IStringFormatIdentifier interface

The contract that a format identifier class implements: it says whether it handles an item’s identifier, and formats a value for it.

Each of the eleven format identifier classes of the package implements IStringFormatIdentifier: CurrencySFI, DateTimeSFI, DecimalSFI, ExponentialSFI, FixedPointSFI, GeneralNumericSFI, GenericDateTimeSFI, HexSFI, NumericPaddingSFI, PercentSFI and RoundTripSFI. StringHelper holds one list of them for numeric values and one for dates. For each format item it asks every class of the list that suits the value’s type whether it matches the item’s identifier, and a class that matches formats the value. It does not stop at the first match, so the last matching class decides. The classes of one list match different letters, so at most one of them matches an item.

The interface is declared as a class module with two empty members. A class in a project can implement it, and its methods can be called through the interface, as in the example below. The lists in StringHelper are private and filled when the class is initialised, so there is no way to add a class to them, and StringFormat never calls a class that is not already there.

Methods

GetFormattedValue

Returns the value formatted as the implementing class defines.

Syntax: object.GetFormattedValue ( value, specifier ) As String

value
required A Variant holding the value to format. StringHelper passes a number to the numeric classes and a Date to the date classes.
specifier
required A StringFormatSpecifier describing the format item: its identifier, Precision and CustomSpecifier.

Returns the formatted text. StringHelper applies the item’s Alignment afterwards, so an implementation does not pad the result.

IsIdentifierMatch

Returns whether the implementing class handles the identifier of a format item.

Syntax: object.IsIdentifierMatch ( specifier ) As Boolean

specifier
required A StringFormatSpecifier describing the format item.

Returns True when the class formats items with that identifier. The classes of the package compare the specifier’s identifier with their own letter. The numeric classes ignore the case of the identifier. The date classes treat nine of their letters as case-sensitive and accept C in either case.

Example

This example implements the interface in a class that upper-cases a value for the identifier U, and calls it directly.

Class UpperSFI
    Implements IStringFormatIdentifier

    Private Function IStringFormatIdentifier_GetFormattedValue(ByVal value As Variant, ByVal specifier As StringFormatSpecifier) As String
        IStringFormatIdentifier_GetFormattedValue = UCase$(CStr(value))
    End Function

    Private Function IStringFormatIdentifier_IsIdentifierMatch(ByVal specifier As StringFormatSpecifier) As Boolean
        IStringFormatIdentifier_IsIdentifierMatch = (specifier.identifier = "U")
    End Function
End Class

Dim spec As New StringFormatSpecifier
spec.identifier = "U"

Dim f As IStringFormatIdentifier
Set f = New UpperSFI
Debug.Print f.IsIdentifierMatch(spec)  ' True
Debug.Print f.GetFormattedValue("hello", spec)  ' HELLO

' StringFormat does not know the class, so the identifier is refused.
On Error Resume Next
Debug.Print StringFormat("{0:U}", "hello")
Debug.Print Err.Number & ": " & Err.Description  ' -2147212503: Invalid format string.

See Also