IStateManager Interfaccia

  • Riferimento

Definizione

Spazio dei nomi:
System.Web.UI
Assembly:
System.Web.dll

Definisce le proprietà e i metodi che ogni classe deve implementare per supportare la gestione dello stato di visualizzazione per un controllo server.

public interface class IStateManager
public interface IStateManager
type IStateManager = interface
Public Interface IStateManager
Derivato

Esempio

Nell'esempio di codice seguente viene illustrata una classe che implementa l'interfaccia IStateManager . Include implementazioni della IsTrackingViewState proprietà e dei LoadViewStatemetodi , SaveViewStatee TrackViewState .

// Create a class that implements IStateManager so that
// it can manage its own view state.   
[AspNetHostingPermission(SecurityAction.Demand,
   Level = AspNetHostingPermissionLevel.Minimal)]
public sealed class MyItem : IStateManager
{
    private string _message;

    // The StateBag object that allows you to save
    // and restore view-state information.
    private StateBag _viewstate;

    // The constructor for the MyItem class.
    public MyItem(string mesg)
    {
        _message = mesg;
        _viewstate = new StateBag();
        _viewstate.Add("message", _message);
    }

    // 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 string Message
    {
        get
        {
            return (string)_viewstate["message"];
        }
        set
        {
            _message = value;
            _viewstate.SetItemDirty("message", true);
        }
    }

    // Implement the LoadViewState method. If the saved view state
    // exists, the view-state value is loaded to the MyItem control. 
    void IStateManager.LoadViewState(object savedState)
    {
        _message = (string)_viewstate["message"];
        if (savedState != null)
            ((IStateManager)_viewstate).LoadViewState(savedState);
    }

    // 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.
    object 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 (!((IDictionary)_viewstate).Contains("message") || _viewstate.IsItemDirty("message"))
        {
            _viewstate.Clear();
            // Add the _message property to the StateBag.
            _viewstate.Add("message", _message);
        }
        return ((IStateManager)_viewstate).SaveViewState();
    }


    // Implement the TrackViewState method for this class by
    // calling the TrackViewState method of the class's private
    // _viewstate property.
    void IStateManager.TrackViewState()
    {
        ((IStateManager)_viewstate).TrackViewState();
    }

    // Implement the IsTrackingViewState method for this class 
    // by calling the IsTrackingViewState method of the class's
    // private _viewstate property. 
    bool IStateManager.IsTrackingViewState
    {
        get
        {
            return ((IStateManager)_viewstate).IsTrackingViewState;
        }
    }

    // Create a function that iterates through the view-state
    // values stored for this class and returns the
    // results as a string.
    public string EnumerateViewState()
    {
        string keyName, keyValue;
        string result = String.Empty;
        StateItem myStateItem;
        IDictionaryEnumerator myDictionaryEnumerator = _viewstate.GetEnumerator();
        while (myDictionaryEnumerator.MoveNext())
        {
            keyName = (string)myDictionaryEnumerator.Key;
            myStateItem = (StateItem)myDictionaryEnumerator.Value;
            keyValue = (string)myStateItem.Value;
            result = result + "<br>ViewState[" + keyName + "] = " + keyValue;
        }
        return result;
    }
}

' 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

    ' 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
    ' 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
    ' 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

Commenti

Lo stato di visualizzazione di un controllo server include i valori cumulativi delle proprietà del controllo. Questa interfaccia include metodi che salvano e caricano i valori dello stato di visualizzazione di un controllo server, nonché un metodo che indica al controllo di tenere traccia delle modifiche apportate allo stato di visualizzazione.

Per personalizzare il modo in cui l'applicazione ASP.NET gestisce lo stato di visualizzazione del controllo server, è necessario creare una classe che implementa questa interfaccia perché non è possibile ereditare dalla StateBag classe .

Proprietà

IsTrackingViewState

Quando viene implementata da una classe, ottiene un valore che indica se un controllo server tiene traccia delle modifiche apportate al relativo stato di visualizzazione.

Metodi

LoadViewState(Object)

Quando viene implementato da una classe, carica nel controllo lo stato di visualizzazione salvato in precedenza per il controllo server.
SaveViewState()

Quando viene implementato da una classe, salva le modifiche apportate allo stato di visualizzazione di un controllo server in un Object.
TrackViewState()

Quando viene implementato da una classe, indica al controllo server di tenere traccia delle modifiche apportate allo stato di visualizzazione.

Si applica a

Vedi anche