IFormatProvider.GetFormat(Type) 方法

定义

返回一个对象,该对象为指定类型提供格式设置服务。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

参数

formatType
Type

一个对象,该对象指定要返回的格式对象的类型。An object that specifies the type of format object to return.

返回

如果 IFormatProvider 实现能够提供该类型的对象,则为 formatType 所指定对象的实例;否则为 nullAn instance of the object specified by formatType, if the IFormatProvider implementation can supply that type of object; otherwise, null.

示例

下面的示例演示如何使用实现IFormatProvider接口的类GetFormat和方法。The following example illustrates the use of a class that implements the IFormatProvider interface and the GetFormat method. 类将表示帐号的值转换为格式化的12位数帐号。AcctNumberFormat Int64The AcctNumberFormat class converts an Int64 value that represents an account number to a formatted 12-digit account number. GetFormat ICustomFormatter GetFormat如果参数引用了实现的类, 则其方法返回对自身的引用; 否则返回nullformatTypeIts 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

然后, AcctNumberFormat可以将类的实例作为参数传递给提供格式设置或分析服务的方法。An instance of the AcctNumberFormat class can then be passed as an argument to a method that provides formatting or parsing services. 例如, 下面的代码将AcctNumberFormat类传递String.Format(IFormatProvider, String, Object[])给方法, 以生成带格式的12位数帐号。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.

注解

GetFormat是格式设置和分析方法调用的回调方法, 用于检索有关分析操作中输入字符串格式的信息, 或格式设置操作中的输出字符串的格式。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在参数中, 格式设置或分析方法传递执行其操作所需的对象的类型。In the formatType parameter, the formatting or parsing method passes the type of object it requires to perform its operation. IFormatProvider如果实现可以提供此格式设置或分析对象, 则会返回该对象。If the IFormatProvider implementation can supply this formatting or parsing object, it returns that object. 如果不是, 则null返回。If not, it returns null.

例如, 在调用Int32.ToString(IFormatProvider)方法时, 方法自变量是一个IFormatProvider对象, 该对象提供有关当前整数实例的字符串表示形式如何进行格式化的信息。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. 当运行时执行方法时, 它将调用IFormatProvider对象的GetFormat方法, 并NumberFormatInfo向其Type传递一个表示类型的对象。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. 如果对象可以NumberFormatInfo提供对象, 则返回该对象。 IFormatProviderIf the IFormatProvider object can supply a NumberFormatInfo object, it returns that object. 如果无法提供该类型的对象, 它将返回nullIf it cannot supply an object of that type, it returns null.

可以在提供自IFormatProvider定义格式设置GetFormat或分析服务的类中实现接口和方法。You can implement the IFormatProvider interface and the GetFormat method in classes that provide custom formatting or parsing services. 然后IFormatProvider , 将实现作为参数传递给具有类型IFormatProvider为的参数的分析或格式设置方法的任何重载, 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).

适用于