ASP.NET Tutorial/Custom Controls/Validation

Adding an asynchronous callback to validate data (C#)

   <source lang="csharp">

using System; using System.Collections.Generic; using System.ruponentModel; using System.Text; using System.Web.UI; using System.Web.UI.WebControls; namespace WebControlLibrary1 {

   [DefaultProperty("Text")]
   [ToolboxData("<{0}:WebCustomControl1 runat=server></{0}:WebCustomControl1>")]
   public class WebCustomControl1 : WebControl, ICallbackEventHandler
   {
       private string text;
       [Bindable(true)]
       [Category("Appearance")]
       [DefaultValue("")]
       [Themeable(false)]
       public string Text
       {
           get
           {
               return text;
           }
           set
           {
               text = value;
           }
       }
       protected override void Render(HtmlTextWriter output)
       {
           output.RenderBeginTag(HtmlTextWriterTag.Div);
           output.AddAttribute(HtmlTextWriterAttribute.Type, "text");
           output.AddAttribute(HtmlTextWriterAttribute.Id, this.ClientID);
           output.AddAttribute(HtmlTextWriterAttribute.Name, this.ClientID);
           output.AddAttribute(HtmlTextWriterAttribute.Value, this.Text);
           output.AddAttribute("OnBlur", "ClientCallback();");        
           this.AddAttributesToRender(output);
           output.RenderBeginTag(HtmlTextWriterTag.Input);
           output.RenderEndTag();
           output.RenderEndTag();
       }
       protected override void OnPreRender(EventArgs e)
       {
           Page.ClientScript.RegisterStartupScript(
               typeof(Page),
               "ControlFocus", "document.getElementById("" + this.ClientID + "").focus();",
               true);
           Page.ClientScript.RegisterStartupScript(
               typeof(Page), "ClientCallback",
               "function ClientCallback() {" +
                   "args=document.getElementById("" + this.ClientID + "").value;" +
                   Page.ClientScript.GetCallbackEventReference(this, "args",
                       "CallbackHandler", null, "ErrorHandler", true) + "}",
               true);
       }
       #region ICallbackEventHandler Members
       public void RaiseCallbackEvent(string eventArgument)
       {
           int result;
           if (!Int32.TryParse(eventArgument, out result))
               throw new Exception("The method or operation is not implemented.");
       }
       public string GetCallbackResult()
       {
           return "Valid Data";
       }
       #endregion

   }

}</source>

Adding an asynchronous callback to validate data (VB)

   <source lang="csharp">

Imports System.ruponentModel Imports System.Web.UI <DefaultProperty("Text"), _

ToolboxData("<{0}:WebCustomControl1 runat=server></{0}:WebCustomControl1>")> _

Public Class WebCustomControl1

   Inherits System.Web.UI.WebControls.WebControl
   Implements System.Web.UI.ICallbackEventHandler
   Dim _text As String
   <Bindable(True), Category("Appearance"), Themeable(False), DefaultValue("")> _
   Property [Text]() As String
       Get
           Return _text
       End Get
       Set(ByVal Value As String)
           _text = Value
       End Set
   End Property

   Protected Overrides Sub Render(ByVal output As System.Web.UI.HtmlTextWriter)
       output.RenderBeginTag(HtmlTextWriterTag.Div)
       output.AddAttribute(HtmlTextWriterAttribute.Type, "text")
       output.AddAttribute(HtmlTextWriterAttribute.Id, Me.ClientID)
       output.AddAttribute(HtmlTextWriterAttribute.Name, Me.ClientID)
       output.AddAttribute(HtmlTextWriterAttribute.Value, Me.Text)
       output.AddAttribute("OnBlur", "ClientCallback();")
       Me.AddAttributesToRender(output)
       output.RenderBeginTag(HtmlTextWriterTag.Input)
       output.RenderEndTag()
       output.RenderEndTag()
   End Sub
   Protected Overrides Sub OnPreRender(ByVal e As System.EventArgs)
       Page.ClientScript.RegisterStartupScript(GetType(Page), _
          "ControlFocus", "document.getElementById("" & Me.ClientID & "").focus();", _
          True)
       Page.ClientScript.RegisterStartupScript( _
           GetType(Page), "ClientCallback", _
           "function ClientCallback() {" & _
               "args=document.getElementById("" & Me.ClientID & "").value;" & _
               Page.ClientScript.GetCallbackEventReference(Me, "args", _
                   "CallbackHandler", Nothing, "ErrorHandler", True) + "}", _
           True)
   End Sub

   Public Sub RaiseCallbackEvent(ByVal eventArgument As String) Implements System.Web.UI.ICallbackEventHandler.RaiseCallbackEvent
       Dim result As Int32
       If (Not Int32.TryParse(eventArgument, result)) Then
           Throw New Exception("The method or operation is not implemented.")
       End If
   End Sub
   Public Function GetCallbackResult() As String Implements ICallbackEventHandler.GetCallbackResult
       Return "Valid Data"
   End Function

End Class</source>