ICustomFormatter ICustomFormatter ICustomFormatter ICustomFormatter Interface

定義

定義可支援物件值之自訂格式的方法。Defines a method that supports custom formatting of the value of an object.

public interface class ICustomFormatter
[System.Runtime.InteropServices.ComVisible(true)]
public interface ICustomFormatter
type ICustomFormatter = interface
Public Interface ICustomFormatter
屬性

範例

下列範例會實作ICustomFormatter允許二進位、 八進位和十六進位格式的整數值。The following example implements ICustomFormatter to allow binary, octal, and hexadecimal formatting of integral values. 在此範例中,單一類別, IBinaryFormatter,會實作ICustomFormatterIFormatProviderIn this example, a single class, IBinaryFormatter, implements both ICustomFormatter and IFormatProvider. IFormatProvider.GetFormat方法會判斷是否formatType參數代表ICustomFormatter型別。Its IFormatProvider.GetFormat method determines whether the formatType parameter represents an ICustomFormatter type. 若是如此,請BinaryFormatter傳回的執行個體本身; 否則它會傳回nullIf it does, BinaryFormatter returns an instance of itself; otherwise, it returns null. ICustomFormatter.Format實作會判定 format 參數是否為其中的三個支援的格式字串 ("B"的二進位檔,"O"的八進位和"H"的十六進位) 和格式arg參數適當。Its ICustomFormatter.Format implementation determines whether the format parameter is one of the three supported format strings ("B" for binary, "O" for octal, and "H" for hexadecimal) and formats the arg parameter appropriately. 否則,如果arg不是null,它會呼叫arg參數的IFormattable.ToString實作中,如果有的話,或其無參數ToString方法,如果其中一則否。Otherwise, if arg is not null, it calls the arg parameter's IFormattable.ToString implementation, if one exists, or its parameterless ToString method, if one does not. 如果 argnull,則方法會傳回 String.EmptyIf arg is null, the method returns String.Empty.

using System;
using System.Globalization;
using System.Numerics;

public class BinaryFormatter : IFormatProvider, ICustomFormatter
{
   // IFormatProvider.GetFormat implementation.
   public object GetFormat(Type formatType)
   {
      // Determine whether custom formatting object is requested.
      if (formatType == typeof(ICustomFormatter))
         return this;
      else
         return null;
   }   

   // Format number in binary (B), octal (O), or hexadecimal (H).
   public string Format(string format, object arg, IFormatProvider formatProvider)
   {
      // Handle format string.
      int baseNumber;
      // Handle null or empty format string, string with precision specifier.
      string thisFmt = String.Empty;
      // Extract first character of format string (precision specifiers
      // are not supported).
      if (! String.IsNullOrEmpty(format))
         thisFmt = format.Length > 1 ? format.Substring(0, 1) : format;
         

      // Get a byte array representing the numeric value.
      byte[] bytes;
      if (arg is sbyte)
      {
         string byteString = ((sbyte) arg).ToString("X2");
         bytes = new byte[1] { Byte.Parse(byteString, System.Globalization.NumberStyles.HexNumber ) };
      }
      else if (arg is byte) {
         bytes = new byte[1] { (byte) arg };
      }   
      else if (arg is short) {
         bytes = BitConverter.GetBytes((short) arg);
      }   
      else if (arg is int) {
         bytes = BitConverter.GetBytes((int) arg);
      }   
      else if (arg is long) {
         bytes = BitConverter.GetBytes((long) arg);
      }
      else if (arg is ushort) {
         bytes = BitConverter.GetBytes((ushort) arg);
      }
      else if (arg is uint) {
         bytes = BitConverter.GetBytes((uint) arg);
      }
      else if (arg is ulong) {
         bytes = BitConverter.GetBytes((ulong) arg);                  
      }
      else if (arg is BigInteger) {
         bytes = ((BigInteger) arg).ToByteArray();
      }
      else {
         try {
            return HandleOtherFormats(format, arg); 
         }
         catch (FormatException e) {
            throw new FormatException(String.Format("The format of '{0}' is invalid.", format), e);
         }
      }

