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ConstructorBuilder::GetILGenerator Method ()

 

Gets an ILGenerator for this constructor.

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

public:
ILGenerator^ GetILGenerator()

Return Value

Type: System.Reflection.Emit::ILGenerator^

Returns an ILGenerator object for this constructor.

Exception Condition
InvalidOperationException

The constructor is a default constructor.

-or-

The constructor has MethodAttributes or MethodImplAttributes flags indicating that it should not have a method body.

The runtime generates the code for default constructors. Therefore, if an attempt is made to obtain an ILGenerator, an exception will be thrown.

The following code sample illustrates the use of the GetILGenerator method.

using namespace System;
using namespace System::Threading;
using namespace System::Reflection;
using namespace System::Reflection::Emit;
Type^ DynamicPointTypeGen()
{
   Type^ pointType = nullptr;
   array<Type^>^temp0 = {int::typeid,int::typeid,int::typeid};
   array<Type^>^ctorParams = temp0;
   AppDomain^ myDomain = Thread::GetDomain();
   AssemblyName^ myAsmName = gcnew AssemblyName;
   myAsmName->Name = "MyDynamicAssembly";
   AssemblyBuilder^ myAsmBuilder = myDomain->DefineDynamicAssembly( myAsmName, AssemblyBuilderAccess::RunAndSave );
   ModuleBuilder^ pointModule = myAsmBuilder->DefineDynamicModule( "PointModule", "Point.dll" );
   TypeBuilder^ pointTypeBld = pointModule->DefineType( "Point", TypeAttributes::Public );
   FieldBuilder^ xField = pointTypeBld->DefineField( "x", int::typeid, FieldAttributes::Public );
   FieldBuilder^ yField = pointTypeBld->DefineField( "y", int::typeid, FieldAttributes::Public );
   FieldBuilder^ zField = pointTypeBld->DefineField( "z", int::typeid, FieldAttributes::Public );
   Type^ objType = Type::GetType( "System.Object" );
   ConstructorInfo^ objCtor = objType->GetConstructor( gcnew array<Type^>(0) );
   ConstructorBuilder^ pointCtor = pointTypeBld->DefineConstructor( MethodAttributes::Public, CallingConventions::Standard, ctorParams );
   ILGenerator^ ctorIL = pointCtor->GetILGenerator();

   // NOTE: ldarg.0 holds the "this" reference - ldarg.1, ldarg.2, and ldarg.3
   // hold the actual passed parameters. ldarg.0 is used by instance methods
   // to hold a reference to the current calling bject instance. Static methods
   // do not use arg.0, since they are not instantiated and hence no reference
   // is needed to distinguish them.
   ctorIL->Emit( OpCodes::Ldarg_0 );

   // Here, we wish to create an instance of System::Object by invoking its
   // constructor, as specified above.
   ctorIL->Emit( OpCodes::Call, objCtor );

   // Now, we'll load the current instance in arg 0, along
   // with the value of parameter "x" stored in arg 1, into stfld.
   ctorIL->Emit( OpCodes::Ldarg_0 );
   ctorIL->Emit( OpCodes::Ldarg_1 );
   ctorIL->Emit( OpCodes::Stfld, xField );

   // Now, we store arg 2 "y" in the current instance with stfld.
   ctorIL->Emit( OpCodes::Ldarg_0 );
   ctorIL->Emit( OpCodes::Ldarg_2 );
   ctorIL->Emit( OpCodes::Stfld, yField );

   // Last of all, arg 3 "z" gets stored in the current instance.
   ctorIL->Emit( OpCodes::Ldarg_0 );
   ctorIL->Emit( OpCodes::Ldarg_3 );
   ctorIL->Emit( OpCodes::Stfld, zField );

   // Our work complete, we return.
   ctorIL->Emit( OpCodes::Ret );

