Type.Missing Alan

Tanım

Ad Alanı:

System

Bütünleştirilmiş Kod:

System.Runtime.dll

Bütünleştirilmiş Kod:

netstandard.dll

Bütünleştirilmiş Kod:

mscorlib.dll

Bilgilerde eksik bir değeri temsil Type eder. Bu alan salt okunur durumdadır.

public: static initonly System::Object ^ Missing;

public static readonly object Missing;

 staticval mutable Missing : obj

Public Shared ReadOnly Missing As Object 

Alan Değeri

Object

Örnekler

Aşağıdaki kod örneği, varsayılan bağımsız Missing değişkenleriyle bir yöntemi çağırmak için alanın kullanımını gösterir.

#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.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

Bu kod şu çıkışı oluşturur:

a = 10 b = 55,3 c = 12

a = 10 b = 1,3 c = 1

a = 10 b = 1,2 c = 1

Açıklamalar

Bir Missing parametrenin varsayılan değerini almak için yansıma aracılığıyla çağrı yapmak üzere alanını kullanın. Alan Missing bir parametre değeri için geçirildi ve bu parametre için varsayılan değer yoksa, ArgumentException bir atılan.

Ayrıca bkz.

• Missing