IFormatProvider Interface
Definition
Important
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Provides a mechanism for retrieving an object to control formatting.
public interface class IFormatProviderpublic interface IFormatProvider[System.Runtime.InteropServices.ComVisible(true)]
public interface IFormatProvidertype IFormatProvider = interface[<System.Runtime.InteropServices.ComVisible(true)>]
type IFormatProvider = interfacePublic Interface IFormatProvider- Derived
- Attributes
Examples
The following example illustrates how an IFormatProvider implementation can change the representation of a date and time value. In this case, a single date is displayed by using CultureInfo objects that represent four different cultures.
using System;
using System.Globalization;
public class Example
{
public static void Main()
{
DateTime dateValue = new DateTime(2009, 6, 1, 16, 37, 0);
CultureInfo[] cultures = { new CultureInfo("en-US"),
new CultureInfo("fr-FR"),
new CultureInfo("it-IT"),
new CultureInfo("de-DE") };
foreach (CultureInfo culture in cultures)
Console.WriteLine("{0}: {1}", culture.Name, dateValue.ToString(culture));
}
}
// The example displays the following output:
// en-US: 6/1/2009 4:37:00 PM
// fr-FR: 01/06/2009 16:37:00
// it-IT: 01/06/2009 16.37.00
// de-DE: 01.06.2009 16:37:00
open System
open System.Globalization
let dateValue = DateTime(2009, 6, 1, 16, 37, 0)
let cultures =
[ CultureInfo "en-US"
CultureInfo "fr-FR"
CultureInfo "it-IT"
CultureInfo "de-DE" ]
for culture in cultures do
printfn $"{culture.Name}: {dateValue.ToString culture}"
// The example displays the following output:
// en-US: 6/1/2009 4:37:00 PM
// fr-FR: 01/06/2009 16:37:00
// it-IT: 01/06/2009 16.37.00
// de-DE: 01.06.2009 16:37:00
Imports System.Globalization
Module Example
Public Sub Main()
Dim dateValue As Date = #06/01/2009 4:37PM#
Dim cultures() As CultureInfo = {New CultureInfo("en-US"), _
New CultureInfo("fr-FR"), _
New CultureInfo("it-IT"), _
New CultureInfo("de-DE") }
For Each culture As CultureInfo In cultures
Console.WriteLine("{0}: {1}", culture.Name, dateValue.ToString(culture))
Next
End Sub
End Module
' The example displays the following output:
' en-US: 6/1/2009 4:37:00 PM
' fr-FR: 01/06/2009 16:37:00
' it-IT: 01/06/2009 16.37.00
' de-DE: 01.06.2009 16:37:00
The following example illustrates the use of a class that implements the IFormatProvider interface and the GetFormat method. The AcctNumberFormat class converts an Int64 value that represents an account number to a formatted 12-digit account number. Its GetFormat method returns a reference to the current AcctNumberFormat instance if the formatType parameter refers to a class that implements ICustomFormatter; otherwise, GetFormat returns null.
public class AcctNumberFormat : IFormatProvider, ICustomFormatter
{
private const int ACCT_LENGTH = 12;
public object GetFormat(Type formatType)
{
if (formatType == typeof(ICustomFormatter))
return this;
else
return null;
}
public string Format(string fmt, object arg, IFormatProvider formatProvider)
{
// Provide default formatting if arg is not an Int64.
if (arg.GetType() != typeof(Int64))
try {
return HandleOtherFormats(fmt, arg);
}
catch (FormatException e) {
throw new FormatException(String.Format("The format of '{0}' is invalid.", fmt), e);
}
// Provide default formatting for unsupported format strings.
string ufmt = fmt.ToUpper(CultureInfo.InvariantCulture);
if (! (ufmt == "H" || ufmt == "I"))
try {
return HandleOtherFormats(fmt, arg);
}
catch (FormatException e) {
throw new FormatException(String.Format("The format of '{0}' is invalid.", fmt), e);
}
// Convert argument to a string.
string result = arg.ToString();
// If account number is less than 12 characters, pad with leading zeroes.
if (result.Length < ACCT_LENGTH)
result = result.PadLeft(ACCT_LENGTH, '0');
// If account number is more than 12 characters, truncate to 12 characters.
if (result.Length > ACCT_LENGTH)
result = result.Substring(0, ACCT_LENGTH);
if (ufmt == "I") // Integer-only format.
return result;
// Add hyphens for H format specifier.
else // Hyphenated format.
