CalendarView交互仅单次有效：返回后无法选择日期求助

你的核心问题是每次通过setContentView(R.layout.date_screen)回到日期选择界面时，都会创建一个全新的CalendarView实例，但这个新实例没有绑定任何OnDateChangeListener。第一次启动时你在onCreate里给初始的CalendarView设了监听器，但切换布局后重建的CalendarView没有监听器，所以点击日期完全没反应。

另外还有两个次要问题：

• notesList是onCreate方法的局部变量，虽然当前不会立即丢失，但如果Activity因配置变更（比如旋转屏幕）重建，所有笔记数据会直接丢失，应该改成Activity的成员变量。
• 每次切换布局都重新查找控件，代码冗余且容易出错。

方案1：快速修复现有代码（适合新手过渡） #

把设置CalendarView监听器的逻辑抽成独立函数，每次回到日期选择界面时重新绑定监听器：

package com.effici.application

import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import android.text.Editable
import android.widget.Button
import android.widget.CalendarView
import com.google.android.material.textfield.TextInputEditText

class MainActivity : AppCompatActivity() {
    // 改成成员变量，避免数据丢失
    private val notesList = arrayListOf<Note>()
    private lateinit var dateChoosingCalendar: CalendarView
    private lateinit var noteInputField: TextInputEditText
    private lateinit var backButton: Button

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.date_screen)
        dateChoosingCalendar = findViewById(R.id.dateChoosingCalendar)
        setupCalendarListener()
    }

    // 抽成独立函数，方便重复调用
    private fun setupCalendarListener() {
        dateChoosingCalendar.setOnDateChangeListener { _, year, month, dayOfMonth ->
            val chosenDate = "$dayOfMonth-${month + 1}-$year"
            var noteAlreadyCreated = false
            var noteIndex = 0

            for (i in 0 until notesList.size) {
                if (chosenDate == notesList[i].date) {
                    noteAlreadyCreated = true
                    noteIndex = i
                    break
                }
            }

            if (noteAlreadyCreated) {
                println("Note already created.")
                setContentView(R.layout.note_template)
                initNoteTemplateViews()
                // 加载已有笔记内容
                noteInputField.setText(notesList[noteIndex].text)
                backButton.setOnClickListener {
                    notesList[noteIndex].text = noteInputField.text
                    backToDateScreen()
                }
            } else {
                notesList.add(Note(userinp = null, dateParam = chosenDate))
                noteIndex = notesList.size - 1
                println("A note for $chosenDate is added.")
                setContentView(R.layout.note_template)
                initNoteTemplateViews()
                backButton.setOnClickListener {
                    notesList[noteIndex].text = noteInputField.text
                    backToDateScreen()
                }
            }
        }
    }

    // 初始化笔记模板的控件
    private fun initNoteTemplateViews() {
        noteInputField = findViewById(R.id.noteTakingField)
        backButton = findViewById(R.id.changeButton)
    }

    // 返回日期选择界面并重新绑定监听器
    private fun backToDateScreen() {
        setContentView(R.layout.date_screen)
        dateChoosingCalendar = findViewById(R.id.dateChoosingCalendar)
        setupCalendarListener()
    }
}

class Note(val userinp: Editable?, val dateParam: String) {
    var text: Editable? = userinp
    var date = dateParam
}

方案2：更规范的Android界面切换方式（推荐） #

不要用setContentView来回重建布局，改用同一布局内切换视图可见性的方式，这样视图不会被销毁，监听器一直有效，代码更简洁：

第一步：修改主布局文件（比如命名为activity_main.xml） #

<?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="match_parent"
    android:orientation="vertical">

    <!-- 日期选择界面 -->
    <include
        android:id="@+id/date_container"
        layout="@layout/date_screen"
        android:visibility="visible"/>

    <!-- 笔记编辑界面 -->
    <include
        android:id="@+id/note_container"
        layout="@layout/note_template"
        android:visibility="gone"/>

</LinearLayout>

第二步：修改Activity代码 #

package com.effici.application

import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import android.text.Editable
import android.view.View
import android.widget.Button
import android.widget.CalendarView
import com.google.android.material.textfield.TextInputEditText

class MainActivity : AppCompatActivity() {
    private val notesList = arrayListOf<Note>()
    private lateinit var dateChoosingCalendar: CalendarView
    private lateinit var noteInputField: TextInputEditText
    private lateinit var backButton: Button
    private lateinit var dateContainer: View
    private lateinit var noteContainer: View
    private var currentNoteIndex = -1

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

        // 初始化所有控件
        dateChoosingCalendar = findViewById(R.id.dateChoosingCalendar)
        noteInputField = findViewById(R.id.noteTakingField)
        backButton = findViewById(R.id.changeButton)
        dateContainer = findViewById(R.id.date_container)
        noteContainer = findViewById(R.id.note_container)

        setupCalendarListener()
        setupBackButtonListener()
    }

    private fun setupCalendarListener() {
        dateChoosingCalendar.setOnDateChangeListener { _, year, month, dayOfMonth ->
            val chosenDate = "$dayOfMonth-${month + 1}-$year"
            var noteAlreadyCreated = false
            currentNoteIndex = -1

            // 查找已有笔记
            for (i in notesList.indices) {
                if (chosenDate == notesList[i].date) {
                    noteAlreadyCreated = true
                    currentNoteIndex = i
                    break
                }
            }

            // 切换到笔记界面
            dateContainer.visibility = View.GONE
            noteContainer.visibility = View.VISIBLE

            if (noteAlreadyCreated) {
                println("Note already created.")
                noteInputField.setText(notesList[currentNoteIndex].text)
            } else {
                // 添加新笔记
                notesList.add(Note(null, chosenDate))
                currentNoteIndex = notesList.size - 1
                println("A note for $chosenDate is added.")
                noteInputField.setText("") // 清空输入框
            }
        }
    }

    private fun setupBackButtonListener() {
        backButton.setOnClickListener {
            // 保存当前笔记内容
            if (currentNoteIndex != -1 && currentNoteIndex < notesList.size) {
                notesList[currentNoteIndex].text = noteInputField.text
            }
            // 切换回日期界面
            noteContainer.visibility = View.GONE
            dateContainer.visibility = View.VISIBLE
        }
    }
}

class Note(val userinp: Editable?, val dateParam: String) {
    var text: Editable? = userinp
    var date = dateParam
}

1. 视图不会被反复销毁重建，性能更好，监听器无需重复绑定
2. 代码结构更清晰，避免重复查找控件的冗余逻辑
3. 数据更安全，不会因布局切换丢失临时状态

内容的提问来源于stack exchange，提问作者Nandan Praveen