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• C# Monte Carlo Incremental Risk Calculation optimisation, random numbers, parallel execution

  - by m3ntat

  My current task is to optimise a Monte Carlo Simulation that calculates Capital Adequacy figures by region for a set of Obligors. It is running about 10 x too slow for where it will need to be in production and number or daily runs required. Additionally the granularity of the result figures will need to be improved down to desk possibly book level at some stage, the code I've been given is basically a prototype which is used by business units in a semi production capacity. The application is currently single threaded so I'll need to make it multi-threaded, may look at System.Threading.ThreadPool or the Microsoft Parallel Extensions library but I'm constrained to .NET 2 on the server at this bank so I may have to consider this guy's port, http://www.codeproject.com/KB/cs/aforge_parallel.aspx. I am trying my best to get them to upgrade to .NET 3.5 SP1 but it's a major exercise in an organisation of this size and might not be possible in my contract time frames. I've profiled the application using the trial of dotTrace (http://www.jetbrains.com/profiler). What other good profilers exist? Free ones? A lot of the execution time is spent generating uniform random numbers and then translating this to a normally distributed random number. They are using a C# Mersenne twister implementation. I am not sure where they got it or if it's the best way to go about this (or best implementation) to generate the uniform random numbers. Then this is translated to a normally distributed version for use in the calculation (I haven't delved into the translation code yet). Also what is the experience using the following? http://quantlib.org http://www.qlnet.org (C# port of quantlib) or http://www.boost.org Any alternatives you know of? I'm a C# developer so would prefer C#, but a wrapper to C++ shouldn't be a problem, should it? Maybe even faster leveraging the C++ implementations. I am thinking some of these libraries will have the fastest method to directly generate normally distributed random numbers, without the translation step. Also they may have some other functions that will be helpful in the subsequent calculations. Also the computer this is on is a quad core Opteron 275, 8 GB memory but Windows Server 2003 Enterprise 32 bit. Should I advise them to upgrade to a 64 bit OS? Any links to articles supporting this decision would really be appreciated. Anyway, any advice and help you may have is really appreciated.

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• Which functions in the C standard library commonly encourage bad practice?

  - by Ninefingers

  Hello all, This is inspired by this question and the comments on one particular answer in that I learnt that strncpy is not a very safe string handling function in C and that it pads zeros, until it reaches n, something I was unaware of. Specifically, to quote R.. strncpy does not null-terminate, and does null-pad the whole remainder of the destination buffer, which is a huge waste of time. You can work around the former by adding your own null padding, but not the latter. It was never intended for use as a "safe string handling" function, but for working with fixed-size fields in Unix directory tables and database files. snprintf(dest, n, "%s", src) is the only correct "safe strcpy" in standard C, but it's likely to be a lot slower. By the way, truncation in itself can be a major bug and in some cases might lead to privilege elevation or DoS, so throwing "safe" string functions that truncate their output at a problem is not a way to make it "safe" or "secure". Instead, you should ensure that the destination buffer is the right size and simply use strcpy (or better yet, memcpy if you already know the source string length). And from Jonathan Leffler Note that strncat() is even more confusing in its interface than strncpy() - what exactly is that length argument, again? It isn't what you'd expect based on what you supply strncpy() etc - so it is more error prone even than strncpy(). For copying strings around, I'm increasingly of the opinion that there is a strong argument that you only need memmove() because you always know all the sizes ahead of time and make sure there's enough space ahead of time. Use memmove() in preference to any of strcpy(), strcat(), strncpy(), strncat(), memcpy(). So, I'm clearly a little rusty on the C standard library. Therefore, I'd like to pose the question: What C standard library functions are used inappropriately/in ways that may cause/lead to security problems/code defects/inefficiencies? In the interests of objectivity, I have a number of criteria for an answer: Please, if you can, cite design reasons behind the function in question i.e. its intended purpose. Please highlight the misuse to which the code is currently put. Please state why that misuse may lead towards a problem. I know that should be obvious but it prevents soft answers. Please avoid: Debates over naming conventions of functions (except where this unequivocably causes confusion). "I prefer x over y" - preference is ok, we all have them but I'm interested in actual unexpected side effects and how to guard against them. As this is likely to be considered subjective and has no definite answer I'm flagging for community wiki straight away. I am also working as per C99.

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• Bazaar newbie question about repository structures

  - by esc1729

  I want to use Bazaar on Windows XP for web-development and related tasks. Most of the files are edited locally and then transferred via FTP to the server. Just now the repository sits on my local workstation. Later on it should be shared locally with some co-workers. Perhaps we will use a local Linux server as a centralized repository, but this structure is not decided for now. But first I need to understand the impacts of the different repository setups, which I do not at all. Using Bazaar-Explorer on Windows XP I’ve created a ‘shared tree repository’ from the option list of the init-dialogue in some location dev-filter/. Bazaar Explorer tells me: Created repository with treeless branches at F:/bzr.local/dev-filter Created branch at F:/bzr.local/dev-filter/trunk Created working tree at F:/bzr.local/dev-filter/work OK so far. Now I move a bunch of files into the work directory and add and commit them as Rev 1 ‘Start Revision’. Then I work on some of these files and commit them again as Rev 2. Here my confusion starts. Shouldn’t both revisions go into the trunk? The trunk is still empty, beside the .bzr directory which only holds some management information. If I delete my working directory, which I have tried during these first experiments, everything is gone. There’s obviously no hidden storage of those files. OK. Perhaps I need to push it into the trunk? This does not work either. Entering the work/ directory and initializing the ‘push’ to the trunk, Bazaar-Explorer tells me No new revisions to push. So what? This looks like a severe conceptual misunderstanding about what should happen on my side. Edit, 2010-02-03: Some conclusions What I learned meanwhile is this: I think I should switch to the command line until I really understand what’s going on, at least for creating the repositories and branches. Bazaar Explorer introduces a new level of abstraction which I only can handle if I understand the level beneath One of the secrets of working with Bazaar at least for me is to understand those .bzr directories, their particular properties and states when created with ‘bzr init’, ‘bzr init-repository’, ‘bzr branch’ etc. in all their variants and how they are plumped together. While there’s a whole chapter of ‘Organizing your workspace’ in the Bazaar User Guide, it’s more or less workflow oriented. The manual contains a lot of directory structures for the given examples. What I would prefer beside this and have not (or only rudimentary) found so far is some graphical representation of those ‘Lego like’ .bzr building blocks which create the linking of all the parts. So I started to invent some simple notation while working through the examples and looking into the .bzr directories to document what information is stored there, where does it come from, how and to what is it linked, is it complete or shared, etc. Erich Schreiber

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• Python performance: iteration and operations on nested lists

  - by J.J.

