StateManagedCollection Class
Definition
Important
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Provides a base class for all strongly typed collections that manage IStateManager objects.
public ref class StateManagedCollection abstract : System::Collections::IList, System::Web::UI::IStateManagerpublic abstract class StateManagedCollection : System.Collections.IList, System.Web.UI.IStateManagertype StateManagedCollection = class
interface IList
interface ICollection
interface IEnumerable
interface IStateManagerPublic MustInherit Class StateManagedCollection
Implements IList, IStateManager- Inheritance
-
StateManagedCollection
- Derived
- Implements
Examples
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.
namespace Samples.AspNet.CS.Controls {
using System;
using System.Security.Permissions;
using System.Collections;
using System.ComponentModel;
using System.Drawing;
using System.Web;
using System.Web.UI;
//////////////////////////////////////////////////////////////
//
// 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 abstract Cycle class represents bicycles and tricycles.
//
//////////////////////////////////////////////////////////////
public abstract class Cycle : IStateManager {
protected internal Cycle(int numWheels) : this(numWheels, "Red"){ }
protected internal Cycle(int numWheels, String color) {
numberOfWheels = numWheels;
CycleColor = color;
}
private int numberOfWheels = 0;
public int NumberOfWheels {
get { return numberOfWheels; }
}
public string CycleColor {
get {
object o = ViewState["Color"];
return (null == o) ? String.Empty : o.ToString() ;
}
set {
ViewState["Color"] = value;
}
}
internal void SetDirty() {
ViewState.SetDirty(true);
}
// Because Cycle does not derive from Control, it does not
// have access to an inherited view state StateBag object.
private StateBag viewState;
private StateBag ViewState {
get {
if (viewState == null) {
viewState = new StateBag(false);
if (isTrackingViewState) {
((IStateManager)viewState).TrackViewState();
}
}
return viewState;
}
}
// The IStateManager implementation.
private bool isTrackingViewState;
bool IStateManager.IsTrackingViewState {
get {
return isTrackingViewState;
}
}
void IStateManager.LoadViewState(object savedState) {
object[] cycleState = (object[]) savedState;
// 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) {
throw new ArgumentException("Invalid Cycle View State");
}
// Call LoadViewState on the StateBag object.
((IStateManager)ViewState).LoadViewState(cycleState[0]);
}
// Save the view state by calling the StateBag's SaveViewState
// method.
object IStateManager.SaveViewState() {
object[] cycleState = new object[1];
if (viewState != null) {
cycleState[0] = ((IStateManager)viewState).SaveViewState();
}
return cycleState;
}
// 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.
void IStateManager.TrackViewState() {
isTrackingViewState = true;
if (viewState != null) {
((IStateManager)viewState).TrackViewState();
}
}
}
public sealed class Bicycle : Cycle {
// Create a red Cycle with two wheels.
public Bicycle() : base(2) {}
}
public sealed class Tricycle : Cycle {
// Create a red Cycle with three wheels.
public Tricycle() : base(3) {}
}
}
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
Remarks
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 IStateManager.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 null 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.
Important
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.
