Module TestFormatter
Public Sub Main()
Dim acctNumber As Integer = 12312312
Console.WriteLine(String.Format(New CustomerFormatter, "{0}", acctNumber))
Console.WriteLine(String.Format(New CustomerFormatter, "{0:G}", acctNumber))
End Sub
End Module
Public Class CustomerFormatter : Implements IFormatProvider, ICustomFormatter
Public Function GetFormat(type As Type) As Object _
Implements IFormatProvider.GetFormat
If type Is GetType(ICustomFormatter) Then
Return Me
Else
Return Nothing
End If
End Function
Public Function Format(fmt As String,arg As Object,formatProvider As IFormatProvider) As String _
Implements ICustomFormatter.Format
If Not Me.Equals(formatProvider) Then
Return Nothing
Else
If String.IsNullOrEmpty(fmt) Then fmt = "G"
Dim customerString As String = arg.ToString()
if customerString.Length < 8 Then _
customerString = customerString.PadLeft(8, "0"c)
Select Case fmt
Case "G"
Return customerString.Substring(0, 1) & "-" & _
customerString.Substring(1, 5) & "-" & _
customerString.Substring(6)
Case Else
Throw New FormatException(String.Format("The '{0}' format specifier is not supported.", fmt))
End Select
End If
End Function
End Class