  Problem Hey folks. I'm looking for some advice on python performance. Some background on my problem: Given: A mesh of nodes of size (x,y) each with a value (0...255) starting at 0 A list of N input coordinates each at a specified location within the range (0...x, 0...y) Increment the value of the node at the input coordinate and the node's neighbors within range Z up to a maximum of 255. Neighbors beyond the mesh edge are ignored. (No wrapping) BASE CASE: A mesh of size 1024x1024 nodes, with 400 input coordinates and a range Z of 75 nodes. Processing should be O(x*y*Z*N). I expect x, y and Z to remain roughly around the values in the base case, but the number of input coordinates N could increase up to 100,000. My goal is to minimize processing time. Current results I have 2 current implementations: f1, f2 Running speed on my 2.26 GHz Intel Core 2 Duo with Python 2.6.1: f1: 2.9s f2: 1.8s f1 is the initial naive implementation: three nested for loops. f2 is replaces the inner for loop with a list comprehension. Code is included below for your perusal. Question How can I further reduce the processing time? I'd prefer sub-1.0s for the test parameters. Please, keep the recommendations to native Python. I know I can move to a third-party package such as numpy, but I'm trying to avoid any third party packages. Also, I've generated random input coordinates, and simplified the definition of the node value updates to keep our discussion simple. The specifics have to change slightly and are outside the scope of my question. thanks much! f1 is the initial naive implementation: three nested for loops. 2.9s def f1(x,y,n,z): rows = [] for i in range(x): rows.append([0 for i in xrange(y)]) for i in range(n): inputX, inputY = (int(x*random.random()), int(y*random.random())) topleft = (inputX - z, inputY - z) for i in xrange(max(0, topleft[0]), min(topleft[0]+(z*2), x)): for j in xrange(max(0, topleft[1]), min(topleft[1]+(z*2), y)): if rows[i][j] <= 255: rows[i][j] += 1 f2 is replaces the inner for loop with a list comprehension. 1.8s def f2(x,y,n,z): rows = [] for i in range(x): rows.append([0 for i in xrange(y)]) for i in range(n): inputX, inputY = (int(x*random.random()), int(y*random.random())) topleft = (inputX - z, inputY - z) for i in xrange(max(0, topleft[0]), min(topleft[0]+(z*2), x)): l = max(0, topleft[1]) r = min(topleft[1]+(z*2), y) rows[i][l:r] = [j+1 for j in rows[i][l:r] if j < 255]

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• WebClient security error when accessing the world of warcraft armoury

  - by user348446

  Hello World, I am trying to piece together a solution to a problem. Basically I am using Silverlight 4 with C# 4.0 to access the world of warcraft armoury. If anyone has done this - please oh please provide the working .net 4.0 code. The code I am attempting to run is (e.Error contains a securtiy error): private void button10_Click(object sender, RoutedEventArgs e) { string url = @"http://eu.wowarmory.com/guild-info.xml?r=Eonar&n=Gifted and Talented"; WebClient wc = new WebClient(); // HOW DO I ADD A USER AGENT STRING (RESPONSE MAY VARY (I.E. HTML VS XML) IF PAGE THINKS CALL IS NOT CAPABABLE OF SUPPORTING XML TRANSFORMATIONS) //wc.ResponseHeaders["User-Agent"] = "Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 6.0)"; wc.DownloadStringCompleted += new DownloadStringCompletedEventHandler(wc_DownloadStringCompleted); wc.DownloadStringAsync(new Uri(url)); } void wc_DownloadStringCompleted(object sender, DownloadStringCompletedEventArgs e) { if (e.Error == null) { string result = e.Result; XDocument ArmouryXML = XDocument.Parse(result); ShowGuildies(ArmouryXML); } else { MessageBox.Show("Something is complaining about security but not sure what!"); } } Notes: C# 4.0 The armoury is an XML file - but i believe it reverts to html should the request not be from a browser that supports XML transformation. But i don't think I am getting this far. The armoury has a cross domain policy file on it - this may be the cause of the error (not sure! I have uploaded to a production server I am testing it locally using IIS website I am going insane! Websites have made the suggestion that this problem can be overcome by creating a WebProxy - but I haven't the first clue how to do this. It would be great if someone could take on this challenge and show us all that it is possible. I'd prefer a non-proxy solution first, then try a proxy. The error details: e.Error = {System.Security.SecurityException --- System.Security.SecurityException: Security error. at System.Net.Browser.BrowserHttpWebRequest.InternalEndGetResponse(IAsyncResult asyncResult) at System.Net.Browser.BrowserHttpWebRequest.<c__DisplayClass5. Any intelligent master coders out there who can solve this in their sleep? Thanks if you can! Pass this on to someone who can if you can't. If you know someone who can't, don't pass it to them, but if you know someone can't then presumedly you know how to solve it and would encourage you to give it a go! Cheers! Dan.

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• jQueryUI autocomplete - when no results are returned

  - by Brian M. Hunt

  I'm wondering how one can catch and add a custom handler when empty results are returned from the server when using jQueryUI autocomplete. There seem to be a few questions on this point related to the various jQuery plugins (e.g. jQuery autocomplete display “No data” error message when results empty), but I am wondering if there's a better/simpler way to achieve the same with the jQueryUI autocomplete. It seems to me this is a common use case, and I thought perhaps that jQueryUI had improved on the jQuery autocomplete by adding the ability to cleanly handle this situation. However I've not been able to find documentation of such functionality, and before I hack away at it I'd like to throw out some feelers in case others have seen this before. While probably not particularly influential, I can have the server return anything - e.g. HTTP 204: No Content to a 200/JSON empty list - whatever makes it easiest to catch the result in jQueryUI's autocomplete. My first thought is to pass a callback with two arguments, namely a request object and a response callback to handle the code, per the documentation: The third variation, the callback, provides the most flexibility, and can be used to connect any data source to Autocomplete. The callback gets two arguments: A request object, with a single property called "term", which refers to the value currently in the text input. For example, when the user entered "new yo" in a city field, the Autocomplete term will equal "new yo". A response callback, which expects a single argument to contain the data to suggest to the user. This data should be filtered based on the provided term, and can be in any of the formats described above for simple local data (String-Array or Object-Array with label/value/both properties). When the response callback receives no data, it inserts returns a special one-line object-array that has a label and an indicator that there's no data (so the select/focus recognize it as the indicator that no-data was returned). This seems overcomplicated. I'd prefer to be able to use a source: "http://...", and just have a callback somewhere indicating that no data was returned. Thank you for reading. Brian

