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  • Problem with final branch in a parallel activity

    - by Dan Revell
    This might seem like a silly thing to say, the final branch in a parallel activity so I'll clarify. It's a parallel activity with three branches each containing a simple create task, on task changed and complete task. The branch containing the task that is last to complete seems to break. So every task works in it's own right, but the last one encounters a problem. Say the user clicks the final tasks link to open the attached infopath form and submits that. Execution gets to the event handler for that onTaskChanged where a taskCompleted variable gets set to true which will exit the while loop. I've successfully hit a breakpoint on this line so I know that happens. However the final activity in that branch, the completeTask doesn't get hit. When submit is clicked in the final form, the operation in progess screen says of for quite a while before returning to the workflow status page. The task that was opened and submitted says "Not Started". I can disable any of the branches to leave only two, but the same problem happens with the last to be completed. Earlier on in the workflow I do essencially the same thing. I have another 3 branch parallel activity with each brach containing a task. This one works correctly which leads me to believe that it might be a problem with having two parallel activites in the same sequential workflow. I've considered the possibility that it might be a correlation token problem. The token that every task branch uses is unique to that branch and it's owner activity name is est to that of the branch. It stands to reason that if the task complete variable is indeed getting set to true but the while loop isn't being exited, then there's a wire crossing with the variable somewhere. However I'd still have thought that the task status back on the workflow status page would at least say that the task is in progress. This is a frustrating show stopper of a bug for me. Any thoughts or suggestions would be much appricated so I can investigate them.

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  • VS 2010 Layer Diagram Validation Error is Showing A Dependency That Doesn't Even Exist (AV0001)

    - by Dan
    I'm getting the following validation error on my layer diagram Error 65 AV0001 : Invalid Dependency : Weld.Interface.Core(Assembly) -- Weld.Interface(Namespace) Layers: Application Framework Core, Application Framework | Dependencies: Namespace Reference D:\Projects\Windows Projects\Weld\Weld\ModelingProject1\Weld.layerdiagram 0 0 ModelingProject1 Weld.Interface.Core: This assembly and namespace does not have a reference to Weld.Interface and only references .NET Framework classes Weld.Interface: This assembly and namespace does not have a reference to Weld.Interface There is no dependancy between these two layers in the dependency diagram. I am confused why I am getting this error. No dependency in the project or code, and no dependency is even setup in the layer diagram. Somehow the Validation logic in the layer diagram is seeing a non existant dependency and saying it is an error. Any ideas what either I might have missed or what is causing this problem?

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  • File transfer eating alot of CPU

    - by Dan C.
    I'm trying to transfer a file over a IHttpHandler, the code is pretty simple. However when i start a single transfer it uses about 20% of the CPU. If i were to scale this to 20 simultaneous transfers the CPU is very high. Is there a better way I can be doing this to keep the CPU lower? the client code just sends over chunks of the file 64KB at a time. public void ProcessRequest(HttpContext context) { if (context.Request.Params["secretKey"] == null) { } else { accessCode = context.Request.Params["secretKey"].ToString(); } if (accessCode == "test") { string fileName = context.Request.Params["fileName"].ToString(); byte[] buffer = Convert.FromBase64String(context.Request.Form["data"]); string fileGuid = context.Request.Params["smGuid"].ToString(); string user = context.Request.Params["user"].ToString(); SaveFile(fileName, buffer, user); } } public void SaveFile(string fileName, byte[] buffer, string user) { string DirPath = @"E:\Filestorage\" + user + @"\"; if (!Directory.Exists(DirPath)) { Directory.CreateDirectory(DirPath); } string FilePath = @"E:\Filestorage\" + user + @"\" + fileName; FileStream writer = new FileStream(FilePath, File.Exists(FilePath) ? FileMode.Append : FileMode.Create, FileAccess.Write, FileShare.ReadWrite); writer.Write(buffer, 0, buffer.Length); writer.Close(); }

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  • Rx IObservable buffering to smooth out bursts of events

