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Binder Class

Selects a member from a list of candidates, and performs type conversion from actual argument type to formal argument type.

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

[SerializableAttribute] 
[ClassInterfaceAttribute(ClassInterfaceType::AutoDual)] 
[ComVisibleAttribute(true)] 
public ref class Binder abstract
/** @attribute SerializableAttribute() */ 
/** @attribute ClassInterfaceAttribute(ClassInterfaceType.AutoDual) */ 
/** @attribute ComVisibleAttribute(true) */ 
public abstract class Binder
SerializableAttribute 
ClassInterfaceAttribute(ClassInterfaceType.AutoDual) 
ComVisibleAttribute(true) 
public abstract class Binder

Notes to Inheritors When you inherit from Binder, you must override the following members: BindToMethod, BindToField, SelectMethod, SelectProperty, and ChangeType.

The following example implements and demonstrates all members of the Binder class. The private method CanConvertFrom finds compatible types for a given type.

using namespace System;
using namespace System::Reflection;
using namespace System::Globalization;
using namespace System::Runtime::InteropServices;
public ref class MyBinder: public Binder
{
public:
   MyBinder()
      : Binder()
   {}

private:
   ref class BinderState
   {
   public:
      array<Object^>^args;
   };

public:
   virtual FieldInfo^ BindToField( BindingFlags bindingAttr, array<FieldInfo^>^match, Object^ value, CultureInfo^ culture ) override
   {
      if ( match == nullptr )
            throw gcnew ArgumentNullException( "match" );

      // Get a field for which the value parameter can be converted to the specified field type.
      for ( int i = 0; i < match->Length; i++ )
         if ( ChangeType( value, match[ i ]->FieldType, culture ) != nullptr )
                  return match[ i ];

      return nullptr;
   }

   virtual MethodBase^ BindToMethod( BindingFlags bindingAttr, array<MethodBase^>^match, array<Object^>^%args, array<ParameterModifier>^ modifiers, CultureInfo^ culture, array<String^>^names, [Out]Object^% state ) override
   {
      // Store the arguments to the method in a state Object*.
      BinderState^ myBinderState = gcnew BinderState;
      array<Object^>^arguments = gcnew array<Object^>(args->Length);
      args->CopyTo( arguments, 0 );
      myBinderState->args = arguments;
      state = myBinderState;
      if ( match == nullptr )
            throw gcnew ArgumentNullException;

      // Find a method that has the same parameters as those of the args parameter.
      for ( int i = 0; i < match->Length; i++ )
      {
         // Count the number of parameters that match.
         int count = 0;
         array<ParameterInfo^>^parameters = match[ i ]->GetParameters();

         // Go on to the next method if the number of parameters do not match.
         if ( args->Length != parameters->Length )
                  continue;

         // Match each of the parameters that the user expects the method to have.
         for ( int j = 0; j < args->Length; j++ )
         {
            // If the names parameter is not 0, then reorder args.
            if ( names != nullptr )
            {
               if ( names->Length != args->Length )
                              throw gcnew ArgumentException( "names and args must have the same number of elements." );

               for ( int k = 0; k < names->Length; k++ )
                  if ( String::Compare( parameters[ j ]->Name, names[ k ] ) == 0 )
                                    args[ j ] = myBinderState->args[ k ];
            }

            // Determine whether the types specified by the user can be converted to the parameter type.
            if ( ChangeType( args[ j ], parameters[ j ]->ParameterType, culture ) != nullptr )
                        count += 1;
            else
                        break;
         }
         if ( count == args->Length )
                  return match[ i ];
      }
      return nullptr;
   }

   virtual Object^ ChangeType( Object^ value, Type^ myChangeType, CultureInfo^ culture ) override
   {
      // Determine whether the value parameter can be converted to a value of type myType.
      if ( CanConvertFrom( value->GetType(), myChangeType ) )

