Android Kotlin – 来自对象列表的ListView适配器

我是新来的Android，并没有完全得到它的概念呢。 我正在尝试从https://www.raywenderlich.com/category/android （一个非常简单的提醒应用程序 – 它显示一个字符串列表作为提醒）的教程进行更改。 MainActivity的代码是：

package com.example.reminderapp import android.app.Activity import android.app.AlertDialog import android.content.BroadcastReceiver import android.content.Context import android.content.Intent import android.content.IntentFilter import android.content.res.Configuration import java.text.SimpleDateFormat import android.support.v7.app.AppCompatActivity import android.os.Bundle import android.util.Log import android.view.View import android.widget.AdapterView import android.widget.ArrayAdapter import kotlinx.android.synthetic.main.activity_main.* import java.util.* class MainActivity : AppCompatActivity() { private val taskList: MutableList<Task> = mutableListOf() private val taskListDesciptors: MutableList<String> = mutableListOf() private val adapter by lazy { makeAdapter(taskListDesciptors) } //private val adapter by lazy { makeAdapterTask(taskList) } private val tickReceiver by lazy { makeBroadcastReceiver() } private val ADD_TASK_REQUEST = 1 private val PREFS_TASKS = "prefs_tasks" private val KEY_TASKS_LIST = "tasks_list" companion object { private const val LOG_TAG = "MainActivityLog" private fun getCurrentTimeStamp(): String { val simpleDateFormat = SimpleDateFormat("yyyy-MM-dd HH:mm:ss", Locale.US) val now = Date() return simpleDateFormat.format(now) } } override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) setContentView(R.layout.activity_main) taskListView.adapter = adapter taskListView.onItemClickListener = AdapterView.OnItemClickListener { parent, view, position, id -> } val savedList = getSharedPreferences(PREFS_TASKS, Context.MODE_PRIVATE).getString(KEY_TASKS_LIST, null) if (savedList != null) { val items = savedList.split(",".toRegex()).dropLastWhile { it.isEmpty() }.toTypedArray() //taskList.addAll(items) } taskListView.onItemClickListener = AdapterView.OnItemClickListener { _, _, position, _ -> taskSelected(position) } } override fun onResume() { // 1 super.onResume() // 2 dateTimeTextView.text = getCurrentTimeStamp() // 3 registerReceiver(tickReceiver, IntentFilter(Intent.ACTION_TIME_TICK)) } override fun onPause() { // 4 super.onPause() // 5 try { unregisterReceiver(tickReceiver) } catch (e: IllegalArgumentException) { Log.e(MainActivity.LOG_TAG, "Time tick Receiver not registered", e) } } override fun onActivityResult(requestCode: Int, resultCode: Int, data: Intent?) { // 1 if (requestCode == ADD_TASK_REQUEST) { // 2 if (resultCode == Activity.RESULT_OK) { // 3 //val task = data?.getStringExtra(TaskDescriptionActivity.EXTRA_TASK_DESCRIPTION) val task = data?.getSerializableExtra(TaskDescriptionActivity.EXTRA_TASK_DESCRIPTION) as Task task?.let { taskList.add(task) taskListDesciptors.add(task.taskDescription) // TODO: WHY DO I NEED THIS?! // 4 adapter.notifyDataSetChanged() } //adapter.notifyDataSetChanged() } } } override fun onStop() { super.onStop() // Save all data which you want to persist. val savedList = StringBuilder() for (task in taskList) { savedList.append(task) savedList.append(",") } getSharedPreferences(PREFS_TASKS, Context.MODE_PRIVATE).edit() .putString(KEY_TASKS_LIST, savedList.toString()).apply() } override fun onConfigurationChanged(newConfig: Configuration?) { super.onConfigurationChanged(newConfig) } fun addTaskClicked(view: View) { val intent = Intent(this, TaskDescriptionActivity::class.java) startActivityForResult(intent, ADD_TASK_REQUEST) } private fun TasksListToDescriptionsList(list: List<Task>) : List<String>{ val retMutableList: MutableList<String> = mutableListOf() for (task in list) { retMutableList.add(task.taskDescription) } val retList: List<String> = retMutableList return retList } private fun makeAdapter(list: List<String>): ArrayAdapter<String> { return ArrayAdapter(this, android.R.layout.simple_list_item_1, list) } private fun makeAdapterTask(list: List<Task>): ArrayAdapter<String> { return ArrayAdapter(this, android.R.layout.simple_list_item_1, TasksListToDescriptionsList(list)) } private fun makeBroadcastReceiver(): BroadcastReceiver { return object : BroadcastReceiver() { override fun onReceive(context: Context, intent: Intent?) { if (intent?.action == Intent.ACTION_TIME_TICK) { dateTimeTextView.text = getCurrentTimeStamp() } } } } private fun taskSelected(position: Int) { // 1 AlertDialog.Builder(this) // 2 .setTitle(R.string.alert_title) // 3 .setMessage(taskList[position].taskDescription) .setPositiveButton(R.string.delete, { _, _ -> taskList.removeAt(position) taskListDesciptors.removeAt(position) adapter.notifyDataSetChanged() }) .setNegativeButton(R.string.cancel, { dialog, _ -> dialog.cancel() }) // 4 .create() // 5 .show() } } 

我的问题关于private val adapter by lazy { makeAdapter(taskListDesciptors) }和private val adapter by lazy { makeAdapter(taskList) } 。 taskListDesciptors是一个字符串列表，taskList是在另一个文件中声明的一个对象列表：

 public class Task (description: String, date: Date) : Serializable { val taskDescription = description val dateTime = date } 

如果我private val adapter by lazy { makeAdapter(taskListDesciptors) }使用private val adapter by lazy { makeAdapter(taskListDesciptors) } ，ListView每次都会更新，但是如果我使用private val adapter by lazy { makeAdapter(taskList) }它不会。

我错过了什么？

谢谢！

阮经天