SessionViewState.cs source code in C# .NET

                        Code:
                         / 4.0 / 4.0 / untmp / DEVDIV_TFS / Dev10 / Releases / RTMRel / ndp / fx / src / MIT / System / Web / UI / MobileControls / SessionViewState.cs / 1305376 / SessionViewState.cs
                        
                        
                            //------------------------------------------------------------------------------ 
// 
//     Copyright (c) Microsoft Corporation.  All rights reserved.
// 
//----------------------------------------------------------------------------- 

using System; 
using System.Collections; 
using System.Diagnostics;
using System.ComponentModel; 
using System.Globalization;
using System.IO;
using System.Runtime.Serialization;
using System.Text; 
using System.Web;
using System.Web.SessionState; 
using System.Web.Util; 
using System.Web.UI;
using System.Security.Permissions; 

namespace System.Web.UI.MobileControls
{
    /* 
     * Session-based view state.
     * 
     * When saving view state on the server as session data, some critical problems 
     * arise. The core issue behind most of these is how to handle the user
     * clicking the Back button. When the user does this, there is no corresponding 
     * notification to the server, and the client and server session state are thrown
     * out of [....].
     *
     * This class attempts to alleviate this by storing a small history of view states 
     * in session data.
     * 
     * To save session view state, construct a new object, set the ViewState and ActiveForm 
     * properties, and call Save. You'll get back a reference that contains the
     * state reference to write out. 
     *
     * To load session view state, construct a new object, and call Load. The class will
     * attempt to construct the view state from its history.
     * 
     * Copyright (c) 2000 Microsoft Corporation
     */ 
 
    [Obsolete("The System.Web.Mobile.dll assembly has been deprecated and should no longer be used. For information about how to develop ASP.NET mobile applications, see http://go.microsoft.com/fwlink/?LinkId=157231.")]
    internal class SessionViewState 
    {
        private static readonly String ViewStateKey = "ViewState";
        private Object _state;
 
        internal SessionViewState() {
        } 
 
        internal /*public*/ Object ViewState
        { 
            get
            {
                return _state;
            } 
            set
            { 
                _state = value; 
            }
        } 

        internal /*public*/ Pair Save(MobilePage page)
        {
            SessionViewStateHistory history = (SessionViewStateHistory)page.Session[ViewStateKey]; 
            if (history == null)
            { 
                history = new SessionViewStateHistory(HttpContext.Current); 
                page.Session[ViewStateKey] = history;
            } 

            SessionViewStateHistoryItem historyItem = new SessionViewStateHistoryItem();
            SaveTo(historyItem);
            #if TRACE 
            historyItem.Url = page.Request.FilePath;
            #endif 
            return history.Push(historyItem); 
        }
 
        internal /*public*/ void Load(MobilePage page, Pair id)
        {
            _state = null;
 
            SessionViewStateHistory history = (SessionViewStateHistory)page.Session[ViewStateKey];
            if (history != null) 
            { 
                SessionViewStateHistoryItem historyItem = history.Find(id);
                if (historyItem != null) 
                {
                    LoadFrom(historyItem);
                }
            } 
        }
 
        private void SaveTo(SessionViewStateHistoryItem historyItem) 
        {
            historyItem.ViewState = _state; 
        }

        private void LoadFrom(SessionViewStateHistoryItem historyItem)
        { 
            _state = historyItem.ViewState;
        } 
 
        #if TRACE
        internal /*public*/ void Dump(MobilePage page, out ArrayList arr) 
        {
            SessionViewStateHistory history;
            if ((page is IRequiresSessionState) && !(page is IReadOnlySessionState))
            { 
                history = (SessionViewStateHistory)page.Session[ViewStateKey];
            } 
            else 
            {
                history = null; 
            }

            if (history != null)
            { 
                history.Dump(out arr);
            } 
            else 
            {
                arr = new ArrayList(); 
            }
        }
        #endif
 
        [
            Serializable 
        ] 
        private class SessionViewStateHistoryItem : ISerializable
        { 
            #if TRACE
            public String Url;
            public String Id;
            #endif 
            public Object ViewState;
 
            public SessionViewStateHistoryItem() 
            {
            } 

            public SessionViewStateHistoryItem(SerializationInfo info, StreamingContext context)
            {
                String s = (String)info.GetString("s"); 
                if (s.Length > 0)
                { 
                    ViewState = new LosFormatter().Deserialize(s); 
                }
                else 
                {
                    ViewState = null;
                }
            } 

