IFormatProvider.GetFormat(Type) Method

Definition

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.

public:
 System::Object ^ GetFormat(Type ^ formatType);
public object GetFormat (Type formatType);
abstract member GetFormat : Type -> obj
Public Function GetFormat (formatType As Type) As Object

Parameters

formatType
Type

物件,指定要傳回的格式化物件的型別。An object that specifies the type of format object to return.

Returns

Object

如果 IFormatProvider 實作可以提供該型別的物件則為 formatType 所指定的物件執行個體,否則為 nullAn instance of the object specified by formatType, if the IFormatProvider implementation can supply that type of object; otherwise, null.

Examples

下列範例說明如何使用可執行 IFormatProvider 介面和 GetFormat 方法的類別。The following example illustrates the use of a class that implements the IFormatProvider interface and the GetFormat method. AcctNumberFormat 類別會將代表帳戶號碼的 Int64 值轉換成格式化的12位數帳戶號碼。The AcctNumberFormat class converts an Int64 value that represents an account number to a formatted 12-digit account number. 如果 formatType 參數參考的類別會執行 ICustomFormatter,則其 GetFormat 方法會傳回本身的參考。否則,GetFormat 會傳回 nullIts GetFormat method returns a reference to itself 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,可以將 AcctNumberFormat 類別的實例當做引數傳遞至提供格式化或剖析服務的方法。An instance of the AcctNumberFormat class can then be passed as an argument to a method that provides formatting or parsing services. 例如,下列程式碼會將 AcctNumberFormat 類別傳遞至 String.Format(IFormatProvider, String, Object[]) 方法,以產生格式化的12位數的帳戶號碼。For example, the following code passes an AcctNumberFormat class to the String.Format(IFormatProvider, String, Object[]) method to generate 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.

Remarks

GetFormat 是一種回呼方法,可將剖析作業中的輸入字串格式,或在格式化作業中的輸出字串格式,叫用以抓取資料的格式和剖析方法。GetFormat is a callback method that formatting and parsing methods invoke to retrieve information about the format of the input string in parsing operations or the format of the output string in formatting operations. formatType 參數中,格式化或剖析方法會傳遞執行其作業所需的物件類型。In the formatType parameter, the formatting or parsing method passes the type of object it requires to perform its operation. 如果 IFormatProvider 的執行可以提供此格式化或剖析物件,它會傳回該物件。If the IFormatProvider implementation can supply this formatting or parsing object, it returns that object. 如果不是,則會傳回 nullIf not, it returns null.

例如,在 Int32.ToString(IFormatProvider) 方法的呼叫中,方法引數是一個 IFormatProvider 物件,它會提供如何格式化目前整數實例之字串表示的相關資訊。For example, in the call to the Int32.ToString(IFormatProvider) method, the method argument is an IFormatProvider object that provides information about how the string representation of the current integer instance might be formatted. 當執行時間執行方法時,它會呼叫 IFormatProvider 物件的 GetFormat 方法,並將代表 NumberFormatInfo 類型的 Type 物件傳遞給它。When the runtime executes the method, it calls the IFormatProvider object's GetFormat method and passes it a Type object that represents the NumberFormatInfo type. 如果 IFormatProvider 物件可以提供 NumberFormatInfo 物件,則會傳回該物件。If the IFormatProvider object can supply a NumberFormatInfo object, it returns that object. 如果它無法提供該類型的物件,則會傳回 nullIf it cannot supply an object of that type, it returns null.

您可以在提供自訂格式或剖析服務的類別中,執行 IFormatProvider 介面和 GetFormat 方法。You can implement the IFormatProvider interface and the GetFormat method in classes that provide custom formatting or parsing services. 然後,IFormatProvider 的實作為引數傳遞至剖析或格式化方法的任何多載,其具有 IFormatProvider類型的參數,例如 String.Format(IFormatProvider, String, Object[])Int32.ToString(String, IFormatProvider)DateTime.Parse(String, IFormatProvider)The IFormatProvider implementation is then passed as an argument to any overload of a parsing or formatting method that has a parameter of type IFormatProvider, such as String.Format(IFormatProvider, String, Object[]), Int32.ToString(String, IFormatProvider), or DateTime.Parse(String, IFormatProvider).

Applies to