StateManagedCollection.CreateKnownType Method (Int32)

 

When overridden in a derived class, creates an instance of a class that implements IStateManager. The type of object created is based on the specified member of the collection returned by the GetKnownTypes method.

Namespace:   System.Web.UI
Assembly:  System.Web (in System.Web.dll)

Protected Overridable Function CreateKnownType (
	index As Integer
) As Object

Parameters

index
Type: System.Int32

The index, from the ordered list of types returned by GetKnownTypes, of the type of IStateManager to create.

Return Value

Type: System.Object

An instance of a class derived from IStateManager, according to the index provided.

Exception Condition
InvalidOperationException

In all cases when not overridden in a derived class.

The CreateKnownType method is called internally by the StateManagedCollection collection in its implementation of the StateManagedCollection.IStateManager.LoadViewState method. Derived collections override the CreateKnownType method to return a default instance of the IStateManager type identified by the provided index, which maps to one of the types returned by the GetKnownTypes method.

The following code example demonstrates how a strongly typed StateManagedCollection class implements the CreateKnownType method. The CycleCollection implementation of CreateKnownType returns the default instance of either a Bicycle or Tricycle object, depending on the index passed. This code example is part of a larger example provided for the StateManagedCollection class.

'////////////////////////////////////////////////////////////
'
' The strongly typed CycleCollection class is a collection
' that contains Cycle class instances, which implement the
' IStateManager interface.
'
'////////////////////////////////////////////////////////////
<AspNetHostingPermission(SecurityAction.Demand, _
    Level:=AspNetHostingPermissionLevel.Minimal)> _
               Public NotInheritable Class CycleCollection
    Inherits StateManagedCollection

    Private Shared _typesOfCycles() As Type = _
        {GetType(Bicycle), GetType(Tricycle)}

    Protected Overrides Function CreateKnownType(ByVal index As Integer) As Object
        Select Case index
            Case 0
                Return New Bicycle()
            Case 1
                Return New Tricycle()
            Case Else
                Throw New ArgumentOutOfRangeException("Unknown Type")
        End Select

    End Function


    Protected Overrides Function GetKnownTypes() As Type()
        Return _typesOfCycles

    End Function


    Protected Overrides Sub SetDirtyObject(ByVal o As Object)
        CType(o, Cycle).SetDirty()

    End Sub
End Class

.NET Framework
Available since 2.0
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