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ParameterInfo.IsOptional Property

Gets a value indicating whether this parameter is optional.

[Visual Basic]
Public ReadOnly Property IsOptional As Boolean
[C#]
public bool IsOptional {get;}
[C++]
public: __property bool get_IsOptional();
[JScript]
public function get IsOptional() : Boolean;

Property Value

true if the parameter is optional; otherwise, false.

Remarks

This method depends on an optional metadata flag. This flag can be inserted by compilers, but the compilers are not obligated to do so.

This method utilizes the Optional flag of the ParameterAttributes enumerator.

To get the ParameterInfo array, first get the method and then call MethodBase.GetParameters.

Example

[Visual Basic] 
Imports System
Imports System.Reflection
Imports System.Threading
Imports System.Reflection.Emit
Imports Microsoft.VisualBasic



Public Class ParameterInfo_IsIn_IsOut_IsOptional
   
   Public Shared Sub DefineMethod()
      Dim myAssemblyName As New AssemblyName()
      myAssemblyName.Name = "MyAssembly"
      ' Get the assesmbly builder from the application domain associated with the current thread.
      Dim myAssemblyBuilder As AssemblyBuilder = Thread.GetDomain().DefineDynamicAssembly(myAssemblyName, AssemblyBuilderAccess.RunAndSave)
      ' Create a dynamic module in the assembly.
      Dim myModuleBuilder As ModuleBuilder = myAssemblyBuilder.DefineDynamicModule("MyModule", "MyAssembly.dll")
      ' Create a type in the module.
      Dim myTypeBuilder As TypeBuilder = myModuleBuilder.DefineType("MyType")
      ' Create a method called MyMethod.
      Dim myMethodBuilder As MethodBuilder = myTypeBuilder.DefineMethod("MyMethod", MethodAttributes.Public Or MethodAttributes.HideBySig Or MethodAttributes.Static, GetType(String), New Type() {GetType(Integer), GetType(Short), GetType(Long)})
      ' Set the attributes for the parameters of the method.
      ' Set the attribute for the first parameter to IN.
      Dim myParameterBuilder As ParameterBuilder = myMethodBuilder.DefineParameter(1, ParameterAttributes.In, "MyIntParameter")
      ' Set the attribute for the second parameter to OUT.
      myParameterBuilder = myMethodBuilder.DefineParameter(2, ParameterAttributes.Out, "MyShortParameter")
      ' Set the attribute for the third parameter to OPTIONAL.
      myParameterBuilder = myMethodBuilder.DefineParameter(3, ParameterAttributes.Optional Or ParameterAttributes.HasDefault, "MyLongParameter")
      ' Get the Microsoft Intermediate Language generator for the method.
      Dim myILGenerator As ILGenerator = myMethodBuilder.GetILGenerator()
      ' Use the utility method to generate the MSIL instructions that print a string to the console.
      myILGenerator.EmitWriteLine("Hello World!")
      ' Generate the "ret" MSIL instruction.
      myILGenerator.Emit(OpCodes.Ret)
      ' End the creation of the type.
      myTypeBuilder.CreateType()
   End Sub 'DefineMethod
   
   
   Public Shared Sub Main()
      ' Create a dynamic assembly with a type named 'MyType'.
      DefineMethod()
      
      ' Get the assemblies currently loaded in the application domain.
      Dim myAssemblies As [Assembly]() = Thread.GetDomain().GetAssemblies()
      Dim myAssembly As [Assembly] = Nothing
      ' Get the assembly named MyAssembly.
      Dim i As Integer
      For i = 0 To myAssemblies.Length - 1
         If [String].Compare(myAssemblies(i).GetName(False).Name, "MyAssembly") = 0 Then
            myAssembly = myAssemblies(i)
         End If 
      Next i
      If Not (myAssembly Is Nothing) Then
         ' Get a type named MyType.
         Dim myType As Type = myAssembly.GetType("MyType")
         ' Get a method named MyMethod from the type.
         Dim myMethodBase As MethodBase = myType.GetMethod("MyMethod")
         ' Get the parameters associated with the method.
         Dim myParameters As ParameterInfo() = myMethodBase.GetParameters()
         Console.WriteLine(ControlChars.Cr + "The method {0} has the {1} parameters :", myMethodBase, myParameters.Length)
         ' Print the IN, OUT and OPTIONAL attributes associated with each of the parameters.
         For i = 0 To myParameters.Length - 1
            If myParameters(i).IsIn Then
               Console.WriteLine(ControlChars.Tab + "The {0} parameter has the In attribute", i + 1)
            End If
            If myParameters(i).IsOptional Then
               Console.WriteLine(ControlChars.Tab + "The {0} parameter has the Optional attribute", i + 1)
            End If
            If myParameters(i).IsOut Then
               Console.WriteLine(ControlChars.Tab + "The {0} parameter has the Out attribute", i + 1)
            End If
         Next i
      Else
         Console.WriteLine("Could not find a assembly named 'MyAssembly' for the current application domain")
      End If
   End Sub 'Main
End Class 'ParameterInfo_IsIn_IsOut_IsOptional 

