Binder Class
Selects a member from a list of candidates, and performs type conversion from actual argument type to formal argument type.
Assembly: mscorlib (in mscorlib.dll)
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.
The following example implements and demonstrates all members of the Binder class. The private method CanConvertFrom finds compatible types for a given type.
Imports System Imports System.Reflection Imports System.Globalization Imports Microsoft.VisualBasic Public Class MyBinder Inherits Binder Public Sub New() MyBase.new() End Sub 'New Private Class BinderState Public args() As Object End Class 'BinderState 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 'BindToField 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 'BindToMethod 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) ' Return null. Else 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 'ReorderArgumentArray 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 'SelectMethod 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 'SelectProperty ' 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 'CanConvertFrom End Class 'MyBinder Public Class MyClass1 Public myFieldB As Short Public myFieldA As Integer Public Overloads Sub MyMethod(ByVal i As Long, ByVal k As Char) Console.WriteLine(ControlChars.NewLine & "This is MyMethod(long i, char k).") End Sub 'MyMethod Public Overloads Sub MyMethod(ByVal i As Long, ByVal j As Long) Console.WriteLine(ControlChars.NewLine & "This is MyMethod(long i, long j).") End Sub 'MyMethod End Class 'MyClass1 Public Class Binder_Example Public Shared Sub Main() ' Get the type of MyClass1. Dim myType As Type = GetType(MyClass1) ' Get the instance of MyClass1. Dim myInstance As New MyClass1() Console.WriteLine(ControlChars.Cr & "Displaying the results of using the MyBinder binder.") Console.WriteLine() ' 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) Console.WriteLine(MyMethod) ' Invoke MyMethod. myMethod.Invoke(myInstance, BindingFlags.InvokeMethod, New MyBinder(), New [Object]() {CInt(32), CInt(32)}, CultureInfo.CurrentCulture) End Sub 'Main End Class 'Binder_Example
Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98, Windows CE, Windows Mobile for Smartphone, Windows Mobile for Pocket PC, Xbox 360, Zune
The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.