Article
11/17/2011

Binder Class

Microsoft Silverlight will reach end of support after October 2021. Learn more.

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

Inheritance Hierarchy

System.Object
System.Reflection.Binder

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

Syntax

'Declaration
<ClassInterfaceAttribute(ClassInterfaceType.AutoDual)> _
<ComVisibleAttribute(True)> _
Public MustInherit Class Binder

[ClassInterfaceAttribute(ClassInterfaceType.AutoDual)]
[ComVisibleAttribute(true)]
public abstract class Binder

The Binder type exposes the following members.

Constructors

	Name	Description
	Binder	Initializes a new instance of the Binder class.

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Methods

	Name	Description
	BindToField	Selects a field from the given set of fields, based on the specified criteria.
	BindToMethod	Selects a method to invoke from the given set of methods, based on the supplied arguments.
	ChangeType	Changes the type of the given Object to the given Type.
	Equals(Object)	Determines whether the specified Object is equal to the current Object. (Inherited from Object.)
	Finalize	Allows an object to try to free resources and perform other cleanup operations before the Object is reclaimed by garbage collection. (Inherited from Object.)
	GetHashCode	Serves as a hash function for a particular type. (Inherited from Object.)
	GetType	Gets the Type of the current instance. (Inherited from Object.)
	MemberwiseClone	Creates a shallow copy of the current Object. (Inherited from Object.)
	ReorderArgumentArray	Upon returning from BindToMethod, restores the args argument to what it was when it came from BindToMethod.
	SelectMethod	Selects a method from the given set of methods, based on the argument type.
	SelectProperty	Selects a property from the given set of properties, based on the specified criteria.
	ToString	Returns a string that represents the current object. (Inherited from Object.)

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Remarks

Implementations of the Binder class are used by methods such as Type.InvokeMember, which selects from a set of possible members to execute, based on a set of parameter types and argument values; Type.GetMethod, which selects a method based on parameter types; and so on.

A default implementation of the Binder class is provided by the Type.DefaultBinder property.

Notes to Inheritors

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

Examples

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

Note:
To run this example, see Building Examples That Use a Demo Method and a TextBlock Control.

Imports System.Reflection
Imports System.Globalization
Imports System.Threading

Public Class MyBinder
   Inherits Binder
   Public Sub New()
      MyBase.new()
   End Sub 
   Private Class BinderState
      Public args() As Object
   End Class 

   Public Overrides Function BindToField(ByVal bindingAttr As BindingFlags, ByVal match() As FieldInfo, ByVal value As Object, ByVal culture As CultureInfo) As FieldInfo
      If match Is Nothing Then
         Throw New ArgumentNullException("match")
      End If
      ' Get a field for which the value parameter can be converted to the specified field type.
      Dim i As Integer
      For i = 0 To match.Length - 1
         If Not (ChangeType(value, match(i).FieldType, culture) Is Nothing) Then
            Return match(i)
         End If
      Next i
      Return Nothing
   End Function 

   Public Overrides Function BindToMethod(ByVal bindingAttr As BindingFlags, ByVal match() As MethodBase, ByRef args() As Object, ByVal modifiers() As ParameterModifier, ByVal culture As CultureInfo, ByVal names() As String, ByRef state As Object) As MethodBase
      ' Store the arguments to the method in a state object.
      Dim myBinderState As New BinderState()
      Dim arguments() As Object = New [Object](args.Length) {}
      args.CopyTo(arguments, 0)
      myBinderState.args = arguments
      state = myBinderState