      switch (thisFmt.ToUpper())
      {
         // Binary formatting.
         case "B":
            baseNumber = 2;
            break;        
         case "O":
            baseNumber = 8;
            break;
         case "H":
            baseNumber = 16;
            break;
         // Handle unsupported format strings.
         default:
         try {
            return HandleOtherFormats(format, arg); 
         }
         catch (FormatException e) {
            throw new FormatException(String.Format("The format of '{0}' is invalid.", format), e);
         }
      }
   
      // Return a formatted string.
      string numericString = String.Empty;
      for (int ctr = bytes.GetUpperBound(0); ctr >= bytes.GetLowerBound(0); ctr--)
      {
         string byteString = Convert.ToString(bytes[ctr], baseNumber);
         if (baseNumber == 2)
            byteString = new String('0', 8 - byteString.Length) + byteString;
         else if (baseNumber == 8)
            byteString = new String('0', 4 - byteString.Length) + byteString;
         // Base is 16.
         else     
            byteString = new String('0', 2 - byteString.Length) + byteString;

         numericString +=  byteString + " ";
      }
      return numericString.Trim();
   }

   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;
   }
}
Imports System.Globalization
Imports System.Numerics

Public Class BinaryFormatter : Implements IFormatProvider, ICustomFormatter
   ' IFormatProvider.GetFormat implementation.
   Public Function GetFormat(formatType As Type) As Object _
                   Implements IFormatProvider.GetFormat
      ' Determine whether custom formatting object is requested.
      If formatType Is GetType(ICustomFormatter) Then
         Return Me
      Else
         Return Nothing
      End If
   End Function   

   ' Format number in binary (B), octal (O), or hexadecimal (H).
   Public Function Format(fmt As String, arg As Object, _
                          formatProvider As IFormatProvider) As String _
                   Implements ICustomFormatter.Format

     ' Handle format string.
      Dim base As Integer
      ' Handle null or empty format string, string with precision specifier.
      Dim thisFmt As String = String.Empty
      ' Extract first character of format string (precision specifiers
      ' are not supported by BinaryFormatter).
      If Not String.IsNullOrEmpty(fmt) Then
         thisFmt = CStr(IIf(fmt.Length > 1, fmt.Substring(0, 1), fmt))
      End If
         


      ' Get a byte array representing the numeric value.
      Dim bytes() As Byte
      If TypeOf(arg) Is SByte Then
         Dim byteString As String = CType(arg, SByte).ToString("X2")
         bytes = New Byte(0) { Byte.Parse(byteString, System.Globalization.NumberStyles.HexNumber ) }
      ElseIf TypeOf(arg) Is Byte Then
         bytes = New Byte(0) { CType(arg, Byte) }
      ElseIf TypeOf(arg) Is Int16 Then
         bytes = BitConverter.GetBytes(CType(arg, Int16))
      ElseIf TypeOf(arg) Is Int32 Then
         bytes = BitConverter.GetBytes(CType(arg, Int32))
      ElseIf TypeOf(arg) Is Int64 Then
         bytes = BitConverter.GetBytes(CType(arg, Int64))
      ElseIf TypeOf(arg) Is UInt16 Then
         bytes = BitConverter.GetBytes(CType(arg, UInt16))
      ElseIf TypeOf(arg) Is UInt32 Then
         bytes = BitConverter.GetBytes(CType(arg, UInt64))
      ElseIf TypeOf(arg) Is UInt64 Then
         bytes = BitConverter.GetBytes(CType(arg, UInt64))                  
      ElseIf TypeOf(arg) Is BigInteger Then
         bytes = CType(arg, BigInteger).ToByteArray()
      Else
         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

