ICustomFormatter.Format(String, Object, IFormatProvider) 方法
定義
重要
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利用指定的格式及文化特定格式資訊，將指定物件的值轉換為等效的字串表示。
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 -> stringPublic Function Format (format As String, arg As Object, formatProvider As IFormatProvider) As String參數
- format
- String
一個包含格式化規範的格式字串。
- arg
- Object
要格式化的物件。
- formatProvider
- IFormatProvider
一個提供當前實例格式資訊的物件。
傳回
該值 arg的字串表示，格式化為 formatformatProvider和 。
範例
以下範例實作 ICustomFormatter 了整數值的二進位、八進位與十六進位格式化。 其 ICustomFormatter.Format 實作會判斷格式參數是否為三種支援的格式字串之一（「B」代表二進位，「O」代表八進位，「H」代表十六進位），並適當格式化參數 arg 。 否則，若arg不存在null，則呼叫參數的arg實作（若存在），若不存在則呼叫IFormattable.ToString無參數ToString方法。 若 arg ， null則方法返回 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接著可以透過將物件作為MyFormatter方法的provider參數傳遞Format來提供自訂格式，如下範例所示。
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)
備註
ICustomFormatter.Format 是一個回調方法。 它是透過支援自訂格式的方法來呼叫的，例如 String.Format(IFormatProvider, String, Object[]) 或 StringBuilder.AppendFormat(IFormatProvider, String, Object[])。 該實作對複合 格式字串中的每個格式項目呼叫一次。 例如，在以下陳述中，該 ICustomFormatter.Format 方法被呼叫了三次。
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))
arg參數是物件清單中，其零為基礎的位置對應特定格式項目的索引。
參數包含 format 一個格式字串，該字串是 formatString 格式項目的組成部分。 若格式項目無 formatString 分量，則 的 format 值為 null。 如果 format 是 null，根據 的 arg類型，你可能可以使用你選擇的預設格式規格。
參數 formatProvider 是 IFormatProvider 提供格式化的 arg實作。 通常，它是你 ICustomFormatter 實作的一個實例。 如果 formatProvider 是 null，則忽略該參數。
你實作的 Format 方法必須包含以下功能，讓 .NET Framework 能提供你不支援的格式化。 如果你的格式化方法不支援某種格式，請判斷被格式化的物件是否實作了該 IFormattable 介面。 如果有，就呼叫 IFormattable.ToString 該介面的方法。 否則，呼叫底層物件的預設 Object.ToString 方法。 以下程式碼說明了此模式。
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()
