material-components/material-components-android · error · IllegalArgumentException

start Month cannot be after current Month

Error message

start Month cannot be after current Month

What it means

CalendarConstraints validates its month window in the constructor: if openAt (the month the picker opens on) is set and start.compareTo(openAt) > 0 — i.e. the opening month lies before the lower bound — it throws IllegalArgumentException. The bounds must satisfy start <= openAt <= end for a coherent picker.

Source

Thrown at lib/java/com/google/android/material/datepicker/CalendarConstraints.java:74

    boolean isValid(long date);
  }

  private CalendarConstraints(
      @NonNull Month start,
      @NonNull Month end,
      @NonNull DateValidator validator,
      @Nullable Month openAt,
      int firstDayOfWeek) {
    Objects.requireNonNull(start, "start cannot be null");
    Objects.requireNonNull(end, "end cannot be null");
    Objects.requireNonNull(validator, "validator cannot be null");
    this.start = start;
    this.end = end;
    this.openAt = openAt;
    this.firstDayOfWeek = firstDayOfWeek;
    this.validator = validator;
    if (openAt != null && start.compareTo(openAt) > 0) {
      throw new IllegalArgumentException("start Month cannot be after current Month");
    }
    if (openAt != null && openAt.compareTo(end) > 0) {
      throw new IllegalArgumentException("current Month cannot be after end Month");
    }
    if (firstDayOfWeek < 0
        || firstDayOfWeek > UtcDates.getUtcCalendar().getMaximum(Calendar.DAY_OF_WEEK)) {
      throw new IllegalArgumentException("firstDayOfWeek is not valid");
    }
    monthSpan = start.monthsUntil(end) + 1;
    yearSpan = end.year - start.year + 1;
  }

  boolean isWithinBounds(long date) {
    return start.getDay(1) <= date && date <= end.getDay(end.daysInMonth);
  }

  /**
   * Returns the {@link DateValidator} that determines whether a date can be clicked and selected.

View on GitHub (pinned to ac7e18efee)

Solutions

1. Clamp openAt into [start, end] before building: openAt = max(start, min(openAt, end)) using Month.compareTo.
2. If opening month is unknown, leave openAt null (picker opens at start or today).
3. When deriving openAt from a saved selection, validate the selection still satisfies current constraints first.

Example fix

// before
val constraints = CalendarConstraints.Builder()
    .setStart(startMonth)
    .setOpenAt(savedOpenAt) // savedOpenAt < startMonth -> throws
    .build()

// after
val openAt = if (savedOpenAt != null && savedOpenAt in startMonth..endMonth) savedOpenAt else null
val constraints = CalendarConstraints.Builder()
    .setStart(startMonth)
    .setOpenAt(openAt)
    .build()

fun buildConstraints(start: Month, end: Month, openAt: Month?): CalendarConstraints {
  val clampedOpenAt = openAt?.let { maxOf(start, it, compareBy { it }) } // ensure openAt >= start
  // simpler explicit form:
  val safeOpenAt = when {
    openAt == null -> null
    openAt < start -> null // or start
    openAt > end -> end
    else -> openAt
  }
  return CalendarConstraints.Builder()
      .setStart(start).setEnd(end).setOpenAt(safeOpenAt).build()
}

When it happens

Trigger: Building CalendarConstraints via Builder with setStart(monthA) and setOpenAt(monthB) where monthB < monthA (e.g. start = today, openAt = a year ago); computing openAt from a saved selection that predates a newly configured start bound.

Common situations: Persisting a user's last-viewed month and later tightening constraints (e.g. 'no dates before today'); restoring picker state in onSaveInstanceState flows where start/end changed between sessions.

Related errors

• current Month cannot be after end Month
• firstDayOfWeek is not valid
• Only Gregorian calendars are supported.
• There must be a keyline marked as focal.
• No color resources provided for harmonization.

AI-assisted analysis of material-components/material-components-android@ac7e18efee (2026-08-14). Data as JSON: /api/errors/cc4a938128c030bc. Report an issue: GitHub.