      Select Case thisFmt.ToUpper()
         ' Binary formatting.
         Case "B"
            base = 2        
         Case "O"
            base = 8
         Case "H"
            base = 16
         ' Handle unsupported format strings.
         Case Else
            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 Select
      
      ' Return a formatted string.
      Dim numericString As String = String.Empty
      For ctr As Integer = bytes.GetUpperBound(0) To bytes.GetLowerBound(0) Step -1
         Dim byteString As String = Convert.ToString(bytes(ctr), base)
         If base = 2 Then
            byteString = New String("0"c, 8 - byteString.Length) + byteString
         ElseIf base = 8 Then
            byteString = New String("0"c, 4 - byteString.Length) + byteString
         ' Base is 16.
         Else     
            byteString = New String("0"c, 2 - byteString.Length) + byteString
         End If
         numericString +=  byteString + " "
      Next
      Return numericString.Trim()
   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

BinaryFormatter 然後可以用來提供自訂的格式,藉由傳遞BinaryFormatter物件做provider參數Format方法,如下列範例所示。BinaryFormatter can then be used to provide custom formatting by passing a BinaryFormatter object as the provider parameter of the Format method, as the following example shows.

public class Example
{
   public static void Main()
   {
      Console.WindowWidth = 100;
      
      byte byteValue = 124;
      Console.WriteLine(String.Format(new BinaryFormatter(), 
                                      "{0} (binary: {0:B}) (hex: {0:H})", byteValue));
      
      int intValue = 23045;
      Console.WriteLine(String.Format(new BinaryFormatter(), 
                                      "{0} (binary: {0:B}) (hex: {0:H})", intValue));
      
      ulong ulngValue = 31906574882;
      Console.WriteLine(String.Format(new BinaryFormatter(), 
                                      "{0}\n   (binary: {0:B})\n   (hex: {0:H})", 
                                      ulngValue));

      BigInteger bigIntValue = BigInteger.Multiply(Int64.MaxValue, 2);
      Console.WriteLine(String.Format(new BinaryFormatter(), 
                                      "{0}\n   (binary: {0:B})\n   (hex: {0:H})", 
                                      bigIntValue));
   }
}
// The example displays the following output:
//    124 (binary: 01111100) (hex: 7c)
//    23045 (binary: 00000000 00000000 01011010 00000101) (hex: 00 00 5a 05)
//    31906574882
//       (binary: 00000000 00000000 00000000 00000111 01101101 11000111 10110010 00100010)
//       (hex: 00 00 00 07 6d c7 b2 22)
//    18446744073709551614
//       (binary: 00000000 11111111 11111111 11111111 11111111 11111111 11111111 11111111 11111110)
//       (hex: 00 ff ff ff ff ff ff ff fe)
Public Module Example
   Public Sub Main
      Console.WindowWidth = 100
      
      Dim byteValue As Byte = 124
      Console.WriteLine(String.Format(New BinaryFormatter(), _
                                      "{0} (binary: {0:B}) (hex: {0:H})", byteValue))
      
      Dim intValue As Integer = 23045
      Console.WriteLine(String.Format(New BinaryFormatter(), _
                                      "{0} (binary: {0:B}) (hex: {0:H})", intValue))
      
      Dim ulngValue As ULong = 31906574882
      Console.WriteLine(String.Format(New BinaryFormatter(), _
                                      "{0} {1}   (binary: {0:B}) {1}   (hex: {0:H})", _
                                      ulngValue, vbCrLf))

      Dim bigIntValue As BigInteger = BigInteger.Multiply(Int64.MaxValue, 2)
      Console.WriteLine(String.Format(New BinaryFormatter(), _
                                      "{0} {1}   (binary: {0:B}) {1}   (hex: {0:H})", _
                                      bigIntValue, vbCrLf))
   End Sub
End Module
' The example displays the following output:
'    124 (binary: 01111100) (hex: 7c)
'    23045 (binary: 00000000 00000000 01011010 00000101) (hex: 00 00 5a 05)
'    31906574882
'       (binary: 00000000 00000000 00000000 00000111 01101101 11000111 10110010 00100010)
'       (hex: 00 00 00 07 6d c7 b2 22)
'    18446744073709551614
'       (binary: 00000000 11111111 11111111 11111111 11111111 11111111 11111111 11111111 11111110)
'       (hex: 00 ff ff ff ff ff ff ff fe)

