IFormattable 接口

定义

提供一种功能,用以将对象的值格式化为字符串表示形式。

public interface class IFormattable
public interface IFormattable
[System.Runtime.InteropServices.ComVisible(true)]
public interface IFormattable
type IFormattable = interface
[<System.Runtime.InteropServices.ComVisible(true)>]
type IFormattable = interface
Public Interface IFormattable
派生
属性

示例

下面的示例定义一个实现 Temperature 接口的 IFormattable 类。 该类支持四种格式说明符:“G”和“C”,指示温度以摄氏度显示:“F”,指示温度将在华氏度中显示:和“K”,表示温度将显示在凯尔文。 此外,实现 IFormattable.ToString 还可以处理为 null 空的格式字符串。 类定义的Temperature另外两ToString种方法只是包装对实现的IFormattable.ToString调用。

using System;
using System.Globalization;

public class Temperature : IFormattable
{
   private decimal temp;

   public Temperature(decimal temperature)
   {
      if (temperature < -273.15m)
        throw new ArgumentOutOfRangeException(String.Format("{0} is less than absolute zero.",
                                              temperature));
      this.temp = temperature;
   }

   public decimal Celsius
   {
      get { return temp; }
   }

   public decimal Fahrenheit
   {
      get { return temp * 9 / 5 + 32; }
   }

   public decimal Kelvin
   {
      get { return temp + 273.15m; }
   }

   public override string ToString()
   {
      return this.ToString("G", CultureInfo.CurrentCulture);
   }

   public string ToString(string format)
   {
      return this.ToString(format, CultureInfo.CurrentCulture);
   }

   public string ToString(string format, IFormatProvider provider)
   {
      if (String.IsNullOrEmpty(format)) format = "G";
      if (provider == null) provider = CultureInfo.CurrentCulture;

      switch (format.ToUpperInvariant())
      {
         case "G":
         case "C":
            return temp.ToString("F2", provider) + " °C";
         case "F":
            return Fahrenheit.ToString("F2", provider) + " °F";
         case "K":
            return Kelvin.ToString("F2", provider) + " K";
         default:
            throw new FormatException(String.Format("The {0} format string is not supported.", format));
      }
   }
}
open System
open System.Globalization

type Temperature(temperature: decimal) =
    do 
        if temperature < -273.15M then
            raise (ArgumentOutOfRangeException $"{temperature} is less than absolute zero.")

    member _.Celsius =
        temperature

    member _.Fahrenheit =
        temperature * 9M / 5M + 32M

    member _.Kelvin =
        temperature + 273.15m

    override this.ToString() =
        this.ToString("G", CultureInfo.CurrentCulture)

    member this.ToString(format) =
        this.ToString(format, CultureInfo.CurrentCulture)

    member this.ToString(format, provider: IFormatProvider) =
        let format =
            if String.IsNullOrEmpty format then "G"
            else format

        let provider =
            if isNull provider then 
                CultureInfo.CurrentCulture :> IFormatProvider
            else provider

        match format.ToUpperInvariant() with
        | "G" | "C" ->
            temperature.ToString("F2", provider) + " °C"
        | "F" ->
            this.Fahrenheit.ToString("F2", provider) + " °F"
        | "K" ->
            this.Kelvin.ToString("F2", provider) + " K"
        | _ ->
            raise (FormatException $"The {format} format string is not supported.")

    interface IFormattable with
        member this.ToString(format, provider) = this.ToString(format, provider)
Imports System.Globalization

Public Class Temperature : Implements IFormattable
   Private temp As Decimal
   
   Public Sub New(temperature As Decimal)
      If temperature < -273.15 Then _ 
        Throw New ArgumentOutOfRangeException(String.Format("{0} is less than absolute zero.", _
                                              temperature))
      Me.temp = temperature
   End Sub
   
   Public ReadOnly Property Celsius As Decimal
      Get
         Return temp
      End Get
   End Property
   
   Public ReadOnly Property Fahrenheit As Decimal
      Get
         Return temp * 9 / 5 + 32
      End Get
   End Property
   
   Public ReadOnly Property Kelvin As Decimal
      Get
         Return temp + 273.15d
      End Get
   End Property

   Public Overrides Function ToString() As String
      Return Me.ToString("G", CultureInfo.CurrentCulture)
   End Function
      
   Public Overloads Function ToString(fmt As String) As String
      Return Me.ToString(fmt, CultureInfo.CurrentCulture)
   End Function
   
   Public Overloads Function ToString(fmt As String, provider As IFormatProvider) _
                   As String _
                   Implements IFormattable.ToString
      If String.IsNullOrEmpty(fmt) Then fmt = "G"
      If provider Is Nothing Then provider = CultureInfo.CurrentCulture
      