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• iPhone UIWebView: loadData does not work with certain types (Excel, MSWord, PPT, RTF)

  - by Thomas Tempelmann

  My task is to display the supported document types on an iPhone with OS 3.x, such as .pdf, .rtf, .doc, .ppt, .png, .tiff etc. Now, I have stored these files only encrypted on disk. For security reasons, I want to avoid storing them unencrypted on disk. Hence, I prefer to use loadData:MIMEType:textEncodingName:baseURL: instead of loadRequest: to display the document because loadData allows me to pass the content in a NSData object, i.e. I can decrypt the file in memory and have no need to store it on disk, as it would be required when using loadRequest. The problem is that loadData does not appear to work with all file types: Testing shows that all picture types seem to work fine, as well as PDFs, while the more complex types don't. I get a errors such as: NSURLErrorDomain Code=100 NSURLErrorDomain Code=102 WebView appears to need a truly working URL for accessing the documents as a file, despite me offering all content via the NSData object already. Here's the code I use to display the content: [webView loadData:data MIMEType:type textEncodingName:@"utf-8" baseURL:nil]; The mime-type is properly set, e.g. to "application/msword" for .doc files. Does anyone know how I could get loadData to work with all types that loadRequest supports? Or, alternatively, is there some way I can tell which types do work for sure (i.e. officially sanctioned by Apple) with loadData? Then I can work twofold, creating a temp unencrypted file only for those cases that loadData won't like. Update Looks like I'm not the first one running into this. See here: http://osdir.com/ml/iPhoneSDKDevelopment/2010-03/msg00216.html So, I guess, that's the status quo, and nothing I can do about it. Someone suggested a work-around which might work, though: http://osdir.com/ml/iPhoneSDKDevelopment/2010-03/msg00219.html Basically, the idea is to provide a tiny http server that serves the file (from memory in my case), and then use loadRequest. This is probably a bit more memory-intensive, though, as both the server and the webview will probably both hold the entire contents in memory as two copies then, as opposed to using loadData, where both would rather share the same data object. (Mind you, I'll have to hold the decrypted data in memory, that's the whole point here).

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• ASP.Net Web Farm Monitoring

  - by cisellis

  I am looking for suggestions on doing some simple monitoring of an ASP.Net web farm as close to real-time as possible. The objectives of this question are to: Identify the best way to monitor several Windows Server production boxes during short (minutes long) period of ridiculous load Receive near-real-time feedback on a few key metrics about each box. These are simple metrics available via WMI such as CPU, Memory and Disk Paging. I am defining my time constraints as soon as possible with 120 seconds delayed being the absolute upper limit. Monitor whether any given box is up (with "up" being defined as responding web requests in a reasonable amount of time) Here are more details, things I've tried, etc. I am not interested in logging. We have logging solutions in place. I have looked at solutions such as ELMAH which don't provide much in the way of hardware monitoring and are not visible across an entire web farm. ASP.Net Health Monitoring is too broad, focuses too much on logging and is not acceptable for deep analysis. We are on Amazon Web Services and we have looked into CloudWatch. It looks great but messages in the forum indicate that the metrics are often a few minutes behind, with one thread citing 2 minutes as the absolute soonest you could expect to receive the feedback. This would be good to have for later analysis but does not help us real-time Stuff like JetBrains profiler is good for testing but again, not helpful during real-time monitoring. The closest out-of-box solution I've seen is Nagios which is free and appears to measure key indicators on any kind of box, including Windows. However, it appears to require a Linux box to run itself on and a good deal of manual configuration. I'd prefer to not spend my time mining config files and then be up a creek when it fails in production since Linux is not my main (or even secondary) environment. Are there any out-of-box solutions that I am missing? Obviously a windows-based solution that is easy to setup is ideal. I don't require many bells and whistles. In the absence of an out-of-box solution, it seems easy for me to write something simple to handle what I need. I've been thinking a simple client-server setup where the server requests a few WMI metrics from each client over http and sticks them in a database. We could then monitor the metrics via a query or a dashboard or something. If the client doesn't respond, it's effectively down. Any problems with this, best practices, or other ideas? Thanks for any help/feedback.

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• Visual Web Developer 2008 Express and XHTML 1.1 (not applying)

  - by Mike Valeriano

  Hello. I may be missing something since I'm not used to work with IDEs for web development, so please understand if I'm doing something stupid. I've picked a copy of Beginning ASP.NET 3.5 in C# and VB to try and learn this thing quickly. I'm no HTML guru, but I know something about the DTDs and I want to either use XHTML 1.0 Strict or XHTML 1.1 while learning the ins and outs of ASP.NET. Following the book (just started actually), I'm not having any trouble understanding the concepts, since I have a C# background, but what I don't understand is how VWD goes about applying the schema you select for validation. The book explains that the drop-down list on the toolbar is enough to set this, so that's what I did: I've selected XHTML 1.1 (since there is no 1.0 strict option, what I find really odd) and then started the project. The thing is that the code generated automatically for the Default page had the XHTML 1.0 transitional DTD. Every other page added had the same DTD, even though XHTML 1.1 is still the selected schema in the drop-down list. I decided to test it out and there it was: inserting some text in the design view and then applying a bold formatting just inserted < b tags on the code. Changing color does add a span tag with added CSS though. What I want to know is: if I want strict XHTML (or 1.1) should I just code it manually? Or is there a "fix" for this problem (having a schema selected but not applied by the IDE)? Am I missing something really easy and dumb? I have no problem with coding it manually - I actually prefer doing that. The thing is that I really wanna try this WYSIWYG approach for once, since some developers swear by it. Plus I don't know yet if I'll need special tags for ASP.NET, so I think having them inserted automatically should be the best practice. I couldn't find any similar problems around (MSDN, Google, here), and as far as the book goes (up to the point I've read), this is the expected VWD behavior, which I find suspect at least. Sorry for the long text (and poor English - not my primary language). Thanks in advance for any help/tips.

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• Does weak typing offer any advantages?

