packages/flutter/lib/src/material/date.dart - mirrors/flutter - Git at Google

 // Copyright 2014 The Flutter Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.

 import 'package:flutter/foundation.dart';

 import 'material_localizations.dart';

 /// Utility functions for working with dates.
 class DateUtils {
   // This class is not meant to be instantiated or extended; this constructor
   // prevents instantiation and extension.
   DateUtils._();

   /// Returns a [DateTime] with the date of the original, but time set to
   /// midnight.
   static DateTime dateOnly(DateTime date) {
     return DateTime(date.year, date.month, date.day);
   }

   /// Returns a [DateTimeRange] with the dates of the original, but with times
   /// set to midnight.
   ///
   /// See also:
   ///  * [dateOnly], which does the same thing for a single date.
   static DateTimeRange datesOnly(DateTimeRange range) {
     return DateTimeRange(start: dateOnly(range.start), end: dateOnly(range.end));
   }

   /// Returns true if the two [DateTime] objects have the same day, month, and
   /// year, or are both null.
   static bool isSameDay(DateTime? dateA, DateTime? dateB) {
     return
       dateA?.year == dateB?.year &&
       dateA?.month == dateB?.month &&
       dateA?.day == dateB?.day;
   }

   /// Returns true if the two [DateTime] objects have the same month and
   /// year, or are both null.
   static bool isSameMonth(DateTime? dateA, DateTime? dateB) {
     return
       dateA?.year == dateB?.year &&
       dateA?.month == dateB?.month;
   }

   /// Determines the number of months between two [DateTime] objects.
   ///
   /// For example:
   ///
   /// ```dart
   /// DateTime date1 = DateTime(2019, 6, 15);
   /// DateTime date2 = DateTime(2020, 1, 15);
   /// int delta = DateUtils.monthDelta(date1, date2);
   /// ```
   ///
   /// The value for `delta` would be `7`.
   static int monthDelta(DateTime startDate, DateTime endDate) {
     return (endDate.year - startDate.year) * 12 + endDate.month - startDate.month;
   }

   /// Returns a [DateTime] that is [monthDate] with the added number
   /// of months and the day set to 1 and time set to midnight.
   ///
   /// For example:
   ///
   /// ```dart
   /// DateTime date = DateTime(2019, 1, 15);
   /// DateTime futureDate = DateUtils.addMonthsToMonthDate(date, 3);
   /// ```
   ///
   /// `date` would be January 15, 2019.
   /// `futureDate` would be April 1, 2019 since it adds 3 months.
   static  DateTime addMonthsToMonthDate(DateTime monthDate, int monthsToAdd) {
     return DateTime(monthDate.year, monthDate.month + monthsToAdd);
   }

   /// Returns a [DateTime] with the added number of days and time set to
   /// midnight.
   static DateTime addDaysToDate(DateTime date, int days) {
     return DateTime(date.year, date.month, date.day + days);
   }

   /// Computes the offset from the first day of the week that the first day of
   /// the [month] falls on.
   ///
   /// For example, September 1, 2017 falls on a Friday, which in the calendar
   /// localized for United States English appears as:
   ///
   ///     S M T W T F S
   ///     _ _ _ _ _ 1 2
   ///
   /// The offset for the first day of the months is the number of leading blanks
   /// in the calendar, i.e. 5.
   ///
   /// The same date localized for the Russian calendar has a different offset,
   /// because the first day of week is Monday rather than Sunday:
   ///
   ///     M T W T F S S
   ///     _ _ _ _ 1 2 3
   ///
   /// So the offset is 4, rather than 5.
   ///
   /// This code consolidates the following:
   ///
   /// - [DateTime.weekday] provides a 1-based index into days of week, with 1
   ///   falling on Monday.
   /// - [MaterialLocalizations.firstDayOfWeekIndex] provides a 0-based index
   ///   into the [MaterialLocalizations.narrowWeekdays] list.
   /// - [MaterialLocalizations.narrowWeekdays] list provides localized names of
   ///   days of week, always starting with Sunday and ending with Saturday.
   static int firstDayOffset(int year, int month, MaterialLocalizations localizations) {
     // 0-based day of week for the month and year, with 0 representing Monday.
     final int weekdayFromMonday = DateTime(year, month).weekday - 1;