備註

ICustomFormatter介面會包含單一方法ICustomFormatter.FormatThe ICustomFormatter interface includes a single method, ICustomFormatter.Format. 當參考或實值型別,會實作這個介面Format方法會傳回物件的值的自訂格式的字串表示。When this interface is implemented by a reference or value type, the Format method returns a custom-formatted string representation of an object's value.

通常ICustomFormatter介面透過實作IFormatProvider介面,以自訂行為的兩個.NET Framework 複合字串格式化方法包含IFormatProvider參數。Typically, the ICustomFormatter interface is implemented with the IFormatProvider interface to customize the behavior of two .NET Framework composite string formatting methods that include an IFormatProvider parameter. 具體而言,ICustomFormatter介面可以提供自訂格式的值傳遞至物件String.Format(IFormatProvider, String, Object[])StringBuilder.AppendFormat(IFormatProvider, String, Object[])方法。Specifically, the ICustomFormatter interface can provide custom formatting of the value of an object passed to the String.Format(IFormatProvider, String, Object[]) and StringBuilder.AppendFormat(IFormatProvider, String, Object[]) methods.

提供自訂的物件值的表示,需要您下列:Providing a custom representation of an object's value requires that you do the following:

  1. 定義類別可實作ICustomFormatter介面和其單一的成員,Format方法。Define a class that implements the ICustomFormatter interface and its single member, the Format method.

  2. 定義類別可實作IFormatProvider介面和其單一的成員,GetFormat方法。Define a class that implements the IFormatProvider interface and its single member, the GetFormat method. GetFormat方法傳回的執行個體您ICustomFormatter實作。The GetFormat method returns an instance of your ICustomFormatter implementation. 通常,單一類別會實作ICustomFormatterIFormatProviderOften, a single class implements both ICustomFormatter and IFormatProvider. 在此情況下,類別的GetFormat實作只會傳回本身的執行個體。In that case, the class's GetFormat implementation just returns an instance of itself.

  3. 傳遞IFormatProvider實作做provider引數String.Format(IFormatProvider, String, Object[])方法或類似的方法。Pass the IFormatProvider implementation as the provider argument of the String.Format(IFormatProvider, String, Object[]) method or a comparable method.

.NET Framework 方法接著會使用您的自訂格式設定而不它自己。The .NET Framework method will then use your custom formatting instead of its own.

給實施者的注意事項

Common language runtime 會嘗試使用您ICustomFormatter實作複合格式字串中的每個格式項目。The common language runtime attempts to use your ICustomFormatter implementation for every format item in a composite format string. 如此一來,您應該預期您ICustomFormatter實作會呼叫以提供格式化服務物件或它的值不是設計來處理。As a result, you should expect that your ICustomFormatter implementation will be called to provide formatting services to objects or values that it is not designed to handle. 在這些情況下,您Format(String, Object, IFormatProvider)方法必須呼叫適當的格式化方法,該物件或值。In these cases, your Format(String, Object, IFormatProvider) method must call the appropriate formatting method for that object or value.

有兩種類型的ICustomFormatter實作: 內建和擴充功能。There are two kinds of ICustomFormatter implementations: intrinsic and extension.

內建函式的實作都是提供應用程式定義物件的自訂格式的實作。Intrinsic implementations are implementations that provide custom formatting for an application-defined object. 在此情況下,您的實作應該包括下列各項:In this case, your implementation should include the following: -定義的格式字串會定義物件的格式。- A definition of format strings that define the formatting of the object. 格式字串是選擇性的。Format strings are optional. 一般而言,"G"或"g"格式字串會定義一般的 (或最常使用的) 格式。Typically, a "G" or "g" format string defines the general (or most commonly used) format. 不過,您可以自由定義任何您選擇的格式字串。However, you are free to define any format strings that you choose. 您也可以自行決定它們是否區分大小寫或不區分大小寫的。You are also free to decide whether they are case-sensitive or case-insensitive.