      If match Is Nothing Then
         Throw New ArgumentNullException()
      End If
      ' Find a method that has the same parameters as those of args.
      Dim i As Integer
      For i = 0 To match.Length - 1
         ' Count the number of parameters that match.
         Dim count As Integer = 0
         Dim parameters As ParameterInfo() = match(i).GetParameters()
         ' Go on to the next method if the number of parameters do not match.
         If args.Length <> parameters.Length Then
            GoTo ContinueFori
         End If
         ' Match each of the parameters that the user expects the method to have.
         Dim j As Integer
         For j = 0 To args.Length - 1
            ' If names is not null, then reorder args.
            If Not (names Is Nothing) Then
               If names.Length <> args.Length Then
                  Throw New ArgumentException("names and args must have the same number of elements.")
               End If
               Dim k As Integer
               For k = 0 To names.Length - 1
                  If String.Compare(parameters(j).Name, names(k).ToString()) = 0 Then
                     args(j) = myBinderState.args(k)
                  End If
               Next k
            End If 
            ' Determine whether the types specified by the user can be converted to parameter type.
            If Not (ChangeType(args(j), parameters(j).ParameterType, culture) Is Nothing) Then
               count += 1
            Else
               Exit For
            End If
         Next j
         ' Determine whether the method has been found.
         If count = args.Length Then
            Return match(i)
         End If
ContinueFori:
      Next i
      Return Nothing
   End Function 

   Public Overrides Function ChangeType(ByVal value As Object, ByVal myChangeType As Type, ByVal culture As CultureInfo) As Object
      ' Determine whether the value parameter can be converted to a value of type myType.
      If CanConvertFrom(value.GetType(), myChangeType) Then
         ' Return the converted object.
         Return Convert.ChangeType(value, myChangeType, culture)
      Else
         ' Return null.
         Return Nothing
      End If
   End Function 'ChangeType

   Public Overrides Sub ReorderArgumentArray(ByRef args() As Object, ByVal state As Object)
      'Redimension the array to hold the state values.
      ReDim args(CType(state, BinderState).args.Length)
      ' Return the args that had been reordered by BindToMethod.
      CType(state, BinderState).args.CopyTo(args, 0)
   End Sub 

   Public Overrides Function SelectMethod(ByVal bindingAttr As BindingFlags, ByVal match() As MethodBase, ByVal types() As Type, ByVal modifiers() As ParameterModifier) As MethodBase
      If match Is Nothing Then
         Throw New ArgumentNullException("match")
      End If
      Dim i As Integer
      For i = 0 To match.Length - 1
         ' Count the number of parameters that match.
         Dim count As Integer = 0
         Dim parameters As ParameterInfo() = match(i).GetParameters()
         ' Go on to the next method if the number of parameters do not match.
         If types.Length <> parameters.Length Then
            GoTo ContinueFori
         End If
         ' Match each of the parameters that the user expects the method to have.
         Dim j As Integer
         For j = 0 To types.Length - 1
            ' Determine whether the types specified by the user can be converted to parameter type.
            If CanConvertFrom(types(j), parameters(j).ParameterType) Then
               count += 1
            Else
               Exit For
            End If
         Next j ' Determine whether the method has been found.
         If count = types.Length Then
            Return match(i)
         End If
ContinueFori:
      Next i
      Return Nothing
   End Function 

   Public Overrides Function SelectProperty(ByVal bindingAttr As BindingFlags, ByVal match() As PropertyInfo, ByVal returnType As Type, ByVal indexes() As Type, ByVal modifiers() As ParameterModifier) As PropertyInfo
      If match Is Nothing Then
         Throw New ArgumentNullException("match")
      End If
      Dim i As Integer
      For i = 0 To match.Length - 1
         ' Count the number of indexes that match.
         Dim count As Integer = 0
         Dim parameters As ParameterInfo() = match(i).GetIndexParameters()

