CODEWITHSUNDEEP
vb.net
1321941
1321941

Reputation: 2180

Get boolean input from user in VB.net

I have a variable which is a boolean datatype and using the windows console I am looking to store use input inside it. I know how to do this using if statements and data validation, but I am looking to see if vb has a method to handle this naturally?

For the sake of showing some code:

Dim tOrF As Boolean
tOrF = Console.ReadLine

Thanks

Upvotes: 2

Views: 3208

Answers (3)

Mark Hurd
Mark Hurd

Reputation: 10931

Back in VB6 when we wanted to cater for humans adjusting registry entries, I created CRegBool (note this was from an Option Compare Text module):

'----------------------------------------------------------------------
' Function: CRegBool
'
' Purpose:
'   Converts settings value that could have been 'adjusted' by a human to a Boolean.
'
' Arguments:
'   Variant     Value to convert to Boolean.
'   Boolean(Opt)Default value.
'
' Returns:
'   Boolean     True if the value represents an 'affirmative' or non-zero value.
'               False if the value represents a 'negative' or zero value.
'               Otherwise returns default value.
'
' Errors:
'   Only those thrown by CStr (or LCase$).
'
' Notes:
'   Default value should probably never be False unless the Else Case is expanded
' to catch Val(rv) <> 0 -> True; Nevertheless, it is False rather a lot...
'
'   Use LCase$ if Option Compare Binary in operation.
'
' Revision History:
'   070615 MEH Moved from MsgU:modMsgUI.
'   070907 MEH Added commentary.
'   070928 MEH Updated commentary to highlight LCase$ is needed if not Option Compare Text.
'----------------------------------------------------------------------
Public Function CRegBool(ByVal RegValue As Variant, Optional ByVal DefaultValue As Boolean = True) As Boolean

  Select Case CStr(RegValue) 'LCase$(CStr(RegValue)) '
  Case "0", "00", "0x0", "&h0", "false", "no", "off", "n"
    CRegBool = False
  Case "1", "01", "0x1", "&h1", "true", "yes", "on", "-1", "y"
    CRegBool = True
  Case Else
    CRegBool = DefaultValue
  End Select

End Function

A quick VB.NET conversion, using my latest known issues (specifically that UPPERCASE is slightly better to compare against):

'''----------------------------------------------------------------------
''' Function: CRegBool
'''
''' <summary>
'''   Converts settings value that could have been 'adjusted' by a human to a Boolean.
''' </summary>
'''
''' <parameter name="">Value to convert to Boolean.</parameter>
''' <parameter name="">Default value.</parameter>
'''
''' <returns>
'''   True if the value represents an 'affirmative' or non-zero value.
'''   False if the value represents a 'negative' or zero value.
'''   Otherwise returns default value.
''' </returns>
'''
''' <remarks>
'''   Default value should probably never be False unless the Else Case is expanded
'''  to catch Val(rv) <> 0 -> True; Nevertheless, it is False rather a lot...
'''
'''   Use UCase if Option Compare Binary in operation.
''' </remarks>
'''
''' <revisionhistory>
'''   070615 MEH Moved from MsgU:modMsgUI.
'''   070907 MEH Added commentary.
'''   070928 MEH Updated commentary to highlight UCase is needed if not Option Compare Text.
'''   120924 MEH Converted to VB.NET in the SO text box without testing...
''' </revisionhistory>
'''----------------------------------------------------------------------
Public Function CRegBool(ByVal RegValue As Object, Optional ByVal DefaultValue As Boolean = True) As Boolean

  Select Case CStr(RegValue) 'UCase(CStr(RegValue)) '
  Case "0", "00", "0X0", "&H0", "FALSE", "NO", "OFF", "N"
    CRegBool = False
  Case "1", "01", "0X1", "&H1", "TRUE", "YES", "ON", "-1", "Y"
    CRegBool = True
  Case Else
    CRegBool = DefaultValue
  End Select

End Function

Upvotes: 0

John Woo
John Woo

Reputation: 263933

You can use TryParse method to check if the value being entered is a valid boolean value or else it will throw an exception,

Tries to convert the specified string representation of a logical value to its Boolean equivalent. A return value indicates whether the conversion succeeded or failed.

     Dim flag As Boolean 
     Dim value as String = Console.ReadLine()
     If Boolean.TryParse(value, flag) Then
        Console.WriteLine("'{0}' --> {1}", value, flag)
     Else
        Console.WriteLine("Unable to parse '{0}'.", 
                          If(value Is Nothing, "<null>", value))
     End If

Upvotes: 2

SLaks
SLaks

Reputation: 888233

You could call Boolean.Parse(Console.ReadLine()).

This will throw an exception if the user doesn't type True or False.

Upvotes: 0

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