    - by Dan
    I have an Observable sequence that produces events in rapid bursts (ie: five events one right after another, then a long delay, then another quick burst of events, etc.). I want to smooth out these bursts by inserting a short delay between events. Imagine the following diagram as an example: Raw: --oooo--------------ooooo-----oo----------------ooo| Buffered: --o--o--o--o--------o--o--o--o--o--o--o---------o--o--o| My current approach is to generate a metronome-like timer via Observable.Interval() that signals when it's ok to pull another event from the raw stream. The problem is that I can't figure out how to then combine that timer with my raw unbuffered observable sequence. IObservable.Zip() is close to doing what I want, but it only works so long as the raw stream is producing events faster than the timer. As soon as there is a significant lull in the raw stream, the timer builds up a series of unwanted events that then immediately pair up with the next burst of events from the raw stream. Ideally, I want an IObservable extension method with the following function signature that produces the bevaior I've outlined above. Now, come to my rescue StackOverflow :) public static IObservable<T> Buffered(this IObservable<T> src, TimeSpan minDelay) PS. I'm brand new to Rx, so my apologies if this is a trivially simple question... 1. Simple yet flawed approach Here's my initial naive and simplistic solution that has quite a few problems: public static IObservable<T> Buffered<T>(this IObservable<T> source, TimeSpan minDelay) { Queue<T> q = new Queue<T>(); source.Subscribe(x => q.Enqueue(x)); return Observable.Interval(minDelay).Where(_ => q.Count > 0).Select(_ => q.Dequeue()); } The first obvious problem with this is that the IDisposable returned by the inner subscription to the raw source is lost and therefore the subscription can't be terminated. Calling Dispose on the IDisposable returned by this method kills the timer, but not the underlying raw event feed that is now needlessly filling the queue with nobody left to pull events from the queue. The second problem is that there's no way for exceptions or end-of-stream notifications to be propogated through from the raw event stream to the buffered stream - they are simply ignored when subscribing to the raw source. And last but not least, now I've got code that wakes up periodically regardless of whether there is actually any work to do, which I'd prefer to avoid in this wonderful new reactive world. 2. Way overly complex appoach To solve the problems encountered in my initial simplistic approach, I wrote a much more complicated function that behaves much like IObservable.Delay() (I used .NET Reflector to read that code and used it as the basis of my function). Unfortunately, a lot of the boilerplate logic such as AnonymousObservable is not publicly accessible outside the system.reactive code, so I had to copy and paste a lot of code. This solution appears to work, but given its complexity, I'm less confident that its bug free. I just can't believe that there isn't a way to accomplish this using some combination of the standard Reactive extensions. I hate feeling like I'm needlessly reinventing the wheel, and the pattern I'm trying to build seems like a fairly standard one.

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  • Python halts while iteratively processing my 1GB csv file

    - by Dan
    I have two files: metadata.csv: contains an ID, followed by vendor name, a filename, etc hashes.csv: contains an ID, followed by a hash The ID is essentially a foreign key of sorts, relating file metadata to its hash. I wrote this script to quickly extract out all hashes associated with a particular vendor. It craps out before it finishes processing hashes.csv stored_ids = [] # this file is about 1 MB entries = csv.reader(open(options.entries, "rb")) for row in entries: # row[2] is the vendor if row[2] == options.vendor: # row[0] is the ID stored_ids.append(row[0]) # this file is 1 GB hashes = open(options.hashes, "rb") # I iteratively read the file here, # just in case the csv module doesn't do this. for line in hashes: # not sure if stored_ids contains strings or ints here... # this probably isn't the problem though if line.split(",")[0] in stored_ids: # if its one of the IDs we're looking for, print the file and hash to STDOUT print "%s,%s" % (line.split(",")[2], line.split(",")[4]) hashes.close() This script gets about 2000 entries through hashes.csv before it halts. What am I doing wrong? I thought I was processing it line by line. ps. the csv files are the popular HashKeeper format and the files I am parsing are the NSRL hash sets. http://www.nsrl.nist.gov/Downloads.htm#converter UPDATE: working solution below. Thanks everyone who commented! entries = csv.reader(open(options.entries, "rb")) stored_ids = dict((row[0],1) for row in entries if row[2] == options.vendor) hashes = csv.reader(open(options.hashes, "rb")) matches = dict((row[2], row[4]) for row in hashes if row[0] in stored_ids) for k, v in matches.iteritems(): print "%s,%s" % (k, v)

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  • Why does my Excel add-in only half work?

