ICustomFormatter.Format(String, Object, IFormatProvider) 方法

参考

定义

命名空间:: System

程序集:: System.Runtime.dll

程序集:: mscorlib.dll

程序集:: netstandard.dll

重要

一些信息与预发行产品相关，相应产品在发行之前可能会进行重大修改。对于此处提供的信息，Microsoft 不作任何明示或暗示的担保。

使用指定的格式和区域性特定格式信息将指定对象的值转换为它的等效字符串表示形式。

public:
 System::String ^ Format(System::String ^ format, System::Object ^ arg, IFormatProvider ^ formatProvider);

public string Format (string format, object arg, IFormatProvider formatProvider);

public string Format (string? format, object? arg, IFormatProvider? formatProvider);

abstract member Format : string * obj * IFormatProvider -> string

Public Function Format (format As String, arg As Object, formatProvider As IFormatProvider) As String

参数

format: String

包含格式规范的格式字符串。

arg: Object

要设置其格式的对象。

formatProvider: IFormatProvider

一个对象，提供有关当前实例的区域性特定格式信息。

String

arg 的值的字符串表示形式，格式由 format 和 formatProvider 指定。

示例

以下示例实现 ICustomFormatter 以允许整数值的二进制、八进制和十六进制格式。其 ICustomFormatter.Format 实现确定 format 参数是否是三个受支持的格式字符串之一， (“B”表示二进制，“O”表示八进制，“H”表示十六进制) ，并适当设置参数的格式 arg 。否则，如果 arg 不是 null，则调用 arg 参数的 IFormattable.ToString 实现（如果存在），或者调用其无 ToString 参数方法（如果不存在）。如果 arg 为 null，则此方法返回 String.Empty。

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

public class MyFormatter : 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;
    }
}

open System
open System.Globalization
open System.Numerics

type MyFormatter() =
    interface IFormatProvider with
        // IFormatProvider.GetFormat implementation.
        member this.GetFormat(formatType: Type) =
            // Determine whether custom formatting object is requested.
            if formatType = typeof<ICustomFormatter> then
                this
            else
                null

    interface ICustomFormatter with
        // Format number in binary (B), octal (O), or hexadecimal (H).
        member this.Format(format, arg: obj, formatProvider: IFormatProvider) =
            // Handle null or empty format string, string with precision specifier.
            let thisFmt =
                // Extract first character of format string (precision specifiers
                // are not supported).
                if String.IsNullOrEmpty format |> not then
                    if format.Length > 1 then 
                        format.Substring(0, 1) 
                    else 
                        format
                else
                    String.Empty

            // Get a byte array representing the numeric value.
            let bytes =
                match arg with
                | :? sbyte as arg ->
                    let byteString = arg.ToString "X2"
                    Some [| Byte.Parse(byteString, NumberStyles.HexNumber) |]
                | :? byte as arg ->
                    Some [| arg |]
                | :? int16 as arg ->
                    BitConverter.GetBytes arg
                    |> Some
                | :? int as arg ->
                    BitConverter.GetBytes arg
                    |> Some
                | :? int64 as arg ->
                    BitConverter.GetBytes arg
                    |> Some
                | :? uint16 as arg ->
                    BitConverter.GetBytes arg
                    |> Some
                | :? uint as arg ->
                    BitConverter.GetBytes arg
                    |> Some
                | :? uint64 as arg ->
                    BitConverter.GetBytes arg
                    |> Some
                | :? bigint as arg ->
                    arg.ToByteArray()
                    |> Some
                | _ ->
                    None
            let baseNumber =
                match thisFmt.ToUpper() with
                    // Binary formatting.
                    | "B" -> Some 2
                    | "O" -> Some 8
                    | "H" -> Some 16
                    // Handle unsupported format strings.
                    | _ -> None

            match bytes, baseNumber with
            | Some bytes, Some baseNumber ->
                // Return a formatted string.
                let mutable numericString = String.Empty
                for i = bytes.GetUpperBound 0 to bytes.GetLowerBound 0 do
                    let byteString = Convert.ToString(bytes[i], baseNumber)
                    let byteString =
                        match baseNumber with
                        | 2 ->
                            String('0', 8 - byteString.Length) + byteString
                        | 8 ->
                            String('0', 4 - byteString.Length) + byteString
                        // Base is 16.
                        | _ ->
                            String('0', 2 - byteString.Length) + byteString
                    numericString <- numericString + byteString + " "
                numericString.Trim()
            | _ ->
                try
                    this.HandleOtherFormats(format, arg)
                with :? FormatException as e ->
                    raise (FormatException($"The format of '{format}' is invalid.", e))
                    
    member private this.HandleOtherFormats(format, arg: obj) =
        match arg with
        | :? IFormattable as arg ->
            arg.ToString(format, CultureInfo.CurrentCulture)
        | null ->
            String.Empty
        | _ ->
            string arg