      // Return the converted Object*.
      return Convert::ChangeType( value, myChangeType ); // Return 0.
      else
            0;
   }

   virtual void ReorderArgumentArray( array<Object^>^%args, Object^ state ) override
   {
      // Return the args that had been reordered by BindToMethod.
      (safe_cast<BinderState^>(state))->args->CopyTo( args, 0 );
   }

   virtual MethodBase^ SelectMethod( BindingFlags bindingAttr, array<MethodBase^>^match, array<Type^>^types, array<ParameterModifier>^ modifiers ) override
   {
      if ( match == nullptr )
            throw gcnew ArgumentNullException( "match" );

      for ( int i = 0; i < match->Length; i++ )
      {
         // Count the number of parameters that match.
         int count = 0;
         array<ParameterInfo^>^parameters = match[ i ]->GetParameters();

         // Go on to the next method if the number of parameters do not match.
         if ( types->Length != parameters->Length )
                  continue;

         // Match each of the parameters that the user expects the method to have.
         for ( int j = 0; j < types->Length; j++ )

            // Determine whether the types specified by the user can be converted to parameter type.
            if ( CanConvertFrom( types[ j ], parameters[ j ]->ParameterType ) )
                        count += 1;
            else
                        break;

         // Determine whether the method has been found.
         if ( count == types->Length )
                  return match[ i ];
      }
      return nullptr;
   }

   virtual PropertyInfo^ SelectProperty( BindingFlags bindingAttr, array<PropertyInfo^>^match, Type^ returnType, array<Type^>^indexes, array<ParameterModifier>^ modifiers ) override
   {
      if ( match == nullptr )
            throw gcnew ArgumentNullException( "match" );

      for ( int i = 0; i < match->Length; i++ )
      {
         // Count the number of indexes that match.
         int count = 0;
         array<ParameterInfo^>^parameters = match[ i ]->GetIndexParameters();

         // Go on to the next property if the number of indexes do not match.
         if ( indexes->Length != parameters->Length )
                  continue;

         // Match each of the indexes that the user expects the property to have.
         for ( int j = 0; j < indexes->Length; j++ )
            // Determine whether the types specified by the user can be converted to index type.
            if ( CanConvertFrom( indexes[ j ], parameters[ j ]->ParameterType ) )
                        count += 1;
            else
                        break;

         // Determine whether the property has been found.
         if ( count == indexes->Length )

         // Determine whether the return type can be converted to the properties type.
         if ( CanConvertFrom( returnType, match[ i ]->GetType() ) )
                  return match[ i ];
         else
                  continue;
      }
      return nullptr;
   }

private:

   // Determines whether type1 can be converted to type2. Check only for primitive types.
   bool CanConvertFrom( Type^ type1, Type^ type2 )
   {
      if ( type1->IsPrimitive && type2->IsPrimitive )
      {
         TypeCode typeCode1 = Type::GetTypeCode( type1 );
         TypeCode typeCode2 = Type::GetTypeCode( type2 );

         // If both type1 and type2 have the same type, return true.
         if ( typeCode1 == typeCode2 )
                  return true;

         // Possible conversions from Char follow.
         if ( typeCode1 == TypeCode::Char )
         {
            switch ( typeCode2 )
            {
               case TypeCode::UInt16:
                  return true;

               case TypeCode::UInt32:
                  return true;

               case TypeCode::Int32:
                  return true;

               case TypeCode::UInt64:
                  return true;

               case TypeCode::Int64:
                  return true;

               case TypeCode::Single:
                  return true;

               case TypeCode::Double:
                  return true;

               default:
                  return false;
            }
         }

         // Possible conversions from Byte follow.
         if ( typeCode1 == TypeCode::Byte )
         {
            switch ( typeCode2 )
            {
               case TypeCode::Char:
                  return true;

               case TypeCode::UInt16:
                  return true;

               case TypeCode::Int16:
                  return true;

               case TypeCode::UInt32:
                  return true;

               case TypeCode::Int32:
                  return true;

               case TypeCode::UInt64:
                  return true;

               case TypeCode::Int64:
                  return true;

               case TypeCode::Single:
                  return true;

               case TypeCode::Double:
                  return true;