    - by Dan Crowther
    I've created an Excel add-in using Visual Studio 2008. It has a ribbon, a bunch of panes and code that adds sheets and ranges and gets information scraped from a web page. When I run it on my dev PC it works perfectly. I used the Publish command to publich it and installed on a Windows XP virtual PC. The installation seemed fine and when I open Excel I see my ribbon. If I click a button that shows a pane, up pops the pane. If I enter some details into the pane that should create a range and populate it with data from a web page, the range is created but the web page is not visited (I have tested that I have connectivity). One of my buttons adds a hidden worksheet and another displays or hides that sheet. One of these buttons is not working. I've tried everything I can think of. I'm wondering if there are any permissions or trust issues I need to deal with?

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  • How to write specs with MSpec for code that changes Thread.CurrentPrincipal?

    - by Dan Jensen
    I've been converting some old specs to MSpec (were using NUnit/SpecUnit). The specs are for a view model, and the view model in question does some custom security checking. We have a helper method in our specs which will setup fake security credentials for the Thread.CurrentPrincipal. This worked fine in the old unit tests, but fails in MSpec. Specifically, I'm getting this exception: "System.Runtime.Serialization.SerializationException: Type is not resolved for member" It happens when part of the SUT tries to read the app config file. If I comment out the line which sets the CurrentPrincipal (or simply call it after the part that checks the config file), the error goes away, but the tests fail due to lack of credentials. Similarly, if I set the CurrentPrincipal to null, the error goes away, but again the tests fail because the credentials aren't set. I've googled this, and found some posts about making sure the custom principal is serializable when it crosses AppDomain boundaries (usually in reference to web apps). In our case, this is not a web app, and I'm not crossing any AppDomains. Our pincipal object is also serializable. I downloaded the source for MSpec, and found that the ConsoleRunner calls a class named AppDomainRunner. I haven't debugged into it, but it looks like it's running the specs in different app domains. So does anyone have any ideas on how I can overcome this? I really like MSpec, and would love to use it exclusively. But I need to be able to supply fake security credentials while running the tests. Thanks! Update: here's the spec class: [Subject(typeof(CountryPickerViewModel))] public class When_the_user_makes_a_selection : PickerViewModelSpecsBase { protected static CountryPickerViewModel picker; Establish context = () => { SetupFakeSecurityCredentials(); CreateFactoryStubs(); StubLookupServicer<ICountryLookupServicer>() .WithData(BuildActiveItems(new [] { "USA", "UK" })); picker = new CountryPickerViewModel(ViewFactory, ViewModelFactory, BusinessLogicFactory, CacheFactory); }; Because of = () => picker.SelectedItem = picker.Items[0]; Behaves_like<Picker_that_has_a_selected_item> a_picker_with_a_selection; } We have a number of these "picker" view models, all of which exhibit some common behavior. So I'm using the Behaviors feature of MSpec. This particular class is simulating the user selecting something from the (WPF) control which is bound to this VM. The SetupFakeSecurityCredentials() method is simply setting Thread.CurrentPrincipal to an instance of our custom principal, where the prinipal has been populated will full-access rights. Here's a fake CountryPickerViewModel which is enough to cause the error: public class CountryPickerViewModel { public CountryPickerViewModel(IViewFactory viewFactory, IViewModelFactory viewModelFactory, ICoreBusinessLogicFactory businessLogicFactory, ICacheFactory cacheFactory) { Items = new Collection<int>(); var validator = ValidationFactory.CreateValidator<object>(); } public int SelectedItem { get; set; } public Collection<int> Items { get; private set; } } It's the ValidationFactory call which blows up. ValidationFactory is an Enterprise Library object, which tries to access the config.

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  • How to join data frames in R (inner, outer, left, right)?

    - by Dan Goldstein
    Given two data frames df1 = data.frame(CustomerId=c(1:6),Product=c(rep("Toaster",3),rep("Radio",3))) df2 = data.frame(CustomerId=c(2,4,6),State=c(rep("Alabama",2),rep("Ohio",1))) > df1 CustomerId Product 1 Toaster 2 Toaster 3 Toaster 4 Radio 5 Radio 6 Radio > df2 CustomerId State 2 Alabama 4 Alabama 6 Ohio How can I do database style, i.e., sql style, joins? That is, how do I get: An inner join of df1 and df1 An outer join of df1 and df2 A left outer join of df1 and df2 A right outer join of df1 and df2 P.S. IKT-JARQ (I Know This - Just Adding R Questions) Extra credit: How can I do a sql style select statement?

