使用NumberPicker展示日期时遇LocalDate日期值无效异常的求助

问题场景 #

使用NumberPicker展示日期，核心代码如下：

val numberPicker = binding.numberPicker
val values = getArrayDates(date.toString()) //EventsBottomSheet.kt:45
numberPicker.minValue = 0
numberPicker.maxValue = values.size - 1
numberPicker.displayedValues = values.toArray(arrayOfNulls<String>(values.size))
numberPicker.wrapSelectorWheel = true
numberPicker.setOnValueChangedListener { _, _, newVal ->
    binding.dateText.text = newVal.toString()
}

getArrayDates方法实现：

private fun getArrayDates(referenceDate : String) : ArrayList<String>{
    val datesList = referenceDate.split("/")
    val localeDate = LocalDate.of(datesList[0].toInt(), Month.of(datesList[1].toInt()), datesList[2].toInt()) //EventsBottomSheet.kt:65 (related with exception)
    val monthsToDisplay = listOf(localeDate.minusMonths(1), localeDate, localeDate.plusMonths(1))
    val daysList = ArrayList<String>()
    val formatter = DateTimeFormatter.ofLocalizedDate(FormatStyle.LONG)
    for (month in monthsToDisplay) {
        val yearMonth = YearMonth.from(month)
        for (day in 1..yearMonth.lengthOfMonth()) {
            daysList.add(yearMonth.atDay(day).format(formatter))
        }
    }
    return daysList
}

观测到date值格式为"21/05/2023"（日/月/年），转换为LocalDate时抛出异常：

FATAL EXCEPTION: main
Process: com.ahmetkaan.kediy, PID: 19391
j$.time.DateTimeException: Invalid value for DayOfMonth (valid values 1 - 28/31): 2023
    at j$.time.temporal.ValueRange.checkValidValue(ValueRange.java:311)
    at j$.time.temporal.ChronoField.checkValidValue(ChronoField.java:713)
    at j$.time.LocalDate.of(LocalDate.java:250)
    at com.ahmetkaan.kediy.EventsBottomSheet.getArrayDates(EventsBottomSheet.kt:65)
    ...

已排除前导零、日期合法性问题（date在之前Fragment中由LocalDate定义）。

异常原因 #

异常提示DayOfMonth传入了2023，核心问题是参数顺序完全颠倒：

• LocalDate.of(year, month, dayOfMonth)的参数顺序是「年、月、日」
• 但拆分"21/05/2023"后，datesList[0]是日（21）、datesList[1]是月（05）、datesList[2]是年（2023），你却把年份传给了dayOfMonth参数，触发无效值异常。

解决方案 #

方案1：直接修正参数顺序 #

调整LocalDate.of的参数，匹配日/月/年的格式：

// 修正参数顺序：年(datesList[2])、月(datesList[1])、日(datesList[0])
val localeDate = LocalDate.of(datesList[2].toInt(), Month.of(datesList[1].toInt()), datesList[0].toInt())

方案2：用DateTimeFormatter解析（更规范） #

手动拆分字符串容易出错，推荐用格式化器直接解析符合格式的字符串：

private fun getArrayDates(referenceDate : String) : ArrayList<String>{
    // 定义日/月/年的格式器
    val formatter = DateTimeFormatter.ofPattern("dd/MM/yyyy")
    val localeDate = LocalDate.parse(referenceDate, formatter)
    
    val monthsToDisplay = listOf(localeDate.minusMonths(1), localeDate, localeDate.plusMonths(1))
    val daysList = ArrayList<String>()
    val displayFormatter = DateTimeFormatter.ofLocalizedDate(FormatStyle.LONG)
    for (month in monthsToDisplay) {
        val yearMonth = YearMonth.from(month)
        for (day in 1..yearMonth.lengthOfMonth()) {
            daysList.add(yearMonth.atDay(day).format(displayFormatter))
        }
    }
    return daysList
}

方案3：直接传递LocalDate（最优） #

既然date本身就是LocalDate类型，完全没必要转成字符串再解析，直接传LocalDate能彻底避免格式问题：

// 调用时直接传LocalDate
val values = getArrayDates(date)

// 修改方法参数为LocalDate
private fun getArrayDates(referenceDate : LocalDate) : ArrayList<String>{
    val monthsToDisplay = listOf(referenceDate.minusMonths(1), referenceDate, referenceDate.plusMonths(1))
    val daysList = ArrayList<String>()
    val formatter = DateTimeFormatter.ofLocalizedDate(FormatStyle.LONG)
    for (month in monthsToDisplay) {
        val yearMonth = YearMonth.from(month)
        for (day in 1..yearMonth.lengthOfMonth()) {
            daysList.add(yearMonth.atDay(day).format(formatter))
        }
    }
    return daysList
}

内容的提问来源于stack exchange，提问作者Ahmet Kaan