               default:
                  return false;
            }
         }

         // Possible conversions from SByte follow.
         if ( typeCode1 == TypeCode::SByte )
         {
            switch ( typeCode2 )
            {
               case TypeCode::Int16:
                  return true;

               case TypeCode::Int32:
                  return true;

               case TypeCode::Int64:
                  return true;

               case TypeCode::Single:
                  return true;

               case TypeCode::Double:
                  return true;

               default:
                  return false;
            }
         }

         // Possible conversions from UInt16 follow.
         if ( typeCode1 == TypeCode::UInt16 )
         {
            switch ( typeCode2 )
            {
               case TypeCode::UInt32:
                  return true;

               case TypeCode::Int32:
                  return true;

               case TypeCode::UInt64:
                  return true;

               case TypeCode::Int64:
                  return true;

               case TypeCode::Single:
                  return true;

               case TypeCode::Double:
                  return true;

               default:
                  return false;
            }
         }

         // Possible conversions from Int16 follow.
         if ( typeCode1 == TypeCode::Int16 )
         {
            switch ( typeCode2 )
            {
               case TypeCode::Int32:
                  return true;

               case TypeCode::Int64:
                  return true;

               case TypeCode::Single:
                  return true;

               case TypeCode::Double:
                  return true;

               default:
                  return false;
            }
         }

         // Possible conversions from UInt32 follow.
         if ( typeCode1 == TypeCode::UInt32 )
         {
            switch ( typeCode2 )
            {
               case TypeCode::UInt64:
                  return true;

               case TypeCode::Int64:
                  return true;

               case TypeCode::Single:
                  return true;

               case TypeCode::Double:
                  return true;

               default:
                  return false;
            }
         }

         // Possible conversions from Int32 follow.
         if ( typeCode1 == TypeCode::Int32 )
         {
            switch ( typeCode2 )
            {
               case TypeCode::Int64:
                  return true;

               case TypeCode::Single:
                  return true;

               case TypeCode::Double:
                  return true;

               default:
                  return false;
            }
         }

         // Possible conversions from UInt64 follow.
         if ( typeCode1 == TypeCode::UInt64 )
         {
            switch ( typeCode2 )
            {
               case TypeCode::Single:
                  return true;

               case TypeCode::Double:
                  return true;

               default:
                  return false;
            }
         }

         // Possible conversions from Int64 follow.
         if ( typeCode1 == TypeCode::Int64 )
         {
            switch ( typeCode2 )
            {
               case TypeCode::Single:
                  return true;

               case TypeCode::Double:
                  return true;

               default:
                  return false;
            }
         }

         // Possible conversions from Single follow.
         if ( typeCode1 == TypeCode::Single )
         {
            switch ( typeCode2 )
            {
               case TypeCode::Double:
                  return true;

               default:
                  return false;
            }
         }
      }

      return false;
   }

};

public ref class MyClass1
{
public:
   short myFieldB;
   int myFieldA;
   void MyMethod( long i, char k )
   {
      Console::WriteLine( "\nThis is MyMethod(long i, char k)" );
   }

   void MyMethod( long i, long j )
   {
      Console::WriteLine( "\nThis is MyMethod(long i, long j)" );
   }
};

int main()
{
   // Get the type of MyClass1.
   Type^ myType = MyClass1::typeid;

   // Get the instance of MyClass1.
   MyClass1^ myInstance = gcnew MyClass1;
   Console::WriteLine( "\nDisplaying the results of using the MyBinder binder.\n" );

   // Get the method information for MyMethod.
   array<Type^>^types = {short::typeid,short::typeid};
   MethodInfo^ myMethod = myType->GetMethod( "MyMethod", static_cast<BindingFlags>(BindingFlags::Public | BindingFlags::Instance), gcnew MyBinder, types, nullptr );
   Console::WriteLine( myMethod );

   // Invoke MyMethod.
   array<Object^>^obj = {32,32};
   myMethod->Invoke( myInstance, BindingFlags::InvokeMethod, gcnew MyBinder, obj, CultureInfo::CurrentCulture );
}

import System.*;
import System.Reflection.*;
import System.Globalization.*;

public class MyBinder extends Binder
{
    public MyBinder()
    {
    } //MyBinder

    private class BinderState
    {
        public Object args[];
    } //BinderState

    public FieldInfo BindToField(BindingFlags bindingAttr, FieldInfo match[], 
        Object value, CultureInfo culture)
    {
        if (match == null) {
            throw new ArgumentNullException("match");
        }

