Custom CustomValidator: Properties Window Problems

[philaphan80@yahoo.com]

Hello. I'm still rather new to building custom controls, so please be
gentle. ;)

What I'd like to be able to do, when validating, is drop my
CustomServerValidator (see below) and a generic Label control onto the
page. Then, all I'd have to do is set two properties:
ControlToValidate and my custom ErrorLabel. The custom control would
handle the rest at runtime, including sending the appropriate error
message to the Label tied to ErrorLabel.

I'd like the ErrorLabel property to act similarly to the
ControlToValidate property. When I choose ErrorLabel in the Properties
window, I'd like to see a dropdown filled with a list of objects -- in
this case, of type Label -- currently available on the form.

This is where the error occurs. The dropdown works properly, but if I
choose one of the labels, I get the following error message in Design
mode:

------------------------------------------------------------------------------------------------------------------------
Error Rendering Control - CustomServerValidator1
An unhandled exception has occurred.
Cannot create an object of type 'System.Web.UI.WebControls.Label' from
its string representation 'Label1' for the 'ErrorLabel' property.
------------------------------------------------------------------------------------------------------------------------

If I change the ErrorLabel property to type String, the error
disappears, but then I have to enter the Label's name manually.

How would I go about fixing this?

Also, one follow-up question.........

Because the CustomValidator derives from type Label, all of my
CustomServerValidators show up in the Properties dropdown list as well.
Once the issue above is fixed, is there any way to further "filter"
the dropdown to show only *pure* Label controls?

Thanks in advance!



Public Class CustomServerValidator
Inherits System.Web.UI.WebControls.CustomValidator

Private _ErrorLabel As Label

<Browsable(True)> _
Public Property ErrorLabel() As Label
Get
Return _ErrorLabel
End Get
Set(ByVal value As Label)
_ErrorLabel = value
End Set
End Property

Public Sub New()

Me.EnableClientScript = False
Me.ValidateEmptyText = True

End Sub

<...unrelated code removed...>

End Class

[Gaurav Vaish \(www.EdujiniOnline.com\)]

> This is where the error occurs. The dropdown works properly, but if I

> choose one of the labels, I get the following error message in Design
> mode:
>
> ------------------------------------------------------------------------------------------------------------------------
> Error Rendering Control - CustomServerValidator1
> An unhandled exception has occurred.
> Cannot create an object of type 'System.Web.UI.WebControls.Label' from
> its string representation 'Label1' for the 'ErrorLabel' property.
> ------------------------------------------------------------------------------------------------------------------------

Let the property be of type 'String' because in the aspx, it has to be added
declaratively, something like:

<my:CustomServerValidator id='...' ControlToValidate='idOfControlToValidate'
.... />

Add the following attribute to the property:

TypeConverter(typeof(System.Web.UI.WebControls.Val idatedControlConverter))


--
Happy Hacking,
Gaurav Vaish | [url]www.mastergaurav.com[/url]
[url]www.edujinionline.com[/url]
[url]http://articles.edujinionline.com/webservices[/url]
-----------------------------------------

[philaphan80@yahoo.com]

Thanks for your quick response, Gaurav! I appreciate the help.

I wasn't able to use your line of code exactly as you supplied it,
becuase ValidatedControlConverter returns a list of controls on the
page which can be validated. (I needed a list of controls on the page
matching type Label.) However, it pointed me in the right direction.

After poking around Google Groups and the Help file a bit more, I found
what I was looking for -- CustomIDConverter.

I created a new class which inherits CustomIDConverter and overrides
the Filter method. It basically filters out any of the controls ready
to be listed if they don't match the specified type. At Design time,
the dropdown in the Properties window now shows only the labels on the
form. It also excludes my CustomServerValidator, because it's not a
*true* Label.

My revised code is below for anyone who might run into a similar
situation.



Public Class LabelConverter
Inherits ControlIDConverter

Protected Overrides Function FilterControl(ByVal control As
System.Web.UI.Control) As Boolean

If Not TypeOf (control) Is Label Then
Return False
End If

Return MyBase.FilterControl(control)

End Function

End Class

Public Class CustomServerValidator
Inherits System.Web.UI.WebControls.CustomValidator

Private _ErrorLabel As String

<Browsable(True), TypeConverter(GetType(LabelConverter))> _
Public Property ErrorLabel() As String
Get
Return _ErrorLabel
End Get
Set(ByVal value As String)
_ErrorLabel = value
End Set
End Property

Public Sub New()

Me.EnableClientScript = False
Me.ValidateEmptyText = True

End Sub

<...unrelated code removed...>

End Class

[Gaurav Vaish \(www.EdujiniOnline.com\)]

> I wasn't able to use your line of code exactly as you supplied it,

> becuase ValidatedControlConverter returns a list of controls on the
> page which can be validated. (I needed a list of controls on the page
> matching type Label.) However, it pointed me in the right direction.

Yes... it will list down all controls that have an attribute
"ValidationProperty" (System.Web.UI.ValidationPropertyAttribute)

> After poking around Google Groups and the Help file a bit more, I found
> what I was looking for -- CustomIDConverter.

Yes... that's the root of all Control-To-Validate filters.

> Protected Overrides Function FilterControl(ByVal control As
> System.Web.UI.Control) As Boolean
>
> If Not TypeOf (control) Is Label Then
> Return False
> End If
>
> Return MyBase.FilterControl(control)
>
> End Function

How about something like this:

If TypeOf(control) is Label OR TypeOf(control) is CustomServerValidator Then
Return True
Else
Return False
End If

Don't call MyBase.FilterControl(control)
because that will always return "true".


--
Happy Hacking,
Gaurav Vaish | [url]www.mastergaurav.com[/url]
[url]www.edujinionline.com[/url]
[url]http://articles.edujinionline.com/webservices[/url]
-----------------------------------------

[philaphan80@yahoo.com]

> How about something like this:

>
> If TypeOf(control) is Label OR TypeOf(control) is CustomServerValidator Then
> Return True
> Else
> Return False
> End If

No, that wouldn't work, because it would display my own control in the
dropdown list. The way I listed it above works well, because it
excludes anything that's not a Label.

Thanks again for your help, Gaurav. You saved me from a lot of time
and frustration.

[Gaurav Vaish \(www.EdujiniOnline.com\)]

> No, that wouldn't work, because it would display my own control in the

> dropdown list. The way I listed it above works well, because it
> excludes anything that's not a Label.

Hmm... chicken and egg problem in that case...

> Thanks again for your help, Gaurav. You saved me from a lot of time
> and frustration.

Always welcome!


--
Happy Hacking,
Gaurav Vaish | [url]www.mastergaurav.com[/url]
[url]www.edujinionline.com[/url]
[url]http://articles.edujinionline.com/webservices[/url]
-----------------------------------------

[philaphan80@yahoo.com]

> Hmm... chicken and egg problem in that case...

You're right, Gaurav.

When I was testing this previously, I only had one
CustomServerValidator on the page. Once I dropped a second one onto
the page, it was available to the first one as a possible ErrorLabel
control. The first was available to the second as well.

It seems by default, the control filters itself from the list even when
overridden. But the other ones are fair game. (That's why I never saw
my control in the dropdown list! It was automatically filtering
itself.)

Anyway, I've modified the code and figured it was worth posting here in
case anyone else runs into a similar problem.


If TypeOf (control) Is BaseValidator Then
Return False
ElseIf Not TypeOf (control) Is Label Then
Return False
Else
Return True
End If