Type.Missing Type.Missing Type.Missing Type.Missing Field

Definition

Stellt einen in den Type-Informationen fehlenden Wert dar.Represents a missing value in the Type information. Dieses Feld ist schreibgeschützt.This field is read-only.

public: static initonly System::Object ^ Missing;
public static readonly object Missing;
 staticval mutable Missing : obj
Public Shared ReadOnly Missing As Object 

Feldwert

Beispiele

Das folgende Codebeispiel zeigt die Verwendung der Missing Feld, eine Methode mit ihren Standardargumenten aufzurufen.The following code example shows the use of the Missing field to invoke a method with its default arguments.

#using <System.dll>

using namespace System;
using namespace System::Reflection;
using namespace System::CodeDom::Compiler;

ref class Example
{
public:
    static void Main()
    {
        // VB source for example. Not all versions of CS and CPP compilers
        // support optional arguments.
        String^ codeLines =
            "Imports System\n\n" +
            "Public Class OptionalArg\n" +
            "  Public Sub MyMethod(ByVal a As Integer, _\n" +
            "    Optional ByVal b As Double = 1.2, _\n" +
            "    Optional ByVal c As Integer = 1)\n\n" +
            "    Console.WriteLine(\"a = \" & a & \" b = \" & b & \" c = \" & c)\n" +
            "  End Sub\n" +
            "End Class\n";

        // Generate a OptionalArg instance from the source above.
        Object^ o = GenerateObjectFromSource("OptionalArg", codeLines, "VisualBasic");
        Type^ t;

        t = o->GetType();
        BindingFlags bf = BindingFlags::Public | BindingFlags::Instance |
            BindingFlags::InvokeMethod | BindingFlags::OptionalParamBinding;

        t->InvokeMember("MyMethod", bf, nullptr, o, gcnew array<Object^> {10, 55.3, 12});
        t->InvokeMember("MyMethod", bf, nullptr, o, gcnew array<Object^> {10, 1.3, Type::Missing});
        t->InvokeMember("MyMethod", bf, nullptr, o, gcnew array<Object^> {10, Type::Missing, Type::Missing});
    }

private:
    static Object^ GenerateObjectFromSource(String^ objectName,
        String^ sourceLines, String^ providerName)
    {
        Object^ genObject = nullptr;
        CodeDomProvider^ codeProvider = CodeDomProvider::CreateProvider(providerName);
        CompilerParameters^ cp = gcnew CompilerParameters();

        cp->GenerateExecutable = false;
        cp->GenerateInMemory = true;

        CompilerResults^ results =
            codeProvider->CompileAssemblyFromSource(cp, sourceLines);
        if (results->Errors->Count == 0)
        {
            genObject = results->CompiledAssembly->CreateInstance(objectName);
        }

        return genObject;
    }
};

int main()
{
    Example::Main();
}
using System;
using System.Reflection;
using System.CodeDom.Compiler;

class Example
{
    public static void Main()
    {
        // VB source for example. Not all versions of CS and CPP compilers
        // support optional arguments.
        string codeLines =
            "Imports System\n\n" +
            "Public Class OptionalArg\n" +
            "  Public Sub MyMethod(ByVal a As Integer, _\n" +
            "    Optional ByVal b As Double = 1.2, _\n" +
            "    Optional ByVal c As Integer = 1)\n\n" +
            "    Console.WriteLine(\"a = \" & a & \" b = \" & b & \" c = \" & c)\n" +
            "  End Sub\n" +
            "End Class\n";

        // Generate a OptionalArg instance from the source above.
        object o = GenerateObjectFromSource("OptionalArg", codeLines, "VisualBasic");
        Type t;

        t = o.GetType();
        BindingFlags bf = BindingFlags.Public | BindingFlags.Instance |
            BindingFlags.InvokeMethod | BindingFlags.OptionalParamBinding;

        t.InvokeMember("MyMethod", bf, null, o, new object[] {10, 55.3, 12});
        t.InvokeMember("MyMethod", bf, null, o, new object[] {10, 1.3, Type.Missing});
        t.InvokeMember("MyMethod", bf, null, o, new object[] {10, Type.Missing, Type.Missing});
    }

    private static object GenerateObjectFromSource(string objectName,
        string sourceLines, string providerName)
    {
        object genObject = null;
        CodeDomProvider codeProvider = CodeDomProvider.CreateProvider(providerName);
        CompilerParameters cp = new CompilerParameters();

        cp.GenerateExecutable = false;
        cp.GenerateInMemory = true;

        CompilerResults results =
            codeProvider.CompileAssemblyFromSource(cp, sourceLines);
        if (results.Errors.Count == 0)
        {
            genObject = results.CompiledAssembly.CreateInstance(objectName);
        }

        return genObject;
    }
}
Imports System
Imports System.Reflection

Public Class OptionalArg
    Public Sub MyMethod(ByVal a As Integer, _
        Optional ByVal b As Double = 1.2, _
        Optional ByVal c As Integer = 1)
        
        Console.WriteLine("a = " & a & " b = " & b & " c = " & c)
    End Sub
End Class

Class Example
    Public Shared Sub Main()
        Dim o As New OptionalArg()
        Dim t As Type
        t = GetType(OptionalArg)

        Dim bf As BindingFlags = _
            BindingFlags.Public Or BindingFlags.Instance Or _
            BindingFlags.InvokeMethod Or BindingFlags.OptionalParamBinding

        t.InvokeMember("MyMethod", bf, Nothing, o, New Object() {10, 55.3, 12})
        t.InvokeMember("MyMethod", bf, Nothing, o, New Object() {10, 1.3, Type.Missing})
        t.InvokeMember("MyMethod", bf, Nothing, o, New Object() {10, Type.Missing, Type.Missing})
    End Sub
End Class

Dieser Code erzeugt die folgende Ausgabe:This code produces the following output:

eine = 10 b = 55.3 c = 12a = 10 b = 55.3 c = 12

eine = 10 b = 1.3 c = 1a = 10 b = 1.3 c = 1

eine = 10 b 1.2 c = 1 =a = 10 b = 1.2 c = 1

Hinweise

Verwenden der Missing Feld in einem Aufruf über Reflektion, um den Standardwert eines Parameters zu erhalten.Use the Missing field for invocation through reflection to obtain the default value of a parameter. Wenn die Missing Feld für einen Parameterwert übergeben, und es gibt keinen Standardwert für diesen Parameter ein ArgumentException ausgelöst.If the Missing field is passed in for a parameter value and there is no default value for that parameter, an ArgumentException is thrown.

Gilt für:

Siehe auch