| 1 状态管理概述 | |||||||||||||||
| Control.ViewState :状态信息的字典。ViewState为StateBag的实例。 | |||||||||||||||
| 管理 ASP.NET 服务器控件的视图状态。 |
| 为支持服务器控件的视图状态管理而必须实现的属性和方法。
| ||||||||||
| 2 如何在自定义控件中实现自定义状态管理？ | |||
| 重载：LoadViewState与SaveViewState |
3.1 代码
using System;
using System.Collections.Generic;
using System.Text;
using System.Web;
using System.Web.UI;
namespace AspnetEssential.CustomerControl
{
/// <summary>
/// BarGraphControl
/// </summary>
/// <remarks>
/// 简单的图表控件。根据描述，值绘制图表
/// </remarks>
public class BarGraphControl:Control
{
/// <summary>
/// 描述列表
/// </summary>
private List<string> _description;
/// <summary>
/// 值列表
/// </summary>
private List<int> _values;
/// <summary>
/// 最大值(用于计算相BarItem的相对长度,本程序为实现此功能)
/// </summary>
private int _max;
/// <summary>
/// 构造函数中初始化控件的默认值
/// </summary>
public BarGraphControl()
{
_description = new List<string>();
_values = new List<int>();
}
/// <summary>
/// 添加键值对
/// </summary>
/// <param name="name"></param>
/// <param name="value"></param>
public void AddItem(string name,int value)
{
_description.Add(name);
_values.Add(value);
if(value>_max)
{
_max = value;
}
}
#region State Manager
protected override object SaveViewState()
{
object[] vState = new object[4];
vState[0] = base.SaveViewState();
vState[1] = _description;
vState[2] = _values;
vState[3] = _max;
return vState;
}
protected override void LoadViewState(object savedState)
{
//base.LoadViewState(savedState);
if(savedState !=null)
{
object[] vState =(object[])savedState;
if(vState[0]!=null)
{
base.LoadViewState(vState[0]);
}
if (vState[1] != null)
{
_description=(List<string>)vState[1];
}
if (vState[2] != null)
{
_values=(List<int>)vState[2];
}
if (vState[3] != null)
{
_max=(int)vState[3];
}
}
}
#endregion
#region Render
/// <summary>
/// 呈现
/// </summary>
/// <param name="writer"></param>
protected override void Render(HtmlTextWriter writer)
{
//base.Render(writer);
writer.AddAttribute(HtmlTextWriterAttribute.Id, this.ClientID);
writer.AddAttribute(HtmlTextWriterAttribute.Bordercolor, "red");
//单元格内容与单元格边框的距离
writer.AddAttribute(HtmlTextWriterAttribute.Cellpadding, "0");
//单元格之间的距离
writer.AddAttribute(HtmlTextWriterAttribute.Cellspacing, "0");
writer.RenderBeginTag(HtmlTextWriterTag.Table);
//bar的颜色
string color = string.Empty;
//绘制tr,td
for(int i=0;i<_values.Count;i++ )
{
//tr
writer.RenderBeginTag(HtmlTextWriterTag.Tr);
//td
writer.RenderBeginTag(HtmlTextWriterTag.Td);
writer.WriteEncodedText(_description[i]);
writer.RenderEndTag();
writer.RenderBeginTag(HtmlTextWriterTag.Td);
//writer.AddAttribute(HtmlTextWriterAttribute.Width, _values[i].ToString());
writer.AddStyleAttribute(HtmlTextWriterStyle.BorderColor, "blue");
writer.AddStyleAttribute(HtmlTextWriterStyle.BorderStyle, "solid");
writer.AddStyleAttribute(HtmlTextWriterStyle.BorderWidth, "1px");
color=((i % 2) == 0 ? "red" : "blue");
writer.AddStyleAttribute(HtmlTextWriterStyle.BackgroundColor, color);
writer.AddStyleAttribute(HtmlTextWriterStyle.Width, _values[i].ToString()+"px");
writer.RenderBeginTag(HtmlTextWriterTag.Div);
writer.RenderEndTag();
writer.RenderEndTag();
writer.RenderEndTag();
}
writer.RenderEndTag();
}
#endregion
}
}
3.2 控件使用实例
private const int MAXCOUNT = 10;
protected void Page_Load(object sender, EventArgs e)
{
if(!this.IsPostBack)
{
AddBarGraphValue(this.BarGraphControl1);
}
}
/// <summary>
/// 生成控件的随机数据
/// </summary>
/// <param name="barControl"></param>
private void AddBarGraphValue(BarGraphControl barControl)
{
Random rd = null;
for (int i = 0; i < MAXCOUNT;i++ )
{
rd = new Random(i);
int currentValue= rd.Next(100);
