Tio Luiso's Blog

Problems with bound FlowDocuments in ListViews

2010-04-09T12:10:00.001+02:00

I’ve been working with WPF for a time. And it’s a technology I’ve fallen in love with. It’s really powerful, yet it is really simple in some ways. Requires a thinking switch. If you have worked with Windows Forms, you’ll tend to think Windows-Forms-like, so you need to learn to think WPF-like.

However, I have encountered a problem that can arise when you bind a list of a custom entity that has a FlowDocument property to a ListView. Let me try to explain.

I create a custom entity, like this one:

public class MyEntity
{
private FlowDocument _myFlowDocument;

        public FlowDocument MyFlowDocument
        {
            get
            {
                return _myFlowDocument;
            }
            set
            {
                _myFlowDocument = value;
            }
        }
    }

then, in my Window, I create a listview bound to a list of this custom entity. Like this:

Then you run the application, and you see the list with the flowdocuments, which is nice. You scroll down to see all the items (I have created 200 in my test). And it works. You scroll up again and the application explodes, with an exception that says “Document belongs to another FlowDocumentScrollViewer already.” Huh? What’s happening?

The problem happens because of 2 different things:

FlowDocument is a little special and keeps its own state when bound. Trying to bind a single FlowDocument to 2 controls throws that exception
ListView, by default uses a VirtualizingStackPanel. Meaning that it only creates controls (based on its template) that are inside its viewport. Items not yet visited don’t have their controls created, and items that go out of scope have their controls destroyed.

So what happens is quite obvious. When you start the application, first items have their templates rendered and they bind their FlowDocument. When you scroll down, that first items go out of scope and the controls are destroyed. When you scroll up again, controls are created again, but the same old controls, new ones. And when they try to bind to FlowDocument, they remember it is already bound.

My solution is to disable VirtualizingStackPanel for that ListView, with the attached property VirtualizingStackPanel.IsVirtualizing="False". Warning: This causes the whole visual tree to be created just once in the beginning, causing the application to start a little more slow, and to use more memory. However, there are times that you haven’t many options.

Resetting SAGEM 1500WD

2007-05-07T15:58:00.001+02:00

I have ADSL, yeah!. Last friday I got my router. I asked for a Thomson router, but instead I got a Sagem 1500wd. Well, I preferred the other, but if it works, I'll keep it.

I start Internet Explorer and try to enter the router configuration pages. Enter the IP, press enter... And the router resets. Damn!. Well, I wait the router to reload again and enter the IP and press enter. It resets again!!!.

After some time trying to enter the configuration pages (and resetting the router), I tried accessing it via lan (instead of wifi). It resets. Tried to access it with another browser (Opera), and it doesn't reset!!!.

Now I'm starting to go nuts. Ok, let me get it straight. Somehow, there must be something in the HTTP request that makes the router reset. Well, I start Wireshark and capture each of the requests (Opera and IE). They look like this:

OPERA

GET / HTTP/1.1
User-Agent: Opera/9.20 (Windows NT 5.1; U; es-es)
Host: 192.168.0.1
Accept: text/html, application/xml;q=0.9, application/xhtml+xml, image/png, image/jpeg, image/gif, image/x-xbitmap, */*;q=0.1
Accept-Language: es-ES,es;q=0.9,en;q=0.8
Accept-Charset: iso-8859-1, utf-8, utf-16, *;q=0.1
Accept-Encoding: deflate, gzip, x-gzip, identity, *;q=0
Connection: Keep-Alive, TE
TE: deflate, gzip, chunked, identity, trailers

INTERNET EXPLORER

GET / HTTP/1.1
Accept: image/gif, image/x-xbitmap, image/jpeg, image/pjpeg, application/x-shockwave-flash, application/vnd.ms-excel, application/vnd.ms-powerpoint, application/msword, application/xaml+xml, application/vnd.ms-xpsdocument, application/x-ms-xbap, application/x-ms-application, application/ag-plugin, */*
Accept-Language: es-us
UA-CPU: x86
Accept-Encoding: gzip, deflate
User-Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 5.1; .NET CLR 1.1.4322; .NET CLR 2.0.50727; .NET CLR 3.0.04506.30; InfoPath.1)
Host: 192.168.0.1
Proxy-Connection: Keep-Alive

Then I start Fiddler2 and try to create an HTTP request. I start with Opera requests (and I get a response). And try to change parts of the request with IE request. My first thought was to try User-Agent. It doesn't crash. My 2nd try was to change Accept. And it crashes!!!.