[C#] 

using System;
using System.Reflection;
using System.Threading;
using System.Reflection.Emit;

public class ParameterInfo_IsIn_IsOut_IsOptional
{
   public static void DefineMethod()
   {
      AssemblyName myAssemblyName = new AssemblyName();
      myAssemblyName.Name = "MyAssembly";
      // Get the assembly builder from the application domain associated with the current thread.
      AssemblyBuilder myAssemblyBuilder = Thread.GetDomain().DefineDynamicAssembly(myAssemblyName, AssemblyBuilderAccess.RunAndSave);
      // Create a dynamic module in the assembly.
      ModuleBuilder myModuleBuilder = myAssemblyBuilder.DefineDynamicModule("MyModule", "MyAssembly.dll");
      // Create a type in the module.
      TypeBuilder myTypeBuilder = myModuleBuilder.DefineType("MyType");
      // Create a method called MyMethod.
      MethodBuilder myMethodBuilder = myTypeBuilder.DefineMethod("MyMethod",MethodAttributes.Public | MethodAttributes.HideBySig |
                                                                           MethodAttributes.Static, typeof(string), new Type[] {typeof(int), typeof(short), typeof(long)});
      // Set the attributes for the parameters of the method.
      // Set the attribute for the first parameter to IN.
      ParameterBuilder myParameterBuilder = myMethodBuilder.DefineParameter(1, ParameterAttributes.In, "MyIntParameter");
      // Set the attribute for the second parameter to OUT.
      myParameterBuilder = myMethodBuilder.DefineParameter(2, ParameterAttributes.Out, "MyShortParameter");
      // Set the attribute for the third parameter to OPTIONAL.
      myParameterBuilder = myMethodBuilder.DefineParameter(3, ParameterAttributes.Optional | ParameterAttributes.HasDefault, "MyLongParameter");
      // Get the Microsoft Intermediate Language generator for the method.
      ILGenerator myILGenerator = myMethodBuilder.GetILGenerator();
      // Use the utility method to generate the MSIL instructions that print a string to the console.
      myILGenerator.EmitWriteLine("Hello World!");
      // Generate the "ret" MSIL instruction.
      myILGenerator.Emit(OpCodes.Ret);
      // End the creation of the type.
      myTypeBuilder.CreateType();
   }

   public static void Main()
   {
      // Create a dynamic assembly with a type named MyType.
      DefineMethod();

      // Get the assemblies currently loaded in the application domain.
      Assembly[] myAssemblies = Thread.GetDomain().GetAssemblies();
      Assembly myAssembly = null;
      // Get the assembly named MyAssembly.
      for(int i = 0; i < myAssemblies.Length; i++)
         if(String.Compare(myAssemblies[i].GetName(false).Name, "MyAssembly") == 0)
            myAssembly = myAssemblies[i];

      if(myAssembly != null)
      {
         // Get a type named MyType.
         Type myType = myAssembly.GetType("MyType");
         // Get a method named MyMethod from the type.
         MethodBase myMethodBase = myType.GetMethod("MyMethod");
         // Get the parameters associated with the method.
         ParameterInfo[] myParameters = myMethodBase.GetParameters();
         Console.WriteLine("\nThe method {0} has the {1} parameters :", 
            myMethodBase, myParameters.Length);
         // Print the IN, OUT and OPTIONAL attributes associated with each of the parameters.
         for(int i = 0; i < myParameters.Length; i++)
         {
            if(myParameters[i].IsIn)
               Console.WriteLine("\tThe {0} parameter has the In attribute", 
                                       i + 1);
            if(myParameters[i].IsOptional)
               Console.WriteLine("\tThe {0} parameter has the Optional attribute",
                                       i + 1);
            if(myParameters[i].IsOut)
               Console.WriteLine("\tThe {0} parameter has the Out attribute",
                                       i + 1);
         }
      }
      else
         Console.WriteLine("Could not find a assembly named 'MyAssembly' for the current application domain");
   }
}

[C++] 