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  • Compiling .NET component that uses a non specific required version of a 3rd Party Vendor component

    - by Dan
    If someone were to develop a .NET component that relied on non specific versions of a vendor DLL - let's say it worked with My3rdPartyComponent.dll which is a .NET assembly, but it didn't matter which version. Some instances of classes found in this component would need to be passed into my component. Developers would reference my component dll but not have access to the source code. Basically, I want to be able to require the user to pass in an instance of 3rdPartyComponent.MyClass to my component functions but I do not care if it's version 1.1, 2.2, 2.23.980, etc of the 3rd party dll. Is there a way to do this while still typing the parameter I want to be passed in to my component? I don't want to use Object as the reference. In my component project I could specify SpecificVersion=True on the assembly reference. Will this solve my problem or will there be other 'dll hell' issues to deal with that I am not seeing?

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  • UINavigationController and memory management

    - by Dan Ray
    - (void)launchSearch { EventsSearchViewController *searchController = [[EventsSearchViewController alloc] initWithNibName:@"EventsSearchView" bundle:nil]; [self.navigationController pushViewController:searchController animated:YES]; //[searchController release]; } Notice the [searchController release] is commented out. I've understood that pushing searchController onto the navigation controller retains it, and I should release it from my code. I did just alloc/init it, after all, and if I don't free it, it'll leak. With that line commented out, navigation works great. With it NOT commented out, I can navigate INTO this view okay, but coming back UP a level crashes with a *** -[CFArray release]: message sent to deallocated instance 0x443a9e0 error. What's happening here? Is the NavigationController releasing it for me somehow when it goes out of view? The boilerplate that comes on a UINavigationController template in XCode has the newly-pushed controller getting released. But when I do it, it fails.

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  • How can I embed a youtube video using variable widths/heights for a dynamic width web page?

    - by Dan Gayle
    I want to set a youtube video to 100% width so that it scales appropriately in a dynamic width column on a web page I am designing. The problem is that the height doesn't behave like the height of an image. Instead of scaling proportionately, it either collapses (if set to "auto" or left blank) or it scales seemingly random if set to a percentage. How can I get it to remain proportionate while still dynamic?

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  • partial entity loading and management in silverlight / wcf ria

    - by Dan Wray
    I have a Silverlight 4 app which pulls entities down from a database using WCF RIA services. These data objects are fairly simple, just a few fields but one of those fields contains binary data of an arbitrarily size. The application needs access to this data basically asap after a user has logged in, to display in a list, enable selection etc. My problem is because of the size of this data, the load times are not acceptable and can approach the default timeout of the RIA service. I'd like to somehow partially load the objects into my local data context so that I have the IDs, names etc but not the binary data. I could then at a later point (ie when it's actually needed) populate the binary fields of those objects I need to display. Any suggestions on how to accomplish this would be welcome. Another approach which has occurred to me whilst writing this question (how often does that happen?!) is that I could move the binary data into a seperate database table joined to the original record 1:1 which would allow me to make use of RIA's lazy loading on that binary data. again.. comments welcome! Thanks.

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  • What is the best way to merge mp3 files?

    - by Dan Williams
    I've got many, many mp3 files that I would like to merge into a single file. I've used the command line method copy /b 1.mp3+2.mp3 3.mp3 but it's a pain when there's a lot of them and their namings are inconsistent. The time never seems to come out right either.

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  • IS there a simple way to remove Alt-Character shortcuts at runtime

    - by Dan Neely
    I have a dialog with a number of Alt-Letter shortcuts on labels for textboxes/etc. This dialog can present data in either an editable or a read-only mode. I've received a request to hide the underlines for the shortcuts if the dialog is in read only mode. Other than editing the label text at runtime (ugh) is there any way to remove them? If you don't know what I'm referring to by alt-Letter shortcuts see this question.

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  • jQuery/Javascript to replace broken images

    - by Dan Lord
    I have a web page that includes a bunch of images. Sometimes the image isn't available so a broken image is displayed in the clients browser. How do I use jQuery to get the set of images, filter it to broken images then replace the src? --I thought it would be easier to do this with Jquery, but It turned out much easier to just use a pure javascript solution. i.e the one provided by Prestaul

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  • What statistics can be maintained for a set of numerical data without iterating?