         ' Go on to the next property if the number of indexes do not match.
         If indexes.Length <> parameters.Length Then
            GoTo ContinueFori
         End If
         ' Match each of the indexes that the user expects the property to have.
         Dim j As Integer
         For j = 0 To indexes.Length - 1
            ' Determine whether the types specified by the user can be converted to index type.
            If CanConvertFrom(indexes(j), parameters(j).ParameterType) Then
               count += 1
            Else
               Exit For
            End If
         Next j ' Determine whether the property has been found.
         If count = indexes.Length Then
            ' Determine whether the return type can be converted to the properties type.
            If CanConvertFrom(returnType, match(i).PropertyType) Then
               Return match(i)
            Else
               GoTo ContinueFori
            End If
         End If
ContinueFori:
      Next i
      Return Nothing
   End Function 

   ' Determine whether type1 can be converted to type2. Check only for primitive types.
   Private Function CanConvertFrom(ByVal type1 As Type, ByVal type2 As Type) As Boolean
      If type1.IsPrimitive And type2.IsPrimitive Then
         Dim typeCode1 As TypeCode = Type.GetTypeCode(type1)
         Dim typeCode2 As TypeCode = Type.GetTypeCode(type2)
         ' If both type1 and type2 have same type, return true.
         If typeCode1 = typeCode2 Then
            Return True
         End If ' Possible conversions from Char follow.
         If typeCode1 = TypeCode.Char Then
            Select Case 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
               Case Else
                  Return False
            End Select
         End If ' Possible conversions from Byte follow.
         If typeCode1 = TypeCode.Byte Then
            Select Case 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
               Case Else
                  Return False
            End Select
         End If ' Possible conversions from SByte follow.
         If typeCode1 = TypeCode.SByte Then
            Select Case 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
               Case Else
                  Return False
            End Select
         End If ' Possible conversions from UInt16 follow.
         If typeCode1 = TypeCode.UInt16 Then
            Select Case 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
               Case Else
                  Return False
            End Select
         End If ' Possible conversions from Int16 follow.
         If typeCode1 = TypeCode.Int16 Then
            Select Case typeCode2
               Case TypeCode.Int32
                  Return True
               Case TypeCode.Int64
                  Return True
               Case TypeCode.Single
                  Return True
               Case TypeCode.Double
                  Return True
               Case Else
                  Return False
            End Select
         End If ' Possible conversions from UInt32 follow.
         If typeCode1 = TypeCode.UInt32 Then
            Select Case typeCode2
               Case TypeCode.UInt64
                  Return True
               Case TypeCode.Int64
                  Return True
               Case TypeCode.Single
                  Return True
               Case TypeCode.Double
                  Return True
               Case Else
                  Return False
            End Select
         End If ' Possible conversions from Int32 follow.
         If typeCode1 = TypeCode.Int32 Then
            Select Case typeCode2
               Case TypeCode.Int64
                  Return True
               Case TypeCode.Single
                  Return True
               Case TypeCode.Double
                  Return True
               Case Else
                  Return False
            End Select
         End If ' Possible conversions from UInt64 follow.
         If typeCode1 = TypeCode.UInt64 Then
            Select Case typeCode2
               Case TypeCode.Single
                  Return True
               Case TypeCode.Double
                  Return True
               Case Else
                  Return False
            End Select
         End If ' Possible conversions from Int64 follow.
         If typeCode1 = TypeCode.Int64 Then
            Select Case typeCode2
               Case TypeCode.Single
                  Return True
               Case TypeCode.Double
                  Return True
               Case Else
                  Return False
            End Select
         End If ' Possible conversions from Single follow.
         If typeCode1 = TypeCode.Single Then
            Select Case typeCode2
               Case TypeCode.Double
                  Return True
               Case Else
                  Return False
            End Select
         End If
      End If
      Return False
   End Function 
End Class 


Public Class Example
   Public myFieldB As Short
   Public myFieldA As Integer
   Private Shared outputBlock As System.Windows.Controls.TextBlock

   Public Overloads Sub MyMethod(ByVal i As Long, ByVal k As Char)
      outputBlock.Text += String.Format("This is MyMethod(Long i, Char k).") & vbCrLf
   End Sub 

