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StateManagedCollection Class

Provides a base class for all strongly typed collections that manage IStateManager objects.

Namespace:  System.Web.UI
Assembly:  System.Web (in System.Web.dll)
'Declaration
<AspNetHostingPermissionAttribute(SecurityAction.InheritanceDemand, Level := AspNetHostingPermissionLevel.Minimal)> _
<AspNetHostingPermissionAttribute(SecurityAction.LinkDemand, Level := AspNetHostingPermissionLevel.Minimal)> _
Public MustInherit Class StateManagedCollection _
	Implements IList, ICollection, IEnumerable, IStateManager
'Usage
Dim instance As StateManagedCollection

The StateManagedCollection class is the base class for all strongly typed collections that store IStateManager elements, including DataControlFieldCollection, ParameterCollection, StyleCollection, TreeNodeBindingCollection, and others. The StateManagedCollection collection manages its own state as well as the state of the elements it contains. Therefore, a call to SaveViewState saves the state of the collection and the state of all the elements currently contained by the collection.

The most important methods to consider when deriving from the StateManagedCollection class are CreateKnownType, GetKnownTypes, OnValidate, SetDirty, and SetDirtyObject. The CreateKnownType and GetKnownTypes methods are used to store an index in view state for the type of a contained element. Storing an index rather than a fully qualified type name improves performance. The OnValidate method is called whenever elements of the collection are manipulated, and validates the elements according to business rules. Currently, the implementation of the OnValidate method prohibits Nothing objects from being stored in the collection; however, you can override this method to define your own validation behavior in a derived type. The SetDirty method forces the entire collection to be serialized to view state, rather than just serializing changes made to state since the last time it was loaded. The SetDirtyObject method is an abstract method you can implement to perform this same behavior at the element level.

Security noteSecurity Note:

StateManagedCollection stores assembly-qualified type names of the collection items in view state. A site visitor could decode the view state and retrieve the type name. If this scenario creates a security concern in your Web site, you can manually encrypt the type name before placing it in the view state.

The following code example demonstrates how to derive a strongly typed collection class from StateManagedCollection to contain IStateManager objects. In this example, the CycleCollection is derived to contain instances of the abstract Cycle class, which can be either Bicycle or Tricycle objects. The Cycle class implements the IStateManager interface because it stores the value of the CycleColor property in view state.

Imports System
Imports System.Security.Permissions
Imports System.Collections
Imports System.ComponentModel
Imports System.Drawing
Imports System.Web
Imports System.Web.UI

Namespace Samples.AspNet.VB.Controls
    '//////////////////////////////////////////////////////////// 
    
    ' 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 
    '//////////////////////////////////////////////////////////// 
    
    ' The abstract Cycle class represents bicycles and tricycles. 
    
    '//////////////////////////////////////////////////////////// 

    MustInherit Public Class Cycle
        Implements IStateManager


        Friend Protected Sub New(ByVal numWheels As Integer) 
            MyClass.New(numWheels, "Red")

        End Sub 

        Friend Protected Sub New(ByVal numWheels As Integer, ByVal color As String) 
            numOfWheels = numWheels
            CycleColor = color

        End Sub 

        Private numOfWheels As Integer = 0    
        Public ReadOnly Property NumberOfWheels() As Integer  
            Get 
                Return numOfWheels
            End Get 
        End Property  

        Public Property CycleColor() As String  
            Get 
                Dim o As Object = ViewState("Color")
                If o Is Nothing Then  
                    Return String.Empty
                Else   
                    Return o.ToString()
                End If             
            End Get 
            Set
                ViewState("Color") = value
            End Set 
        End Property 


        Friend Sub SetDirty() 
            ViewState.SetDirty(True)

        End Sub 

        ' Because Cycle does not derive from Control, it does not  
        ' have access to an inherited view state StateBag object. 
        Private cycleViewState As StateBag

        Private ReadOnly Property ViewState() As StateBag 
            Get 
                If cycleViewState Is Nothing Then
                    cycleViewState = New StateBag(False)
                    If trackingViewState Then
                        CType(cycleViewState, IStateManager).TrackViewState()
                    End If 
                End If 
                Return cycleViewState
            End Get 
        End Property 

        ' The IStateManager implementation. 
        Private trackingViewState As Boolean 

        ReadOnly Property IsTrackingViewState() As Boolean _
            Implements IStateManager.IsTrackingViewState
            Get 
                Return trackingViewState
            End Get 
        End Property 


        Sub LoadViewState(ByVal savedState As Object) _
            Implements IStateManager.LoadViewState
            Dim cycleState As Object() = CType(savedState, Object())

            ' In SaveViewState, an array of one element is created. 
            ' Therefore, if the array passed to LoadViewState has  
            ' more than one element, it is invalid. 
            If cycleState.Length <> 1 Then 
                Throw New ArgumentException("Invalid Cycle View State")
            End If 

            ' Call LoadViewState on the StateBag object.
            CType(ViewState, IStateManager).LoadViewState(cycleState(0))

        End Sub 


        ' Save the view state by calling the StateBag's SaveViewState 
        ' method. 
        Function SaveViewState() As Object Implements IStateManager.SaveViewState
            Dim cycleState(0) As Object

            If Not (cycleViewState Is Nothing) Then
                cycleState(0) = _
                CType(cycleViewState, IStateManager).SaveViewState()
            End If 
            Return cycleState

        End Function 


        ' Begin tracking view state. Check the private variable, because  
        ' if the view state has not been accessed or set, then it is not being  
        ' used and there is no reason to store any view state. 
        Sub TrackViewState() Implements IStateManager.TrackViewState
            trackingViewState = True 
            If Not (cycleViewState Is Nothing) Then
                CType(cycleViewState, IStateManager).TrackViewState()
            End If 

        End Sub 
    End Class 


    Public NotInheritable Class Bicycle
        Inherits Cycle


        ' Create a red Cycle with two wheels. 
        Public Sub New()
            MyBase.New(2)

        End Sub 
    End Class 

    Public NotInheritable Class Tricycle
        Inherits Cycle


        ' Create a red Cycle with three wheels. 
        Public Sub New()
            MyBase.New(3)

        End Sub 
    End Class 
End Namespace
Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.

Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98

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: 3.5, 3.0, 2.0
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