In most applications, you need some form of date function returning the current date and time. VB.Net also provides powerful tools for date arithmetic that makes manipulating dates easy.
DateTime value type represents dates and times with values ranging from 00:00:00, January 1, 0001 to 11:59:59 P.M., December 31, 9999 in the Gregorian calendar.You can assign an initial value to a new DateTime value in many different ways.
The following code creates a specific date using the DateTime constructor specifying the year, month, day, hour, minute, and second.
Private Sub Example1()
Dim date1 = New DateTime(2017, 12, 11, 7, 39, 22)
Console.WriteLine(date1)
End Sub
You can assign the DateTime object a date and time value returned by a property or method.
Public Sub Example2()
Dim date1 As DateTime = DateTime.Now
Dim date2 As DateTime = DateTime.UtcNow
Dim date3 As DateTime = DateTime.Today
Console.WriteLine(date1)
Console.WriteLine(date2)
Console.WriteLine(date3)
End Sub
The above example assigns the current date and time, the current Coordinated Universal Time (UTC) date and time, and the current date to three new DateTime variables.
The Parse, ParseExact, TryParse, and TryParseExact methods all convert a string to its equivalent date and time value. The following examples use the Parse and ParseExact methods to parse a string and convert it to a DateTime value.
Public Sub Example3()
Dim dateString = "5/1/2008 8:30:52 AM"
Dim date1 As DateTime =
DateTime.Parse(dateString, System.Globalization.CultureInfo.InvariantCulture)
Console.WriteLine(date1)
Dim iso8601String = "20080501T08:30:52Z"
Dim dateISO8602 As DateTime =
DateTime.ParseExact(iso8601String, "yyyyMMddTHH:mm:ssZ", System.Globalization.CultureInfo.InvariantCulture)
Console.WriteLine(date1)
End Sub
The second format uses a form supported by the ISO 8601 standard for representing date and time in string format. This standard representation is often used to transfer date information in web services.
The following example uses the TryParseExact(String, String[], IFormatProvider, DateTimeStyles, DateTime) method to convert strings that must be either in a "yyyyMMdd" format or a "HHmmss" format to DateTime values.
Public Sub Example4()
Dim formats As String() = {"yyyyMMdd", "HHmmss"}
Dim dateStrings As String() = {"20130816", "20131608", " 20130816 ", "115216", "521116", " 115216 "}
Dim parsedDate As DateTime
For Each dateStr In dateStrings
If DateTime.TryParseExact(dateStr, formats, Nothing, System.Globalization.DateTimeStyles.AllowWhiteSpaces Or System.Globalization.DateTimeStyles.AdjustToUniversal, parsedDate) Then
Console.WriteLine($"{dateStr} --> {parsedDate}")
Else
Console.WriteLine($"Cannot convert {dateStr}")
End If
Next
End Sub
If a string cannot be parsed, the Parse and ParseExact methods throw an exception.
TryParse and TryParseExact methods return a Boolean value that indicates whether the conversion succeeded or failed.TryParse or TryParseExact methods in scenarios where performance is important.