   // Now, let's create three very simple methods so we can see our fields.
   array<String^>^temp1 = {"GetX","GetY","GetZ"};
   array<String^>^mthdNames = temp1;
   System::Collections::IEnumerator^ myEnum = mthdNames->GetEnumerator();
   while ( myEnum->MoveNext() )
   {
      String^ mthdName = safe_cast<String^>(myEnum->Current);
      MethodBuilder^ getFieldMthd = pointTypeBld->DefineMethod( mthdName, MethodAttributes::Public, int::typeid, nullptr );
      ILGenerator^ mthdIL = getFieldMthd->GetILGenerator();
      mthdIL->Emit( OpCodes::Ldarg_0 );
      if ( mthdName->Equals( "GetX" ) )
            mthdIL->Emit( OpCodes::Ldfld, xField );
      else
      if ( mthdName->Equals( "GetY" ) )
            mthdIL->Emit( OpCodes::Ldfld, yField );
      else
      if ( mthdName->Equals( "GetZ" ) )
            mthdIL->Emit( OpCodes::Ldfld, zField );



      mthdIL->Emit( OpCodes::Ret );
   }

   pointType = pointTypeBld->CreateType();

   // Let's save it, just for posterity.
   myAsmBuilder->Save( "Point.dll" );
   return pointType;
}

int main()
{
   Type^ myDynamicType = nullptr;
   Object^ aPoint = nullptr;
   array<Type^>^temp2 = {int::typeid,int::typeid,int::typeid};
   array<Type^>^aPtypes = temp2;
   array<Object^>^temp3 = {4,5,6};
   array<Object^>^aPargs = temp3;

   // Call the  method to build our dynamic class.
   myDynamicType = DynamicPointTypeGen();
   Console::WriteLine( "Some information about my new Type '{0}':", myDynamicType->FullName );
   Console::WriteLine( "Assembly: '{0}'", myDynamicType->Assembly );
   Console::WriteLine( "Attributes: '{0}'", myDynamicType->Attributes );
   Console::WriteLine( "Module: '{0}'", myDynamicType->Module );
   Console::WriteLine( "Members: " );
   System::Collections::IEnumerator^ myEnum = myDynamicType->GetMembers()->GetEnumerator();
   while ( myEnum->MoveNext() )
   {
      MemberInfo^ member = safe_cast<MemberInfo^>(myEnum->Current);
      Console::WriteLine( "-- {0} {1};", member->MemberType, member->Name );
   }

   Console::WriteLine( "---" );

   // Let's take a look at the constructor we created.
   ConstructorInfo^ myDTctor = myDynamicType->GetConstructor( aPtypes );
   Console::WriteLine( "Constructor: {0};", myDTctor );
   Console::WriteLine( "---" );

   // Now, we get to use our dynamically-created class by invoking the constructor.
   aPoint = myDTctor->Invoke( aPargs );
   Console::WriteLine( "aPoint is type {0}.", aPoint->GetType() );

   // Finally, let's reflect on the instance of our new type - aPoint - and
   // make sure everything proceeded according to plan.
   Console::WriteLine( "aPoint.x = {0}", myDynamicType->InvokeMember( "GetX", BindingFlags::InvokeMethod, nullptr, aPoint, gcnew array<Object^>(0) ) );
   Console::WriteLine( "aPoint.y = {0}", myDynamicType->InvokeMember( "GetY", BindingFlags::InvokeMethod, nullptr, aPoint, gcnew array<Object^>(0) ) );
   Console::WriteLine( "aPoint.z = {0}", myDynamicType->InvokeMember( "GetZ", BindingFlags::InvokeMethod, nullptr, aPoint, gcnew array<Object^>(0) ) );

   // +++ OUTPUT +++
   // Some information about my new Type 'Point':
   // Assembly: 'MyDynamicAssembly, Version=0.0.0.0'
   // Attributes: 'AutoLayout, AnsiClass, NotPublic, Public'
   // Module: 'PointModule'
   // Members:
   // -- Field x;
   // -- Field y;
   // -- Field z;
   // -- Method GetHashCode;
   // -- Method Equals;
   // -- Method ToString;
   // -- Method GetType;
   // -- Constructor .ctor;
   // ---
   // Constructor: Void .ctor(Int32, Int32, Int32);
   // ---
   // aPoint is type Point.
   // aPoint.x = 4
   // aPoint.y = 5
   // aPoint.z = 6
}

.NET Framework
Available since 1.1
Silverlight
Available since 2.0
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