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• How to track deleted self-tracking entities in ObservableCollection without memory leaks

  - by Yannick M.

  In our multi-tier business application we have ObservableCollections of Self-Tracking Entities that are returned from service calls. The idea is we want to be able to get entities, add, update and remove them from the collection client side, and then send these changes to the server side, where they will be persisted to the database. Self-Tracking Entities, as their name might suggest, track their state themselves. When a new STE is created, it has the Added state, when you modify a property, it sets the Modified state, it can also have Deleted state but this state is not set when the entity is removed from an ObservableCollection (obviously). If you want this behavior you need to code it yourself. In my current implementation, when an entity is removed from the ObservableCollection, I keep it in a shadow collection, so that when the ObservableCollection is sent back to the server, I can send the deleted items along, so Entity Framework knows to delete them. Something along the lines of: protected IDictionary<int, IList> DeletedCollections = new Dictionary<int, IList>(); protected void SubscribeDeletionHandler<TEntity>(ObservableCollection<TEntity> collection) { var deletedEntities = new List<TEntity>(); DeletedCollections[collection.GetHashCode()] = deletedEntities; collection.CollectionChanged += (o, a) => { if (a.OldItems != null) { deletedEntities.AddRange(a.OldItems.Cast<TEntity>()); } }; } Now if the user decides to save his changes to the server, I can get the list of removed items, and send them along: ObservableCollection<Customer> customers = MyServiceProxy.GetCustomers(); customers.RemoveAt(0); MyServiceProxy.UpdateCustomers(customers); At this point the UpdateCustomers method will verify my shadow collection if any items were removed, and send them along to the server side. This approach works fine, until you start to think about the life-cycle these shadow collections. Basically, when the ObservableCollection is garbage collected there is no way of knowing that we need to remove the shadow collection from our dictionary. I came up with some complicated solution that basically does manual memory management in this case. I keep a WeakReference to the ObservableCollection and every few seconds I check to see if the reference is inactive, in which case I remove the shadow collection. But this seems like a terrible solution... I hope the collective genius of StackOverflow can shed light on a better solution. Thanks!

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• Playing an InputStream video in Blackberry JDE.

  - by Jenny

  I think I'm using InputStream incorrectly with a Blackberry 9000 simulator: I found some sample code, http://www.blackberry.com/knowledgecenterpublic/livelink.exe/fetch/2000/348583/800332/1089414/How%5FTo%5F-%5FPlay%5Fvideo%5Fwithin%5Fa%5FBlackBerry%5Fsmartphone%5Fapplication.html?nodeid=1383173&vernum=0 that lets you play video from within a Blackberry App. The code claims it can handle HTTP, but it's taken some fandangling to get it to actually approach doing so: http://pastie.org/609491 Specifically, I'm doing: StreamConnection s = null; s = (StreamConnection)Connector.open("http://10.252.9.15/eggs.3gp"); HttpConnection c = (HttpConnection)s; InputStream i = c.openInputStream(); System.out.println("~~~~~I have a connection?~~~~~~" + c); System.out.println("~~~~~I have a URL?~~~~" + c.getURL()); System.out.println("~~~~~I have a type?~~~~" + c.getType()); System.out.println("~~~~~I have a status?~~~~~~" + c.getResponseCode()); System.out.println("~~~~~I have a stream?~~~~~~" + i); player = Manager.createPlayer(i, c.getType()); I've found that this is the only way I can get an InputStream from an HTTPConnection without causing a: "JUM Error 104: Uncaught NullPointer Exception". (That is, the casting as a StreamConnection, and THEN as an HttpConnection stops it from crashing). However, I'm still not streaming video. Before, a stream wasn't able to be created (it would crash with the null pointer exception). Now, a stream is being made, the debugger claims it's begining to stream video from it...and nothing happens. No video plays. The app doesn't freeze, or crash or anything. I can 'pause' and 'play' freely, and get appropriate debug messages for both. But no video shows up. If I'm playing a video stored locally on the blackberry, everything is fine (it actually plays the video), so I know the Player itself is working fine, I"m just wondering if maybe I have something wrong with my stream? The API says the player can take in an InputStream. Is there a specific kind it needs? How can I query my inputstream to know if it's valid? It existing is further than I've gotten before. -Jenny Edit: I'm on a Blackberry Bold simulator (9000). I've heard that some versions of phones do NOT stream video via HTTP, however, the Bold does. I have yet to see examples of this though. When I go to the internet and point at a blackberry playable video, it attempts to stream, and then asks me to physically download the file (and then plays fine once I download). Edit: Also, I have a physical blackberry Bold, as well, but it can't stream either (I've gone to m.youtube.com, only to get a server/content not found error). Is there something special I need to do to stream RTSP content?