   Public Overloads Sub MyMethod(ByVal i As Long, ByVal j As Long)
      outputBlock.Text += String.Format("This is MyMethod(Long i, Long j).") & vbCrLf
   End Sub 

   Public Shared Sub Demo(ByVal outputBlock As System.Windows.Controls.TextBlock)
      Example.outputBlock = outputBlock

      ' Get the type of Example.
      Dim myType As Type = GetType(Example)

      ' Get the instance of Example.
      Dim myInstance As Object = New Example()

      outputBlock.Text &= "Displaying the results of using the MyBinder binder." & vbCrLf

      ' Get the method information for MyMethod.
      Dim myMethod As MethodInfo = _
         myType.GetMethod("MyMethod", _
                          BindingFlags.Public Or BindingFlags.Instance, _
                          New MyBinder(), _
                          New Type() {GetType(Short), GetType(Short)}, _
                          Nothing)
      outputBlock.Text &= myMethod.ToString() & vbCrLf

      ' Invoke MyMethod using an instance of MyBinder.
      myType.InvokeMember("MyMethod", _
                          BindingFlags.InvokeMethod, _
                          New MyBinder(), _
                          myInstance, _
                          New Object() {CInt(32), CInt(32)})
   End Sub 
End Class 

' This code produces the following output:
'
'Displaying the results of using the MyBinder binder.
'Void MyMethod(Int64, Int64)
'This is MyMethod(Long i, Long j).

using System;
using System.Reflection;
using System.Globalization;

public class MyBinder : Binder
{
   public MyBinder()
      : base()
   {
   }

   private class BinderState
   {
      public object[] args;
   }

   public override 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, match[i].FieldType, culture) != null)
            return match[i];
      return null;
   }

   public override MethodBase BindToMethod(
       BindingFlags bindingAttr,
       MethodBase[] match,
       ref object[] args,
       ParameterModifier[] modifiers,
       CultureInfo culture,
       string[] names,
       out 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 = 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 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(parameters[j].Name, names[k].ToString()) == 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) != null)
               count += 1;
            else
               break;
         }
         // Determine whether the method has been found.
         if (count == args.Length)
            return match[i];
      }
      return null;
   }

   public override 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, culture);
      else
         // Return null.
         return null;
   }

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

   public override 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 = 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 null;
   }

   public override 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 = 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].PropertyType))
               return match[i];
            else
               continue;
      }
      return null;
   }

   // Determines whether type1 can be converted to type2. Check only for primitive types.
   private 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 class Example
{
   public short myFieldB;
   public int myFieldA;
   private static System.Windows.Controls.TextBlock outputBlock;

   public void MyMethod(long i, char k)
   {
      outputBlock.Text += String.Format("This is MyMethod(long i, char k)\n");
   }
   public void MyMethod(long i, long j)
   {
      outputBlock.Text += String.Format("This is MyMethod(long i, long j)\n");
   }

   public static void Demo(System.Windows.Controls.TextBlock outputBlock)
   {
      Example.outputBlock = outputBlock;

      // Get the type of Example.
      Type myType = typeof(Example);

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

      outputBlock.Text += "Displaying 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[] { typeof(short), typeof(short) }, 
                          null);
      outputBlock.Text += myMethod.ToString() + "\n";

      // Invoke MyMethod.
      myType.InvokeMember("MyMethod", 
                          BindingFlags.InvokeMethod, 
                          new MyBinder(), 
                          myInstance, 
                          new Object[] { (int)32, (int)32 });
   }
}

/* This code produces the following output:

Displaying the results of using the MyBinder binder.
Void MyMethod(Int64, Int64)
This is MyMethod(long i, long j).
 */

Version Information

Silverlight

Supported in: 5, 4, 3

Silverlight for Windows Phone

Supported in: Windows Phone OS 7.1, Windows Phone OS 7.0

XNA Framework

Supported in: Xbox 360, Windows Phone OS 7.0

Platforms

For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.

Thread Safety

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