DynamicObject.TrySetIndex Method (SetIndexBinder, Object(), Object)
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.
Assembly: System.Core (in System.Core.dll)
Public Overridable Function TrySetIndex ( binder As SetIndexBinder, indexes As Object(), value As Object ) As Boolean
Provides information about the operation.
The indexes that are used in the operation. For example, for the sampleObject = 10 operation in C# (sampleObject(3) = 10 in Visual Basic), where sampleObject is derived from the DynamicObject class, indexes is equal to 3.
Return ValueType: 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 = 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 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 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
Available since 4.5
Available since 4.0
Portable Class Library
Supported in: portable .NET platforms
Available since 4.0
Windows Phone Silverlight
Available since 8.0
Available since 8.1