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DynamicObject.TrySetIndex Method

Provides the implementation for operations that set a value by index. Classes derived from the DynamicObject class can override this method to specify dynamic behavior for operations that access objects by a specified index.

Namespace:  System.Dynamic
Assembly:  System.Core (in System.Core.dll)

'Declaration
Public Overridable Function TrySetIndex ( _
	binder As SetIndexBinder, _
	indexes As Object(), _
	value As Object _
) As Boolean

Parameters

binder
Type: System.Dynamic.SetIndexBinder
Provides information about the operation.
indexes
Type: System.Object()
The indexes that are used in the operation. For example, for the sampleObject[3] = 10 operation in C# (sampleObject(3) = 10 in Visual Basic), where sampleObject is derived from the DynamicObject class, indexes[0] is equal to 3.
value
Type: System.Object
The value to set to the object that has the specified index. For example, for the sampleObject[3] = 10 operation in C# (sampleObject(3) = 10 in Visual Basic), where sampleObject is derived from the DynamicObject class, value is equal to 10.

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 language-specific run-time exception is thrown.

Classes derived from the DynamicObject class can override this method to specify how operations that access an object 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 language-specific run-time exception is thrown.)

If this method is overridden, it is automatically invoked when you have an operation like sampleObject[3] = 10 in C# or sampleObject(3) = 10 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" & index) = 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


.NET Framework

Supported in: 4

.NET Framework Client Profile

Supported in: 4

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

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

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