IFormatProvider 介面

定義

提供機制來擷取要控制格式的物件。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
衍生
屬性

範例

下列範例說明IFormatProvider執行如何變更日期和時間值的標記法。The following example illustrates how an IFormatProvider implementation can change the representation of a date and time value. 在此情況下, 會使用CultureInfo代表四個不同文化特性的物件來顯示單一日期。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

下列範例說明如何使用可實作為IFormatProvider介面GetFormat和方法的類別。The following example illustrates the use of a class that implements the IFormatProvider interface and the GetFormat method. 類別會將代表帳戶號碼的值轉換成格式化的12位數帳戶號碼。Int64 AcctNumberFormatThe AcctNumberFormat class converts an Int64 value that represents an account number to a formatted 12-digit account number. 如果GetFormat ICustomFormatter參數參考null到執行的類別, AcctNumberFormat則其方法會傳回目前實例的參考; 否則GetFormat會傳回。 formatTypeIts 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

然後, IFormatProvider可以在對格式化和剖析作業的呼叫中使用執行的類別。The class that implements IFormatProvider can then be used in a call to a formatting and parsing operation. 例如, 下列程式碼會呼叫String.Format(IFormatProvider, String, Object[])方法, 以產生包含格式化12位數帳戶號碼的字串。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.

備註

介面IFormatProvider所提供的物件, 可提供格式化和剖析作業的格式設定資訊。The IFormatProvider interface supplies an object that provides formatting information for formatting and parsing operations. 格式化作業會將類型的值轉換為該值的字串表示。Formatting operations convert the value of a type to the string representation of that value. 典型的格式化方法是ToString類型的方法, Format以及。Typical formatting methods are the ToString methods of a type, as well as Format. 剖析作業會將值的字串表示轉換成具有該值的類型。Parsing operations convert the string representation of a value to a type with that value. 一般剖析方法為ParseTryParseTypical parsing methods are Parse and TryParse.

介面IFormatProvider是由單一IFormatProvider.GetFormat方法所組成。The IFormatProvider interface consists of a single method, IFormatProvider.GetFormat. GetFormat是回呼方法:剖析或格式化方法會呼叫它, 並將代表Type格式化或剖析方法所預期之物件類型的物件傳遞給它, 以提供格式資訊。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. GetFormat方法會負責傳回該類型的物件。The GetFormat method is responsible for returning an object of that type.

IFormatProvider藉由格式化和剖析方法, 通常會隱含地使用執行。IFormatProvider implementations are often used implicitly by formatting and parsing methods. 例如, DateTime.ToString(String)方法會隱含地使用代表IFormatProvider系統目前文化特性的實作為。For example, the DateTime.ToString(String) method implicitly uses an IFormatProvider implementation that represents the system's current culture. IFormatProvider您也可以透過具有型IFormatProvider別參數的方法 ( Int32.Parse(String, IFormatProvider)例如和String.Format(IFormatProvider, String, Object[])) 明確地指定執行。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[]).

.NET Framework 包含下列三個預先定義IFormatProvider的執行, 可提供用來格式化或剖析數值和日期和時間值的文化特性特定資訊: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:

.NET Framework 也支援自訂格式。The .NET Framework also supports custom formatting. 這通常牽涉到建立同時IFormatProvider執行和ICustomFormatter的格式化類別。This typically involves the creation of a formatting class that implements both IFormatProvider and ICustomFormatter. 然後, 這個類別的實例會當做參數傳遞給執行自訂格式化作業的方法, 例如, String.Format(IFormatProvider, String, Object[])範例會提供這類自訂執行的圖例, 將數位格式化為12位數的帳戶號碼。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.

方法

GetFormat(Type)

傳回物件,這個物件為所指定型別提供格式化服務。Returns an object that provides formatting services for the specified type.

適用於

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