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IStateManager Interface

Defines the properties and methods any class must implement to support view state management for a server control.

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

'Declaration
Public Interface IStateManager

The IStateManager type exposes the following members.

  NameDescription
Public propertyIsTrackingViewStateWhen implemented by a class, gets a value indicating whether a server control is tracking its view state changes.
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  NameDescription
Public methodLoadViewStateWhen implemented by a class, loads the server control's previously saved view state to the control.
Public methodSaveViewStateWhen implemented by a class, saves the changes to a server control's view state to an Object.
Public methodTrackViewStateWhen implemented by a class, instructs the server control to track changes to its view state.
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A server control's view state comprises the cumulative values of the control's properties. This interface includes methods that save and load a server control's view state values, as well as a method that instructs the control to track any changes to its view state.

To customize the way your ASP.NET application manages server control view state, you must create a class that implements this interface because you cannot inherit from the StateBag class.

The following code example shows a class that implements the IStateManager interface. It includes implementations of the IsTrackingViewState property and the LoadViewState, SaveViewState, and TrackViewState methods.

' Create a class that implements IStateManager so that 
' it can manage its own view state.   

<AspNetHostingPermission(SecurityAction.Demand, _
   Level:=AspNetHostingPermissionLevel.Minimal)> _
Public NotInheritable Class MyItem
    Implements IStateManager
    Private _message As String 

    ' The StateBag object that allows you to save 
    ' and restore view-state information. 
    Private _viewstate As StateBag


    ' The constructor for the MyItem class. 
    Public Sub New(ByVal mesg As String)
        _message = mesg
        _viewstate = New StateBag()
        _viewstate.Add("message", _message)
    End Sub 'New 

    ' Create a Message property that reads from and writes 
    ' to view state. If the set accessor writes the message 
    ' value to view state, the StateBag.SetItemDirty method 
    ' is called, telling view state that the item has changed.  

    Public Property Message() As String 
        Get 
            Return CStr(_viewstate("message"))
        End Get 
        Set(ByVal value As String)
            _message = value
            _viewstate.SetItemDirty("message", True)
        End Set 
    End Property 

    ' Implement the LoadViewState method. If the saved view state 
    ' exists, the view-state value is loaded to the MyItem  
    ' control.  
    Sub LoadViewState(ByVal savedState As Object) Implements IStateManager.LoadViewState
        _message = CStr(_viewstate("message"))
        If Not (savedState Is Nothing) Then 
            CType(_viewstate, IStateManager).LoadViewState(savedState)
        End If 
    End Sub 'LoadViewState
    ' Implement the SaveViewState method. If the StateBag 
    ' that stores the MyItem class's view state contains 
    ' a value for the message property and if the value 
    ' has changed since the TrackViewState method was last  
    ' called, all view state for this class is deleted,  
    ' using the StateBag.Clear method,and the new value is added. 
    Function SaveViewState() As Object Implements IStateManager.SaveViewState
        ' Check whether the message property exists in  
        ' the ViewState property, and if it does, check 
        ' whether it has changed since the most recent 
        ' TrackViewState method call. 
        If Not CType(_viewstate, IDictionary).Contains("message") OrElse _viewstate.IsItemDirty("message") Then
            _viewstate.Clear()
            ' Add the _message property to the StateBag.
            _viewstate.Add("message", _message)
        End If 
        Return CType(_viewstate, IStateManager).SaveViewState()
    End Function 'IStateManager.SaveViewState


    ' Implement the TrackViewState method for this class by 
    ' calling the TrackViewState method of the class's private 
    ' _viewstate property. 
    Sub TrackViewState() Implements IStateManager.TrackViewState
        CType(_viewstate, IStateManager).TrackViewState()
    End Sub 'IStateManager.TrackViewState
    ' Implement the IsTrackingViewState method for this class  
    ' by calling the IsTrackingViewState method of the class's 
    ' private _viewstate property.  

    ReadOnly Property IsTrackingViewState() As Boolean Implements IStateManager.IsTrackingViewState
        Get 
            Return CType(_viewstate, IStateManager).IsTrackingViewState
        End Get 
    End Property 

    ' Create a function that iterates through the view-state 
    ' values stored for this class and returns the 
    ' results as a string. 
    Public Function EnumerateViewState() As String 
        Dim keyName, keyValue As String 
        Dim result As String = [String].Empty
        Dim myStateItem As StateItem
        Dim myDictionaryEnumerator As IDictionaryEnumerator = _viewstate.GetEnumerator()
        While myDictionaryEnumerator.MoveNext()
            keyName = CStr(myDictionaryEnumerator.Key)
            myStateItem = CType(myDictionaryEnumerator.Value, StateItem)
            keyValue = CStr(myStateItem.Value)
            result = result + "<br>ViewState[" + keyName + "] = " + keyValue
        End While 
        Return result
    End Function 'EnumerateViewState
End Class 'MyItem 

.NET Framework

Supported in: 4.6, 4.5, 4, 3.5, 3.0, 2.0, 1.1
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