CODEWITHSUNDEEP
c#vb.net
Kobojunkie
Kobojunkie

Reputation: 6545

Weird situation with Empty String

I have code to parse Date Field only if String is not null or empty but I get the following Exception

Conversion from string " " to type 'Date' is not valid.

Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

Exception Details: System.InvalidCastException: Conversion from string " " to type 'Date' is not valid.

Source Error: 

Line 29:         
Line 30:  If (Not String.IsNullOrEmpty(last_login)) Then 
Line 31:    If  String.Format("{0:MM/dd/yy H:mm:ss}", last_login) < Now.AddMinutes(-5) Then
Line 32:      Return "height:100%;width:100% ;background-color:#FF0000;font-weight: bold; color: #000000"
Line 33:    Else

Anyone please explain?

Upvotes: 1

Views: 313

Answers (6)

dbasnett
dbasnett

Reputation: 11773

.TryParse is fine with string = nothing

Dim dLast As DateTime
If DateTime.TryParse(last_login, dLast) Then
    If (dLast < Now.AddMinutes(-5)) Then
        Return "height:100%;width:100% ;background-color:#FF0000;font-weight: bold; color: #000000"
    End If
End If

Upvotes: 1

lincolnk
lincolnk

Reputation: 11238

This is a mess. You're trying to use date formatting symbols on a string, to produce a string, to compare with a date.

Let's try this instead.

Dim dLast As DateTime
If ((Not last_login Is Nothing) AndAlso DateTime.TryParse(last_login.Trim(), dLast)) Then
    If (dLast < Now.AddMinutes(-5)) Then
        Return "height:100%;width:100% ;background-color:#FF0000;font-weight: bold; color: #000000"
    End If
End If

edit: check for null string before access it.

Upvotes: 3

Kirk Woll
Kirk Woll

Reputation: 77546

" " is not the empty string. (There's a space inside.) Perhaps you should call .Trim():

last_login != null && last_login.Trim().Length > 0

Or if you're using .NET 4, IsNullOrWhitespace is even better:

string.IsNullOrWhitespace(last_login)

Edited, thanks to @Anthony and @Joel.

Upvotes: 6

max
max

Reputation: 34407

It seems like you need String.IsNullOrWhiteSpace(). I see a space character inside quotes.

Upvotes: 1

Shiraz Bhaiji
Shiraz Bhaiji

Reputation: 65391

It is not null or empty. It is a space. You could try trimming it.

Upvotes: 0

Wonko the Sane
Wonko the Sane

Reputation: 10813

" " is a space, which is neither null nor empty. You can Trim() the string first, and then check for null, Empty, or Length == 0.

Upvotes: 0

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