     // 0-based start of week depending on the locale, with 0 representing Sunday.
     int firstDayOfWeekIndex = localizations.firstDayOfWeekIndex;

     // firstDayOfWeekIndex recomputed to be Monday-based, in order to compare with
     // weekdayFromMonday.
     firstDayOfWeekIndex = (firstDayOfWeekIndex - 1) % 7;

     // Number of days between the first day of week appearing on the calendar,
     // and the day corresponding to the first of the month.
     return (weekdayFromMonday - firstDayOfWeekIndex) % 7;
   }

   /// Returns the number of days in a month, according to the proleptic
   /// Gregorian calendar.
   ///
   /// This applies the leap year logic introduced by the Gregorian reforms of
   /// 1582. It will not give valid results for dates prior to that time.
   static int getDaysInMonth(int year, int month) {
     if (month == DateTime.february) {
       final bool isLeapYear = (year % 4 == 0) && (year % 100 != 0) || (year % 400 == 0);
       return isLeapYear ? 29 : 28;
     }
     const List<int> daysInMonth = <int>[31, -1, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31];
     return daysInMonth[month - 1];
   }
 }

 /// Mode of date entry method for the date picker dialog.
 ///
 /// In [calendar] mode, a calendar grid is displayed and the user taps the
 /// day they wish to select. In [input] mode a TextField] is displayed and
 /// the user types in the date they wish to select.
 ///
 /// [calendarOnly] and [inputOnly] are variants of the above that don't
 /// allow the user to change to the mode.
 ///
 /// See also:
 ///
 ///  * [showDatePicker] and [showDateRangePicker], which use this to control
 ///    the initial entry mode of their dialogs.
 enum DatePickerEntryMode {
   /// User picks a date from calendar grid. Can switch to [input] by activating
   /// a mode button in the dialog.
   calendar,

   /// User can input the date by typing it into a text field.
   ///
   /// Can switch to [calendar] by activating a mode button in the dialog.
   input,

   /// User can only pick a date from calendar grid.
   ///
   /// There is no user interface to switch to another mode.
   calendarOnly,

   /// User can only input the date by typing it into a text field.
   ///
   /// There is no user interface to switch to another mode.
   inputOnly,
 }

 /// Initial display of a calendar date picker.
 ///
 /// Either a grid of available years or a monthly calendar.
 ///
 /// See also:
 ///
 ///  * [showDatePicker], which shows a dialog that contains a Material Design
 ///    date picker.
 ///  * [CalendarDatePicker], widget which implements the Material Design date picker.
 enum DatePickerMode {
   /// Choosing a month and day.
   day,

   /// Choosing a year.
   year,
 }

 /// Signature for predicating dates for enabled date selections.
 ///
 /// See [showDatePicker], which has a [SelectableDayPredicate] parameter used
 /// to specify allowable days in the date picker.
 typedef SelectableDayPredicate = bool Function(DateTime day);

 /// Encapsulates a start and end [DateTime] that represent the range of dates.
 ///
 /// The range includes the [start] and [end] dates. The [start] and [end] dates
 /// may be equal to indicate a date range of a single day. The [start] date must
 /// not be after the [end] date.
 ///
 /// See also:
 ///  * [showDateRangePicker], which displays a dialog that allows the user to
 ///    select a date range.
 @immutable
 class DateTimeRange {
   /// Creates a date range for the given start and end [DateTime].
   DateTimeRange({
     required this.start,
     required this.end,
   }) : assert(!start.isAfter(end));

   /// The start of the range of dates.
   final DateTime start;

   /// The end of the range of dates.
   final DateTime end;

   /// Returns a [Duration] of the time between [start] and [end].
   ///
   /// See [DateTime.difference] for more details.
   Duration get duration => end.difference(start);

   @override
   bool operator ==(Object other) {
     if (other.runtimeType != runtimeType) {
       return false;
     }
     return other is DateTimeRange
       && other.start == start
       && other.end == end;
   }

   @override
   int get hashCode => Object.hash(start, end);

