为什么自定义Asp.Net控件包含一个集合属性时会在设计时出错？运行时没有问题？

Question

aspx代码如下，为什么VS2008在设计时下会出现错误：

创建控件时出错
未能对属性"Items"设置"cjl:Test"

<%@ Register Assembly="MySite.Controls" Namespace="MySite.Controls" TagPrefix="cjl" %>

<cjl:Test ID="Pager1" runat="server">

 <Items>

  <cjl:Item Text="33" />

 </Items>

</cjl:Test>

控件代码如下

using System.Collections.Generic;

using System.ComponentModel;

using System.Web.UI;



namespace MySite.Controls

{

 [ToolboxData("<{0}:test runat=\"server\"></{0}:test>")]

 [ParseChildren(true)]

 [PersistChildren(false)]

 public class Test : Control

 {

  [PersistenceMode(PersistenceMode.InnerProperty)]

  [DesignerSerializationVisibilityAttribute(DesignerSerializationVisibility.Content)]

  [NotifyParentProperty(true)]

  public ItemCollection Items

  {

   get

   {

    object obj = ViewState["Items"];

    if (obj == null)

    {

     return null;

    }

    return obj as ItemCollection;

   }

   set

   {

    EnsureChildControls();

    ViewState["Items"] = value;

   }

  }



 }

 public class ItemCollection : List<Item>

 {

 }

 public class Item 

 {

  public string Text { get; set; }

 }

}

Answer 1

[ToolboxData("<{0}:test runat=\"server\"></{0}:test>")]

    [ParseChildren(true)]

    [PersistChildren(false)]

 public class Test : Control

 {

  [PersistenceMode(PersistenceMode.InnerProperty)]
     [DesignerSerializationVisibilityAttribute(DesignerSerializationVisibility.Content)]
    [TypeConverter(typeof( CollectionConverter))]

     [NotifyParentProperty(true)]

  public ItemCollection Items

  {

   get

   {

    object obj = ViewState["Items"];

    if (obj == null)

    {

     return null;

    }

    return obj as ItemCollection;

   }

   set

   {

    EnsureChildControls();

    ViewState["Items"] = value;

   }

  }

 

 

 public class ItemCollection : List<Item>

 {

 }
   
 public class Item

 {
  public string Text { get; set; }

 }

}

---

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Answer 2

我这里还是不行，显示同样的错误。

Answer 3

 

参考 http://officenotes.spaces.live.com/blog/cns!43AE5D331F584382!328.entry

终于找到了解决方法

集合属性Items不要Set方法，将其注释后就可以在设计时正确显示了。

get

   {

    object obj = ViewState["Items"];

    if (obj == null)

    {

     return return ew ItemCollection();

    }

    return obj as ItemCollection;

   }

/*set

   {

    EnsureChildControls();

    ViewState["Items"] = value;

   }*/