Then I realize that my IE Accept string is > 255 chars. So I trim it down to 255. And it works.

Am I the only one that uses IE? Am I the only one that has this kind of problem? Will this DoS attack work only from the inside? OR FROM THE WAN PORT TOO???????.

I'll find out.

Anonymous Access and Forms Authentication in WSS v3

2007-02-15T15:27:00.001+01:00

Well, finally I am working with it, and I have been told to configure a MOSS instalation with 2 zones: An internet portal and an Intranet portal.

The intranet should have Integrated Windows Authentication, and the Internet Portal should have Forms authentication.

WSS v3 and MOSS 2007 allow to use different membershi providers, and thus enable a really incredible flexibility.

However, configuring it right is a little nightmare. And once you have configured it, you have to add users (the only place I've seen so far to perform this task is Web Site Administration Tool. And in order to make it work, you have to install Visual Studio and create a Virtual Directory inside the MOSS Web Application).

All things considered, it ended well, but that kind of configuration needs improvements.

I wouldn't have been able to achieve it without http://channel9.msdn.com/ShowPost.aspx?PostID=229709

AJAX Control Toolkit experiences

2007-02-01T12:36:00.001+01:00

In the project I'm currently in, we are using ASP.NET AJAX Extensions. We use certain controls, like a Calendar, Tabs... So we tried Ajax Control Toolkit. At first sight, it looks really nice. It has an awesome calendar. However, when we (Pedroafa and me) tried to use it, we found a curious bug.

When you insert the calendar (we found the same behaviour with the Tabs) in an empty page, it works, it's nice. However, when you insert it into a FormView (say, in the EditItem template), it loses all the style. Hmmmmm. After searching the internet for someone with a problem like that one, we found it here. Or something like it, anyway.

It looks like the CalendarExtender loads its CSS when you receive a page that contains one directly from the server, but not when it's created in an AJAXlike way.

They say a workaround is to have another TextBox outside the Formview and another CalendarExtender bound to it, and make them invisible. They're invisible, but they load the CSS, so when you create the one in the FormView, it's correctly formatted.

After seeing that kind of bug, we decided we were not using the Control Toolkit until it was more stable.

However it was about time they created a Tab control. Hope we can use it soon.

Technorati tags: AJAX

Load Testing ASP.NET AJAX Web Sites

2007-01-26T13:10:00.001+01:00

Some people complained about the frequency of my posting. Well, I usually post when there are things worth posting. Daily work isn't that interesting. Nowadays I'm developing some reports for a Web Site using Reporting Services. Nothing very exciting.

But today, I've tried to perform a Web Test using Visual Studio 2005 in a ASP.NET AJAX Web Site. The problem is, when you're recording the test, AJAX asynchronous calls won't appear. Dammit!!!.

Is all lost? No!. I've found in MSDN someone in the community section (great improvement, by the way) posted a workaround. Fiddler is a tool that records HTTP Sessions. Well, it captures AJAX postbacks, too. But what is more interesting: You can save them as Visual Studio 2005 Web Tests!!!.

What does that mean? You're never the first one to encounter a problem.

SPSv3 and MOSS 2007, here I go

2006-11-29T18:44:00.000+01:00

I worked for some time with MOSS 2003. I was both amazed by the capabilities and wondered if they would straighten things one time. Now MOSS 2007 is out, and looks like I'm going to work with it. So far, looks good. There are many improvements. Some of them, I would have killed in the past for them. Per-item security, master pages, totlly integrated with ASP.NET 2.0...

