LINQ and XML for compact framework

[Jon Skeet [C# MVP]]

Re: LINQ and XML for compact framework

On May 1, 2:21 pm, Wan <luo...@gmail.c omwrote:

<snip>

Actual Output has nothing changed. However, if I created a normal
framework console application project. And copy, paste this code, it
will do the job. That's why I want to ask how to use LINQ to modify
XML in compact framework.

Okay, now we're getting somewhere. I can see three possible reasons to
start with:

1) It might not be finding the MessageStaus element
2) It might be finding the MessageStaus element but failing to change
the value properly
3) It might not be able to save the file back to disk
4) It might be throwing an exception, which you're silently swallowing

Try putting some kind of alert (e.g. a MessageBox.Show or
Console.WriteLi ne) in the foreach loop, to check for condition 1.
Try saving something totally different (e.g. a new XElement) to disk
to check for condition 3.
Try putting an alert in your catch block to check for condition 4.

Jon

[Wan]

Re: LINQ and XML for compact framework

On May 1, 2:38 pm, "Jon Skeet [C# MVP]" <sk...@pobox.co mwrote:

On May 1, 2:21 pm, Wan <luo...@gmail.c omwrote:
>
<snip>
>

Actual Output has nothing changed.  However, if I created a normal
framework console application project. And copy, paste this code, it
will do the job.  That's why I want to ask how to use LINQ to modify
XML in compact framework.

>
Okay, now we're getting somewhere. I can see three possible reasons to
start with:
>
1) It might not be finding the MessageStaus element
2) It might be finding the MessageStaus element but failing to change
the value properly
3) It might not be able to save the file back to disk
4) It might be throwing an exception, which you're silently swallowing
>
Try putting some kind of alert (e.g. a MessageBox.Show or
Console.WriteLi ne) in the foreach loop, to check for condition 1.
Try saving something totally different (e.g. a new XElement) to disk
to check for condition 3.
Try putting an alert in your catch block to check for condition 4.
>
Jon

First of all, thanks for your suggestion. I put some alerts as you
told, I can see that the

IEnumerable<XEl ementmsgs = from el in root.Descendant s("Message")
where
el.Element("Mes sageID").Value == MsgID
select el;

foreach (XElement el in msgs)
{
el.Element("Mes sageStaus").Set Value(newStatus .ToString());
}

'msgs' is empty. There is two possiblities here.
1) from el in root.Descendant s("Message")
where el.Element("Mes sageID").Value == MsgID
select el;
This LINQ statement is not working.

2) After the LINQ found the records, it fail to copy the value to
IEnumerable<XEl ementmsgs

As I said, I have tested this code and same LINQ statement on a
desktop console application. It works fine.


Regards,
Wan

[Jon Skeet [C# MVP]]

Re: LINQ and XML for compact framework

On May 1, 2:54 pm, Wan <luo...@gmail.c omwrote:

<snip>

'msgs' is empty. There is two possiblities here.
1) from el in root.Descendant s("Message")
where el.Element("Mes sageID").Value == MsgID
select el;
This LINQ statement is not working.

Right. What happens if you remove the where clause? Is it successfully
finding the messages themselves when unfiltered? That would also
verify that it's managed to load the document appropriately.

2) After the LINQ found the records, it fail to copy the value to
IEnumerable<XEl ementmsgs

That's just assignment - pretty unlikely to fail.

As I said, I have tested this code and same LINQ statement on a
desktop console application. It works fine.

Sure. The trick is narrowing down where the difference is :)

Jon

[Wan]

Re: LINQ and XML for compact framework

On May 1, 3:08 pm, "Jon Skeet [C# MVP]" <sk...@pobox.co mwrote:

On May 1, 2:54 pm, Wan <luo...@gmail.c omwrote:
>
<snip>
>

'msgs' is empty.  There is two possiblities here.
1)  from el in root.Descendant s("Message")
     where el.Element("Mes sageID").Value == MsgID
     select el;
    This LINQ statement is not working.

>
Right. What happens if you remove the where clause? Is it successfully
finding the messages themselves when unfiltered? That would also
verify that it's managed to load the document appropriately.
>

2) After the LINQ found the records, it fail to copy the value to
IEnumerable<XEl ementmsgs

>
That's just assignment - pretty unlikely to fail.
>

As I said, I have tested this code and same LINQ statement on a
desktop console application.  It works fine.

>
Sure. The trick is narrowing down where the difference is :)
>
Jon

Hi Jon

Check this out:

http://farm3.static.flickr.com/2188/2457050340_5840ee808b_o.jpg

I have got a screent shot here.

I've removed the where clause, it is still the same.

Regards,
Wan

[Jon Skeet [C# MVP]]

Re: LINQ and XML for compact framework

On May 1, 3:18 pm, Wan <luo...@gmail.c omwrote:

<snip>

Check this out:http://farm3.static.flickr.com/2188/...40ee808b_o.jpg
I have got a screent shot here.

