Datetime - Отримайте наступний вівторок

Як я можу отримати дату наступного вівторка?

У PHP це так просто, як strtotime('next tuesday');.

Як я можу досягти чогось подібного в .NET

Як я вже згадував у коментарях, є різні речі, які ви могли б мати на увазі під «наступним вівторком», але цей код дає вам «наступний вівторок, або сьогодні, якщо це вже вівторок»:

DateTime today = DateTime.Today;
// The (... + 7) % 7 ensures we end up with a value in the range [0, 6]
int daysUntilTuesday = ((int) DayOfWeek.Tuesday - (int) today.DayOfWeek + 7) % 7;
DateTime nextTuesday = today.AddDays(daysUntilTuesday);

Якщо ви хочете дати "тиждень часу", якщо вже вівторок, ви можете скористатися:

// This finds the next Monday (or today if it's Monday) and then adds a day... so the
// result is in the range [1-7]
int daysUntilTuesday = (((int) DayOfWeek.Monday - (int) today.DayOfWeek + 7) % 7) + 1;

... або ви можете використовувати оригінальну формулу, але вже від завтра:

DateTime tomorrow = DateTime.Today.AddDays(1);
// The (... + 7) % 7 ensures we end up with a value in the range [0, 6]
int daysUntilTuesday = ((int) DayOfWeek.Tuesday - (int) tomorrow.DayOfWeek + 7) % 7;
DateTime nextTuesday = tomorrow.AddDays(daysUntilTuesday);

EDIT: Просто, щоб зробити це приємним і універсальним:

public static DateTime GetNextWeekday(DateTime start, DayOfWeek day)
{
    // The (... + 7) % 7 ensures we end up with a value in the range [0, 6]
    int daysToAdd = ((int) day - (int) start.DayOfWeek + 7) % 7;
    return start.AddDays(daysToAdd);
}

Отже, щоб отримати значення для "сьогодні чи протягом наступних 6 днів":

DateTime nextTuesday = GetNextWeekday(DateTime.Today, DayOfWeek.Tuesday);

Щоб отримати значення для "наступного вівторка без сьогоднішнього дня":

DateTime nextTuesday = GetNextWeekday(DateTime.Today.AddDays(1), DayOfWeek.Tuesday);

Для цього слід зробити фокус:

static DateTime GetNextWeekday(DayOfWeek day)
{
    DateTime result = DateTime.Now.AddDays(1);
    while( result.DayOfWeek != day )
        result = result.AddDays(1);
    return result;
}

Існує менше багатослівних та більш розумних / елегантних рішень цієї проблеми, але наведена нижче функція C # справді добре працює в ряді ситуацій.

/// <summary>
/// Find the closest weekday to the given date
/// </summary>
/// <param name="includeStartDate">if the supplied date is on the specified day of the week, return that date or continue to the next date</param>
/// <param name="searchForward">search forward or backward from the supplied date. if a null parameter is given, the closest weekday (ie in either direction) is returned</param>
public static DateTime ClosestWeekDay(this DateTime date, DayOfWeek weekday, bool includeStartDate = true, bool? searchForward=true)
{
    if (!searchForward.HasValue && !includeStartDate) 
    {
        throw new ArgumentException("if searching in both directions, start date must be a valid result");
    }
    var day = date.DayOfWeek;
    int add = ((int)weekday - (int)day);
    if (searchForward.HasValue)
    {
        if (add < 0 && searchForward.Value)
        {
            add += 7;
        }
        else if (add > 0 && !searchForward.Value)
        {
            add -= 7;
        }
        else if (add == 0 && !includeStartDate)
        {
            add = searchForward.Value ? 7 : -7;
        }
    }
    else if (add < -3) 
    {
        add += 7; 
    }
    else if (add > 3)
    {
        add -= 7;
    }
    return date.AddDays(add);
}

DateTime nextTuesday = DateTime.Today.AddDays(((int)DateTime.Today.DayOfWeek - (int)DayOfWeek.Tuesday) + 7);

@Jon Skeet хороша відповідь.

За попередній день:

private DateTime GetPrevWeekday(DateTime start, DayOfWeek day) {
    // The (... - 7) % 7 ensures we end up with a value in the range [0, 6]
    int daysToRemove = ((int) day - (int) start.DayOfWeek - 7) % 7;
    return start.AddDays(daysToRemove);
}

Дякую!!

