StateManagedCollection.CreateKnownType(Int32) Method

  • Reference

Definition

Namespace:
System.Web.UI
Assembly:
System.Web.dll

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.

protected:
 virtual System::Object ^ CreateKnownType(int index);
protected virtual object CreateKnownType (int index);
abstract member CreateKnownType : int -> obj
override this.CreateKnownType : int -> obj
Protected Overridable Function CreateKnownType (index As Integer) As Object

Parameters

index
Int32

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

Returns

Object

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

Exceptions

InvalidOperationException

In all cases when not overridden in a derived class.

Examples

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 sealed class CycleCollection : StateManagedCollection {
    
    private static readonly Type[] _typesOfCycles 
        = new Type[] { typeof(Bicycle), typeof(Tricycle) };

    protected override object CreateKnownType(int index) {
        switch(index) {
            case 0:
                return new Bicycle();
            case 1:
                return new Tricycle();                    
            default:
                throw new ArgumentOutOfRangeException("Unknown Type");
        }            
    }

    protected override Type[] GetKnownTypes() {
        return _typesOfCycles;
    }

    protected override void SetDirtyObject(object o) {
        ((Cycle)o).SetDirty();
    }
}

'////////////////////////////////////////////////////////////
'
' 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

Remarks

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.

Applies to

See also