That's focusing on the debugger side of things, which I believe is a
red herring. Concentrate on diagnostics which don't require the
debugger.

I've removed the where clause, it is still the same.

So if you put a call to MessageBox.Show in the foreach loop, having
removed the where clause, you're still not seeing anything? That's
worrying.

When you a call to MessageBox.Show in the exception handler, did it
show any exceptions being thrown?

If you put a call to MessageBox.Show after the call to Save(), did it
show the code getting there successfully?

Jon

[Wan]

Re: LINQ and XML for compact framework

On May 1, 3:40 pm, "Jon Skeet [C# MVP]" <sk...@pobox.co mwrote:

On May 1, 3:18 pm, Wan <luo...@gmail.c omwrote:
>
<snip>
>

Check this out:http://farm3.static.flickr.com/2188/...40ee808b_o.jpg
I have got a screent shot here.

>
That's focusing on the debugger side of things, which I believe is a
red herring. Concentrate on diagnostics which don't require the
debugger.
>

I've removed the where clause, it is still the same.

>
So if you put a call to MessageBox.Show in the foreach loop, having
removed the where clause, you're still not seeing anything? That's
worrying.
>
When you a call to MessageBox.Show in the exception handler, did it
show any exceptions being thrown?
>
If you put a call to MessageBox.Show after the call to Save(), did it
show the code getting there successfully?
>
Jon

Yes, I still see nothing. And the {"NullReference Exception"} was
thrown. the Save() statement was not excuted.

Wan

[Jon Skeet [C# MVP]]

Re: LINQ and XML for compact framework

On May 1, 3:59 pm, Wan <luo...@gmail.c omwrote:

Yes, I still see nothing. And the {"NullReference Exception"} was
thrown.

Ah! Now we're getting somewhere! So what was the stack trace? Where
was the exception being thrown?

the Save() statement was not excuted.

No wonder, if an earlier statement was throwing an exception. This is
why it's a really bad idea to swallow exceptions without logging
them :)

Jon

[Wan]

Re: LINQ and XML for compact framework

On May 1, 4:16 pm, "Jon Skeet [C# MVP]" <sk...@pobox.co mwrote:

On May 1, 3:59 pm, Wan <luo...@gmail.c omwrote:
>

Yes, I still see nothing.  And the {"NullReference Exception"} was
thrown.

>
Ah! Now we're getting somewhere! So what was the stack trace? Where
was the exception being thrown?
>

 the Save() statement was not excuted.

>
No wonder, if an earlier statement was throwing an exception. This is
why it's a really bad idea to swallow exceptions without logging
them :)
>
Jon

The exception was thrown inside the foreach statement. After it
excute
el.Element("Mes sageStaus").Set Value(newStatus .ToString());
this line of code, the exception was fired.


Here is the stack trace:
at xmlCFtest.Form1 .updateMsg(Stri ng MsgID, Int32 newStatus)
at xmlCFtest.Form1 ..ctor()
at xmlCFtest.Progr am.Main()

Wan

[Jon Skeet [C# MVP]]

Re: LINQ and XML for compact framework

On May 1, 4:39 pm, Wan <luo...@gmail.c omwrote:

The exception was thrown inside the foreach statement.

Hang on - you said before that it wasn't getting inside the foreach
statement. You said that "msgs" was empty - which means it wouldn't be
trying to set the value.

Which is it?

After it excute
el.Element("Mes sageStaus").Set Value(newStatus .ToString());
this line of code, the exception was fired.

After it executed that, or during the execution? My guess is that
el.Element("Mes sageStaus") is returning null, but you really need to
make sure your diagnostics are consistent before you go any further.
If it *is* going into the foreach loop, work out why you thought it
wasn't.

Then look at "el" (again, with a message box or something similar) to
see whether it really does have a MessageStaus element.

Jon

[Wan]

Re: LINQ and XML for compact framework

On May 1, 5:41 pm, "Jon Skeet [C# MVP]" <sk...@pobox.co mwrote:

On May 1, 4:39 pm, Wan <luo...@gmail.c omwrote:
>

The exception was thrown inside the foreach statement.

>
Hang on - you said before that it wasn't getting inside the foreach
statement. You said that "msgs" was empty - which means it wouldn't be
trying to set the value.
>
Which is it?
>

After it excute
el.Element("Mes sageStaus").Set Value(newStatus .ToString());
this line of code, the exception was fired.

>
After it executed that, or during the execution? My guess is that
el.Element("Mes sageStaus") is returning null, but you really need to
make sure your diagnostics are consistent before you go any further.
If it *is* going into the foreach loop, work out why you thought it
wasn't.
>
Then look at "el" (again, with a message box or something similar) to
see whether it really does have a MessageStaus element.
>
Jon

Hi Jon
Problem is solved. The LINQ statement I wrote was incorrect. Because
in my XML, I have namespace, but I didn't specify it in my XElement.

Thanks very much for your help :-)

Best Regards,
Wan