      Select Case fmt.ToUpperInvariant()
         Case "G", "C"
            Return temp.ToString("F2", provider) + " °C" 
         Case "F"
            Return Fahrenheit.ToString("F2", provider) + " °F"
         Case "K"
            Return Kelvin.ToString("F2", provider) + " K"
         Case Else
            Throw New FormatException(String.Format("The {0} format string is not supported.", fmt))
      End Select
   End Function
End Class

下面的示例随后直接或使用复合格式字符串调用 IFormattable.ToString 实现。

public class Example
{
   public static void Main()
   {
      // Use composite formatting with format string in the format item.
      Temperature temp1 = new Temperature(0);
      Console.WriteLine("{0:C} (Celsius) = {0:K} (Kelvin) = {0:F} (Fahrenheit)\n", temp1);

      // Use composite formatting with a format provider.
      temp1 = new Temperature(-40);
      Console.WriteLine(String.Format(CultureInfo.CurrentCulture, "{0:C} (Celsius) = {0:K} (Kelvin) = {0:F} (Fahrenheit)", temp1));
      Console.WriteLine(String.Format(new CultureInfo("fr-FR"), "{0:C} (Celsius) = {0:K} (Kelvin) = {0:F} (Fahrenheit)\n", temp1));

      // Call ToString method with format string.
      temp1 = new Temperature(32);
      Console.WriteLine("{0} (Celsius) = {1} (Kelvin) = {2} (Fahrenheit)\n",
                        temp1.ToString("C"), temp1.ToString("K"), temp1.ToString("F"));

      // Call ToString with format string and format provider
      temp1 = new Temperature(100)      ;
      NumberFormatInfo current = NumberFormatInfo.CurrentInfo;
      CultureInfo nl = new CultureInfo("nl-NL");
      Console.WriteLine("{0} (Celsius) = {1} (Kelvin) = {2} (Fahrenheit)",
                        temp1.ToString("C", current), temp1.ToString("K", current), temp1.ToString("F", current));
      Console.WriteLine("{0} (Celsius) = {1} (Kelvin) = {2} (Fahrenheit)",
                        temp1.ToString("C", nl), temp1.ToString("K", nl), temp1.ToString("F", nl));
   }
}
// The example displays the following output:
//    0.00 °C (Celsius) = 273.15 K (Kelvin) = 32.00 °F (Fahrenheit)
//
//    -40.00 °C (Celsius) = 233.15 K (Kelvin) = -40.00 °F (Fahrenheit)
//    -40,00 °C (Celsius) = 233,15 K (Kelvin) = -40,00 °F (Fahrenheit)
//
//    32.00 °C (Celsius) = 305.15 K (Kelvin) = 89.60 °F (Fahrenheit)
//
//    100.00 °C (Celsius) = 373.15 K (Kelvin) = 212.00 °F (Fahrenheit)
//    100,00 °C (Celsius) = 373,15 K (Kelvin) = 212,00 °F (Fahrenheit)
open System
open System.Globalization

[<EntryPoint>]
let main _ =
    // Use composite formatting with format string in the format item.
    let temp1 = Temperature 0
    Console.WriteLine("{0:C} (Celsius) = {0:K} (Kelvin) = {0:F} (Fahrenheit)\n", temp1)

    // Use composite formatting with a format provider.
    let temp1 = Temperature -40
    String.Format(CultureInfo.CurrentCulture, "{0:C} (Celsius) = {0:K} (Kelvin) = {0:F} (Fahrenheit)", temp1)
    |> printfn "%s"
    String.Format(CultureInfo "fr-FR", "{0:C} (Celsius) = {0:K} (Kelvin) = {0:F} (Fahrenheit)\n", temp1)
    |> printfn "%s"

    // Call ToString method with format string.
    let temp1 = Temperature 32
    Console.WriteLine("{0} (Celsius) = {1} (Kelvin) = {2} (Fahrenheit)\n",
                      temp1.ToString "C", temp1.ToString "K", temp1.ToString "F")

    // Call ToString with format string and format provider
    let temp1 = Temperature 100      
    let current = NumberFormatInfo.CurrentInfo
    let nl = CultureInfo "nl-NL"
    Console.WriteLine("{0} (Celsius) = {1} (Kelvin) = {2} (Fahrenheit)",
                      temp1.ToString("C", current), temp1.ToString("K", current), temp1.ToString("F", current))
    Console.WriteLine("{0} (Celsius) = {1} (Kelvin) = {2} (Fahrenheit)",
                      temp1.ToString("C", nl), temp1.ToString("K", nl), temp1.ToString("F", nl))
    0

