如何动态加载web control在postback后记住视图状态(viewstate)

最新推荐文章于 2020-09-26 13:14:13 发布

原创最新推荐文章于 2020-09-26 13:14:13 发布 · 1.2k 阅读

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#postback #web #pair #object #string #null

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在设计ASP.NET的Web程序时，运行时加入的Web控件因在SaveViewState之后加入，postback后数据会丢失。本文通过重写表单的SaveViewState和LoadViewState，设计了一个继承自Panel的容器控件来解决该问题，给出了详细代码实现。

在我们设计asp.net的web程序时，有时表单上的web contorl不是在设计就有的。而是在运行时才加入的。可是这就带来了一个问题，就是web contorl因为在SaveViewState之后加入，所以并没有保存，在poskback后所有已写的数据，将丢失.如何来解决上面的问题呢。我写了一个算是个web contorl的容器控件，它的由Panel继承而来的。

主要是重写表单的SaveViewState和LoadViewState:

using System.Web.UI.Design;
using System.Web.UI.Design.WebControls;
using System.Web.UI.WebControls;
using System.ComponentModel;
using System.Xml;

namespace DBauer.Web.UI.WebControls
{
[Designer("System.Web.UI.Design.ControlDesigner"),
ToolboxData("<{0}:DynamicControlsPanel runat=server></{0}:DynamicControlsPanel>")]

public class DynamicControlsPanel : Panel
{
#region 自定义的属性

  [DefaultValue(HandleDynamicControls.DontPersist)]
  public HandleDynamicControls ControlsWithoutIDs
  {
   get
   {
    if(ViewState["ControlsWithoutIDs"] == null)
     return HandleDynamicControls.DontPersist;
    else
     return (HandleDynamicControls) ViewState["ControlsWithoutIDs"];
   }
   set { ViewState["ControlsWithoutIDs"] = value; }
  }

#endregion 自定义的属性

  #region 视图状态管理

  protected override void LoadViewState(object savedState)
  {
   object[] viewState = (object[]) savedState;

   Pair persistInfo = (Pair) viewState[0];
   foreach(Pair pair in (ArrayList) persistInfo.Second)
   {
    RestoreChildStructure(pair, this);
   }

base.LoadViewState(viewState[1]);
}

  protected override object SaveViewState()
  {
   if(HttpContext.Current == null)
    return null;

   object[] viewState = new object[2];
   viewState[0] = PersistChildStructure(this, "C");
   viewState[1] = base.SaveViewState();
   return viewState;
  }

  private void RestoreChildStructure(Pair persistInfo, Control parent)
  {
   Control control;

string[] persistedString = persistInfo.First.ToString().Split(';');

   string[] typeName = persistedString[1].Split(':');
   switch(typeName[0])
   {

    case "C":
     Type type = Type.GetType(typeName[1], true, true);
     try
     {
      control = (Control) Activator.CreateInstance(type);
     }
     catch(Exception e)
     {
      throw new ArgumentException(String.Format("类型 '{0}' 不能恢复状态", type.

ToString()), e);
     }
     break;
    default:
     throw new ArgumentException("无法识别的类型.不能恢复状态.");
   }

control.ID = persistedString[2];

   switch(persistedString[0])
   {
    case "C":
     parent.Controls.Add(control);
     break;
   }

   foreach(Pair pair in (ArrayList) persistInfo.Second)
   {
    RestoreChildStructure(pair, control);
   }
  }

  private Pair PersistChildStructure(Control control, string controlCollectionName)
  {
   string typeName;
   ArrayList childPersistInfo = new ArrayList();

   if(control.ID == null)
   {
    if(ControlsWithoutIDs == HandleDynamicControls.ThrowException)
     throw new NotSupportedException("你必须设置你的ID");
    else if (ControlsWithoutIDs == HandleDynamicControls.DontPersist)
     return null;
   }

typeName = "C:" + control.GetType().AssemblyQualifiedName;

string persistedString = controlCollectionName + ";" + typeName + ";" + control.ID;

   if(!(control is UserControl) && !(control is CheckBoxList))
   {
    for(int counter = 0; counter < control.Controls.Count; counter++)
    {
     Control child = control.Controls[counter];
     Pair pair = PersistChildStructure(child, "C");
     if(pair != null)
      childPersistInfo.Add(pair);
    }
   }

   return new Pair(persistedString, childPersistInfo);
  }
  #endregion 视图状态管理

  #region 重化控件样式
  protected override void Render(System.Web.UI.HtmlTextWriter writer)
  {
   base.Render(writer);
  }
  //
  #endregion 重化控件样式
}

public enum HandleDynamicControls
{
  DontPersist,
  Persist,
  ThrowException
}
}

希望能给有这方面问题的朋友一点帮肋.同时也欢迎大家改写的更好