StateItem クラス

定義

ビューステート情報が複数の Web 要求間で永続化されている場合に、StateBag クラスに保存されている項目を表します。Represents an item that is saved in the StateBag class when view state information is persisted between Web requests. このクラスは継承できません。This class cannot be inherited.

public ref class StateItem sealed
public sealed class StateItem
type StateItem = class
Public NotInheritable Class StateItem
継承
StateItem

次のコード例では、StateItem クラスの Value および IsDirty プロパティを使用して、単純なカスタム ASP.NET サーバーコントロールクラス (StateBagSample) の状態を保存します。The following code example uses the Value and IsDirty properties of the StateItem class to save the state of a simple custom ASP.NET server control class, StateBagSample. ページがサーバーにポストされると、IsDirty プロパティによって、項目が変更されたかどうかがチェックされます。When the page has posted to the server, the IsDirty property checks whether the item has been modified. 状態値は、Value プロパティにアクセスすることによって表示されます。The state values are displayed by accessing the Value property.

// Create a namespace that contains a class, MyItem,
// that implements the IStateManager interface and 
// another, MyControl, that overrides its own view-state
// management methods to use those of MyItem.
using System;
using System.Web;
using System.Web.UI;
using System.Collections;
using System.Security.Permissions;

namespace StateBagSample
{
    // 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;
        }
    }
    // This class contains an instance of the MyItem class as 
    // private member. It overrides the state management methods 
    // of the Control class, since it has to invoke state 
    // management methods of MyItem whenever its own
    // view state is being saved, loaded, or tracked.
    [AspNetHostingPermission(SecurityAction.Demand,
       Level = AspNetHostingPermissionLevel.Minimal)]
    public sealed class MyControl : Control
    {
        private MyItem myItem;
        public MyControl()
            : base()
        {
            myItem = new MyItem("Hello World!");
        }
        // Override the LoadViewState method of the Control class.
        protected override void LoadViewState(object savedState)
        {
            if (savedState != null)
            {
                object[] myState = (object[])savedState;
                if (myState[0] != null)
                    base.LoadViewState(myState[0]);
                if (myState[1] != null)
                    ((IStateManager)myItem).LoadViewState(myState[1]);
            }
        }
        // Override the TrackViewState method of the Control class
        // to call the version of this method that was 
        // implemented in the MyItem class.
        protected override void TrackViewState()
        {
            base.TrackViewState();
            if (myItem != null)
                ((IStateManager)myItem).TrackViewState();
        }

        // Override the SaveViewState method of the Control class to
        // call the version of this method that was implemented by
        // the MyItem class.
        protected override object SaveViewState()
        {
            object baseState = base.SaveViewState();
            object itemState = (myItem != null) ? ((IStateManager)myItem).SaveViewState() : null;
            object[] myState = new object[2];
            myState[0] = baseState;
            myState[1] = itemState;
            return myState;
        }

        public void SetMessage(string mesg)
        {
            myItem.Message = mesg;
        }

        public string GetMessage()
        {
            return myItem.Message;
        }

        // Display the contents of Message and ViewState properties. 
        protected override void Render(HtmlTextWriter output)
        {
            // Track changes to  view state before rendering.
            TrackViewState();
            output.Write("Message: " + myItem.Message);
            output.Write("<br>");
            output.Write("<br>Enumerating the view state of the custom control<br>");
            output.Write(myItem.EnumerateViewState());
        }
    }
}
' Create a namespace that contains a class, MyItem,
' that implements the IStateManager interface and 
' another, MyControl, that overrides its own view-state
' management methods to use those of MyItem.
Imports System.Web
Imports System.Web.UI
Imports System.Collections
Imports System.Security.Permissions

Namespace StateBagSampleVB

    ' 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

    ' This class contains an instance of the MyItem class as 
    ' private member. It overrides the state management methods 
    ' of the Control class, since it has to invoke state 
    ' management methods of MyItem whenever its own
    ' view state is being saved, loaded, or tracked.