// The example displays the following output:
//    0.00 °C (Celsius) = 273.15 K (Kelvin) = 32.00 °F (Fahrenheit)
//
//    -40.00 °C (Celsius) = 233.15 K (Kelvin) = -40.00 °F (Fahrenheit)
//    -40,00 °C (Celsius) = 233,15 K (Kelvin) = -40,00 °F (Fahrenheit)
//
//    32.00 °C (Celsius) = 305.15 K (Kelvin) = 89.60 °F (Fahrenheit)
//
//    100.00 °C (Celsius) = 373.15 K (Kelvin) = 212.00 °F (Fahrenheit)
//    100,00 °C (Celsius) = 373,15 K (Kelvin) = 212,00 °F (Fahrenheit)
Module Example
   Public Sub Main()
      ' Use composite formatting with format string in the format item.
      Dim temp1 As New Temperature(0)
      Console.WriteLine("{0:C} (Celsius) = {0:K} (Kelvin) = {0:F} (Fahrenheit)", temp1)
      Console.WriteLine()
      
      ' Use composite formatting with a format provider.
      temp1 = New Temperature(-40)
      Console.WriteLine(String.Format(CultureInfo.CurrentCulture, "{0:C} (Celsius) = {0:K} (Kelvin) = {0:F} (Fahrenheit)", temp1))
      Console.WriteLine(String.Format(New CultureInfo("fr-FR"), "{0:C} (Celsius) = {0:K} (Kelvin) = {0:F} (Fahrenheit)", temp1))
      Console.WriteLine()
      
      ' Call ToString method with format string.
      temp1 = New Temperature(32)
      Console.WriteLine("{0} (Celsius) = {1} (Kelvin) = {2} (Fahrenheit)", _
                        temp1.ToString("C"), temp1.ToString("K"), temp1.ToString("F"))
      Console.WriteLine()

      ' Call ToString with format string and format provider
      temp1 = New Temperature(100)      
      Dim current As NumberFormatInfo = NumberFormatInfo.CurrentInfo
      Dim nl As New CultureInfo("nl-NL") 
      Console.WriteLine("{0} (Celsius) = {1} (Kelvin) = {2} (Fahrenheit)", _
                        temp1.ToString("C", current), temp1.ToString("K", current), temp1.ToString("F", current))
      Console.WriteLine("{0} (Celsius) = {1} (Kelvin) = {2} (Fahrenheit)", _
                        temp1.ToString("C", nl), temp1.ToString("K", nl), temp1.ToString("F", nl))
   End Sub
End Module
' The example displays the following output:
'       0.00 °C (Celsius) = 273.15 K (Kelvin) = 32.00 °F (Fahrenheit)
'       
'       -40.00 °C (Celsius) = 233.15 K (Kelvin) = -40.00 °F (Fahrenheit)
'       -40,00 °C (Celsius) = 233,15 K (Kelvin) = -40,00 °F (Fahrenheit)
'       
'       32.00 °C (Celsius) = 305.15 K (Kelvin) = 89.60 °F (Fahrenheit)
'       
'       100.00 °C (Celsius) = 373.15 K (Kelvin) = 212.00 °F (Fahrenheit)
'       100,00 °C (Celsius) = 373,15 K (Kelvin) = 212,00 °F (Fahrenheit)

注解

IFormattable 接口基于格式字符串和格式提供程序将对象转换为其字符串表示形式。

格式字符串通常定义对象的常规外观。 例如,.NET Framework支持以下内容:

还可以定义自己的格式字符串以支持应用程序定义类型的格式设置。

格式提供程序返回一个格式对象,该对象通常定义用于将对象转换为其字符串表示形式的符号。 例如,将数字转换为货币值时,格式提供程序定义结果字符串中显示的货币符号。 .NET Framework定义三种格式提供程序:

此外,还可以定义自己的自定义格式提供程序,以提供格式设置中使用的区域性特定、特定于职业或行业特定的信息。 有关使用自定义格式提供程序实现自定义格式的详细信息,请参阅 ICustomFormatter

IFormattable 接口定义一个方法, ToString该方法为实现类型提供格式设置服务。 可以直接调用该方法 ToString 。 此外,它由Convert.ToString(Object)方法Convert.ToString(Object, IFormatProvider)以及使用.NET Framework中的复合格式设置功能的方法自动调用。 此类方法包括 Console.WriteLine(String, Object)String.Format等等 StringBuilder.AppendFormat(String, Object)。 该方法 ToString 针对方法的格式字符串中的每个格式项调用。

接口 IFormattable 由基数据类型实现。

实施者说明

需要对字符串 ToString() 格式设置进行更多控制而不是应实现 IFormattable的类。

实现的 IFormattable 类必须支持“G” (常规) 格式说明符。 除了“G”说明符,类还可以定义它支持的格式说明符列表。 此外,类必须准备好处理格式说明符。null 有关格式设置和格式设置代码的详细信息,请参阅 格式设置类型

方法

ToString(String, IFormatProvider)

使用指定格式对当前实例的值设置格式。

适用于

另请参阅