  - by sub

  Don't confuse this with static vs. dynamic typing! You all know JavaScripts/PHPs infamous type systems: PHP example: echo "123abc"+2; // 125 - the reason for this is explained // in the PHP docs but still: This hurts echo "4"+1; // 5 - Oh please echo "ABC"*5; // 0 - WTF // That's too much, seriously now. // This here might be actually a use for weak typing, but no - // it has to output garbage. JavaScript example: // A good old JavaScript, maybe you'll do better? alert("4"+1); // 51 - Oh come on. alert("abc"*3); // NaN - What the... // Have your creators ever heard of the word "consistence"? Python example: # Python's type system is actually a mix # It spits errors on senseless things like the first example below AND # allows intelligent actions like the second example. >>> print("abc"+1) Traceback (most recent call last): File "<pyshell#2>", line 1, in <module> print("abc"+1) TypeError: Can't convert 'int' object to str implicitly >>> print("abc"*5) abcabcabcabcabc Ruby example: puts 4+"1" // Type error - as supposed puts "abc"*4 // abcabcabcabc - makes sense After these examples it should be clear that PHP/JavaScript probably have the most inconsistent type systems out there. This is a fact and really not subjective. Now when having a closer look at the type systems of Ruby and Python it seems like they are having a much more intelligent and consistent type system. I think these examples weren't really necessary as we all know that PHP/JavaScript have a weak and Python/Ruby have a strong type system. I just wanted to mention why I'm asking this. Now I have two questions: When looking at those examples, what are the advantages of PHPs and JavaScripts type systems? I can only find downsides: They are inconsistent and I think we know that this is not good Types conversions are hardly controllable Bugs are more likely to happen and much harder to spot Do you prefer one of the both systems? Why? Personally I have worked with PHP, JavaScript and Python so far and must say that Pythons type system has really only advantages over PHPs and JavaScripts. Does anybody here not think so? Why then?

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• How to better create stacked bar graphs with multiple variables from ggplot2?

  - by deoksu

  I often have to make stacked barplots to compare variables, and because I do all my stats in R, I prefer to do all my graphics in R with ggplot2. I would like to learn how to do two things: First, I would like to be able to add proper percentage tick marks for each variable rather than tick marks by count. Counts would be confusing, which is why I take out the axis labels completely. Second, there must be a simpler way to reorganize my data to make this happen. It seems like the sort of thing I should be able to do natively in ggplot2 with plyR, but the documentation for plyR is not very clear (and I have read both the ggplot2 book and the online plyR documentation. My best graph looks like this, the code to create it follows: the R code I use to get it is the following: library(epicalc) ### recode the variables to factors ### recode(c(int_newcoun, int_newneigh, int_neweur, int_newusa, int_neweco, int_newit, int_newen, int_newsp, int_newhr, int_newlit, int_newent, int_newrel, int_newhth, int_bapo, int_wopo, int_eupo, int_educ), c(1,2,3,4,5,6,7,8,9, NA), c('Very Interested','Somewhat Interested','Not Very Interested','Not At All interested',NA,NA,NA,NA,NA,NA)) ### Combine recoded variables to a common vector Interest1<-c(int_newcoun, int_newneigh, int_neweur, int_newusa, int_neweco, int_newit, int_newen, int_newsp, int_newhr, int_newlit, int_newent, int_newrel, int_newhth, int_bapo, int_wopo, int_eupo, int_educ) ### Create a second vector to label the first vector by original variable ### a1<-rep("News about Bangladesh", length(int_newcoun)) a2<-rep("Neighboring Countries", length(int_newneigh)) [...] a17<-rep("Education", length(int_educ)) Interest2<-c(a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, a11, a12, a13, a14, a15, a16, a17) ### Create a Weighting vector of the proper length ### Interest.weight<-rep(weight, 17) ### Make and save a new data frame from the three vectors ### Interest.df<-cbind(Interest1, Interest2, Interest.weight) Interest.df<-as.data.frame(Interest.df) write.csv(Interest.df, 'C:\\Documents and Settings\\[name]\\Desktop\\Sweave\\InterestBangladesh.csv') ### Sort the factor levels to display properly ### Interest.df$Interest1<-relevel(Interest$Interest1, ref='Not Very Interested') Interest.df$Interest1<-relevel(Interest$Interest1, ref='Somewhat Interested') Interest.df$Interest1<-relevel(Interest$Interest1, ref='Very Interested') Interest.df$Interest2<-relevel(Interest$Interest2, ref='News about Bangladesh') Interest.df$Interest2<-relevel(Interest$Interest2, ref='Education') [...] Interest.df$Interest2<-relevel(Interest$Interest2, ref='European Politics') detach(Interest) attach(Interest) ### Finally create the graph in ggplot2 ### library(ggplot2) p<-ggplot(Interest, aes(Interest2, ..count..)) p<-p+geom_bar((aes(weight=Interest.weight, fill=Interest1))) p<-p+coord_flip() p<-p+scale_y_continuous("", breaks=NA) p<-p+scale_fill_manual(value = rev(brewer.pal(5, "Purples"))) p update_labels(p, list(fill='', x='', y='')) I'd very much appreciate any tips, tricks or hints. Thanks.

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• C# and NpgsqlDataAdapter returning a single string instead of a data table

  - by tme321

  I have a postgresql db and a C# application to access it. I'm having a strange error with values I return from a NpgsqlDataAdapter.Fill command into a DataSet. I've got this code: NpgsqlCommand n = new NpgsqlCommand(); n.Connection = connector; // a class member NpgsqlConnection DataSet ds = new DataSet(); DataTable dt = new DataTable(); // DBTablesRef are just constants declared for // the db table names and columns ArrayList cols = new ArrayList(); cols.Add(DBTablesRef.all); //all is just * ArrayList idCol = new ArrayList(); idCol.Add(DBTablesRef.revIssID); ArrayList idVal = new ArrayList(); idVal.Add(idNum); // a function parameter // Select builder and Where builder are just small // functions that return an sql statement based // on the parameters. n is passed to the where // builder because the builder uses named // parameters and sets them in the NpgsqlCommand // passed in String select = SelectBuilder(DBTablesRef.revTableName, cols) + WhereBuilder(n,idCol, idVal); n.CommandText = select; try { NpgsqlDataAdapter da = new NpgsqlDataAdapter(n); ds.Reset(); // filling DataSet with result from NpgsqlDataAdapter da.Fill(ds); // C# DataSet takes multiple tables, but only the first is used here dt = ds.Tables[0]; } catch (Exception e) { Console.WriteLine(e.ToString()); } So my problem is this: the above code works perfectly, just like I want it to. However, if instead of doing a select on all (*) if I try to name individual columns to return from the query I get the information I asked for, but rather than being split up into seperate entries in the data table I get a string in the first index of the data table that looked something like: "(0,5,false,Bob Smith,7)" And the data is correct, I would be expecting 0, then 5, then a boolean, then some text etc. But I would (obviously) prefer it to not be returned as just one big string. Anyone know why if I do a select on * I get a datatable as expected, but if I do a select on specific columns I get a data table with one entry that is the string of the values I'm asking for?