   @override
   String toString() => '$start - $end';
 }
	// Copyright 2014 The Flutter Authors. All rights reserved.
	// Use of this source code is governed by a BSD-style license that can be
	// found in the LICENSE file.

	import 'package:flutter/foundation.dart';

	import 'material_localizations.dart';

	/// Utility functions for working with dates.
	class DateUtils {
	// This class is not meant to be instantiated or extended; this constructor
	// prevents instantiation and extension.
	DateUtils._();

	/// Returns a [DateTime] with the date of the original, but time set to
	/// midnight.
	static DateTime dateOnly(DateTime date) {
	return DateTime(date.year, date.month, date.day);
	}

	/// Returns a [DateTimeRange] with the dates of the original, but with times
	/// set to midnight.
	///
	/// See also:
	/// * [dateOnly], which does the same thing for a single date.
	static DateTimeRange datesOnly(DateTimeRange range) {
	return DateTimeRange(start: dateOnly(range.start), end: dateOnly(range.end));
	}

	/// Returns true if the two [DateTime] objects have the same day, month, and
	/// year, or are both null.
	static bool isSameDay(DateTime? dateA, DateTime? dateB) {
	return
	dateA?.year == dateB?.year &&
	dateA?.month == dateB?.month &&
	dateA?.day == dateB?.day;
	}

	/// Returns true if the two [DateTime] objects have the same month and
	/// year, or are both null.
	static bool isSameMonth(DateTime? dateA, DateTime? dateB) {
	return
	dateA?.year == dateB?.year &&
	dateA?.month == dateB?.month;
	}

	/// Determines the number of months between two [DateTime] objects.
	///
	/// For example:
	///
	/// ```dart
	/// DateTime date1 = DateTime(2019, 6, 15);
	/// DateTime date2 = DateTime(2020, 1, 15);
	/// int delta = DateUtils.monthDelta(date1, date2);
	/// ```
	///
	/// The value for `delta` would be `7`.
	static int monthDelta(DateTime startDate, DateTime endDate) {
	return (endDate.year - startDate.year) * 12 + endDate.month - startDate.month;
	}

	/// Returns a [DateTime] that is [monthDate] with the added number
	/// of months and the day set to 1 and time set to midnight.
	///
	/// For example:
	///
	/// ```dart
	/// DateTime date = DateTime(2019, 1, 15);
	/// DateTime futureDate = DateUtils.addMonthsToMonthDate(date, 3);
	/// ```
	///
	/// `date` would be January 15, 2019.
	/// `futureDate` would be April 1, 2019 since it adds 3 months.
	static DateTime addMonthsToMonthDate(DateTime monthDate, int monthsToAdd) {
	return DateTime(monthDate.year, monthDate.month + monthsToAdd);
	}

	/// Returns a [DateTime] with the added number of days and time set to
	/// midnight.
	static DateTime addDaysToDate(DateTime date, int days) {
	return DateTime(date.year, date.month, date.day + days);
	}

	/// Computes the offset from the first day of the week that the first day of
	/// the [month] falls on.
	///
	/// For example, September 1, 2017 falls on a Friday, which in the calendar
	/// localized for United States English appears as:
	///
	/// S M T W T F S
	/// _ _ _ _ _ 1 2
	///
	/// The offset for the first day of the months is the number of leading blanks
	/// in the calendar, i.e. 5.
	///
	/// The same date localized for the Russian calendar has a different offset,
	/// because the first day of week is Monday rather than Sunday:
	///
	/// M T W T F S S
	/// _ _ _ _ 1 2 3
	///
	/// So the offset is 4, rather than 5.
	///
	/// This code consolidates the following:
	///
	/// - [DateTime.weekday] provides a 1-based index into days of week, with 1
	/// falling on Monday.
	/// - [MaterialLocalizations.firstDayOfWeekIndex] provides a 0-based index
	/// into the [MaterialLocalizations.narrowWeekdays] list.
	/// - [MaterialLocalizations.narrowWeekdays] list provides localized names of
	/// days of week, always starting with Sunday and ending with Saturday.
	static int firstDayOffset(int year, int month, MaterialLocalizations localizations) {
	// 0-based day of week for the month and year, with 0 representing Monday.
	final int weekdayFromMonday = DateTime(year, month).weekday - 1;

