.NET Framework - using the XPath ID command

Asked By p_le_sueur_

21-Jun-07 08:01 AM

Dear All,

Can anybody offer me advice or examples on using the "id"
command in XPath? (within InfoPath!); and also confirm that
I am trying to use the correct function for what I want to
accomplish?

I am experimenting with InfoPath for a project whereby I
set conditional formatting for a text field based on the
value of a dropdown field.

The dropdown field is referred to by name within a second
text field, allowing the actual dropdown referenced to
change at runtime.


The resultant XML from my experimental template looks like
this:



The process is this:

The my:txtbox1 control in the InfoPath template will have a
conditional format on it which will pick up the name of a
control (my:DDLChoice) from the my:TextBox2 control, and make
my:TextBox1 visible if DDLChoice is "Yes" or invisible if it
is "No".


I am having problems with the expression in the conditional
formatting on TxtBox1; what I have so far is:


id(concat("../my:", ../my:TxtBox2)) = "No"

But this gives the following error:

InfoPath cannot open the following view: View 1
The XSL transform for the View XSL failed.

This name may not begin with the '.' character:

-->.<--./my:


I have run another test where I have placed the following expression
into the default value for TxtBox1 (and removed the conditional
formatting):

concat("../my:", TxtBox2)

When I preview the form I get the following in TxtBox1:

../my:DDLChoice

Which looks to me like it is picking up the fieldname correctly;
however;
If I try and add the id function around it:

id(concat("../my:", ../my:TxtBox2))

I get this error when validating the function:

This name may not begin with the '.' character:

-->.<--./my:DDLChoice


I'm obviously missing something with regard to the "id" function
(undoubtedly due to my lack of experience with XPath), can
anybody help, or provide any useful examples??

Thanks in anticipation,

Paul Le Sueur.

21-Jun-07 09:23 AM

An ID value in XML is not allowed to start with a dot '.' so that is why
you get the error message as the argument you pass to the id function
'../my:DDLChoice' starts with a dot.

It is not clear to me what you want to achieve, using the id function
makes sense if you have a DTD or schema defining ID values, otherwise
not. The snippet of XML your post shows does not refer a DTD or schema
at all so it is not clear whether using the id function makes any sense.


--

Martin Honnen --- MVP XML
http://JavaScript.FAQTs.com/

21-Jun-07 10:10 AM

Hi Martin,

Thanks for your reply!

My understanding of the id function was that it would allow me to
return the value of the field named within the id command, so in
the example from my original posting:

my:TxtBox2 contains a string with name of my dropdown list

my:TxtBox1 contains a default value function to pick up the value
from the dropdown list named in my:TxtBox2. So this would be:

id(concat("../my:", ../my:TxtBox2))

where concat("../my:", ../my:TxtBox2) is concatenating the string

If I run this concat command on it's own it returns

so the id command should be looking for the value in the
DDLChoice field, effectively through the following syntax:
id("../my:DDLChoice")
However, this doesn't work!!

I hope this makes sense, and explains a bit more about what I am
trying to do...

Thanks again!

Paul Le Sueur.

21-Jun-07 10:22 AM

The id function is defined here:
so
id("someId")
returns a node set with the element having the id 'someId'. For that to
work there needs to be a schema or DTD declaring attributes of type ID.




The ID type is defined here:
A valid ID value cannot start with a dot so that is why you get an error
when passing in "../my:DDLChoice".

--

Martin Honnen --- MVP XML
http://JavaScript.FAQTs.com/

21-Jun-07 10:27 AM

* p_le_sueur_1@hotmail.com wrote in microsoft.public.xml:

The id(...) function returns an element with the specified ID. This is a
globally unique name an element can carry in an attribute if it has been
declared as being of type "ID" using a schema, DTD, or other means. It's
not suitable to retrieve values of any kind, generally, you have to use
an expression that evalutes to a specific node and retrieve its string
value; often this happens implictly.

I recommend you read up on namespaces. In XML documents, attributes and
elements have names consisting of two components, the namespace name and
the local name. If you have <my:example xmlns:my='http://...'/>, that is
an { 'http://...', 'example' } element, not a "my:example" element. To
use namespaced elements and attributes in XPath expressions, you have to
declare a prefix for the namespace name and specify the prefix in the
expression.

As an example, string(/.../my:Group1/my:DDLChoice) would evaluate to the
string "Yes" as that is the elements value in your initial example. For
this to work, you have to tell the processor 'my' stands for something
else, for whatever you have specified in the xmlns:my='...' declaration
in the document.
--
Björn Höhrmann · mailto:bjoern@hoehrmann.de · http://bjoern.hoehrmann.de
Weinh. Str. 22 · Telefon: +49(0)621/4309674 · http://www.bjoernsworld.de
68309 Mannheim · PGP Pub. KeyID: 0xA4357E78 · http://www.websitedev.de/