IStateManager Interface

Definition

定义任何类为支持服务器控件的视图状态管理而必须实现的属性和方法。Defines the properties and methods any class must implement to support view state management for a server control.

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

Examples

下面的代码示例演示实现 IStateManager 接口的类。The following code example shows a class that implements the IStateManager interface. 它包括 IsTrackingViewState 属性和 LoadViewStateSaveViewStateTrackViewState 方法的实现。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 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

Remarks

服务器控件的视图状态包含控件属性的累计值。A server control's view state comprises the cumulative values of the control's properties. 此接口包括保存和加载服务器控件的视图状态值的方法,以及指示控件跟踪其视图状态更改的方法。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.

若要自定义 ASP.NET 应用程序管理服务器控件视图状态的方式,必须创建一个实现此接口的类,因为不能从 StateBag 类继承。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.

Properties

IsTrackingViewState

当由类实现时,获取一个值,通过该值指示服务器控件是否正在跟踪其视图状态更改。When implemented by a class, gets a value indicating whether a server control is tracking its view state changes.

Methods

LoadViewState(Object)

当由类实现时,将服务器控件以前保存的视图状态加载到控件。When implemented by a class, loads the server control's previously saved view state to the control.

SaveViewState()

当由类实现时,将服务器控件的视图状态更改保存到 ObjectWhen implemented by a class, saves the changes to a server control's view state to an Object.

TrackViewState()

由类实现时,指示服务器控件跟踪其视图状态的更改。When implemented by a class, instructs the server control to track changes to its view state.

Applies to

See also