IFormatProvider Interface

Definição

Fornece um mecanismo para recuperar um objeto para controlar a formatação.Provides a mechanism for retrieving an object to control formatting.

public interface class IFormatProvider
[System.Runtime.InteropServices.ComVisible(true)]
public interface IFormatProvider
type IFormatProvider = interface
Public Interface IFormatProvider
Derivado
Atributos

Exemplos

O exemplo a seguir ilustra como IFormatProvider uma implementação pode alterar a representação de um valor de data e hora.The following example illustrates how an IFormatProvider implementation can change the representation of a date and time value. Nesse caso, uma única data é exibida usando CultureInfo objetos que representam quatro culturas diferentes.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
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

O exemplo a seguir ilustra o uso de uma classe que implementa IFormatProvider a interface e GetFormat o método.The following example illustrates the use of a class that implements the IFormatProvider interface and the GetFormat method. A AcctNumberFormat classe converte um Int64 valor que representa um número de conta para um número de conta de 12 dígitos formatado.The AcctNumberFormat class converts an Int64 value that represents an account number to a formatted 12-digit account number. Seu GetFormat método retornará uma referência à instância atual AcctNumberFormat se o formatType parâmetro se referir a uma classe que ICustomFormatterimplementa; caso GetFormat contrário null, retornará.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;
   }
}
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

A classe que implementa IFormatProvider pode ser usada em uma chamada para uma operação de análise e formatação.The class that implements IFormatProvider can then be used in a call to a formatting and parsing operation. Por exemplo, o código a seguir chama String.Format(IFormatProvider, String, Object[]) o método para gerar uma cadeia de caracteres que contém um número de conta de 12 dígitos formatado.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.
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.

Comentários

A IFormatProvider interface fornece um objeto que fornece informações de formatação para as operações de formatação e análise.The IFormatProvider interface supplies an object that provides formatting information for formatting and parsing operations. As operações de formatação convertem o valor de um tipo na representação de cadeia de caracteres desse valor.Formatting operations convert the value of a type to the string representation of that value. Os métodos de formatação típicos são os ToString métodos de um tipo, bem como. FormatTypical formatting methods are the ToString methods of a type, as well as Format. As operações de análise convertem a representação de cadeia de caracteres de um valor em um tipo com esse valor.Parsing operations convert the string representation of a value to a type with that value. Os métodos típicos de Parse análise TryParsesão e.Typical parsing methods are Parse and TryParse.

A IFormatProvider interface consiste em um único método, IFormatProvider.GetFormat.The IFormatProvider interface consists of a single method, IFormatProvider.GetFormat. GetFormaté um método de retorno de chamada: O método de análise ou de formatação o chama e passa um Type objeto que representa o tipo de objeto que o método de formatação ou de análise espera fornecerá informações de formatação.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. O GetFormat método é responsável por retornar um objeto desse tipo.The GetFormat method is responsible for returning an object of that type.

IFormatProvideras implementações geralmente são usadas implicitamente pelos métodos de formatação e análise.IFormatProvider implementations are often used implicitly by formatting and parsing methods. Por exemplo, o DateTime.ToString(String) método usa implicitamente uma IFormatProvider implementação que representa a cultura atual do sistema.For example, the DateTime.ToString(String) method implicitly uses an IFormatProvider implementation that represents the system's current culture. IFormatProvideras IFormatProvider String.Format(IFormatProvider, String, Object[])implementações também podem ser especificadas explicitamente por métodos que têm um parâmetro do tipo, como e. Int32.Parse(String, IFormatProvider)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[]).

O .NET Framework inclui as três implementações IFormatProvider predefinidas a seguir para fornecer informações específicas de cultura que são usadas na formatação ou análise de valores numéricos e de data e hora: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:

O .NET Framework também dá suporte à formatação personalizada.The .NET Framework also supports custom formatting. Isso normalmente envolve a criação de uma classe de formatação que implementa IFormatProvider e ICustomFormatter.This typically involves the creation of a formatting class that implements both IFormatProvider and ICustomFormatter. Uma instância dessa classe é passada como um parâmetro para um método que executa uma operação de formatação personalizada, String.Format(IFormatProvider, String, Object[]) como o exemplo fornece uma ilustração de tal implementação personalizada que formata um número como um número de conta de 12 dígitos.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.

Métodos

GetFormat(Type)

Retorna um objeto que fornece serviços de formatação para o tipo especificado.Returns an object that provides formatting services for the specified type.

Aplica-se a

Veja também