            [SecurityPermissionAttribute(SecurityAction.Demand, SerializationFormatter=true)] 
            void ISerializable.GetObjectData(SerializationInfo info, StreamingContext context) 
            {
                if (ViewState != null) 
                {
                    StringWriter s = new StringWriter(CultureInfo.InvariantCulture);
                    new LosFormatter().Serialize(s, ViewState);
                    info.AddValue("s", s.ToString()); 
                }
                else 
                { 
                    info.AddValue("s", String.Empty);
                } 
            }
        }

        // Session view state history. This is the history record kept in each session. 

        [ 
            Serializable 
        ]
        private class SessionViewStateHistory 
        {
            private int _historySize;
            private SessionViewStateHistoryItem[] _history;
            private int _currentHistoryIndex = 0; 
            private int _historyUsed = 0;
            private DateTime _sessionUniqueID = DateTime.Now; 
            private int _currentHistoryID = 0; 

            public SessionViewStateHistory(HttpContext context) 
            {
                _historySize = ControlsConfig.GetFromContext(context).SessionStateHistorySize;
                if (_historySize < 1)
                { 
                    throw new Exception(
                        SR.GetString(SR.SessionViewState_InvalidSessionStateHistory)); 
                } 

                _history = new SessionViewStateHistoryItem[_historySize]; 
            }

            public Pair Push(SessionViewStateHistoryItem item)
            { 
                Pair id = new Pair(_sessionUniqueID, _currentHistoryID);
                _currentHistoryID++; 
 
                _history[_currentHistoryIndex] = item;
                _currentHistoryIndex = (_currentHistoryIndex + 1) % _historySize; 
                if (_historyUsed < _historySize)
                {
                    _historyUsed++;
                } 

                #if TRACE 
                item.Id = _currentHistoryID.ToString(CultureInfo.InvariantCulture); 
                #endif
 
                return id;
            }

            public SessionViewStateHistoryItem Find(Pair id) 
            {
                // First make sure that the page is from the current session. 
                DateTime uniqueID = (DateTime) id.First; 
                if (DateTime.Compare(uniqueID, _sessionUniqueID) != 0)
                { 
                    return null;
                }

                // Now check if we actually still have it. 
                int historyID = (int) id.Second;
                int distance = _currentHistoryID - historyID; 
 
                if (distance <= 0)
                { 
                    // Shouldn't happen, but this would be a forward jump.
                    return null;
                }
                else if (distance > _historyUsed) 
                {
                    // Gone way back. Empty history, but return null. 
                    _historyUsed = 0; 
                    return null;
                } 
                else
                {
                    int foundIndex = (_currentHistoryIndex + _historySize - distance) %
                                     _historySize; 
                    // Make the found item the top of the stack.
                    _currentHistoryIndex = (foundIndex + 1) % _historySize; 
                    _currentHistoryID = historyID + 1; 
                    _historyUsed -= distance - 1;
                    return _history[foundIndex]; 
                }
            }

            #if TRACE 
            public void Dump(out ArrayList arr)
            { 
                arr = new ArrayList(); 
                int n = _currentHistoryIndex;
                for (int i = 0; i < _historyUsed; i++) 
                {
                    n = n - 1;
                    if (n == -1)
                    { 
                        n = _history.Length - 1;
                    } 
 
                    SessionViewStateHistoryItem item = _history[n];
                    if (item != null) 
                    {
                        arr.Add(String.Format(CultureInfo.InvariantCulture, "{0}({1})", item.Url, item.Id));
                    }
                    else 
                    {
                        arr.Add("(null)"); 
                    } 
                }
            } 
            #endif
        }

    } 
}

// File provided for Reference Use Only by Microsoft Corporation (c) 2007.
Link Menu

Network programming in C#, Network Programming in VB.NET, Network Programming in .NET
This book is available now!
Buy at Amazon US or
Buy at Amazon UK
SessionViewState.cs source code in C# .NET

Source code for the .NET framework in C#

Code:

Link Menu
