Provides the implementation for operations that get a value by index. Classes derived from the DynamicObject class can override this method to specify dynamic behavior for indexing operations.
(in System.Core.dll)
Visual Basic (Declaration)
Public Overridable Function TryGetIndex ( _
binder As GetIndexBinder, _
indexes As Object(), _
<OutAttribute> ByRef result As Object _
) As Boolean
Dim instance As DynamicObject
Dim binder As GetIndexBinder
Dim indexes As Object()
Dim result As Object
Dim returnValue As Boolean
returnValue = instance.TryGetIndex(binder, _
indexes, result)
public virtual bool TryGetIndex(
GetIndexBinder binder,
Object[] indexes,
out Object result
)
public:
virtual bool TryGetIndex(
GetIndexBinder^ binder,
array<Object^>^ indexes,
[OutAttribute] Object^% result
)
abstract TryGetIndex :
binder:GetIndexBinder *
indexes:Object[] *
result:Object byref -> bool
override TryGetIndex :
binder:GetIndexBinder *
indexes:Object[] *
result:Object byref -> bool
Parameters
- binder
- Type: System.Dynamic..::.GetIndexBinder
Provides information about the operation.
- indexes
- Type: array<System..::.Object>[]()[]
The indexes that are used in the operation. For example, for the sampleObject[3] operation in C# (sampleObject(3) in Visual Basic), where sampleObject is derived from the DynamicObject class, indexes[0] is equal to 3.
- result
- Type: System..::.Object%
The result of the index operation.
Return Value
Type:
System..::.Boolean
true if the operation is successful; otherwise, false. If this method returns false, the run-time binder of the language determines the behavior. (In most cases, a run-time exception is thrown.)
Classes derived from the DynamicObject class can override this method to specify how getting a value by index should be performed for a dynamic object. When the method is not overridden, the run-time binder of the language determines the behavior. (In most cases, a run-time exception is thrown.)
If this method is overridden, it is automatically invoked when you have an operation like sampleObject[3] in C# or sampleObject(3) in Visual Basic, where sampleObject is derived from the DynamicObject class.
Assume that you want to create an object in which properties can be accessed either by names such as Property0, Property1, and so on, or by index, so that, for example, sampleObject.Property0 is equivalent to sampleObject[0] in C# or sampleObject(0) in Visual Basic.
The following code example demonstrates the SampleDynamicObject class, which is derived from the DynamicObject class. The SampleDynamicObject class contains an object of the Dictionary<string, object> type (Dictionary(Of String, Object) in Visual Basic) to store the key-value pairs. SampleDynamicObject overrides the TrySetIndex and TryGetIndex methods to enable access by index. It overrides the TrySetMember and TryGetMember methods to enable access by property name.
' The class derived from DynamicObject.
Public Class SampleDynamicObject
Inherits DynamicObject
' The inner dictionary to store field names and values.
Dim dictionary As New Dictionary(Of String, Object)
' Get the property value.
Public Overrides Function TryGetMember(
ByVal binder As System.Dynamic.GetMemberBinder,
ByRef result As Object) As Boolean
Return dictionary.TryGetValue(binder.Name, result)
End Function
' Set the property value.
Public Overrides Function TrySetMember(
ByVal binder As System.Dynamic.SetMemberBinder,
ByVal value As Object) As Boolean
dictionary(binder.Name) = value
Return True
End Function
' Set the property value by index.
Public Overrides Function TrySetIndex(
ByVal binder As System.Dynamic.SetIndexBinder,
ByVal indexes() As Object, ByVal value As Object) As Boolean
Dim index As Integer = CInt(indexes(0))
' If a corresponding property already exists, set the value.
If (dictionary.ContainsKey("Property" & index)) Then
dictionary("Property") = value
Else
' If a property does not exist, create it.
dictionary.Add("Property" & index, value)
End If
Return True
End Function
' Get the property value by index.
Public Overrides Function TryGetIndex(
ByVal binder As System.Dynamic.GetIndexBinder,
ByVal indexes() As Object, ByRef result As Object) As Boolean
Dim index = CInt(indexes(0))
Return dictionary.TryGetValue("Property" & index, result)
End Function
End Class
Sub Test()
' Creating a dynamic object.
Dim sampleObject As Object = New SampleDynamicObject()
' Creating Property0.
' The TrySetMember method is called.
sampleObject.Property0 = "Zero"
' Getting the value by index.
' The TryGetIndex method is called.
Console.WriteLine(sampleObject(0))
' Setting the property value by index.
' The TrySetIndex method is called.
' (This method also creates Property1.)
sampleObject(1) = 1
' Getting the Property1 value.
' The TryGetMember method is called.
Console.WriteLine(sampleObject.Property1)
' The following statement produces a run-time exception
' because there is no corresponding property.
' Console.WriteLine(sampleObject(2))
End Sub
' This code example produces the following output:
' Zero
' 1
// The class derived from DynamicObject.
public class SampleDynamicObject : DynamicObject
{
// The inner dictionary to store field names and values.
Dictionary<string, object> dictionary
= new Dictionary<string, object>();
// Get the property value.
public override bool TryGetMember(
GetMemberBinder binder, out object result)
{
return dictionary.TryGetValue(binder.Name, out result);
}
// Set the property value.
public override bool TrySetMember(
SetMemberBinder binder, object value)
{
dictionary[binder.Name] = value;
return true;
}
// Set the property value by index.
public override bool TrySetIndex(
SetIndexBinder binder, object[] indexes, object value)
{
int index = (int)indexes[0];
// If a corresponding property already exists, set the value.
if (dictionary.ContainsKey("Property" + index))
dictionary["Property"] = value;
else
// If a corresponding property does not exist, create it.
dictionary.Add("Property" + index, value);
return true;
}
// Get the property value by index.
public override bool TryGetIndex(
GetIndexBinder binder, object[] indexes, out object result)
{
int index = (int)indexes[0];
return dictionary.TryGetValue("Property" + index, out result);
}
}
class Program
{
static void Test(string[] args)
{
// Creating a dynamic object.
dynamic sampleObject = new SampleDynamicObject();
// Creating Property0.
// The TrySetMember method is called.
sampleObject.Property0 = "Zero";
// Getting the value by index.
// The TryGetIndex method is called.
Console.WriteLine(sampleObject[0]);
// Setting the property value by index.
// The TrySetIndex method is called.
// (This method also creates Property1.)
sampleObject[1] = 1;
// Getting the Property1 value.
// The TryGetMember method is called.
Console.WriteLine(sampleObject.Property1);
// The following statement produces a run-time exception
// because there is no corresponding property.
//Console.WriteLine(sampleObject[2]);
}
}
// This code example produces the following output:
// Zero
// 1
Windows 7, Windows Vista, Windows XP SP2, Windows Server 2008, Windows Server 2003
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.
.NET Framework
Supported in: 4
.NET Framework Client Profile
Supported in: 4
Reference