	// 0-based start of week depending on the locale, with 0 representing Sunday.
	int firstDayOfWeekIndex = localizations.firstDayOfWeekIndex;

	// firstDayOfWeekIndex recomputed to be Monday-based, in order to compare with
	// weekdayFromMonday.
	firstDayOfWeekIndex = (firstDayOfWeekIndex - 1) % 7;

	// Number of days between the first day of week appearing on the calendar,
	// and the day corresponding to the first of the month.
	return (weekdayFromMonday - firstDayOfWeekIndex) % 7;
	}

	/// Returns the number of days in a month, according to the proleptic
	/// Gregorian calendar.
	///
	/// This applies the leap year logic introduced by the Gregorian reforms of
	/// 1582. It will not give valid results for dates prior to that time.
	static int getDaysInMonth(int year, int month) {
	if (month == DateTime.february) {
	final bool isLeapYear = (year % 4 == 0) && (year % 100 != 0) \|\| (year % 400 == 0);
	return isLeapYear ? 29 : 28;
	}
	const List<int> daysInMonth = <int>[31, -1, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31];
	return daysInMonth[month - 1];
	}
	}

	/// Mode of date entry method for the date picker dialog.
	///
	/// In [calendar] mode, a calendar grid is displayed and the user taps the
	/// day they wish to select. In [input] mode a TextField] is displayed and
	/// the user types in the date they wish to select.
	///
	/// [calendarOnly] and [inputOnly] are variants of the above that don't
	/// allow the user to change to the mode.
	///
	/// See also:
	///
	/// * [showDatePicker] and [showDateRangePicker], which use this to control
	/// the initial entry mode of their dialogs.
	enum DatePickerEntryMode {
	/// User picks a date from calendar grid. Can switch to [input] by activating
	/// a mode button in the dialog.
	calendar,

	/// User can input the date by typing it into a text field.
	///
	/// Can switch to [calendar] by activating a mode button in the dialog.
	input,

	/// User can only pick a date from calendar grid.
	///
	/// There is no user interface to switch to another mode.
	calendarOnly,

	/// User can only input the date by typing it into a text field.
	///
	/// There is no user interface to switch to another mode.
	inputOnly,
	}

	/// Initial display of a calendar date picker.
	///
	/// Either a grid of available years or a monthly calendar.
	///
	/// See also:
	///
	/// * [showDatePicker], which shows a dialog that contains a Material Design
	/// date picker.
	/// * [CalendarDatePicker], widget which implements the Material Design date picker.
	enum DatePickerMode {
	/// Choosing a month and day.
	day,

	/// Choosing a year.
	year,
	}

	/// Signature for predicating dates for enabled date selections.
	///
	/// See [showDatePicker], which has a [SelectableDayPredicate] parameter used
	/// to specify allowable days in the date picker.
	typedef SelectableDayPredicate = bool Function(DateTime day);

	/// Encapsulates a start and end [DateTime] that represent the range of dates.
	///
	/// The range includes the [start] and [end] dates. The [start] and [end] dates
	/// may be equal to indicate a date range of a single day. The [start] date must
	/// not be after the [end] date.
	///
	/// See also:
	/// * [showDateRangePicker], which displays a dialog that allows the user to
	/// select a date range.
	@immutable
	class DateTimeRange {
	/// Creates a date range for the given start and end [DateTime].
	DateTimeRange({
	required this.start,
	required this.end,
	}) : assert(!start.isAfter(end));

	/// The start of the range of dates.
	final DateTime start;

	/// The end of the range of dates.
	final DateTime end;

	/// Returns a [Duration] of the time between [start] and [end].
	///
	/// See [DateTime.difference] for more details.
	Duration get duration => end.difference(start);

	@override
	bool operator ==(Object other) {
	if (other.runtimeType != runtimeType) {
	return false;
	}
	return other is DateTimeRange
	&& other.start == start
	&& other.end == end;
	}

	@override
	int get hashCode => Object.hash(start, end);

	@override
	String toString() => '$start - $end';
	}