-測試,以確保物件的型別傳遞至您Format(String, Object, IFormatProvider)方法是您應用程式定義的類型。- A test to ensure that the type of the object passed to your Format(String, Object, IFormatProvider) method is your application-defined type. 如果不是,您應該呼叫物件的IFormattable實作中,如果有的話,或其ToString()方法,如果沒有。If it is not, you should call the object's IFormattable implementation, if one exists, or its ToString() method, if it does not. 您應該準備好處理這些方法呼叫可能會擲回任何例外狀況。You should be prepared to handle any exceptions these method calls might throw.

-處理 null 的格式字串,如果您的實作支援格式字串的程式碼。- Code to handle a null format string, if your implementation supports format strings. 最常見的方法是使用一般格式規範取代為 null 的格式字串。The most common approach is to replace a null format string with the general format specifier.

-程式碼來處理您的實作支援的任何格式字串。- Code to handle any format strings that your implementation supports.

-程式碼來處理不支援的格式字串。- Code to handle format strings that you do not support. 最常見的方法是將會擲回FormatException,雖然您可以提供預設格式。The most common approach is to throw a FormatException, although you can provide default formatting.

延伸模組實作都是已格式化支援型別提供自訂格式的實作。Extension implementations are implementations that provide custom formatting for a type that already has formatting support. 例如,您可以定義CustomerNumberFormatter格式化以特定的數字之間的連字號的整數類資料類型。For example, you could define a CustomerNumberFormatter that formats an integral type with hyphens between specific digits. 在此情況下,您的實作應該包括下列各項:In this case, your implementation should include the following: -定義的擴充物件的格式設定的格式字串。- A definition of format strings that extend the formatting of the object. 這些格式字串是必要的但它們必須與現有格式字串的類型衝突。These format strings are required, but they must not conflict with the type's existing format strings. 比方說,如果您在擴充格式的Int32類型,您不應該實作"C"、"D"、"E"、"F"和"G"格式規範,其他項目。For example, if you are extending formatting for the Int32 type, you should not implement the "C", "D", "E", "F", and "G" format specifiers, among others.

-物件的型別傳遞至測試您Format(String, Object, IFormatProvider)方法是其格式設定您的延伸模組支援的類型。- A test that the type of the object passed to your Format(String, Object, IFormatProvider) method is a type whose formatting your extension supports. 如果不是,呼叫物件的IFormattable實作中,如果有的話,或物件的無參數ToString()方法,如果沒有。If it is not, call the object's IFormattable implementation, if one exists, or the object's parameterless ToString() method, if it does not. 您應該準備好處理這些方法呼叫可能會擲回任何例外狀況。You should be prepared to handle any exceptions these method calls might throw.

-程式碼來處理您的延伸模組支援的任何格式字串。- Code to handle any format strings that your extension supports.

-程式碼來處理您的延伸模組不支援的任何格式字串。- Code to handle any format strings that your extension does not support. 這些應該傳遞至型別的IFormattable實作。These should be passed on to the type's IFormattable implementation. 您應該準備好處理這些方法呼叫可能會擲回任何例外狀況。You should be prepared to handle any exceptions these method calls might throw.

方法

Format(String, Object, IFormatProvider) Format(String, Object, IFormatProvider) Format(String, Object, IFormatProvider) Format(String, Object, IFormatProvider)

使用指定的格式和特定文化特性 (Culture) 的格式資訊,將指定物件值轉換成相等的字串表示。Converts the value of a specified object to an equivalent string representation using specified format and culture-specific formatting information.

適用於

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