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ParameterInfo.IsOptional Property

Gets a value indicating whether this parameter is optional.

Namespace: System.Reflection
Assembly: mscorlib (in mscorlib.dll)

public bool IsOptional { get; }
/** @property */
public boolean get_IsOptional ()

public function get IsOptional () : boolean

Not applicable.

Property Value

true if the parameter is optional; otherwise, false.

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.

The following example shows how to test method parameters for the ParameterAttributes.In, ParameterAttributes.Out, and ParameterAttributes.Optional attributes.

The example contains a DefineMethod method that does the following:

  • Creates a dynamic assembly containing a MyType type.

  • Adds a MyMethod method to MyType. MyMethod has three parameters. The first parameter is defined with ParameterAttributes.In, the second with ParameterAttributes.Out, and the third with ParameterAttributes.Optional.

  • Calls TypeBuilder.CreateType to complete the type.

After executing DefineMethod, the example searches the assemblies that are currently loaded until it finds the dynamic assembly. It loads MyType from the assembly, gets a MethodInfo object for the MyMethod method, and examines the parameters. The example uses the IsIn, IsOut, and IsOptional properties to display information about the parameters.


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");
   }
}

import System.*;  
import System.Reflection.*;  
import System.Threading.*;  
import System.Reflection.Emit.*;  

public class ParameterInfo_IsIn_IsOut_IsOptional
{
    public static void DefineMethod()
    {
        AssemblyName myAssemblyName = new AssemblyName();
        myAssemblyName.set_Name("MyAssembly");
        // Get the assembly builder from the application domain associated 
        // with the current thread.
        AssemblyBuilder myAssemblyBuilder = System.Threading.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, String.class.ToType(), 
            new Type[] { int.class.ToType(), short.class.ToType(),
            long.class.ToType() });
        // 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();
    } //DefineMethod

    public static void main(String[] args)
    {
        // Create a dynamic assembly with a type named MyType.
        DefineMethod();
        // Get the assemblies currently loaded in the application domain.
        Assembly myAssemblies[] = System.Threading.Thread.GetDomain().
            GetAssemblies();
        Assembly myAssembly = null;
        // Get the assembly named MyAssembly.
        for (int i = 0; i < myAssemblies.get_Length(); i++) {
            if (String.Compare(myAssemblies[i].GetName(false).get_Name(),
                "MyAssembly") == 0) {
                myAssembly = (Assembly)myAssemblies.get_Item(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, (Int32)myParameters.get_Length());
            // Print the IN, OUT and OPTIONAL attributes associated with 
            // each of the parameters.
            for (int i = 0; i < myParameters.get_Length(); i++) {
                if (myParameters[i].get_IsIn()) {
                    Console.WriteLine("\tThe {0} parameter has the In attribute",
                        (Int32)(i + 1));
                }
                if (myParameters[i].get_IsOptional()) {
                    Console.WriteLine("\tThe {0} parameter has the Optional "
                        + "attribute", (Int32)(i + 1));
                }
                if (myParameters[i].get_IsOut()) {
                    Console.WriteLine("\tThe {0} parameter has the Out "
                        + "attribute", (Int32)(i + 1));
                }
            }
        }
        else {
            Console.WriteLine("Could not find a assembly named 'MyAssembly' "
                + "for the current application domain");
        }
    } //main
} //ParameterInfo_IsIn_IsOut_IsOptional 

Windows 98, Windows Server 2000 SP4, Windows Millennium Edition, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition

The Microsoft .NET Framework 3.0 is supported on Windows Vista, Microsoft Windows XP SP2, and Windows Server 2003 SP1.

.NET Framework

Supported in: 3.0, 2.0, 1.1, 1.0

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