Constructors
| StateManagedCollection() |
Initializes a new instance of the StateManagedCollection class. |
Properties
| Count |
Gets the number of elements contained in the StateManagedCollection collection. |
Methods
| Clear() |
Removes all items from the StateManagedCollection collection. |
| CopyTo(Array, Int32) |
Copies the elements of the StateManagedCollection collection to an array, starting at a particular array index. |
| CreateKnownType(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. |
| Equals(Object) |
Determines whether the specified object is equal to the current object. (Inherited from Object) |
| GetEnumerator() |
Returns an iterator that iterates through the StateManagedCollection collection. |
| GetHashCode() |
Serves as the default hash function. (Inherited from Object) |
| GetKnownTypes() |
When overridden in a derived class, gets an array of IStateManager types that the StateManagedCollection collection can contain. |
| GetType() |
Gets the Type of the current instance. (Inherited from Object) |
| MemberwiseClone() |
Creates a shallow copy of the current Object. (Inherited from Object) |
| OnClear() |
When overridden in a derived class, performs additional work before the Clear() method removes all items from the collection. |
| OnClearComplete() |
When overridden in a derived class, performs additional work after the Clear() method finishes removing all items from the collection. |
| OnInsert(Int32, Object) |
When overridden in a derived class, performs additional work before the IList.Insert(Int32, Object) or IList.Add(Object) method adds an item to the collection. |
| OnInsertComplete(Int32, Object) |
When overridden in a derived class, performs additional work after the IList.Insert(Int32, Object) or IList.Add(Object) method adds an item to the collection. |
| OnRemove(Int32, Object) |
When overridden in a derived class, performs additional work before the IList.Remove(Object) or IList.RemoveAt(Int32) method removes the specified item from the collection. |
| OnRemoveComplete(Int32, Object) |
When overridden in a derived class, performs additional work after the IList.Remove(Object) or IList.RemoveAt(Int32) method removes the specified item from the collection. |
| OnValidate(Object) |
When overridden in a derived class, validates an element of the StateManagedCollection collection. |
| SetDirty() |
Forces the entire StateManagedCollection collection to be serialized into view state. |
| SetDirtyObject(Object) |
When overridden in a derived class, instructs an |
| ToString() |
Returns a string that represents the current object. (Inherited from Object) |
Explicit Interface Implementations
| ICollection.Count |
Gets the number of elements contained in the StateManagedCollection collection. |
| ICollection.IsSynchronized |
Gets a value indicating whether the StateManagedCollection collection is synchronized (thread safe). This method returns |
| ICollection.SyncRoot |
Gets an object that can be used to synchronize access to the StateManagedCollection collection. This method returns |
| IEnumerable.GetEnumerator() |
Returns an iterator that iterates through the StateManagedCollection collection. |
| IList.Add(Object) |
Adds an item to the StateManagedCollection collection. |
| IList.Clear() |
Removes all items from the StateManagedCollection collection. |
| IList.Contains(Object) |
Determines whether the StateManagedCollection collection contains a specific value. |
| IList.IndexOf(Object) |
Determines the index of a specified item in the StateManagedCollection collection. |
| IList.Insert(Int32, Object) |
Inserts an item into the StateManagedCollection collection at the specified index. |
| IList.IsFixedSize |
Gets a value indicating whether the StateManagedCollection collection has a fixed size. This method returns |
| IList.IsReadOnly |
Gets a value indicating whether the StateManagedCollection collection is read-only. |
| IList.Item[Int32] |
Gets the IStateManager element at the specified index. |
| IList.Remove(Object) |
Removes the first occurrence of the specified object from the StateManagedCollection collection. |
| IList.RemoveAt(Int32) |
Removes the IStateManager element at the specified index. |
| IStateManager.IsTrackingViewState |
Gets a value indicating whether the StateManagedCollection collection is saving changes to its view state. |
| IStateManager.LoadViewState(Object) |
Restores the previously saved view state of the StateManagedCollection collection and the IStateManager items it contains. |
| IStateManager.SaveViewState() |
Saves the changes to the StateManagedCollection collection and each IStateManager object it contains since the time the page was posted back to the server. |
| IStateManager.TrackViewState() |
Causes the StateManagedCollection collection and each of the IStateManager objects it contains to track changes to their view state so they can be persisted across requests for the same page. |
Extension Methods
| Cast<TResult>(IEnumerable) |
Casts the elements of an IEnumerable to the specified type. |
| OfType<TResult>(IEnumerable) |
Filters the elements of an IEnumerable based on a specified type. |
| AsParallel(IEnumerable) |
Enables parallelization of a query. |
| AsQueryable(IEnumerable) |
Converts an IEnumerable to an IQueryable. |
Applies to
See also
.NET