1using System;
2using System.Web;
3using System.Web.UI;
4using System.Web.UI.WebControls;
5
6namespace Esc.Common
7{
8    public class CheckBoxListValidator : BaseValidator
9    {
10        #region Fields   ...
11
12
13        private CheckBoxList controlToValidate;
14        #endregion
15        #region Properties   ...
16
17
18        protected CheckBoxList CheckBoxListToValidate
19        {
20            get
21            {
22                if (controlToValidate == null) controlToValidate = FindControl(ControlToValidate) as CheckBoxList;
23
24                return controlToValidate;
25            }
26        }
27        #endregion
28        #region Protected Methods   ...
29
30
31        protected override void AddAttributesToRender(HtmlTextWriter writer)
32        {
33            base.AddAttributesToRender(writer);
34
35            // Add the client-side code (if needed).
36            if (RenderUplevel)
37            {
38                Page.ClientScript.RegisterExpandoAttribute(
39                    ClientID,
40                    "evaluationfunction",
41                    "CheckBoxListValidatorEvaluateIsValid",
42                    false);
43            }
44        }
45
46        protected override bool ControlPropertiesValid()
47        {
48            // make sure ControlToValidate is set.
49            if (ControlToValidate.Length == 0) throw new HttpException(string.Format(Resources.Messages.ControlToValidatePropertyCannotBeBlank, ID));
50
51            // ensure that the control being validated is a CheckBoxList.
52            if (CheckBoxListToValidate == null) throw new HttpException(string.Format(Resources.Messages.CheckBoxListValidatorCanOnlyValidateCheckBoxList));
53
54            // it's good.
55            return true;
56        }
57
58        protected bool EvaluateIsChecked()
59        {
60            CheckBoxList checkBoxList = CheckBoxListToValidate;
61
62            foreach (ListItem li in checkBoxList.Items)
63            {
64                // if any item is selected then the method returns true.
65                if (li.Selected) return true;
66            }
67
68            // no item was selected.
69            return false;
70        }
71
72        protected override bool EvaluateIsValid()
73        {
74            // only one test currently performed.
75            return EvaluateIsChecked();
76        }
77
78        protected override void OnPreRender(EventArgs e)
79        {
80            base.OnPreRender(e);
81
82            // Register the client-side function using WebResource.axd (if needed)
83            // see: http://aspnet.4guysfromrolla.com/articles/080906-1.aspx
84            if (RenderUplevel && Page != null && !Page.ClientScript.IsClientScriptIncludeRegistered(GetType(), "Validators"))
85            {
86                Page.ClientScript.RegisterClientScriptInclude(
87                    GetType(),
88                    "Validators",
89                    Page.ClientScript.GetWebResourceUrl(GetType(), "Esc.Common.Resources.Validators.js"));
90            }
91        }
92        #endregion
93    }
94}

private readonly CheckBoxListValidator myValidator = new CheckBoxListValidator();
myValidator.ID = "myValidator";
myValidator.ControlToValidate = myCheckBoxList.ClientID;
myValidator.ErrorMessage = "Error.";
myValidator.ValidationGroup = validationGroup;
Controls.Add(myValidator);