Well, I hope it doesn't disappoint me.

First Steps with Microsoft PowerShell

2006-11-24T18:19:00.000+01:00

And finally it was released. Since I don't have any real knowledge about that tool, I took my first steps using the manual. My jaw began dropping since page 5 or so, and I'm still reading the user part. I cannot wait to start developing cmd-lets.

I fail to imagine how big a step it is. It's simply incredible. Obviously it isn't that impressive for the average user, but for an administrator it's huge.

Since now it's Vista time, I guess all demos are around WPF and Vista. When Longhorn comes out, I hope they present PowerShell with its due respect.

DotNetNuke Gallery

2006-11-06T18:50:00.000+01:00

Today, I have been trying to find a problem in DotNetNuke. When users navigate to certain page, they get something like:

A critical error has occurred.Object reference not set to an instance of an object.

After a considerable time spent trying to look for the problem, finally found the EventLog table, in which I find that the problem is with Gallery Module. It throws an ArgumentException:
Path cannot be the empty string or all whitespace at the
DotNetNuke.Modules.Gallery.GalleryFolder.Populate. Nice event log, at least.

Finally, I found that bug described at http://support.dotnetnuke.com/issue/ViewIssue.aspx?id=1507.

Looks like they're not fixing it. Don't know why.

Anyone know of an alternative image gallery for DotNetNuke?

Thanks a lot

About CodeCamp, Robot Fights and meeting nice people

2006-10-30T16:42:00.000+01:00

Hi there.

It has passed a long time since my previous (and first) post. Maybe I didn't have anything to say. Maybe didn't have time. I don't know.

The thing is last weekend I was at the CodeCamp at El Escorial, Madrid. Try to imagine: 200 techies with their laptops (75 of which were MVP), 2 days, 8 conferences. Does the idea frighten you?. Well, I was there, too.

And not only I was there, but I had to do (with a workmate) one of the conferences. One about speech technologies in Windows Vista. Last 2 weeks have been studying, looking for information, coding. And finally, there we were.

The conference wasn't without problems. However, I think we did our best to explain what we were trying to explain. We had a good time, and we got some laughs and applauses.

Later, at the end of the day, we had a barbecue and I had the chance to speak with some people I barely knew. And then we went to some party someone was having. From then till the end of the day, my memories become fuzzy. Blame it on the beer.

Next day, there were still 2 conferences remaining, and then a Robot fight. 2 randomly chosen people had to drive a robot (Lego Mindstorm) with their voices, and push the opponent out of a circle. It was funny.

And then CodeCamp was over. But I had a wonderful time and met very nice people.

Welcome to the machine

2006-03-14T11:19:00.000+01:00

Well, first of all, welcome to my brand new blog.

If there's a responsible for me creating a blog, is Miguel Jimenez. He founded MAD.NUG, a group of Madrid .Net developers to which I proudly belong.

Second, I want to explain what you can find here (maybe trying to explain myself). This is a developer blog.

I am a developer, and have been for the last 8 years or so (professionally speaking). Not that I know that much. I try to learn. I enjoy everything I learn. But I realize that I'm not as good a developer as I would want to be (the beginning of the road to becoming a good developer starts with not being over-satisfied with one's work). I'd say I'm better than the average developer. However, in the jobs I've had over the time, I have found many people so full of theirselves that didn't know the half of what I know (and I repeat, I'm not any god). Particularly, I find funny the lack of knowledge present in many (so-called) consultants.

The lessons I've learned? One is never too humble. One can always learn. And one has to feel the need to keep learning. And to share the learning. There have been countless times I was in need of some insight on any technology, and finally found the answer in some forum or blog.

So that's what I'll try to do. I'll post here new things I learn, I'll post here funny things I see.

If someone finds it interesting, or someone can see anything that serves him, then I have accomplished my purpose.

That's it. Welcome to the machine.