WEB CONTROL - Create required text box but not a drop down list

[westmich]

I have the following code for creating a web control. It basically extends a text box and adds a required field validator and an ajax extension. However, when I change the class that it inherits from to a dropdownlist, I get an error.

Imports System
Imports System.Collections.Generic
Imports System.ComponentModel
Imports System.Text
Imports System.Web
Imports System.Web.UI
Imports System.Web.UI.WebControls

Namespace Mindscape
    <DefaultProperty("Text"), ToolboxData("<{0}:tb runat=server></{0}:tb>")> _
    Public Class tb
        Inherits TextBox

        Private oRFV As RequiredFieldValidator
        Private oVCE As AjaxControlToolkit.ValidatorCalloutExtender

        <Bindable(True), DefaultValue(False)> _
        Property Required() As Boolean
            Get
                Return CBool(ViewState(Me.ID & "Required"))
            End Get
            Set(ByVal value As Boolean)
                ViewState(Me.ID & "Required") = value
            End Set
        End Property

        <Bindable(True), DefaultValue("*")> _
        Property ErrorMessage() As String
            Get
                Return ViewState(Me.ID & "ErrorMessage")
            End Get
            Set(ByVal value As String)
                ViewState(Me.ID & "ErrorMessage") = value
            End Set
        End Property

        Protected Overrides Sub OnInit(ByVal e As System.EventArgs)
            Me.BuildControls()
        End Sub

        Protected Overrides Sub Render(ByVal writer As System.Web.UI.HtmlTextWriter)
            MyBase.Render(writer)
            writer.Write("&nbsp;")
            oRFV.RenderControl(writer)
            oVCE.RenderControl(writer)
        End Sub

        Protected Sub BuildControls()
            ' required field validator
            oRFV = New RequiredFieldValidator
            oRFV.ID = Me.ID & "_oRFV"
            oRFV.ControlToValidate = Me.ID
            oRFV.ErrorMessage = Me.ErrorMessage
            oRFV.Enabled = Me.Required
            oRFV.Display = ValidatorDisplay.None
            Me.Controls.Add(oRFV)
            ' required extender
            oVCE = New AjaxControlToolkit.ValidatorCalloutExtender
            oVCE.ID = Me.ID & "_oVCE"
            oVCE.TargetControlID = oRFV.ID
            Me.Controls.Add(oVCE)
        End Sub
    End Class
End Namespace

'MindscapeServerControls.Mindscape.tb' does not allow child controls.

[wwb_99]

You need to inherit from CompositeControl (I think) and then add the textbox and such to that. As the exception notes, TextBoxes cannot have child controls and since you are inheriting from TextBox you are SOL.

Protip: make your composite control implement ITextControl if you want it to behave like a text box.

[westmich]

Thanks for the help. The textbox is fine to add child controls, it's when I make it a drop down list that I get that error. The problem with using the Composite Control is that I have to add properties to mimic what I already have in the textbox. It's not so bad with the textbox, but if I have to do it with a drop down list it will be that much more difficult to add list items.

[westmich]

Wow! I would have thought there would be more discussion on this. That others would have looked into extending the basic input controls.

Basically, I am looking for a text box, drop down list, and radio button list that I can add a few properties to like required. If I go the route of using the composite control, I end up putting a lot development into just trying to get the control to have the same basic functionality of a text box or a drop down list.

[honeymonster]

The composite control is the correct way. You should not extend controls which represent html elements which cannot take child elements.

It's not such a big deal to extend compositecontrol and delegate properties/methods to an embedded textbox.