        // Get a field for which the value parameter can be converted 
        // to the specified field type.
        for (int i = 0; i < match.length; i++) {
            if (ChangeType(value, 
                ((FieldInfo)match.get_Item(i)).get_FieldType(), culture) 
                != null) {
                return (FieldInfo)match.get_Item(i);
            }
        }

        return null;
    } //BindToField

    public MethodBase BindToMethod(BindingFlags bindingAttr, MethodBase match[],
        /**@ref
         */
        Object args[], ParameterModifier modifiers[], CultureInfo culture, 
        String names[],
        /**@ref
         */ Object state)
    {
        // Store the arguments to the method in a state object.
        BinderState myBinderState = new BinderState();
        Object arguments[] = new Object[args.length];

        args.CopyTo(arguments, 0);
        myBinderState.args = arguments;
        state = myBinderState;
        if (match == null) {
            throw new ArgumentNullException();
        }

        // Find a method that has the same parameters as those of the 
        // args parameter.
        for (int i = 0; i < match.length; i++) {
            // Count the number of parameters that match.
            int count = 0;
            ParameterInfo parameters[] = ((MethodBase)match.get_Item(i)).
                GetParameters();

            // Go on to the next method if the number of 
            // parameters do not match.
            if (args.length != parameters.length) {
                continue;
            }

            // Match each of the parameters that the user expects 
            // the method to have.
            for (int j = 0; j < args.length; j++) {
                // If the names parameter is not null, then reorder args.
                if (names != null) {
                    if (names.length != args.length) {
                        throw new ArgumentException("names and args must have "
                            + "the same number of elements.");
                    }

                    for (int k = 0; k < names.length; k++) {
                        if (String.Compare(((ParameterInfo)parameters.
                            get_Item(j)).get_Name(), 
                            names.get_Item(k).ToString()) == 0) {

                            args[j] = myBinderState.args.get_Item(k);
                        }
                    }
                }

                // Determine whether the types specified by the user can be 
                // converted to the parameter type.
                if (ChangeType(args[j], ((ParameterInfo)parameters.get_Item(j)).
                    get_ParameterType(), culture) != null) {
                    count += 1;
                }
                else {
                    break;
                }
            }  
            // Determine whether the method has been found.
            if (count == args.length) {
                return (MethodBase)match.get_Item(i);
            }
        }
        return null;
    } //BindToMethod

    public Object ChangeType(Object value, Type myChangeType, 
        CultureInfo culture)
    {
        // Determine whether the value parameter can be converted to a 
        // value of type myType.
        if (CanConvertFrom(value.GetType(), myChangeType)) {
            // Return the converted object.
            return Convert.ChangeType(value, myChangeType);
        }
        else {
            // Return null.
            return null;
        }
    } //ChangeType

    public void ReorderArgumentArray(
        /**@ref
         */Object args[], Object state)
    {
        // Return the args that had been reordered by BindToMethod.
        ((BinderState)state).args.CopyTo(args, 0);
    } //ReorderArgumentArray


    public MethodBase SelectMethod(BindingFlags bindingAttr, MethodBase match[], 
        Type types[], ParameterModifier modifiers[])
    {
        if (match == null) {
            throw new ArgumentNullException("match");
        }

        for (int i = 0; i < match.length; i++) {
            // Count the number of parameters that match.
            int count = 0;
            ParameterInfo parameters[] = ((MethodBase)match.get_Item(i)).
                GetParameters();

            // Go on to the next method if the number of parameters 
            // do not match.
            if (types.length != parameters.length) {
                continue;
            }