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• XML to be validated against multiple xsd schemas

  - by Michael Rusch

  I'm writing the xsd and the code to validate, so I have great control here. I would like to have an upload facility that adds stuff to my application based on an xml file. One part of the xml file should be validated against different schemas based on one of the values in the other part of it. Here's an example to illustrate: <foo> <name>Harold</name> <bar>Alpha</bar> <baz>Mercury</baz> <!-- ... more general info that applies to all foos ... --> <bar-config> <!-- the content here is specific to the bar named "Alpha" --> </bar-config> <baz-config> <!-- the content here is specific to the baz named "Mercury" --> </baz> </foo> In this case, there is some controlled vocabulary for the content of <bar>, and I can handle that part just fine. Then, based on the bar value, the appropriate xml schema should be used to validate the content of bar-config. Similarly for baz and baz-config. The code doing the parsing/validation is written in Java. Not sure how language-dependent the solution will be. Ideally, the solution would permit the xml author to declare the appropriate schema locations and what-not so that s/he could get the xml validated on the fly in a sufficiently smart editor. Also, the possible values for <bar> and <baz> are orthogonal, so I don't want to do this by extension for every possible bar/baz combo. What I mean is, if there are 24 possible bar values/schemas and 8 possible baz values/schemas, I want to be able to write 1 + 24 + 8 = 33 total schemas, instead of 1 * 24 * 8 = 192 total schemas. Also, I'd prefer to NOT break out the bar-config and baz-config into separate xml files if possible. I realize that might make all the problems much easier, as each xml file would have a single schema, but I'm trying to see if there is a good single-xml-file solution.

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• Need help manipulating WAV (RIFF) Files at a byte level

  - by Eric

  I'm writing an an application in C# that will record audio files (*.wav) and automatically tag and name them. Wave files are RIFF files (like AVI) which can contain meta data chunks in addition to the waveform data chunks. So now I'm trying to figure out how to read and write the RIFF meta data to and from recorded wave files. I'm using NAudio for recording the files, and asked on their forums as well on SO for way to read and write RIFF tags. While I received a number of good answers, none of the solutions allowed for reading and writing RIFF chunks as easily as I would like. But more importantly I have very little experience dealing with files at a byte level, and think this could be a good opportunity to learn. So now I want to try writing my own class(es) that can read in a RIFF file and allow meta data to be read, and written from the file. I've used streams in C#, but always with the entire stream at once. So now I'm little lost that I have to consider a file byte by byte. Specifically how would I go about removing or inserting bytes to and from the middle of a file? I've tried reading a file through a FileStream into a byte array (byte[]) as shown in the code below. System.IO.FileStream waveFileStream = System.IO.File.OpenRead(@"C:\sound.wav"); byte[] waveBytes = new byte[waveFileStream.Length]; waveFileStream.Read(waveBytes, 0, waveBytes.Length); And I could see through the Visual Studio debugger that the first four byte are the RIFF header of the file. But arrays are a pain to deal with when performing actions that change their size like inserting or removing values. So I was thinking I could then to the byte[] into a List like this. List<byte> list = waveBytes.ToList<byte>(); Which would make any manipulation of the file byte by byte a whole lot easier, but I'm worried I might be missing something like a class in the System.IO name-space that would make all this even easier. Am I on the right track, or is there a better way to do this? I should also mention that I'm not hugely concerned with performance, and would prefer not to deal with pointers or unsafe code blocks like this guy. If it helps at all here is a good article on the RIFF/WAV file format.

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• rails paperclip unable to access image from another view

  - by curiousCoder

  my app has an habtm relation b/w listings and categories. now from the categories index page, a user filters select box to view listings in the show page. now i am not able to access images attached to listings in the category show page. listing.rb attr_accessible :placeholder, :categories_ids has_and_belongs_to_many :categories has_attached_file :placeholder, :styles => { :medium => "300x300>", :thumb => "100x100>" }, :default_url => "/images/:style/missing.png", :url => "/system/:hash.:extension", :hash_secret => "longSecretString" categories controller def index @categories = Category.all end def show @categories = Category.find_by_sql ["select distinct l.* from listings l , categories c, categories_listings cl where c.id = cl.category_id and l.id = cl.listing_id and c.id in (?,?)" , params[:c][:id1] , params[:c][:id2]] end the sql just filters and displays the listings in show page where i can show its attributes, but cant access the placeholder. note the plural @categories in show categories show page <ul> <% @categories.each_with_index do |c, index| %> <% if index == 0 %> <li class="first"><%= c.place %></li> <%= image_tag c.placeholder.url(:thumb) %> <li><%= c.price %></li> <% else %> <li><%= c.place %></li> <li><%= c.price %></li> <%= image_tag c.placeholder.url(:thumb) %> <% end %> <% end %> </ul> Access image from different view in a view with paperclip gem ruby on rails this said to make the object plural and call a loop, wch shall allow to access the image. it does not work in this case. undefined method `placeholder' for #<Category:0x5c78640> but the amazing thing is, placeholder will be displayed as an array of all images for all the listings if used as suggested in that stackoverflow, wch is, obviously, not the way i prefer. where's the issue? what am i missing?