    - by Dan Tao
    Update Just for future reference, I'm going to list all of the statistics that I'm aware of that can be maintained in a rolling collection, recalculated as an O(1) operation on every addition/removal (this is really how I should've worded the question from the beginning): Obvious Count Sum Mean Max* Min* Median** Less Obvious Variance Standard Deviation Skewness Kurtosis Mode*** Weighted Average Weighted Moving Average**** OK, so to put it more accurately: these are not "all" of the statistics I'm aware of. They're just the ones that I can remember off the top of my head right now. *Can be recalculated in O(1) for additions only, or for additions and removals if the collection is sorted (but in this case, insertion is not O(1)). Removals potentially incur an O(n) recalculation for non-sorted collections. **Recalculated in O(1) for a sorted, indexed collection only. ***Requires a fairly complex data structure to recalculate in O(1). ****This can certainly be achieved in O(1) for additions and removals when the weights are assigned in a linearly descending fashion. In other scenarios, I'm not sure. Original Question Say I maintain a collection of numerical data -- let's say, just a bunch of numbers. For this data, there are loads of calculated values that might be of interest; one example would be the sum. To get the sum of all this data, I could... Option 1: Iterate through the collection, adding all the values: double sum = 0.0; for (int i = 0; i < values.Count; i++) sum += values[i]; Option 2: Maintain the sum, eliminating the need to ever iterate over the collection just to find the sum: void Add(double value) { values.Add(value); sum += value; } void Remove(double value) { values.Remove(value); sum -= value; } EDIT: To put this question in more relatable terms, let's compare the two options above to a (sort of) real-world situation: Suppose I start listing numbers out loud and ask you to keep them in your head. I start by saying, "11, 16, 13, 12." If you've just been remembering the numbers themselves and nothing more, and then I say, "What's the sum?", you'd have to think to yourself, "OK, what's 11 + 16 + 13 + 12?" before responding, "52." If, on the other hand, you had been keeping track of the sum yourself while I was listing the numbers (i.e., when I said, "11" you thought "11", when I said "16", you thought, "27," and so on), you could answer "52" right away. Then if I say, "OK, now forget the number 16," if you've been keeping track of the sum inside your head you can simply take 16 away from 52 and know that the new sum is 36, rather than taking 16 off the list and them summing up 11 + 13 + 12. So my question is, what other calculations, other than the obvious ones like sum and average, are like this? SECOND EDIT: As an arbitrary example of a statistic that (I'm almost certain) does require iteration -- and therefore cannot be maintained as simply as a sum or average -- consider if I asked you, "how many numbers in this collection are divisible by the min?" Let's say the numbers are 5, 15, 19, 20, 21, 25, and 30. The min of this set is 5, which divides into 5, 15, 20, 25, and 30 (but not 19 or 21), so the answer is 5. Now if I remove 5 from the collection and ask the same question, the answer is now 2, since only 15 and 30 are divisible by the new min of 15; but, as far as I can tell, you cannot know this without going through the collection again. So I think this gets to the heart of my question: if we can divide kinds of statistics into these categories, those that are maintainable (my own term, maybe there's a more official one somewhere) versus those that require iteration to compute any time a collection is changed, what are all the maintainable ones? What I am asking about is not strictly the same as an online algorithm (though I sincerely thank those of you who introduced me to that concept). An online algorithm can begin its work without having even seen all of the input data; the maintainable statistics I am seeking will certainly have seen all the data, they just don't need to reiterate through it over and over again whenever it changes.

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  • How to read a string one letter at a time in python

    - by dan
    I need to convert a string inputed by a user into morse code. The way our professor wants us to do this is to read from a morseCode.txt file, seperate the letters from the morseCode into two lists, then convert each letter to morse code (inserting a new line when there is a space). I have the beginning. What it does is reads the morseCode.txt file and seperates the letters into a list [A, B, ... Z] and the codes into a list ['– – . . – –\n', '. – . – . –\n'...]. We haven't learned "sets" yet, so I can't use that. How would I then take the string that they inputed, go through letter by letter, and convert it to morse code? I'm a bit caught up. Here's what I have right now (not much at all...) morseCodeFile = open('morseCode.txt', 'r') letterList = [] codeList = [] line = morseCodeFile.readline() while line != '': letterList.append(line[0]) codeList.append(line[2:]) line = morseCodeFile.readline() morseCodeFile.close() userInput = input("Enter a string to be converted to morse code or press <enter> to quit ")

