ViewState 作为属性

Question

而不是这个..

    public string Text
    {

        get { return ViewState["Text"] as string; }

        set { ViewState["Text"] = value; }

    }

我想要这个..

    [ViewState]
    public String Text { get; set; }

可以吗？

Answer 1

像这样：

public class BasePage: Page {

    protected override Object SaveViewState() {

        object baseState                      = base.SaveViewState();            
        IDictionary<string, object> pageState = new Dictionary<string, object>();
        pageState.Add("base", baseState);

        // Use reflection to iterate attributed properties, add 
        // each to pageState with the property name as the key

        return pageState;
    }

    protected override void LoadViewState(Object savedState) {

        if (savedState != null) {

            var pageState = (IDictionary<string, object>)savedState;

            if (pageState.Contains("base")) {
                base.LoadViewState(pageState["base"]);
            }

            // Iterate attributed properties. If pageState contains an
            // item with the appropriate key, set the property value.

        }
    }
}

从此类继承的页面可以使用您建议的属性驱动语法。

Answer 2

嗯，这就是我到目前为止所得到的，TY Jeff 为我指明了正确的方向：

测试页：

public partial class Pages_Test : BasePage    {
    [ViewState]
    public String Name { get; set; }

基页：

    #region Support ViewState Attribute

    BindingFlags _flags = BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance;

    protected override Object SaveViewState()
    {
        object _baseState = base.SaveViewState();
        IDictionary<string, object> _pageState = new Dictionary<string, object> { { "base", _baseState } };

        //Use reflection to get properties marked for viewstate

        foreach (PropertyInfo _property in GetType().GetProperties(_flags))
        {
            if (_property.HasAttribute<ViewState>())
            {
                object _value = _property.GetValue(this, _flags , null, null, null);
                _pageState.Add(new KeyValuePair<string, object>(_property.Name, _value));
            }
        }
        return _pageState;
    }

    protected override void LoadViewState(Object savedState)
    {
        if (savedState != null)
        {
            var _pageState = (IDictionary<string, object>)savedState;

            if (_pageState.ContainsKey("base"))
            {
                base.LoadViewState(_pageState["base"]);
            }
            //use reflection to set properties 
            foreach (PropertyInfo _property in GetType().GetProperties(_flags ))
            {
                if (_property.HasAttribute<ViewState>() && _pageState.ContainsKey(_property.Name))
                {
                    object _value = _pageState[_property.Name];
                    _property.SetValue(this, _value, _flags , null, null, null);
                }
            }
        }
    }
    #endregion

属性：

/// <summary>
/// This attribute is used by the BasePage to identify properties that should be persisted to ViewState
/// Note: Private properties are not supported
/// </summary>
[AttributeUsage(AttributeTargets.Property)]
public class ViewState : Attribute
{
    //Marker
}

助手：

public static class PropertyExtension
{
    public static Boolean HasAttribute<T>(this PropertyInfo property)
    {
        object[] attrs = property.GetCustomAttributes(typeof(T), false);
        return attrs != null && attrs.Length == 1;
    }

}

---

编辑

Jan 有一个关于性能的有效观点，我做了一些分析，结果如下：

                 Without Attribute    With Attribute   Increase   Slower %
One Property     
       First Load        0,004897899     0,010734255    0,005836356    219
       Save, postback    0,002353861     0,010478008    0,008124147    445
       Load, Postback    0,001488807     0,00627482     0,004786013    421
   10 properties  
       First Load        0,006184096     0,015288675    0,009104579    247
       Save, postback    0,004061759     0,015052262    0,010990503    371
       Load, Postback    0,0015708       0,005833074    0,004262274    371

              % increase
Avg Page. 0,902215714567075 0,00648

在空页面上增加相当可观，但在平均负载为 1 秒的页面上，增加量为 0.01%。

---

更新：使用 PostSharp、PostSharp4ViewState

第 1 步：确保您的网站已预编译

第 2 步：安装 PostSharp 和 PostSharp4ViewState

第 3 步：参考 PostSharp.Public 和 PostSharp4ViewState

第 4 步：以下是现在有效的代码。

      [Persist(Mode=PersistMode.ViewState)]
      private string _name;
   public String Name { 
    get { return _name; }
    set { _name = value; }
   }

Answer 3

由于大量使用反射，BBorg 的解决方案实际上非常慢。

使用 PostSharp.Laos，通过让您的属性继承自 OnMethodBoundaryAspect，您可以轻松地覆盖 public override void OnInvocation(MethodInvocationEventArgs eventArgs) 并在其中发挥所有作用。这会更快。例如，查看 PostSharp 主页上的 CacheAttribute 示例。

如果您真的想要极速，您可以编写一个 PostSharp 插件，将 MSIL（GetFromViewState、SetInViewState 方法或其他方法）编织到您的属性中，甚至不会有性能损失。

Answer 4

此功能内置于NHibernate Burrow。如果你没有在你的应用程序中使用 NHibernate，NHibernate Burrow 的源代码是可用的here。随意挖掘，看看他们是如何做到的，并删除我们对您有用的任何部分（只要您遵守LGPL license）。

最相关的代码似乎在 StatefulFieldProcessor.cs 第 51 - 72 行。

        /// <summary>
    /// Get the FieldInfo - Attribute pairs that have the customer attribute of type <typeparamref name="AT"/> 
    /// </summary>
    /// <typeparam name="AT"></typeparam>
    /// <returns></returns>
    protected IDictionary<FieldInfo, AT> GetFieldInfo<AT>() where AT : Attribute {
        IDictionary<FieldInfo, AT> retVal = new Dictionary<FieldInfo, AT>();
        foreach (FieldInfo fi in GetFields())
            foreach (AT a in Attribute.GetCustomAttributes(fi, typeof (AT)))
                retVal.Add(fi, a);
        return retVal;
    }

    protected IDictionary<FieldInfo, StatefulField> GetStatefulFields() {
        IDictionary<FieldInfo, StatefulField> retVal;
        Type controlType = Control.GetType();
        if (controlType.Assembly == webAssembly)
            return null;
        if (!fieldInfoCache.TryGetValue(controlType, out retVal))
            fieldInfoCache[controlType] = retVal = GetFieldInfo<StatefulField>();
        return retVal;
    }