#using <mscorlib.dll>

using namespace System;
using namespace System::Reflection;
using namespace System::Threading;
using namespace System::Reflection::Emit;

public __gc class ParameterInfo_IsIn_IsOut_IsOptional
{
public:
   static void DefineMethod()
   {
      AssemblyName* myAssemblyName = new AssemblyName();
      myAssemblyName->Name = S"MyAssembly";
      // Get the assembly builder from the application domain associated with the current thread.
      AssemblyBuilder* myAssemblyBuilder = Thread::GetDomain()->DefineDynamicAssembly(myAssemblyName, AssemblyBuilderAccess::RunAndSave);
      // Create a dynamic module in the assembly.
      ModuleBuilder* myModuleBuilder = myAssemblyBuilder->DefineDynamicModule(S"MyModule", S"MyAssembly.dll");
      // Create a type in the module.
      TypeBuilder* myTypeBuilder = myModuleBuilder->DefineType(S"MyType");
      // Create a method called MyMethod.
      Type* type1[] = {__typeof(int), __typeof(short), __typeof(long)};
      MethodBuilder* myMethodBuilder = myTypeBuilder->DefineMethod(S"MyMethod",
         static_cast<MethodAttributes>(MethodAttributes::Public | MethodAttributes::HideBySig | MethodAttributes::Static),
         __typeof(String), type1);
      // Set the attributes for the parameters of the method.
      // Set the attribute for the first parameter to IN.
      ParameterBuilder* myParameterBuilder = myMethodBuilder->DefineParameter(1, ParameterAttributes::In, S"MyIntParameter");
      // Set the attribute for the second parameter to OUT.
      myParameterBuilder = myMethodBuilder->DefineParameter(2, ParameterAttributes::Out, S"MyShortParameter");
      // Set the attribute for the third parameter to OPTIONAL.
      myParameterBuilder = myMethodBuilder->DefineParameter(3, 
         static_cast<ParameterAttributes>(ParameterAttributes::Optional | ParameterAttributes::HasDefault), S"MyLongParameter");
      // Get the Microsoft Intermediate Language generator for the method.
      ILGenerator* myILGenerator = myMethodBuilder->GetILGenerator();
      // Use the utility method to generate the MSIL instructions that print a String* to the console.
      myILGenerator->EmitWriteLine(S"Hello World!");
      // Generate the S"ret" MSIL instruction.
      myILGenerator->Emit(OpCodes::Ret);
      // End the creation of the type.
      myTypeBuilder->CreateType();
   }
};
void main()
{
   // Create a dynamic assembly with a type named MyType.
   ParameterInfo_IsIn_IsOut_IsOptional::DefineMethod();

   // Get the assemblies currently loaded in the application domain.
   Assembly* myAssemblies[] = Thread::GetDomain()->GetAssemblies();
   Assembly* myAssembly = 0;
   // Get the assembly named MyAssembly.
   for (int i = 0; i < myAssemblies->Length; i++)
      if (String::Compare(myAssemblies[i]->GetName(false)->Name, S"MyAssembly") == 0)
         myAssembly = myAssemblies[i];

   if (myAssembly != 0) {
      // Get a type named MyType.
      Type* myType = myAssembly->GetType(S"MyType");
      // Get a method named MyMethod from the type.
      MethodBase* myMethodBase = myType->GetMethod(S"MyMethod");
      // Get the parameters associated with the method.
      ParameterInfo* myParameters[] = myMethodBase->GetParameters();
      Console::WriteLine(S"\nThe method {0} has the {1} parameters :", 
         myMethodBase, __box(myParameters->Length));
      // Print the IN, OUT and OPTIONAL attributes associated with each of the parameters.
      for (int i = 0; i < myParameters->Length; i++) {
         if (myParameters[i]->IsIn)
            Console::WriteLine(S"\tThe {0} parameter has the In attribute", 
            __box(i + 1));
         if (myParameters[i]->IsOptional)
            Console::WriteLine(S"\tThe {0} parameter has the Optional attribute",
            __box(i + 1));
         if (myParameters[i]->IsOut)
            Console::WriteLine(S"\tThe {0} parameter has the Out attribute",
            __box(i + 1));
      }
   } else
      Console::WriteLine(S"Could not find a assembly named 'MyAssembly' for the current application domain");
}

[JScript] No example is available for JScript. To view a Visual Basic, C#, or C++ example, click the Language Filter button Language Filter in the upper-left corner of the page.

Requirements

Platforms: Windows 98, Windows NT 4.0, Windows Millennium Edition, Windows 2000, Windows XP Home Edition, Windows XP Professional, Windows Server 2003 family

See Also

ParameterInfo Class | ParameterInfo Members | System.Reflection Namespace

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