            // Match each of the parameters that the user expects 
            // the method  to have.
            for (int j = 0; j < types.length; j++) {
                // Determine whether the types specified by the user can be 
                // converted to parameter type.
                if (CanConvertFrom((Type)types.get_Item(j), 
                    ((ParameterInfo)parameters.get_Item(j)).
                    get_ParameterType())) {

                    count += 1;
                }
                else {
                    break;
                } 
            }
            // Determine whether the method has been found.
            if (count == types.length) {
                return (MethodBase)match.get_Item(i);
            }
        }

        return null;
    } //SelectMethod

    public PropertyInfo SelectProperty(BindingFlags bindingAttr, 
        PropertyInfo match[], Type returnType, Type indexes[], 
        ParameterModifier modifiers[])
    {
        if (match == null) {
            throw new ArgumentNullException("match");
        }

        for (int i = 0; i < match.length; i++) {
            // Count the number of indexes that match.
            int count = 0;
            ParameterInfo parameters[] = ((PropertyInfo)match.get_Item(i)).
                GetIndexParameters();

            // Go on to the next property if the number of indexes do not match.
            if (indexes.length != parameters.length) {
                continue;
            }

            // Match each of the indexes that the user expects 
            // the property to have.
            for (int j = 0; j < indexes.length; j++) {
                // Determine whether the types specified by the user 
                // can be converted to index type.
                if (CanConvertFrom((Type)indexes.get_Item(j), 
                    ((ParameterInfo)parameters.get_Item(j)).
                    get_ParameterType())) {

                    count += 1;
                }
                else {
                    break;
                } 
            }
            // Determine whether the property has been found.
            if (count == indexes.length) {
                // Determine whether the return type can be converted 
                // to the properties type.
                if (CanConvertFrom(returnType, match.get_Item(i).GetType())) {
                    return (PropertyInfo)match.get_Item(i);
                }
                else {
                    continue;
                }
            }
        }
        return null;
    } //SelectProperty

    // Determines whether type1 can be converted to type2. 
    // Check only for primitive types.
    private boolean CanConvertFrom(Type type1, Type type2)
    {
        if (type1.get_IsPrimitive() && type2.get_IsPrimitive()) {
            TypeCode typeCode1 = Type.GetTypeCode(type1);
            TypeCode typeCode2 = Type.GetTypeCode(type2);

            // If both type1 and type2 have the same type, return true.
            if (typeCode1.Equals(typeCode2)) {
                return true;
            }

            // Possible conversions from Char follow.
            if (typeCode1.Equals(TypeCode.Char)) {
                switch (typeCode2) {
                    case TypeCode.UInt16 :
                        return true;
                    case TypeCode.UInt32 : 
                        return true;
                    case TypeCode.Int32  : 
                        return true;
                    case TypeCode.UInt64 : 
                        return true;
                    case TypeCode.Int64  : 
                        return true;
                    case TypeCode.Single : 
                        return true;
                    case TypeCode.Double : 
                        return true;
                    default : 
                        return false;
                }
            }

            // Possible conversions from Byte follow.
            if (typeCode1.Equals(TypeCode.Byte)) {
                switch (typeCode2) {
                    case TypeCode.Char   : 
                        return true;
                    case TypeCode.UInt16 : 
                        return true;
                    case TypeCode.Int16  : 
                        return true;
                    case TypeCode.UInt32 : 
                        return true;
                    case TypeCode.Int32  : 
                        return true;
                    case TypeCode.UInt64 :
                        return true;
                    case TypeCode.Int64  :
                        return true;
                    case TypeCode.Single : 
                        return true;
                    case TypeCode.Double : 
                        return true;
                    default : 
                        return false;
                }
            }

            // Possible conversions from SByte follow.
            if (typeCode1.Equals(TypeCode.SByte)) {
                switch (typeCode2) {
                    case TypeCode.Int16  : 
                        return true;
                    case TypeCode.Int32  : 
                        return true;
                    case TypeCode.Int64  : 
                        return true;
                    case TypeCode.Single : 
                        return true;
                    case TypeCode.Double : 
                        return true;
                    default : 
                        return false;
                }
            }

