ParameterInfo.IsOptional 屬性

定義

命名空間:

System.Reflection

組件:

System.Runtime.dll

來源:

ParameterInfo.cs

取得值，指出這個參數是否為選擇項。

public:
 property bool IsOptional { bool get(); };

public bool IsOptional { get; }

member this.IsOptional : bool

Public ReadOnly Property IsOptional As Boolean

屬性值

Boolean

如果參數為選擇項，則為 true，否則為 false。

範例

下列範例示範如何測試、 ParameterAttributes.Out和 ParameterAttributes.Optional 屬性的方法參數ParameterAttributes.In。

此範例包含 DefineMethod 執行下列動作的方法：

• 建立包含 MyType 類型的動態元件。

• MyMethod將方法加入至 MyType。 MyMethod 有三個參數。 第一個參數是使用 ParameterAttributes.In定義，第二個參數則使用 ParameterAttributes.Out，第三個參數則使用 ParameterAttributes.Optional。

• 呼叫 TypeBuilder.CreateType 以完成類型。

執行 DefineMethod之後，此範例會搜尋目前載入的元件，直到找到動態元件為止。 它會從元件載入 MyType 、取得 MethodInfo 方法的 MyMethod 物件，並檢查參數。 此範例會使用 IsIn、 IsOut和 IsOptional 屬性來顯示參數的相關信息。

using namespace System;
using namespace System::Reflection;
using namespace System::Threading;
using namespace System::Reflection::Emit;
void DefineMethod()
{
   AssemblyName^ myAssemblyName = gcnew 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.
   array<Type^>^type1 = {int::typeid,short::typeid,long::typeid};
   MethodBuilder^ myMethodBuilder = myTypeBuilder->DefineMethod( "MyMethod", static_cast<MethodAttributes>(MethodAttributes::Public | MethodAttributes::HideBySig | MethodAttributes::Static), String::typeid, 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, "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, static_cast<ParameterAttributes>(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 S"ret" MSIL instruction.
   myILGenerator->Emit( OpCodes::Ret );

   // End the creation of the type.
   myTypeBuilder->CreateType();
}

int main()
{
   // Create a dynamic assembly with a type named MyType.
   DefineMethod();

   // Get the assemblies currently loaded in the application domain.
   array<Assembly^>^myAssemblies = Thread::GetDomain()->GetAssemblies();
   Assembly^ myAssembly = nullptr;

   // 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 != nullptr )
   {
      // 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.
      array<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" );
}

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");
        }
    }
}

Imports System.Reflection
Imports System.Threading
Imports System.Reflection.Emit

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
   
   
   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
End Class

備註

這個方法取決於選擇性的元數據旗標。 編譯程式可以插入此旗標，但編譯程式不一定要這麼做。

這個方法會 Optional 利用列舉值的 ParameterAttributes 旗標。

若要取得 ParameterInfo 陣列，請先取得 方法，然後呼叫 MethodBase.GetParameters。