Missing Classe

Definizione

public ref class Missing sealed

public ref class Missing sealed : System::Runtime::Serialization::ISerializable

public sealed class Missing

[System.Runtime.InteropServices.ComVisible(true)]
[System.Serializable]
public sealed class Missing : System.Runtime.Serialization.ISerializable

public sealed class Missing : System.Runtime.Serialization.ISerializable

type Missing = class

[<System.Runtime.InteropServices.ComVisible(true)>]
[<System.Serializable>]
type Missing = class
    interface ISerializable

type Missing = class
    interface ISerializable

Public NotInheritable Class Missing

Public NotInheritable Class Missing
Implements ISerializable

Ereditarietà

Object

Missing

Attributi

ComVisibleAttribute SerializableAttribute

Implementazioni

ISerializable

Esempio

Nell'esempio seguente viene illustrato come utilizzare l'oggetto Missing per richiamare un metodo con un argomento predefinito tramite reflection.

using System;
using System.Reflection;

[assembly:CLSCompliant(true)]

public class MissingClass
{
   public static void MethodWithDefault(int value = 33)
   {
      Console.WriteLine("value = {0}", value);
   } 
}

public class Example
{
   public static void Main()
   {
      // Invoke without reflection
      MissingClass.MethodWithDefault();
      
      // Invoke by using reflection.
      Type t = typeof(MissingClass);
      MethodInfo mi = t.GetMethod("MethodWithDefault");
      mi.Invoke(null, new object[] { Missing.Value });
   }
}
// The example displays the following output:
//       value = 33  
//       value = 33

Imports System.Reflection

<Assembly:CLSCompliant(True)>

Public Class MissingClass
   Public Shared Sub MethodWithDefault(Optional value As Integer = 33)
      Console.WriteLine("value = {0}", value)
   End Sub 
End Class   

Public Module Example
   Public Sub Main()
      ' Invoke without reflection.
      MissingClass.MethodWithDefault()
      
      ' Invoke by using reflection.
      Dim t As Type = GetType(MissingClass)
      Dim mi As MethodInfo = t.GetMethod("MethodWithDefault")
      mi.Invoke(Nothing, { Missing.Value })
   End Sub
End Module
' The example displays the following output:
'       value = 33 
'       value = 33

Commenti

La Missing classe viene usata per richiamare un metodo con un argomento predefinito, in genere quando si usa la reflection.

Esiste una sola istanza di Missing, restituita dal Value campo .

Vedi anche

• DBNull