    <AspNetHostingPermission(SecurityAction.Demand, _
       Level:=AspNetHostingPermissionLevel.Minimal)> _
    Public NotInheritable Class MyControl
        Inherits Control
        Private myItem As MyItem

        Public Sub New()
            myItem = New MyItem("Hello World!")
        End Sub

        ' Override the LoadViewState method of the Control class.
        Protected Overrides Sub LoadViewState(ByVal savedState As Object)
            If Not (savedState Is Nothing) Then
                Dim myState As Object() = CType(savedState, Object())
                If Not (myState(0) Is Nothing) Then
                    MyBase.LoadViewState(myState(0))
                End If
                If Not (myState(1) Is Nothing) Then
                    CType(myItem, IStateManager).LoadViewState(myState(1))
                End If
            End If
        End Sub
        ' Override the TrackViewState method of the Control class
        ' to call the version of this method that was 
        ' implemented in the MyItem class.
        Protected Overrides Sub TrackViewState()
            MyBase.TrackViewState()
            If Not (myItem Is Nothing) Then
                CType(myItem, IStateManager).TrackViewState()
            End If
        End Sub

        ' Override the SaveViewState method of the Control class to
        ' call the version of this method that was implemented by
        ' the MyItem class.
        Protected Overrides Function SaveViewState() As Object
            Dim baseState As Object = MyBase.SaveViewState()
            Dim itemState As Object
            If Not (myItem Is Nothing) Then
                itemState = CType(myItem, IStateManager).SaveViewState()
            Else
                itemState = Nothing
            End If

            Dim myState(1) As Object
            myState(0) = baseState
            myState(1) = itemState
            Return myState
        End Function 'SaveViewState


        Public Sub SetMessage(ByVal mesg As String)
            myItem.Message = mesg
        End Sub


        Public Function GetMessage() As String
            Return myItem.Message
        End Function 'GetMessage


        ' Display the contents of Message and ViewState properties. 
        Protected Overrides Sub Render(ByVal output As HtmlTextWriter)
            ' Track changes to  view state before rendering.
            TrackViewState()
            output.Write(("Message: " + myItem.Message))
            output.Write("<br>")
            output.Write("<br>Enumerating the view state of the custom control<br>")
            output.Write(myItem.EnumerateViewState())
        End Sub
    End Class
End Namespace 'StateBagSampleVB

注釈

ビューステートは、ページまたは ASP.NET サーバーコントロールのプロパティ値を累積したもので、非表示フィールドで要求元のブラウザーに送信されます。View state is the accumulation of a page's or an ASP.NET server control's property values and is sent to the requesting browser in a hidden field.

StateItem オブジェクトは、Item[String] プロパティまたは Add メソッドを使用して、ASP.NET サーバーコントロールの StateBag オブジェクトに明示的に追加できます。You can explicitly add StateItem objects to an ASP.NET server control's StateBag object using either the Item[String] property or the Add method. StateBag は、格納されているすべての項目に対する変更を追跡します。The StateBag then tracks changes to all the items that it stores. StateItem オブジェクトに対する変更は、IsDirty プロパティに反映されます。Any changes to a StateItem object are reflected in its IsDirty property. これらの変更は、コントロールがページに表示される直前に、サーバーコントロール処理の保存ビューステートフェーズ中に SaveViewState メソッドを呼び出すことによって保存されます。These changes are saved by a call to the SaveViewState method during the save view state phase of server control processing, just before the control is rendered to the page. 詳細については、「 ASP.NET Web Server Controls」を参照してください。For more information, see ASP.NET Web Server Controls.

プロパティ

IsDirty

StateItem オブジェクトが変更されたかどうかを示す値を取得または設定します。Gets or sets a value indicating whether the StateItem object has been modified.

Value

StateItem オブジェクトに格納されている StateBag オブジェクトの値を取得または設定します。Gets or sets the value of the StateItem object that is stored in the StateBag object.

メソッド

Equals(Object)

指定されたオブジェクトが現在のオブジェクトと等しいかどうかを判定します。Determines whether the specified object is equal to the current object.

(継承元 Object)
GetHashCode()

既定のハッシュ関数として機能します。Serves as the default hash function.

(継承元 Object)
GetType()

現在のインスタンスの Type を取得します。Gets the Type of the current instance.

(継承元 Object)
MemberwiseClone()

現在の Object の簡易コピーを作成します。Creates a shallow copy of the current Object.

(継承元 Object)
ToString()

現在のオブジェクトを表す string を返します。Returns a string that represents the current object.

(継承元 Object)

適用対象

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