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  • cgi.FieldStorage always empty - never returns POSTed form Data

    - by Dan Carlson
    This problem is probably embarrassingly simple. I'm trying to give python a spin. I thought a good way to start doing that would be to create a simple cgi script to process some form data and do some magic. My python script is executed properly by apache using mod_python, and will print out whatever I want it to print out. My only problem is that cgi.FieldStorage() is always empty. I've tried using both POST and GET. Each trial I fill out both form fields. <form action="pythonScript.py" method="POST" name="ARGH"> <input name="TaskName" type="text" /> <input name="TaskNumber" type="text" /> <input type="submit" /> </form> If I change the form to point to a perl script it reports the form data properly. The python page always gives me the same result: number of keys: 0 #!/usr/bin/python import cgi def index(req): pageContent = """<html><head><title>A page from""" pageContent += """Python</title></head><body>""" form = cgi.FieldStorage() keys = form.keys() keys.sort() pageContent += "<br />number of keys: "+str(len(keys)) for key in keys: pageContent += fieldStorage[ key ].value pageContent += """</body></html>""" return pageContent I'm using Python 2.5.2 and Apache/2.2.3. This is what's in my apache conf file (and my script is in /var/www/python): <Directory /var/www/python/> Options FollowSymLinks +ExecCGI Order allow,deny allow from all AddHandler mod_python .py PythonHandler mod_python.publisher </Directory>

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  • Creating IIS Instance over network using MSBuild

    - by Dan
    Is there a way to have MSBuild create an instance of IIS on another remote machine? I do the builds (which occur locally using TeamCity AFAIK), but would like the code to be pushed up to our testing server once the build is completed. I am using IIS 6.x (Windows XP dev and Windows 2k3 Server for testing).

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  • WPF DockPanel doesn't respect the "Filled" control's desired size

    - by Dan Puzey
    I have the following Xaml (simplified for brevity, but will repro the problem in Xamlpad or Kaxaml): <DockPanel Width="400"> <TextBlock DockPanel.Dock="Left" TextWrapping="Wrap"> Lorem ipsum dolor sit amet, consectetur adipiscing elit. Vestibulum massa metus, ornare in fringilla nec, fringilla at orci. Nunc pharetra enim sit amet sapien aliquet eu euismod turpis vehicula. Aenean gravida tempus lectus ut ornare. Nullam massa augue, suscipit vel consectetur fringilla, pretium vitae neque. </TextBlock> <Button MinWidth="100" VerticalAlignment="Center" HorizontalAlignment="Left">Hello world</Button> </DockPanel> My problem is that I want the Button to take its minimum 100px of space, and for the text to wrap suitably to leave that space. However, what happens is that the text wraps as close to 400px as possible, and then the Button is clipped. If I Snoop the output I can see that the button is rendering at the desired 100px, but it's being clipped off the side of the DockPanel. If I reverse the Dock (so the button is docked "Right" and the TextBlock fills) then I get the layout I want, but unfortunately that's not an option due to the surrounding layout. Is there something I can do that will make the DockPanel a) not clip and b) layout in a way that respects the MinWidth? Or am I stuck finding an alternative layout mechanism? Thanks in advance!

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  • Considerations when architecting an application using Dependency Injection

    - by Dan Bryant
    I've begun experimenting with dependency injection (in particular, MEF) for one of my projects, which has a number of different extensibility points. I'm starting to get a feel for what I can do with MEF, but I'd like to hear from others who have more experience with the technology. A few specific cases: My main use case at the moment is exposing various singleton-like services that my extensions make use of. My Framework assembly exposes service interfaces and my Engine assembly contains concrete implementations. This works well, but I may not want to allow all of my extensions to have access to all of my services. Is there a good way within MEF to limit which particular imports I allow a newly instantiated extension to resolve? This particular application has extension objects that I repeatedly instantiate. I can import multiple types of Controllers and Machines, which are instantiated in different combinations for a Project. I couldn't find a good way to do this with MEF, so I'm doing my own type discovery and instantiation. Is there a good way to do this within MEF or other DI frameworks? I welcome input on any other things to watch out for or surprising capabilities you've discovered that have changed the way you architect.

