前几天遇到个问题,有一个DropDownList需要对某些Item对标记。我们大家知道Dropdownlist最终呈现是<select>,最后我们想到html是:
1: <select>
2: <option value="volvo" title="share">Volvo</option>
3: <option value="saab" title="share">Saab</option>
4: <option value="mercedes">Mercedes</option>
5: <option value="audi">Audi</option>
6: </select>
在Server端我们使用Attributes给他们加上title属性, 如以下代码片段:
1: return ddlresultset.Select(t =>
2: {
3: var newitem = new ListItem(t.UserId.HasValue ? t.Name : "*" + t.Name, t.Id.ToString());
4: if (!t.UserId.HasValue)
5: newitem.Attributes.Add("title", "share");
6: return newitem;
7: }).OrderBy(d => d.Text).ToArray();
现在我们绑定上去,当我们做POSTBACK时,发现title属性丢掉了,原因是DropDownList控制没有存储title属性到ViewState。我们看下DropDownList类继承关系:
System.Web.UI.Control
System.Web.UI.WebControls.WebControl
System.Web.UI.WebControls.BaseDataBoundControl
System.Web.UI.WebControls.DataBoundControl
System.Web.UI.WebControls.ListControl
System.Web.UI.WebControls.BulletedList
System.Web.UI.WebControls.CheckBoxList
System.Web.UI.WebControls.DropDownList
System.Web.UI.WebControls.ListBox
System.Web.UI.WebControls.RadioButtonList
相同的问题将出现派生ListControl的控件。解决方法,是重写SaveViewState 与 LoadViewState方法,看如下代码:
1: /// <summary>
2: /// Saves the current view state of the <see cref="T:System.Web.UI.WebControls.ListControl"/> -derived control and the items it contains.
3: /// </summary>
4: /// <returns>
5: /// An <see cref="T:System.Object"/> that contains the saved state of the <see cref="T:System.Web.UI.WebControls.ListControl"/> control.
6: /// </returns>
7: protected override object SaveViewState()
8: {
9: // Create an object array with one element for the CheckBoxList's
10: // ViewState contents, and one element for each ListItem in skmCheckBoxList
11: object[] state = new object[this.Items.Count + 1];
12:
13: object baseState = base.SaveViewState();
14: state[0] = baseState;
15:
16: // Now, see if we even need to save the view state
17: bool itemHasAttributes = false;
18: for (int i = 0; i < this.Items.Count; i++)
19: {
20: if (this.Items[i].Attributes.Count > 0)
21: {
22: itemHasAttributes = true;
23:
24: // Create an array of the item's Attribute's keys and values
25: object[] attribKV = new object[this.Items[i].Attributes.Count * 2];
26: int k = 0;
27: foreach (string key in this.Items[i].Attributes.Keys)
28: {
29: attribKV[k++] = key;
30: attribKV[k++] = this.Items[i].Attributes[key];
31: }
32:
33: state[i + 1] = attribKV;
34: }
35: }
36:
37: // return either baseState or state, depending on whether or not
38: // any ListItems had attributes
39: if (itemHasAttributes)
40: return state;
41: else
42: return baseState;
43: }
44:
45:
46: /// <summary>
47: /// Loads the previously saved view state of the <see cref="T:System.Web.UI.WebControls.DetailsView"/> control.
48: /// </summary>
49: /// <param name="savedState">An <see cref="T:System.Object"/> that represents the state of the <see cref="T:System.Web.UI.WebControls.ListControl"/> -derived control.</param>
50: protected override void LoadViewState(object savedState)
51: {
52: if (savedState == null) return;
53:
54: // see if savedState is an object or object array
55: if (savedState is object[])
56: {
57: // we have an array of items with attributes
58: object[] state = (object[])savedState;
59: base.LoadViewState(state[0]); // load the base state
60:
61: for (int i = 1; i < state.Length; i++)
62: {
63: if (state[i] != null)
64: {
65: // Load back in the attributes
66: object[] attribKV = (object[])state[i];
67: for (int k = 0; k < attribKV.Length; k += 2)
68: this.Items[i - 1].Attributes.Add(attribKV[k].ToString(),
69: attribKV[k + 1].ToString());
70: }
71: }
72: }
73: else
74: // we have just the base state
75: base.LoadViewState(savedState);
76: }
77: }
这样也可实现,我们看下呈现后ViewState中有我们那个title属性了,通过对ViewState的Decode 清晰可见:
很简单,希望对您Develop有帮助!
作者:Petter Liu
出处:http://www.cnblogs.com/wintersun/
本文版权归作者和博客园共有,欢迎转载,但未经作者同意必须保留此段声明,且在文章页面明显位置给出原文连接,否则保留追究法律责任的权利。
该文章也同时发布在我的独立博客中-Petter Liu Blog。
【推荐】编程新体验,更懂你的AI,立即体验豆包MarsCode编程助手
【推荐】凌霞软件回馈社区,博客园 & 1Panel & Halo 联合会员上线
【推荐】抖音旗下AI助手豆包,你的智能百科全书,全免费不限次数
【推荐】博客园社区专享云产品让利特惠,阿里云新客6.5折上折
【推荐】轻量又高性能的 SSH 工具 IShell:AI 加持,快人一步
· [.NET]调用本地 Deepseek 模型
· 一个费力不讨好的项目,让我损失了近一半的绩效!
· .NET Core 托管堆内存泄露/CPU异常的常见思路
· PostgreSQL 和 SQL Server 在统计信息维护中的关键差异
· C++代码改造为UTF-8编码问题的总结
· 实操Deepseek接入个人知识库
· CSnakes vs Python.NET:高效嵌入与灵活互通的跨语言方案对比
· 【.NET】调用本地 Deepseek 模型
· Plotly.NET 一个为 .NET 打造的强大开源交互式图表库
· 上周热点回顾(2.17-2.23)
2009-05-26 用扩展方法生成分割符字符串