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• MVVM: how to set the datacontext of a user control

  - by EVA

  Hi, I'm writing an application in WPF, using the MVVm toolkit and have problems with hooking up the viewmodel and view. The model is created with ado.net entity framework. The viewmodel: public class CustomerViewModel { private Models.Customer customer; //constructor private ObservableCollection<Models.Customer> _customer = new ObservableCollection<Models.Customer>(); public ObservableCollection<Models.Customer> AllCustomers { get { return _customer; } } private Models.Customer _selectedItem; public Models.Customer SelectedItem { get { return _selectedItem; } } public void LoadCustomers() { List<Models.Customer> list = DataAccessLayer.getcustomers(); foreach (Models.Customer customer in list) { this._customer.Add(customer); } } } And the view (no code behind at the moment): <UserControl x:Class="Customers.Customer" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" xmlns:d="http://schemas.microsoft.com/expression/blend/2008" mc:Ignorable="d" xmlns:vm ="clr-namespace:Customers.ViewModels" d:DesignHeight="300" d:DesignWidth="300" xmlns:toolkit="http://schemas.microsoft.com/wpf/2008/toolkit" > <Grid> <toolkit:DataGrid ItemsSource="{Binding AllCustomers}" SelectedItem="{Binding SelectedItem, Mode=TwoWay}" AutoGenerateColumns="True"> </toolkit:DataGrid> <toolkit:DataGrid ItemsSource="{Binding SelectedItem.Orders}"> </toolkit:DataGrid> </Grid> </UserControl> And dataaccesslayer class: class DataAccessLayer { public List<Customer> customers = new List<Customer>(); public static List<Customer> getcustomers() { entities db = new entities(); var customers = from c in db.Customer.Include("Orders") select c; return customers.ToList(); } } The problem is that no data is displayed simply because the data context is not set. I tried to do it in a code-behind but is did not work. I would prefer to do it in a xaml file anyway. Another problem is with the SelectedItem binding - the code is never used. Thanks for help! Regards, EV.

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• Challenge: Neater way of currying or partially applying C#4's string.Join

  - by Damian Powell

  Background I recently read that .NET 4's System.String class has a new overload of the Join method. This new overload takes a separator, and an IEnumerable<T> which allows arbitrary collections to be joined into a single string without the need to convert to an intermediate string array. Cool! That means I can now do this: var evenNums = Enumerable.Range(1, 100) .Where(i => i%2 == 0); var list = string.Join(",",evenNums); ...instead of this: var evenNums = Enumerable.Range(1, 100) .Where(i => i%2 == 0) .Select(i => i.ToString()) .ToArray(); var list = string.Join(",", evenNums); ...thus saving on a conversion of every item to a string, and then the allocation of an array. The Problem However, being a fan of the functional style of programming in general, and method chaining in C# in particular, I would prefer to be able to write something like this: var list = Enumerable.Range(1, 100) .Where(i => i%2 == 0) .string.Join(","); This is not legal C# though. The closest I've managed to get is this: var list = Enumerable.Range(1, 100) .Where(i => i%2 == 0) .ApplyTo( Functional.Curry<string, IEnumerable<object>, string> (string.Join)(",") ); ...using the following extension methods: public static class Functional { public static TRslt ApplyTo<TArg, TRslt>(this TArg arg, Func<TArg, TRslt> func) { return func(arg); } public static Func<T1, Func<T2, TResult>> Curry<T1, T2, TResult>(this Func<T1, T2, TResult> func) { Func<Func<T1, T2, TResult>, Func<T1, Func<T2, TResult>>> curried = f => x => y => f(x, y); return curried(func); } } This is quite verbose, requires explicit definition of the parameters and return type of the string.Join overload I want to use, and relies upon C#4's variance features because we are defining one of the arguments as IEnumerable rather than IEnumerable. The Challenge Can you find a neater way of achieving this using the method-chaining style of programming?

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• Determine the 'Overtype' mode using Javascript

  - by Snorkpete

  We are creating a web app to replace an old-school green-screen application. In the green-screen app, as the user presses the Insert key to switch between overtype and insert modes, the cursor changes to indicate which input mode the user is currently in. In IE (which is the official browser of the company), overtype mode also works, but there's no visual indication as to whether overtype mode is on or not, until the user starts typing and possibly over-writes existing information unexpectedly. I'd like to put some sort of visual indicator on the screen if in overtype mode. How can you determine if the browser is in 'overtype mode' from Javascript? Is there some property or function i can query to determine if the browser is in overtype mode? Even an IE-specific solution would be helpful, since our corporate policy dictates the browser to use as IE7 (pure torture, btw). (I do know that one solution is to do check for key presses of the Insert key. However, it's a solution that I'd prefer to avoid since that method seems a bit flaky & error-prone because I can't guarantee what mode the user would be in BEFORE he/she hits my page. ) The reasoning behind this question: The functionality of this portion of the green-screen app is such that the user can select from a list of 'preformatted bodies of text'. crude eg. The excess for this policy is: $xxxxxx and max limit is:$xxxxxx Date of policy is: xx/xx/xxxx and expires : xx/xx/xxxx Some other irrelevant text After selecting this 'preformatted text', the user would then use overtype to replace the x's with actual values, without disturbing the alignment of the rest of the text. (To be clear, they can still edit any part of the 'preformatted text' if they so wished. It's just that usually, they just wish to replace specific portions of the text. Keeping the alignment is important since these sections of text can end up on printed documents.) Of course, the same effect can be achieved by just selecting the x's to replace first, but it would be helpful (with respect to easing the transition to the web app) to allow old methods of doing things to continue to work, while still allowing 'web methods' to be used by the more tech-savvy users. Essentially, we're trying to make the initial transition from the green-screen app to the web app be as seemless as possible to minimise the resistance from the long-time green-screeners.

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• Django conditional template inheritance

  - by Ed

  I have template that displays object elements with hyperlinks to other parts of my site. I have another function that displays past versions of the same object. In this display, I don't want the hyperlinks. I'm under the assumption that I can't dynamically switch off the hyperlinks, so I've included both versions in the same template. I use an if statement to either display the hyperlinked version or the plain text version. I prefer to keep them in the same template because if I need to change the format of one, it will be easy to apply it to the other right there. The template extends framework.html. Framework has a breadcrumb system and it extends base.html. Base has a simple top menu system. So here's my dilemma. When viewing the standard hyperlink data, I want to see the top menu and the breadcrumbs. But when viewing the past version plain text data, I only want the data, no menu, no breadcrumbs. I'm unsure if this is possible given my current design. I tried having framework inherit the primary template so that I could choose to call either framework (and display the breadcrumbs), or the template itself, thus skipping the breadcrumbs, but I want framework.html available for other templates as well. If framework.html extends a specific template, I lose the ability to display it in other templates. I tried writing an if statement that would display a the top_menu block and the nav_menu block from base.html and framework.html respectively. This would overwrite their blocks and allow me to turn off those elements conditional on the if. Unfortunately, it doesn't appear to be conditional; if the block elements are in the template at all, surrounded by an if or not, I lose the menus. I thought about using {% include %} to pick up the breadcrumbs and a split out top menu. In that case though, I'll have to include it all the time. No more inheritance. Is this the best option given my requirement?

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• How do I avoid the loader lock?