Imports System.Globalization
Imports System.Numerics

Public Class MyFormatter : 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 MyFormatter).
      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

MyFormatter然后，可以通过将对象作为 provider 方法的参数Format传递MyFormatter来提供自定义格式设置，如以下示例所示。

public class Example
{
    public static void Main()
    {
        Console.WindowWidth = 100;

        byte byteValue = 124;
        Console.WriteLine(String.Format(new MyFormatter(),
                                        "{0} (binary: {0:B}) (hex: {0:H})", byteValue));

        int intValue = 23045;
        Console.WriteLine(String.Format(new MyFormatter(),
                                        "{0} (binary: {0:B}) (hex: {0:H})", intValue));

        ulong ulngValue = 31906574882;
        Console.WriteLine(String.Format(new MyFormatter(),
                                        "{0}\n   (binary: {0:B})\n   (hex: {0:H})",
                                        ulngValue));

        BigInteger bigIntValue = BigInteger.Multiply(Int64.MaxValue, 2);
        Console.WriteLine(String.Format(new MyFormatter(),
                                        "{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)

Console.WindowWidth <- 100

let byteValue = 124uy
String.Format(MyFormatter(), "{0} (binary: {0:B}) (hex: {0:H})", byteValue)
|> printfn "%s"

let intValue = 23045
String.Format(MyFormatter(), "{0} (binary: {0:B}) (hex: {0:H})", intValue)
|> printfn "%s"

let ulngValue = 31906574882uL
String.Format(MyFormatter(), "{0}\n   (binary: {0:B})\n   (hex: {0:H})", ulngValue)
|> printfn "%s"

let bigIntValue = BigInteger.Multiply(Int64.MaxValue, 2)
String.Format(MyFormatter(), "{0}\n   (binary: {0:B})\n   (hex: {0:H})", bigIntValue)
|> printfn "%s"

// 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 MyFormatter(), _
                                      "{0} (binary: {0:B}) (hex: {0:H})", byteValue))
      
      Dim intValue As Integer = 23045
      Console.WriteLine(String.Format(New MyFormatter(), _
                                      "{0} (binary: {0:B}) (hex: {0:H})", intValue))
      
      Dim ulngValue As ULong = 31906574882
      Console.WriteLine(String.Format(New MyFormatter(), _
                                      "{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 MyFormatter(), _
                                      "{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)

注解

ICustomFormatter.Format 为回调方法。它由支持自定义格式的方法调用，例如 String.Format(IFormatProvider, String, Object[]) 或 StringBuilder.AppendFormat(IFormatProvider, String, Object[])。对复合格式字符串中的每个格式项调用一次实现。例如，在以下语句中， ICustomFormatter.Format 调用方法三次。

Console.WriteLine(String.Format(new MyFormatter(),
                                "{0} (binary: {0:B}) (hex: {0:H})", byteValue));

String.Format(MyFormatter(), "{0} (binary: {0:B}) (hex: {0:H})", byteValue)
|> printfn "%s"

Console.WriteLine(String.Format(New MyFormatter(), _
                                "{0} (binary: {0:B}) (hex: {0:H})", byteValue))

参数 arg 是对象列表中的对象，其从零开始的位置对应于特定格式项的索引。

参数 format 包含格式字符串，它是 formatString 格式项的组件。如果格式项没有formatString组件，则的formatnull值为。如果 format 为 null，则根据的类型 arg，您可能能够使用所选的默认格式规范。

参数 formatProvider 是一个实现， IFormatProvider 它为 arg提供格式设置。通常，它是实现的 ICustomFormatter 实例。如果 formatProvider 为 null，请忽略该参数。

方法的Format实现必须包含以下功能，以便.NET Framework可以提供不支持的格式设置。如果 format 方法不支持格式，请确定要设置格式的对象是否实现接口 IFormattable 。如果是，请调用 IFormattable.ToString 该接口的方法。否则，请调用基础对象的默认 Object.ToString 方法。以下代码演示了此模式。

if (arg is IFormattable)
    return ((IFormattable)arg).ToString(format, CultureInfo.CurrentCulture);
else if (arg != null)
    return arg.ToString();

match arg with
| :? IFormattable as arg ->
    arg.ToString(format, CultureInfo.CurrentCulture)
| null ->
    String.Empty
| _ ->
    string arg

If TypeOf arg Is IFormattable Then
   Return DirectCast(arg, IFormattable).ToString(fmt, CultureInfo.CurrentCulture)
ElseIf arg IsNot Nothing Then
   Return arg.ToString()

适用于

通过

ICustomFormatter.Format(String, Object, IFormatProvider) 方法

定义

参数

返回

示例

注解

适用于

另请参阅

其他资源