"N95","cat":"WP"};

try {

    JSONObject obj = new JSONObject(json);

    Log.d("My App", obj.toString());

} catch (Throwable t) {
    Log.e("My App", "Could not parse malformed JSON: \"" + json + "\"");
}

如果你想保存，那么你可以使用共享首选项。

【讨论】：