  - by Mark0978

  We have a managed app, that uses an assembly. That assembly uses some unmanaged C++ code. The Managed C++ code is in a dll, that depends on several other dlls. All of those Dlls are loaded by this code. (We load all the dll's that ImageCore.dll depends on first, so we can tell which ones are missing, otherwise it would just show up as ImageCore.dll failed to load, and the log file would give no clues as to why). class Interop { private const int DONT_RESOLVE_DLL_REFERENCES = 1; private static log4net.ILog log = log4net.LogManager.GetLogger("Imagecore.NET"); [DllImport("kernel32.dll", CharSet = CharSet.Auto, SetLastError = true)] private static extern IntPtr LoadLibraryEx(string fileName, IntPtr dummy, int flags); [DllImport("kernel32.dll", CharSet = CharSet.Auto, SetLastError = true)] private static extern IntPtr FreeLibrary(IntPtr hModule); static private String[] libs = { "log4cplus.dll", "yaz.dll", "zlib1.dll", "libxml2.dll" }; public static void PreloadAssemblies() { for (int i=0; i < libs.Length; ++i) { String libname = libs[i]; IntPtr hModule = LoadLibraryEx(libname, IntPtr.Zero, DONT_RESOLVE_DLL_REFERENCES); if(hModule == IntPtr.Zero) { log.Error("Unable to pre-load '" + libname + "'"); throw new DllNotFoundException("Unable to pre-load '" + libname + "'"); } else { FreeLibrary(hModule); } } IntPtr h = LoadLibraryEx("ImageCore.dll", IntPtr.Zero, 0); if (h == IntPtr.Zero) { throw new DllNotFoundException("Unable to pre-load ImageCore.dll"); } } } And this code is called by public class ImageDoc : IDisposable { static ImageDoc() { ImageHawk.ImageCore.Utility.Interop.PreloadAssemblies(); } ... } Which is static constructor. As near as I can understand it, as soon as we attempt to use an ImageDoc object, the dll that contains that assembly is loaded and as part of that load, the static constructor is called which in turn causes several other DLLs to be loaded as well. What I'm trying to figure out, is how do we defer loading of those DLLs so that we don't run smack dab into this loader lock that is being kicked out because of the static constructor. I've pieced this much together by looking at: http://social.msdn.microsoft.com/Forums/en-US/vsto/thread/dd192d7e-ce92-49ce-beef-3816c88e5a86 http://msdn.microsoft.com/en-us/library/aa290048%28VS.71%29.aspx http://forums.devx.com/showthread.php?t=53529 http://www.yoda.arachsys.com/csharp/beforefieldinit.html But I just can't seem to find a way to get these external DLLs to load without it happening at the point the class is loading. I think I need to get these LoadLibrary calls out of the static constructor, but don't know how to get them called before they are needed (except for how it is done here). I would prefer to not have to put this kind of knowledge of the dlls into every app that uses this assembly. (And I'm not sure that would even fix the problem.... The strange thing is that the exception only appears to be happening while running within the debugger, not while running outside the debugger.

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• CSS: Chrome and Safari seem to 'add' border to width, while IE, Firefox & Opera don't

  - by Michiel

  Hey guys, I'm trying to achieve cross-browser consistency for my website, but I have been trying all day now and its driving me nuts (0.38 am here in Europe now..). It's about this page: http://www[insert-dot-here]geld[insert-dash-here]surfen[insert-dot-here]nl/uitbetalingen.html (please note that I prefer this URL not to be made crawlable for seo-bots) If you view this page in IE, Firefox or Opera, everything is fine, but in Chrome and Safari the tables are a little out of line (as you'll probably clearly notice). What seems to be the problem?; it appears to me that in Chrome and Safari the left and right border (2px) in total are added to the set table width, while in the other browsers the border is considered part of the width. The (most) relevant CSS-lines are the following ones (from the tabel.css-file, also available through the page's source file): table.uitbetaling { margin: 11px 18px 10px 19px; border: 1px solid #8ccaee; width: 498px; padding: 0; } table.uitbetaling img, table.uitbetaling td { margin: 0; border: 0; padding: 0; width: 496px; } table.uitbetaling tr { margin: 0; border: 0; padding: 0 1px 0 0; } So basically I have used a table-structure to organize images, like this; (the class of the table is 'uitbetaling') <table> <tr><td><img /></td></tr> <tr><td><img /></td></tr> ... <tr><td><img /></td></tr> </table> If, here, I set the width of 'table.uitbetaling' and 'table.uitbetaling img, table.uitbetaling td' to the same value (e.g. both 496 or 498), the 'problem' in Chrome and Safari is solved, however in Firefox the right side border is than blank. Because the right-side border can't 'fit' in anymore. 'img' and 'td' must be at least 2px more narrow than 'table.uitbetaling' for the right-border be visible in Firefox. Is there any way to solve this? Thanks so much in advance for your insights!!

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• WPF WrapPanel with some items having a height of *

  - by Aphex

  How do I make a WrapPanel with some items having a Height of *? A deceptively simple question that I have been trying to solve. I want a control (or some XAML layout magickry) that behaves similar to a Grid that has some rows with a Height of *, but supports wrapping of columns. Hell; call it a WrapGrid. :) Here's a mockup to visualize this. Imagine a grid defined as such: <Window xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" Title="Window1" Height="400"> <Grid> <Grid.ColumnDefinitions> <ColumnDefinition Width="*"/> </Grid.ColumnDefinitions> <Grid.RowDefinitions> <RowDefinition Height="Auto"/> <RowDefinition Height="*"/> <RowDefinition Height="Auto"/> <RowDefinition Height="*"/> <RowDefinition Height="Auto"/> <RowDefinition Height="Auto"/> </Grid.RowDefinitions> <Button Grid.Row="0" MinHeight="30">I'm auto-sized.</Button> <Button Grid.Row="1" MinHeight="90">I'm star-sized.</Button> <Button Grid.Row="2" MinHeight="30">I'm auto-sized.</Button> <Button Grid.Row="3" MinHeight="90">I'm star-sized, too!</Button> <Button Grid.Row="4" MinHeight="30">I'm auto-sized.</Button> <Button Grid.Row="5" MinHeight="30">I'm auto-sized.</Button> </Grid> </Window> What I want this panel to do is wrap an item into an additional column when the item can not get any smaller than its minHeight. Here is a horrible MSPaint of some mockups I made detailing this process. Recall from the XAML that the auto-sized buttons have minHeights of 30, and the star-sized buttons have minHeights of 90. This mockup is just two grids side by side and I manually moved buttons around in the designer. Conceivably, this could be done programmatically and serve as a sort of convoluted solution to this. How can this be done? I will accept any solution whether it's through xaml or has some code-behind (though I would prefer pure XAML if possible since xaml code behind is tougher to implement in IronPython). Updated with a bounty

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• Which StackOverflow-style MarkDown (WMD) javascript editor should I use?