            // Possible conversions from UInt16 follow.
            if (typeCode1.Equals(TypeCode.UInt16)) {
                switch (typeCode2) {
                    case TypeCode.UInt32 : 
                        return true;
                    case TypeCode.Int32  : 
                        return true;
                    case TypeCode.UInt64 : 
                        return true;
                    case TypeCode.Int64  : 
                        return true;
                    case TypeCode.Single : 
                        return true;
                    case TypeCode.Double : 
                        return true;
                    default : 
                        return false;
                }
            }

            // Possible conversions from Int16 follow.
            if (typeCode1.Equals(TypeCode.Int16)) {
                switch (typeCode2) {
                    case TypeCode.Int32  : 
                        return true;
                    case TypeCode.Int64  : 
                        return true;
                    case TypeCode.Single : 
                        return true;
                    case TypeCode.Double : 
                        return true;
                    default : 
                        return false;
                }
            }

            // Possible conversions from UInt32 follow.
            if (typeCode1.Equals(TypeCode.UInt32)) {
                switch (typeCode2) {
                    case TypeCode.UInt64 : 
                        return true;
                    case TypeCode.Int64  : 
                        return true;
                    case TypeCode.Single : 
                        return true;
                    case TypeCode.Double : 
                        return true;
                    default : 
                        return false;
                }
            }

            // Possible conversions from Int32 follow.
            if (typeCode1.Equals(TypeCode.Int32)) {
                switch (typeCode2) {
                    case TypeCode.Int64  : 
                        return true;
                    case TypeCode.Single : 
                        return true;
                    case TypeCode.Double : 
                        return true;
                    default : 
                        return false;
                }
            }

            // Possible conversions from UInt64 follow.
            if (typeCode1.Equals(TypeCode.UInt64)) {
                switch (typeCode2) {
                    case TypeCode.Single : 
                        return true;
                    case TypeCode.Double : 
                        return true;
                    default : 
                        return false;
                }
            }

            // Possible conversions from Int64 follow.
            if (typeCode1.Equals(TypeCode.Int64)) {
                switch (typeCode2) {
                    case TypeCode.Single : 
                        return true;
                    case TypeCode.Double : 
                        return true;
                    default : 
                        return false;
                }
            }

            // Possible conversions from Single follow.
            if (typeCode1.Equals(TypeCode.Single)) {
                switch (typeCode2) {
                    case TypeCode.Double : 
                        return true;
                    default : 
                        return false;
                }
            }
        }
        return false;
    } //CanConvertFrom
} //MyBinder

public class MyClass1
{
    public short myFieldB;
    public int myFieldA;

    public void MyMethod(long i, char k)
    {
        Console.WriteLine("\nThis is MyMethod(long i, char k)");
    } //MyMethod

    public void MyMethod(long i, long j)
    {
        Console.WriteLine("\nThis is MyMethod(long i, long j)");
    } //MyMethod
} //MyClass1

public class BinderExample
{
    public static void main(String[] args)
    {
        // Get the type of MyClass1.
        Type myType = MyClass1.class.ToType();

        // Get the instance of MyClass1.
        MyClass1 myInstance = new MyClass1();

        Console.WriteLine("\nDisplaying the results of using the "
            + "MyBinder binder.\n");

        // Get the method information for MyMethod.
        MethodInfo myMethod = myType.GetMethod("MyMethod", 
            BindingFlags.Public | BindingFlags.Instance, new MyBinder(), 
            new Type[] { short.class.ToType(), short.class.ToType() }, null);
        Console.WriteLine(myMethod);

        // Invoke MyMethod.
        myMethod.Invoke(myInstance, BindingFlags.InvokeMethod, new MyBinder(),
            new Object[] { (Int32)32, (Int32)32 }, 
            CultureInfo.get_CurrentCulture());
    } //main
} //BinderExample

System.Object
  System.Reflection.Binder

Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.

Windows 98, Windows 2000 SP4, Windows CE, Windows Millennium Edition, Windows Mobile for Pocket PC, Windows Mobile for Smartphone, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see System Requirements.

.NET Framework

Supported in: 2.0, 1.1, 1.0

.NET Compact Framework

Supported in: 2.0, 1.0

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