activity的定时器

class MyAdapter(private val data: List<String>) : RecyclerView.Adapter<MyAdapter.MyViewHolder>() {

    private val progressMap = mutableMapOf<Int, Int>() // 保存每个 item 的加载进度
    private var textData: String = ""

    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): MyViewHolder {
        val view = LayoutInflater.from(parent.context).inflate(R.layout.item_view, parent, false)
        return MyViewHolder(view)
    }

    override fun onBindViewHolder(holder: MyViewHolder, position: Int) {
        val startIndex = progressMap[position] ?: 0 // 获取上次停止的位置
        holder.bind(data[position], startIndex)
    }

    override fun getItemCount(): Int = data.size

    fun updateData(newData: String) {
        textData = newData
        notifyDataSetChanged() // 通知数据更新
    }

    class MyViewHolder(itemView: View) : RecyclerView.ViewHolder(itemView) {
        private val textView: TextView = itemView.findViewById(R.id.textView)
        private val handler: Handler = Handler(Looper.getMainLooper())
        private var currentIndex: Int = 0
        private var accumulatedData: String = ""
        private var updateRunnable: Runnable? = null
        private var isUpdating: Boolean = false

        fun bind(data: String, startIndex: Int) {
            accumulatedData = data
            currentIndex = startIndex
            textView.text = "" // 清空之前的数据

            if (!isUpdating) {
                startTimer()
            }
        }

        private fun startTimer() {
            isUpdating = true

            updateRunnable = object : Runnable {
                override fun run() {
                    if (currentIndex < accumulatedData.length) {
                        val endIndex = (currentIndex + 2).coerceAtMost(accumulatedData.length)
                        val textToUpdate = accumulatedData.substring(currentIndex, endIndex)

                        handler.post {
                            textView.append(textToUpdate)
                        }

                        currentIndex += 2
                        handler.postDelayed(this, 250) // 每250ms更新2个字符
                    } else {
                        isUpdating = false
                    }
                }
            }

            handler.post(updateRunnable!!)
        }

        override fun onViewRecycled() {
            super.onViewRecycled()
            handler.removeCallbacks(updateRunnable!!)
            // 保存当前的加载进度
            (itemView.context as MainActivity).progressMap[adapterPosition] = currentIndex
            isUpdating = false
        }
    }
}

class MainActivity : AppCompatActivity() {

    private lateinit var recyclerView: RecyclerView
    private lateinit var adapter: MyAdapter
    private lateinit var handler: Handler
    private var currentIndex = 0
    private var accumulatedData = "This is a long string that will be updated gradually over time."
    private val delay = 250L // 定时器更新的时间间隔

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        recyclerView = findViewById(R.id.recyclerView)
        recyclerView.layoutManager = LinearLayoutManager(this)

        val data = List(10) { "Item ${it + 1}" } // 示例数据
        adapter = MyAdapter(data)
        recyclerView.adapter = adapter

        handler = Handler(Looper.getMainLooper())
        startTimer() // 启动定时器
    }

    private fun startTimer() {
        // 定时器定时更新每 250 毫秒更新 2 个字符
        handler.postDelayed(object : Runnable {
            override fun run() {
                if (currentIndex < accumulatedData.length) {
                    val endIndex = (currentIndex + 2).coerceAtMost(accumulatedData.length)
                    val textToUpdate = accumulatedData.substring(currentIndex, endIndex)

                    // 通知 Adapter 更新指定的 item
                    adapter.updateData(currentIndex, textToUpdate)

                    currentIndex += 2
                    handler.postDelayed(this, delay)
                }
            }
        }, delay)
    }
}

class MyAdapter(private val data: List<String>) : RecyclerView.Adapter<MyAdapter.MyViewHolder>() {

    private val updatedData = mutableListOf<String>().apply {
        addAll(data) // 初始化数据列表
    }

    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): MyViewHolder {
        val view = LayoutInflater.from(parent.context).inflate(R.layout.item_view, parent, false)
        return MyViewHolder(view)
    }

    override fun onBindViewHolder(holder: MyViewHolder, position: Int) {
        val item = updatedData[position]
        holder.bind(item)
    }

    override fun getItemCount(): Int = updatedData.size

    fun updateData(index: Int, text: String) {
        // 更新指定位置的文本，并通知更新
        updatedData[index] += text
        notifyItemChanged(index)  // 更新指定的 item
    }

    class MyViewHolder(itemView: View) : RecyclerView.ViewHolder(itemView) {
        private val textView: TextView = itemView.findViewById(R.id.textView)

        fun bind(data: String) {
            textView.text = data
        }
    }
}

    <androidx.recyclerview.widget.RecyclerView
        android:id="@+id/recyclerView"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        app:layoutManager="androidx.recyclerview.widget.LinearLayoutManager"
        tools:listitem="@layout/item_view" />

<?xml version="1.0" encoding="utf-8"?>
<androidx.cardview.widget.CardView xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    app:cardCornerRadius="8dp"
    app:cardElevation="4dp"
    tools:context=".MainActivity">

    <androidx.constraintlayout.widget.ConstraintLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content">

        <TextView
            android:id="@+id/textView"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text=""
            android:textSize="16sp"
            android:layout_margin="16dp"
            android:layout_alignParentStart="true"
            android:layout_alignParentTop="true"/>

    </androidx.constraintlayout.widget.ConstraintLayout>
</androidx.cardview.widget.CardView>