  - by Edan Maor

  Background I'm working on an application which requires user-entered content, and I've decided to use a StackOverflow-style MarkDown editor. After researching this topic for the last few days, I realize there are numerous forks of the base WMD editor, some with a few basic enhancements and some with serious differences from the StackOverflow one. Since this will be the heart of the application, I'd like to start with the best code base I can. I'd be happy if anyone can recommend which one of the many solutions out there best fits my needs. Below is requirements, plus what I've managed to find already. I'm hoping this question will help me decide which version to go with, and maybe help me discover a port out there that's an even better fit for my needs. The requirements for my project Live Preview Multiple editors on the same page (not know how many in advance, since the user can dynamically add another editing box). Ability to extend with extra buttons (I'd like a button to upload a picture, instead of just adding an img url). Ability to dynamically show/hide the edit box (and only see the preview box). Not an absolute must, but I'd prefer to stick as close to StackOverflow's look and feel, since it's well known. Don't know if this matters, but the backend is written in Django. Editors I've looked at Here are a few of the code bases I've looked at, with thoughts. Obviously, I might be missing another solution out there. The derobins version. From what I can tell, this is the official StackOverflow version. Seems like it doesn't support multiple editors on one page. JQuery.MarkEdit. Looks very good, but is pretty different from the StackOverflow version. MooWMD. Looks like the winner right now, but I'm a little concerned since it looks less active/hackable than MarkEdit. The wmd-new version. Not sure, looks like an old codebase without much use. The SocialSite branch. Seems like it's not for public use.

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• Which third party website thumbnailing services do you use?

  - by Ben Delarre

  I've got a requirement for showing thumbnails of arbitrary websites. I need to be able to show small thumbnails (120px by 90px), and larger thumbnails of around 480px wide. I'll need to specify the queue and invalid placeholder images and preferably have a pingback when the queued images are processed so I can respond appropriately. I'd also need a simple API I can use either directly embedded in my HTML, or from a simple web request to queue the images. I've been looking at various services ranging from low-fi services, to large scale ones - here's some examples: www.bitpixels.com Uses Google AppEngine, seems like a prototype or a toy. Free! www.websnapr.com Tried using this, made a free account and requested a thumbnail. Waited a few minutes and refreshed a couple of times, and ended up having the account banned. Free is tricky yes, but if I can't try it out successfully I'm disinclined to pay. www.shrinktheweb.com Free account seems to be very quick. Lots of documentation on the site, and even covers local caching of the images to your own server (documentation mostly in PHP). Quality of thumbnails look good, and there appear to be sufficient options for setting thumbnail placeholder images and parameters for altering how the thumbnailing is done. Also supports large 'screenshots' of URLs - very useful for me. Discovered the PRO pricing is an à la carte menu, allowing me to select just the features I want and keep the monthly cost low. Excellent stuff, have decided to use this service. www.thumbalizr.com Good coverage of thumbnail sizes and control options - even allowing specification for browser width when thumbnailing. No ping-back, but I can live without that. Supports local caching of images with PHP API, would prefer .NET, but can port it if necessary. Looks like a fairly professional service but seems fairly expensive for the number of thumbnails you get to generate. apologies for lack of proper linking - spam protection! I'm not entirely convinced by any of them, and since this will be a long term service I'd like some stability and support. I'm willing to pay for the service, but I'd want something that fulfills most if not all of my requirements for that. I should also mention that we're hosted on Windows under IIS, so local solutions involving Xvfb and the like sadly can't be used for this project. So my question is: what services do you use? How have they panned out, are you happy with them?

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• Bind listbox in WPF with grouping

  - by Michael Stoll

  Hi, I've got a collection of ViewModels and want to bind a ListBox to them. Doing some investigation I found this. So my ViewModel look like this (Pseudo Code) interface IItemViewModel { string DisplayName { get; } } class AViewModel : IItemViewModel { string DisplayName { return "foo"; } } class BViewModel : IItemViewModel { string DisplayName { return "foo"; } } class ParentViewModel { IEnumerable<IItemViewModel> Items { get { return new IItemViewModel[] { new AItemViewModel(), new BItemViewModel() } } } } class GroupViewModel { static readonly GroupViewModel GroupA = new GroupViewModel(0); static readonly GroupViewModel GroupB = new GroupViewModel(1); int GroupIndex; GroupViewModel(int groupIndex) { this.GroupIndex = groupIndex; } string DisplayName { get { return "This is group " + GroupIndex.ToString(); } } } class ItemGroupTypeConverter : IValueConverter { object Convert(object value, Type targetType, object parameter, CultureInfo culture) { if (value is AItemViewModel) return GroupViewModel.GroupA; else return GroupViewModel.GroupB; } } And this XAML <UserControl.Resources> <vm:ItemsGroupTypeConverter x:Key="ItemsGroupTypeConverter "/> <CollectionViewSource x:Key="GroupedItems" Source="{Binding Items}"> <CollectionViewSource.GroupDescriptions> <PropertyGroupDescription Converter="{StaticResource ItemsGroupTypeConverter }"/> </CollectionViewSource.GroupDescriptions> </CollectionViewSource> </UserControl.Resources> <ListBox ItemsSource="{Binding Source={StaticResource GroupedItems}}"> <ListBox.GroupStyle> <GroupStyle> <GroupStyle.HeaderTemplate> <DataTemplate> <TextBlock Text="{Binding DisplayName}" FontWeight="bold" /> </DataTemplate> </GroupStyle.HeaderTemplate> </GroupStyle> </ListBox.GroupStyle> <ListBox.ItemTemplate> <DataTemplate> <TextBlock Text="{Binding DisplayName}" /> </DataTemplate> </ListBox.ItemTemplate> </ListBox> This works somehow, exept of the fact that the binding of the HeaderTemplate does not work. Anyhow I'd prefer omitting the TypeConverter and the CollectionViewSource. Isn't there a way to use a property of the ViewModel for Grouping? I know that in this sample scenario it would be easy to replace the GroupViewModel with a string an have it working, but that's not an option. So how can I bind the HeaderTemplate to the GroupViewModel?

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