Articolo
11/18/2011

DateAndTime.DatePart Method (DateInterval, DateTime, FirstDayOfWeek, FirstWeekOfYear)

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Returns an Integer value containing the specified component of a given Date value.

Namespace: Microsoft.VisualBasic
Assembly: Microsoft.VisualBasic (in Microsoft.VisualBasic.dll)

Syntax

'Declaration
Public Shared Function DatePart ( _
    Interval As DateInterval, _
    DateValue As DateTime, _
    FirstDayOfWeekValue As FirstDayOfWeek, _
    FirstWeekOfYearValue As FirstWeekOfYear _
) As Integer

public static int DatePart(
    DateInterval Interval,
    DateTime DateValue,
    FirstDayOfWeek FirstDayOfWeekValue,
    FirstWeekOfYear FirstWeekOfYearValue
)

Parameters

Interval
Type: Microsoft.VisualBasic.DateInterval
Required. DateInterval enumeration value or String expression representing the part of the date/time value you want to return.

DateValue
Type: System.DateTime
Required. Date value that you want to evaluate.

FirstDayOfWeekValue
Type: Microsoft.VisualBasic.FirstDayOfWeek
Optional. A value chosen from the FirstDayOfWeek enumeration that specifies the first day of the week. If not specified, FirstDayOfWeek.Sunday is used.

FirstWeekOfYearValue
Type: Microsoft.VisualBasic.FirstWeekOfYear
Optional. A value chosen from the FirstWeekOfYear enumeration that specifies the first week of the year. If not specified, FirstWeekOfYear.Jan1 is used.

Return Value

Type: System.Int32
Returns an Integer value containing the specified component of a given Date value.

Remarks

You can use the DatePart function to evaluate a date/time value and return a specific component. For example, you might use DatePart to calculate the day of the week or the current hour.

If you choose DateInterval.Weekday for the Interval argument, the returned value is consistent with the values of the FirstDayOfWeek enumeration. If you choose DateInterval.WeekOfYear, DatePart uses the Calendar and CultureInfo classes of the System.Globalization namespace to determine your current settings.

The FirstDayOfWeekValue argument affects calculations that use the DateInterval.Weekday and DateInterval.WeekOfYear Interval settings. The FirstWeekOfYearValue argument affects calculations that specify DateInterval.WeekOfYear for Interval.

Since every Date value is supported by a DateTime structure, its methods give you additional options in retrieving date/time parts. For example, you can obtain the entire date value of a Date variable, with the time value set to midnight, as follows:

Dim CurrDatTim As Date = Now   ' Current date and time.
Dim LastMidnight As Date = CurrDatTim.Date   ' At midnight.

The Interval argument can have one of the following settings.

Enumeration value	String	Part of date/time value to return
DateInterval.Day	d	Day of month (1 through 31)
DateInterval.DayOfYear	y	Day of year (1 through 366)
DateInterval.Hour	h	Hour
DateInterval.Minute	n	Minute
DateInterval.Month	m	Month
DateInterval.Quarter	q	Quarter
DateInterval.Second	s	Second
DateInterval.Weekday	w	Day of week (1 through 7)
DateInterval.WeekOfYear	ww	Week of year (1 through 53)
DateInterval.Year	yyyy	Year

The FirstDayOfWeekValue argument can have one of the following settings.

Enumeration value	Value	Description
FirstDayOfWeek.System	0	First day of week specified in system settings
FirstDayOfWeek.Sunday	1	Sunday (default)
FirstDayOfWeek.Monday	2	Monday (complies with ISO standard 8601, section 3.17)
FirstDayOfWeek.Tuesday	3	Tuesday
FirstDayOfWeek.Wednesday	4	Wednesday
FirstDayOfWeek.Thursday	5	Thursday
FirstDayOfWeek.Friday	6	Friday
FirstDayOfWeek.Saturday	7	Saturday

The FirstWeekOfYearValue argument can have one of the following settings.

Enumeration value	Value	Description
FirstWeekOfYear.System	0	First week of year specified in system settings
FirstWeekOfYear.Jan1	1	Week in which January 1 occurs (default)
FirstWeekOfYear.FirstFourDays	2	Week that has at least four days in the new year (complies with ISO standard 8601, section 3.17)
FirstWeekOfYear.FirstFullWeek	3	First full week in new year

Examples

This example takes a date and, using the DatePart function, displays the quarter of the year in which it occurs.

Dim SecondDate = CDate(DateString)
Dim Msg = "Quarter: " & DatePart(DateInterval.Quarter, SecondDate)

Version Information

Silverlight

Supported in: 5, 4, 3

Platforms

For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.

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