如何实现从一个到另一个 android 的一周变化

Question

Faced with such a task: I am making an app for a university, where every week (starts on Monday at 00:00) has its own name: numerator and denominator. Let's say the current week is the numerator, the next one will be the denominator, then the numerator again, and so on.

I do not understand how it is possible to make the type (numerator or denominator) displayed on my fragment every week, well, it is desirable that at 00:00 on Sunday the week changed to the numerator or denominator, respectively. I am using Kotlin

Answer 1

I would do this in a ViewModel. Expose a LiveData with Boolean value where true/false correspond with numerator week or denominator week. Choose an arbitrary Monday date to use as your baseline to calculate the current day from. I'm arbitrarily using this week's Monday as this baseline epoch.

However, this approach assumes that the university's calendar never, ever breaks the pattern. If they have an inconsistent pattern, you will need a data table to look up what value to use.

class MyViewModel : ViewModel() {

    companion object {
         private val WEEK_TYPE_BASELINE_DAY = LocalDate.of(2021, 11, 1)
    }

    private val mutableWeekType = MutableLiveData<Boolean>()
    val weekType: LiveData<Boolean> get() = mutableWeekType

    init {
        updateCurrentWeekType()
    }

    private fun updateCurrentWeekType() {
        val today = LocalDate.now()
        val weeks = Duration.between(WEEK_TYPE_BASELINE_DAY, today).toDays() / 7L
        mutableWeekType.value = weeks % 2 == 0L

        // In case the week changes while this ViewModel is alive,
        // plan the next update.
        val nextMonday = today.with(TemporalAdjusters.next(DayOfWeek.MONDAY))
        val nextMondayMidnight = LocalDateTime.of(nextMonday, LocalTime.MIDNIGHT)
        val timeToNextChange = Duration.between(LocalDateTime.now(), nextMondayMidnight).toMillis()
        viewModelScope.launch {
            delay(timeToNextChange)
            updateCurrentWeekType()
        }
    }

}

The fragment can observe weekType and modify the text of any UI element based on whether it receives true or false.