ViewStateAutoManager

using System;
using System.Web.UI;
using System.Reflection;
using System.Collections.Generic;
using System.Collections;

namespace My.Common
{
    [AttributeUsage(AttributeTargets.Property)]
    public class ViewStateAttribute : Attribute
    {
    }

    public class BasePage : Page
    {
        protected override object SaveViewState()
        {
            ViewStateAutoManager mgr = new ViewStateAutoManager(this);
            var v = base.SaveViewState();
            return mgr.SaveViewState(v);
        }

        protected override void LoadViewState(object savedState)
        {
            ViewStateAutoManager mgr = new ViewStateAutoManager(this);
            var v = mgr.LoadViewState(savedState);
            base.LoadViewState(v);
        }
    }

    public class BasePart : UserControl
    {
        protected override object SaveViewState()
        {
            ViewStateAutoManager mgr = new ViewStateAutoManager(this);
            var v = base.SaveViewState();
            return mgr.SaveViewState(v);
        }

        protected override void LoadViewState(object savedState)
        {
            ViewStateAutoManager mgr = new ViewStateAutoManager(this);
            var v = mgr.LoadViewState(savedState);
            base.LoadViewState(v);
        }
    }

    public class ViewStateAutoManager
    {
        private static Dictionary<Type, List<PropertyInfo>> _cache = new Dictionary<Type, List<PropertyInfo>>();
        private Control _ctl;

        public ViewStateAutoManager(Control ctl)
        {
            this._ctl = ctl;
        }

        private List<PropertyInfo> GetViewStateProperties(Control ctl)
        {
            var targetType = ctl.GetType();

            if (!_cache.ContainsKey(targetType))
            {
                var pros = targetType.GetProperties(
                    BindingFlags.Public
                    | BindingFlags.NonPublic
                    | BindingFlags.Instance
                    );

                var list = new List<PropertyInfo>();

                foreach (var p in pros)
                {
                    var attr = Attribute.GetCustomAttribute(p, typeof(ViewStateAttribute));
                    if (attr != null)
                    {
                        list.Add(p);
                    }
                }

                _cache[targetType] = list;
            }

            return _cache[targetType];
        }

        private ViewStateList GetViewState()
        {
            var data = new ViewStateList();
            var pros = GetViewStateProperties(_ctl);

            foreach (var p in pros)
            {
                var value = p.GetValue(_ctl, null);
                data.Add(p.Name, value);
            }

            return data;
        }

        public object SaveViewState(object parentViewState)
        {
            var my = GetViewState();
            return new Pair(parentViewState, my);
        }

        private void SetViewState(object viewState)
        {
            var data = viewState as ViewStateList;
            var pros = GetViewStateProperties(_ctl);

            foreach (var p in pros)
            {
                p.SetValue(_ctl, data[p.Name], null);
            }
        }

        public object LoadViewState(object parentViewState)
        {
            var pair = parentViewState as Pair;
            SetViewState(pair.Second);
            return pair.First;
        }
    }

    [Serializable]
    public class ViewStateList : IEnumerable<ViewStateList._Item>
    {
        [Serializable]
        public class _Item
        {
            public string Key;
            public object Value;
            public _Item Next;
        }

        private _Item First;

        public void Add(string key, object value)
        {
            var newItem = new _Item { Key = key, Value = value };

            if (First == null)
            {
                First = newItem;
            }
            else
            {
                _Item last = First;
                while (last.Next != null)
                {
                    last = last.Next;
                }
                last.Next = newItem;
            }
        }

        public object this[string key]
        {
            get
            {
                foreach (var p in this)
                {
                    if (p.Key == key)
                    {
                        return p.Value;
                    }
                }

                return string.Empty;
            }
        }

        #region IEnumerable<_Item> Members

        public IEnumerator<ViewStateList._Item> GetEnumerator()
        {
            for (var p = First; p != null; p = p.Next)
            {
                yield return p;
            }
        }

        #endregion

        #region IEnumerable Members

        IEnumerator IEnumerable.GetEnumerator()
        {
            return this.GetEnumerator();
        }

        #endregion
    }
}