CtypeDynamic : How can i detect if an expression can be converted to a specific Date format

[desanti]

Hello ! I'm using vb.net 2017. I have a code where I should use CTypeDynamic. With other types everything is ok , but if the target type is System.DateTime , I want to detect if the expression can be converted to a Date with the format "dd/mm/yyyy. How can I do that with CTypeDynamic? Thank you !

[Lost User]

Convert it to a string, tryparsing it as a date?

Bastard Programmer from Hell :suss: If you can't read my code, try converting it here[^] "If you just follow the bacon Eddy, wherever it leads you, then you won't have to think about politics." -- Some Bell.

[desanti]

I have it as a string , But if I use CTypeDynamic(str, type1) , and str="11/26/2018" , it shows as correct , but it shouldn't be because is not correct with the format dd/MM/yyyy

[Lost User]

The correct date-format is determined by the system settings, and thus, by the user. You choose a date where it is easy to see which is the day-part and which is the month-part. Now, how about 3/4/2001? The computer isn't allowed to guess, and you can't guess the "correct" place of day's and month within that date.

Bastard Programmer from Hell :suss: If you can't read my code, try converting it here[^] "If you just follow the bacon Eddy, wherever it leads you, then you won't have to think about politics." -- Some Bell.

[desanti]

I want that my program works regardless of how user configure the system date format. So I choose the format dd/MM/yyyy , and the user should input the date in this format. 3/4/2001 should be interpreted as April 3 2001. 26/11/2018 is November 26 11/26/2018 - is invalid

[Lost User]

desanti wrote:

3/4/2001 should be interpreted as April 3 2001. 26/11/2018 is November 26 11/26/2018 - is invalid

So, any date that can be interpreted as M/D/Y should be. Anything that fails is to be assumed D/M/Y, and if that fails, it is invalid. No, I will not participate. Your data is all in the same format, or the entire dataset must be considered invalid. There's a good reason why DateTime.TryParse Method (System) | Microsoft Docs[^] only accepts a single provider. If you don't know what the format is, and start guessing like you do, you're bound to end up with multiple small disasters.

Bastard Programmer from Hell :suss: If you can't read my code, try converting it here[^] "If you just follow the bacon Eddy, wherever it leads you, then you won't have to think about politics." -- Some Bell.

[desanti]

Maybe we are misunderstanding each other. The situation is simple : The user write a date in a textbox. I want that the user write the date in the format : day/month/year. So I want a way to check if what the user has wrote can be converted to a date in that format : - 01/05/2015 - is ok because 01 is a valid for day number , 05 is ok because is valid for month number , 2015 is ok because is valid for year number. - 25/12/2018 - is ok because 25 is a valid for day number , 12 is ok because is valid for month number , 2018 is ok because is valid for year number. - 12/25/2018 - is wrong because 12 is a valid for day number , 25 is wrong because is not valid for month number , 2018 is ok because is valid for year number. So it's wrong !!! What is the problem with this logic ?????

[Lost User]

Why make things difficult for yourself and your user? Use a Calendar Class (System.Windows.Controls) | Microsoft Docs[^]

[desanti]

Ok , what about the case when i'm reading the strings from a text File ?

[Lost User]

Dim source As String() = {"01/05/2015", "25/12/2018", "12/25/2018"}

Sub Main()

    For Each dateCandidate As String In source
        Dim dateResult As Date
        If Date.TryParseExact(
            dateCandidate, "d/M/yyyy",
            CultureInfo.InvariantCulture,
            DateTimeStyles.None,
            dateResult) Then
            Console.WriteLine("Found {0} as valid.", dateResult)
        Else
            Console.WriteLine("Found {0} to be invalid.", dateCandidate)
        End If
    Next
    Console.ReadKey()
End Sub

Bastard Programmer from Hell :suss: If you can't read my code, try converting it here[^] "If you just follow the bacon Eddy, wherever it leads you, then you won't have to think about politics." -- Some Bell.

[Lost User]

Then you do what Eddy already suggested and use DateTime.TryParse Method (System) | Microsoft Docs[^]. Try and make more use of Google and the MSDN documentation.

[desanti]

Thank you , Your code works with these examples and many others. but as I've said , I read values from a text file . Sometimes the string that come from text file is like this : 25/12/2018 00:01:00 This is correct because the date part is correct , but for your code this is invalid.

[Lost User]

desanti wrote:

This is correct because the date part is correct , but for your code this is invalid.

I wrote it that way; if you want different behaviour, look the method up on MSDN.

Bastard Programmer from Hell :suss: If you can't read my code, try converting it here[^] "If you just follow the bacon Eddy, wherever it leads you, then you won't have to think about politics." -- Some Bell.