DateTime nexttuesday=DateTime.Today.AddDays(1);

while(nexttuesday.DayOfWeek!=DayOfWeek.Tuesday)
   nexttuesday = nexttuesday.AddDays(1);

Дуже простий зразок для включення або виключення поточної дати, ви вказуєте дату та день тижня, який вас цікавить.

public static class DateTimeExtensions
{
    /// <summary>
    /// Gets the next date.
    /// </summary>
    /// <param name="date">The date to inspected.</param>
    /// <param name="dayOfWeek">The day of week you want to get.</param>
    /// <param name="exclDate">if set to <c>true</c> the current date will be excluded and include next occurrence.</param>
    /// <returns></returns>
    public static DateTime GetNextDate(this DateTime date, DayOfWeek dayOfWeek, bool exclDate = true)
    {
        //note: first we need to check if the date wants to move back by date - Today, + diff might move it forward or backwards to Today
        //eg: date - Today = 0 - 1 = -1, so have to move it forward
        var diff = dayOfWeek - date.DayOfWeek;
        var ddiff = date.Date.Subtract(DateTime.Today).Days + diff;

        //note: ddiff < 0 : date calculates to past, so move forward, even if the date is really old, it will just move 7 days from date passed in
        //note: ddiff >= (exclDate ? 6 : 7) && diff < 0 : date is into the future, so calculated future weekday, based on date
        if (ddiff < 0 || ddiff >= (exclDate ? 6 : 7) && diff < 0)
            diff += 7; 

        //note: now we can get safe values between 0 - 6, especially if past dates is being used
        diff = diff % 7;

        //note: if diff is 0 and we are excluding the date passed, we will add 7 days, eg: 1 week
        diff += diff == 0 & exclDate ? 7 : 0;

        return date.AddDays(diff);
    }
}

деякі тестові випадки

[TestMethod]
    public void TestNextDate()
    {
        var date = new DateTime(2013, 7, 15);
        var start = date;
        //testing same month - forwardOnly
        Assert.AreEqual(start = start.AddDays(1), date.GetNextDate(DayOfWeek.Tuesday)); //16
        Assert.AreEqual(start = start.AddDays(1), date.GetNextDate(DayOfWeek.Wednesday)); //17
        Assert.AreEqual(start = start.AddDays(1), date.GetNextDate(DayOfWeek.Thursday)); //18
        Assert.AreEqual(start = start.AddDays(1), date.GetNextDate(DayOfWeek.Friday)); //19
        Assert.AreEqual(start = start.AddDays(1), date.GetNextDate(DayOfWeek.Saturday)); //20
        Assert.AreEqual(start = start.AddDays(1), date.GetNextDate(DayOfWeek.Sunday)); //21
        Assert.AreEqual(start.AddDays(1), date.GetNextDate(DayOfWeek.Monday)); //22

        //testing same month - include date
        Assert.AreEqual(start = date, date.GetNextDate(DayOfWeek.Monday, false)); //15
        Assert.AreEqual(start = start.AddDays(1), date.GetNextDate(DayOfWeek.Tuesday, false)); //16
        Assert.AreEqual(start.AddDays(1), date.GetNextDate(DayOfWeek.Wednesday, false)); //17

        //testing month change - forwardOnly
        date = new DateTime(2013, 7, 29);
        start = date;
        Assert.AreEqual(start = start.AddDays(1), date.GetNextDate(DayOfWeek.Tuesday)); //30
        Assert.AreEqual(start = start.AddDays(1), date.GetNextDate(DayOfWeek.Wednesday)); //31
        Assert.AreEqual(start = start.AddDays(1), date.GetNextDate(DayOfWeek.Thursday)); //2013/09/01-month increased
        Assert.AreEqual(start.AddDays(1), date.GetNextDate(DayOfWeek.Friday)); //02

        //testing year change
        date = new DateTime(2013, 12, 30);
        start = date;
        Assert.AreEqual(start = start.AddDays(1), date.GetNextDate(DayOfWeek.Tuesday)); //31
        Assert.AreEqual(start = start.AddDays(1), date.GetNextDate(DayOfWeek.Wednesday)); //2014/01/01 - year increased
        Assert.AreEqual(start = start.AddDays(1), date.GetNextDate(DayOfWeek.Thursday)); //02
    }

Це також може бути продовженням, все залежить

public static class DateTimeExtensions
{
    public static IEnumerable<DateTime> Next(this DateTime date, DayOfWeek day)
    {
        // This loop feels expensive and useless, but the point is IEnumerable
        while(true)
        {
            if (date.DayOfWeek == day)
            {
                yield return date;
            }
            date = date.AddDays(1);
        }
    }
}

Використання

    var today = DateTime.Today;
    foreach(var monday in today.Next(DayOfWeek.Monday))
    {
        Console.WriteLine(monday);
        Console.ReadKey();
    }

Тепер в ароматі oneliner - якщо вам потрібно передати його як параметр в якийсь механізм.

DateTime.Now.AddDays(((int)yourDate.DayOfWeek - (int)DateTime.Now.DayOfWeek + 7) % 7).Day

У цьому конкретному випадку:

DateTime.Now.AddDays(((int)DayOfWeek.Tuesday - (int)DateTime.Now.DayOfWeek + 7) % 7).Day

Ціль C Версія:

+(NSInteger) daysUntilNextWeekday: (NSDate*)startDate withTargetWeekday: (NSInteger) targetWeekday
{
    NSInteger startWeekday = [[NSCalendar currentCalendar] component:NSCalendarUnitWeekday fromDate:startDate];
    return (targetWeekday - startWeekday + 7) % 7;
}