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.
Methods
| Name | Description | |
|---|---|---|
.gif "Public method") .gif "Supported by Silverlight for Windows Phone") .gif "Supported by Xbox 360") |
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.) |
.gif "Protected method") |
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.) |
Top
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.
.gif "Note") 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.