return result.Substring(0, 5) + "-" + result.Substring(5, 3) + "-" + result.Substring(8);
}
private string HandleOtherFormats(string format, object arg)
{
if (arg is IFormattable)
return ((IFormattable)arg).ToString(format, CultureInfo.CurrentCulture);
else if (arg != null)
return arg.ToString();
else
return String.Empty;
}
}
open System
open System.Globalization
type AcctNumberFormat() =
let [<Literal>] ACCT_LENGTH = 12
interface IFormatProvider with
member this.GetFormat(formatType: Type) =
if formatType = typeof<ICustomFormatter> then
this
else
null
interface ICustomFormatter with
member this.Format(fmt: string, arg: obj, formatProvider: IFormatProvider) =
// Provide default formatting if arg is not an Int64.
// Provide default formatting for unsupported format strings.
let ufmt = fmt.ToUpper CultureInfo.InvariantCulture
if arg.GetType() = typeof<Int64> && (ufmt = "H" || ufmt = "I") then
// Convert argument to a string.
let result = string arg
let result =
// If account number is less than 12 characters, pad with leading zeroes.
if result.Length < ACCT_LENGTH then
result.PadLeft(ACCT_LENGTH, '0')
else result
let result =
// If account number is more than 12 characters, truncate to 12 characters.
if result.Length > ACCT_LENGTH then
result.Substring(0, ACCT_LENGTH)
else result
// Integer-only format.
if ufmt = "I" then
result
// Add hyphens for H format specifier.
else // Hyphenated format.
result.Substring(0, 5) + "-" + result.Substring(5, 3) + "-" + result.Substring(8)
else
try
this.HandleOtherFormats(fmt, arg)
with :? FormatException as e ->
raise (FormatException($"The format of '{fmt}' is invalid.", e))
member _.HandleOtherFormats(format: string, arg: obj) =
match arg with
| :? IFormattable as arg ->
arg.ToString(format, CultureInfo.CurrentCulture)
| null ->
string arg
| _ ->
String.Empty
Public Class AcctNumberFormat : Implements IFormatProvider, ICustomFormatter
Private Const ACCT_LENGTH As Integer = 12
Public Function GetFormat(formatType As Type) As Object _
Implements IFormatProvider.GetFormat
If formatType 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
' Provide default formatting if arg is not an Int64.
If Not TypeOf arg Is Int64 Then
Try
Return HandleOtherFormats(fmt, arg)
Catch e As FormatException
Throw New FormatException(String.Format("The format of '{0}' is invalid.", fmt), e)
End Try
End If
' Provider default formatting for unsupported format strings.
Dim ufmt As String = fmt.ToUpper(CultureInfo.InvariantCulture)
If Not (ufmt = "H" Or ufmt = "I") Then
Try
Return HandleOtherFormats(fmt, arg)
Catch e As FormatException
Throw New FormatException(String.Format("The format of '{0}' is invalid.", fmt), e)
End Try
End If
' Convert argument to a string.
Dim result As String = arg.ToString()
' If account number is less than 12 characters, pad with leading zeroes.
If result.Length < ACCT_LENGTH Then result = result.PadLeft(ACCT_LENGTH, "0"c)
' If account number is more than 12 characters, truncate to 12 characters.
If result.Length > ACCT_LENGTH Then result = Left(result, ACCT_LENGTH)
If ufmt = "I" ' Integer-only format.
Return result
' Add hyphens for H format specifier.
Else ' Hypenated format.
Return Left(result, 5) & "-" & Mid(result, 6, 3) & "-" & Right(result, 4)
End If
End Function
Private Function HandleOtherFormats(fmt As String, arg As Object) As String
If TypeOf arg Is IFormattable Then
Return DirectCast(arg, IFormattable).ToString(fmt, CultureInfo.CurrentCulture)
ElseIf arg IsNot Nothing Then
Return arg.ToString()
Else
Return String.Empty
End If
End Function
End Class
The class that implements IFormatProvider can then be used in a call to a formatting and parsing operation. For example, the following code calls the String.Format(IFormatProvider, String, Object[]) method to generate a string that contains a formatted 12-digit account number.
using System;
using System.Globalization;
public enum DaysOfWeek { Monday=1, Tuesday=2 };
public class TestFormatting
{
public static void Main()
{
long acctNumber;
double balance;
DaysOfWeek wday;
string output;
acctNumber = 104254567890;
balance = 16.34;
wday = DaysOfWeek.Monday;
output = String.Format(new AcctNumberFormat(),
"On {2}, the balance of account {0:H} was {1:C2}.",
acctNumber, balance, wday);
Console.WriteLine(output);
wday = DaysOfWeek.Tuesday;
output = String.Format(new AcctNumberFormat(),
"On {2}, the balance of account {0:I} was {1:C2}.",
acctNumber, balance, wday);
Console.WriteLine(output);
}
}
// The example displays the following output:
// On Monday, the balance of account 10425-456-7890 was $16.34.