string title = string.Format("Item:{0}",i.ToString());
barControl.AddItem(title, currentValue);
}
}
3.3 运行说明
页面执行post后控件的状态仍然保留。效果如下图所示。
4 问题：不使用重载LoadViewState与SaveViewState方法，直接把_description等字段发布为存放在viewstate 的属性也应该能达到以上效果，那么什么时候使用重载方法控件的状态管理？
4.1 实验代码
using System;
using System.Collections.Generic;
using System.Text;
using System.Web;
using System.Web.UI;
namespace AspnetEssential.CustomerControl
{
/// <summary>
/// BarGraphControl
/// </summary>
/// <remarks>
/// 简单的图表控件。根据描述，值绘制图表
/// </remarks>
public class BarGraphControlWithViewStateProperty:Control
{
/// <summary>
/// 描述列表
/// </summary>
private List<string> Description
{
get
{
return ViewState["_description"] as List<string>;
}
set
{
ViewState["_description"] = value;
}
}
/// <summary>
/// 值列表
/// </summary>
//private List<int> _values;
private List<int> Values
{
get
{
return ViewState["_values"] as List<int>;
}
set
{
ViewState["_values"] = value;
}
}
/// <summary>
/// 最大值(用于计算相BarItem的相对长度,本程序为实现此功能)
/// </summary>
//private int _max;
private int Max
{
get
{
return (int)ViewState["_max"];
}
set
{
ViewState["_max"] = value;
}
}
/// <summary>
/// 构造函数中初始化控件的默认值
/// </summary>
public BarGraphControlWithViewStateProperty()
{
ViewState["_description"] = new List<string>();
ViewState["_values"] = new List<int>();
ViewState["_max"] = 0;
}
/// <summary>
/// 添加键值对
/// </summary>
/// <param name="name"></param>
/// <param name="value"></param>
public void AddItem(string name,int value)
{
Description.Add(name);
Values.Add(value);
if(value>Max)
{
Max = value;
}
}
#region Render
/// <summary>
/// 呈现
/// </summary>
/// <param name="writer"></param>
protected override void Render(HtmlTextWriter writer)
{
writer.Write(
string.Format("{0} Instance hashCode:{1}",
this.GetType().FullName,
this.GetHashCode()
)
);
//base.Render(writer);
writer.AddAttribute(HtmlTextWriterAttribute.Id, this.ClientID);
writer.AddAttribute(HtmlTextWriterAttribute.Bordercolor, "red");
//单元格内容与单元格边框的距离
writer.AddAttribute(HtmlTextWriterAttribute.Cellpadding, "0");
//单元格之间的距离
writer.AddAttribute(HtmlTextWriterAttribute.Cellspacing, "0");
writer.RenderBeginTag(HtmlTextWriterTag.Table);
//bar的颜色
string color = string.Empty;
//绘制tr,td
for(int i=0;i<Values.Count;i++ )
{
//tr
writer.RenderBeginTag(HtmlTextWriterTag.Tr);
//td
writer.RenderBeginTag(HtmlTextWriterTag.Td);
writer.WriteEncodedText(Description[i]);
writer.RenderEndTag();
writer.RenderBeginTag(HtmlTextWriterTag.Td);
//writer.AddAttribute(HtmlTextWriterAttribute.Width, _values[i].ToString());
writer.AddStyleAttribute(HtmlTextWriterStyle.BorderColor, "blue");
writer.AddStyleAttribute(HtmlTextWriterStyle.BorderStyle, "solid");
writer.AddStyleAttribute(HtmlTextWriterStyle.BorderWidth, "1px");
color=((i % 2) == 0 ? "red" : "blue");
writer.AddStyleAttribute(HtmlTextWriterStyle.BackgroundColor, color);
writer.AddStyleAttribute(HtmlTextWriterStyle.Width, Values[i].ToString() + "px");
writer.RenderBeginTag(HtmlTextWriterTag.Div);
writer.RenderEndTag();
writer.RenderEndTag();
writer.RenderEndTag();
}
writer.RenderEndTag();
}
#endregion
}
}
4.2 BarGraphControlWithViewStateProperty 说明:
4.2.1 此控件在form get 时生成工作正常
4.2.2 在post 时丢失状态
在页面启用 Trace='true' ,时能看到 viewstate 的值,ViewState值肯定不是完全的。
BarGraphControlWithViewStateProperty post时的__ViewState
BarGraphControl post 时的回传数据
5 为什么BarGraphControlWithViewStateProperty 在post中，控件丢失状态？？？
5.1 比较 BarGraphControl与 BarGraphWithViewStateProperty 在get时生成的__ViewState
5.1.1BarGraphControl get时页面生成的__ViewState
<input type="hidden" name="__VIEWSTATE" ));
输出：True
（由于上述文档以前写在excel中，这次复制到writer中导致排版比较恶心，在此向大家致以歉意。文档中有不正确的地方欢迎大家指正。）