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  • What's the right way to do mutable data structures (e.g., skip lists, splay trees) in F#?

    - by dan
    What's a good way to implement mutable data structures in F#? The reason I’m asking is because I want to go back and implement the data structures I learned about in the algorithms class I took this semester (skip lists, splay trees, fusion trees, y-fast tries, van Emde Boas trees, etc.), which was a pure theory course with no coding whatsoever, and I figure I might as well try to learn F# while I’m doing it. I know that I “should” use finger trees to get splay tree functionality in a functional language, and that I should do something with laziness to get skip-list functionality, etc. , but I want to get the basics nailed down before I try playing with purely functional implementations. There are lots of examples of how to do functional data structures in F#, but there isn’t much on how to do mutable data structures, so I started by fixing up the doubly linked list here into something that allows inserts and deletes anywhere. My plan is to turn this into a skip list, and then use a similar structure (discriminated union of a record) for the tree structures I want to implement. Before I start on something more substantial, is there a better way to do mutable structures like this in F#? Should I just use records and not bother with the discriminated union? Should I use a class instead? Is this question "not even wrong"? Should I be doing the mutable structures in C#, and not dip into F# until I want to compare them to their purely functional counterparts? And, if a DU of records is what I want, could I have written the code below better or more idiomatically? It seems like there's a lot of redundancy here, but I'm not sure how to get rid of it. module DoublyLinkedList = type 'a ll = | None | Node of 'a ll_node and 'a ll_node = { mutable Prev: 'a ll; Element : 'a ; mutable Next: 'a ll; } let insert x l = match l with | None -> Node({ Prev=None; Element=x; Next=None }) | Node(node) -> match node.Prev with | None -> let new_node = { Prev=None; Element=x; Next=Node(node)} node.Prev <- Node(new_node) Node(new_node) | Node(prev_node) -> let new_node = { Prev=node.Prev; Element=x; Next=Node(node)} node.Prev <- Node(new_node) prev_node.Next <- Node(new_node) Node(prev_node) let rec nth n l = match n, l with | _,None -> None | _,Node(node) when n > 0 -> nth (n-1) node.Next | _,Node(node) when n < 0 -> nth (n+1) node.Prev | _,Node(node) -> Node(node) //hopefully only when n = 0 :-) let rec printLinkedList head = match head with | None -> () | Node(x) -> let prev = match x.Prev with | None -> "-" | Node(y) -> y.Element.ToString() let cur = x.Element.ToString() let next = match x.Next with | None -> "-" | Node(y) -> y.Element.ToString() printfn "%s, <- %s -> %s" prev cur next printLinkedList x.Next

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  • Facebook og:url ignored in favour of a Facebook hosted page about the og entity

    - by Dan
    I am trying to implement the Like button on my pages. Those pages represent the review page for a product. When a user Likes the page, it shows up in Facebook (not as a link, but as liking an entity), however when you click on the entity in Facebook it links through to a facebook.com hosted page representing the page. I want the user to be redirected to the og:url page? This happens for example when you Like an artist page on Grroveshar: http://grooveshark.com/#!/artist/Elbow/4795 I am clearly "doing it wrong". I am using the following markup to include the SDK. MYAPPID is included by the code generator Facebook provides so I assume it is required. <div id="fb-root"></div> <script>(function(d, s, id) { var js, fjs = d.getElementsByTagName(s)[0]; if (d.getElementById(id)) return; js = d.createElement(s); js.id = id; js.src = "//connect.facebook.net/en_US/all.js#xfbml=1&appId=MYAPPID"; fjs.parentNode.insertBefore(js, fjs); }(document, 'script', 'facebook-jssdk'));</script> Then my code to render the Like button. <div class="fb-like" data-send="false" data-width="450" data-show-faces="true"></div> And finally my og tags: <meta property="og:title" content="My product" /> <meta property="og:type" content="product" /> <meta property="og:url" content="http://site.com/product_1/" /> <meta property="og:image" content="http://site.com/image1.jpg" /> <meta property="og:site_name" content="My-Site-Name.com" /> <meta property="fb:admins" content="MYFACEBOOKID" /> <meta property="fb:app_id" content="MYAPPID" /> Thanks!

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