// On Tuesday, the balance of account 104254567890 was $16.34.
open System
open System.Globalization
type DaysOfWeek = Monday = 1 | Tuesday = 2
[<EntryPoint>]
let main _ =
let acctNumber = 104254567890L
let balance = 16.34
let wday = DaysOfWeek.Monday
let output =
String.Format(AcctNumberFormat(),
"On {2}, the balance of account {0:H} was {1:C2}.",
acctNumber, balance, wday)
printfn $"{output}"
let wday = DaysOfWeek.Tuesday
let output =
String.Format(AcctNumberFormat(),
"On {2}, the balance of account {0:I} was {1:C2}.",
acctNumber, balance, wday)
printfn $"{output}"
0
// The example displays the following output:
// On Monday, the balance of account 10425-456-7890 was $16.34.
// On Tuesday, the balance of account 104254567890 was $16.34.
Imports System.Globalization
Public Enum DaysOfWeek As Long
Monday = 1
Tuesday = 2
End Enum
Module TestFormatting
Public Sub Main()
Dim acctNumber As Long, balance As Double
Dim wday As DaysOfWeek
Dim output As String
acctNumber = 104254567890
balance = 16.34
wday = DaysOfWeek.Monday
output = String.Format(New AcctNumberFormat(), "On {2}, the balance of account {0:H} was {1:C2}.", acctNumber, balance, wday)
Console.WriteLine(output)
wday = DaysOfWeek.Tuesday
output = String.Format(New AcctNumberFormat(), "On {2}, the balance of account {0:I} was {1:C2}.", acctNumber, balance, wday)
Console.WriteLine(output)
End Sub
End Module
' The example displays the following output:
' On Monday, the balance of account 10425-456-7890 was $16.34.
' On Tuesday, the balance of account 104254567890 was $16.34.
Remarks
The IFormatProvider interface supplies an object that provides formatting information for formatting and parsing operations. Formatting operations convert the value of a type to the string representation of that value. Typical formatting methods are the ToString methods of a type, as well as Format. Parsing operations convert the string representation of a value to a type with that value. Typical parsing methods are Parse and TryParse.
The IFormatProvider interface consists of a single method, IFormatProvider.GetFormat. GetFormat is a callback method: The parsing or formatting method calls it and passes it a Type object that represents the type of object that the formatting or parsing method expects will provide formatting information. The GetFormat method is responsible for returning an object of that type.
IFormatProvider implementations are often used implicitly by formatting and parsing methods. For example, the DateTime.ToString(String) method implicitly uses an IFormatProvider implementation that represents the system's current culture. IFormatProvider implementations can also be specified explicitly by methods that have a parameter of type IFormatProvider, such as Int32.Parse(String, IFormatProvider) and String.Format(IFormatProvider, String, Object[]).
The .NET Framework includes the following three predefined IFormatProvider implementations to provide culture-specific information that is used in formatting or parsing numeric and date and time values:
The NumberFormatInfo class, which provides information that is used to format numbers, such as the currency, thousands separator, and decimal separator symbols for a particular culture. For information about the predefined format strings recognized by a NumberFormatInfo object and used in numeric formatting operations, see Standard Numeric Format Strings and Custom Numeric Format Strings.
The DateTimeFormatInfo class, which provides information that is used to format dates and times, such as the date and time separator symbols for a particular culture or the order and format of a date's year, month, and day components. For information about the predefined format strings recognized by a DateTimeFormatInfo object and used in numeric formatting operations, see Standard Date and Time Format Strings and Custom Date and Time Format Strings.
The CultureInfo class, which represents a particular culture. Its GetFormat method returns a culture-specific NumberFormatInfo or DateTimeFormatInfo object, depending on whether the CultureInfo object is used in a formatting or parsing operation that involves numbers or dates and times.
The .NET Framework also supports custom formatting. This typically involves the creation of a formatting class that implements both IFormatProvider and ICustomFormatter. An instance of this class is then passed as a parameter to a method that performs a custom formatting operation, such as String.Format(IFormatProvider, String, Object[]) The example provides an illustration of such a custom implementation that formats a number as a 12-digit account number.
Methods
| GetFormat(Type) |
Returns an object that provides formatting services for the specified type. |