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• Resizing QT's QTextEdit to Match Text Height: maximumViewportSize()

  - by Aaron

  I am trying to use a QTextEdit widget inside of a form containing several QT widgets. The form itself sits inside a QScrollArea that is the central widget for a window. My intent is that any necessary scrolling will take place in the main QScrollArea (rather than inside any widgets), and any widgets inside will automatically resize their height to hold their contents. I have tried to implement the automatic resizing of height with a QTextEdit, but have run into an odd issue. I created a sub-class of QTextEdit and reimplemented sizeHint() like this: QSize OperationEditor::sizeHint() const { QSize sizehint = QTextBrowser::sizeHint(); sizehint.setHeight(this->fitted_height); return sizehint; } this-fitted_height is kept up-to-date via this slot that is wired to the QTextEdit's "contentsChanged()" signal: void OperationEditor::fitHeightToDocument() { this->document()->setTextWidth(this->viewport()->width()); QSize document_size(this->document()->size().toSize()); this->fitted_height = document_size.height(); this->updateGeometry(); } The size policy of the QTextEdit sub-class is: this->setSizePolicy(QSizePolicy::MinimumExpanding, QSizePolicy::Preferred); I took this approach after reading this post. Here is my problem: As the QTextEdit gradually resizes to fill the window, it stops getting larger and starts scrolling within the QTextEdit, no matter what height is returned from sizeHint(). If I initially have sizeHint() return some large constant number, then the QTextEdit is very big and is contained nicely within the outer QScrollArea, as one would expect. However, if sizeHint gradually adjusts the size of the QTextEdit rather than just making it really big to start, then it tops out when it fills the current window and starts scrolling instead of growing. I have traced this problem to be that, no matter what my sizeHint() returns, it will never resize the QTextEdit larger than the value returned from maximumViewportSize(), which is inherited from QAbstractScrollArea. Note that this is not the same number as viewport()-maximumSize(). I am unable to figure out how to set that value. Looking at QT's source code, maximumViewportSize() is returning "the size of the viewport as if the scroll bars had no valid scrolling range." This value is basically computed as the current size of the widget minus (2 * frameWidth + margins) plus any scrollbar widths/heights. This does not make a lot of sense to me, and it's not clear to me why that number would be used anywhere in a way that supercede's the sub-class's sizeHint() implementation. Also, it does seem odd that the single "frameWidth" integer is used in computing both the width and the height. Can anyone please shed some light on this? I suspect that my poor understanding of QT's layout engine is to blame here.

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• Eventlet or gevent or Stackless + Twisted, Pylons, Django and SQL Alchemy

  - by Khorkrak

  We're using Twisted extensively for apps requiring a great deal of asynchronous io. There are some cases where stuff is cpu bound instead and for that we spawn a pool of processes to do the work and have a system for managing these across multiple servers as well - all done in Twisted. Works great. The problem is that it's hard to bring new team members up to speed. Writing asynchronous code in Twisted requires a near vertical learning curve. It's as if humans just don't think that way naturally. We're considering a mixed approach perhaps. Maybe do the xmlrpc server part and process management in Twisted still but the other stuff in code that at least looks synchronous while not being as such. Then again I like explicit over implicit so hmmm. Anyway onto greenlets - how well does that stuff work? So there's Stackless and as you can see from my Gallentean avatar I'm well aware of the tremendous success in it's use for CCP's flagship EVE Online game first hand. What about Eventlet or gevent? Well for now only Eventlet works with Twisted. However gevent claims to be faster since it's not a pure python implementation it instead uses libevent. It also has fewer idiosyncrasies and defects supposedly. The documentation there is minimal in comparison to Eventlet and it's maintained by 1 guy as far as I can tell. This makes me leery but all great projects start this way so... Then there's PyPy - I haven't even finished reading about that one yet - just saw it in this thread: Drawbacks of Stackless. So confusing - I'm wondering what the heck to do - sounds like Eventlet is probably the best bet but is it really stable enough? Anyone out there have any experience with it? Should we go with Stackless instead as it's been around and is proven technology - just like Twisted is as well - and they do work together nicely. But still I hate having to have a separate version of Python to do this. what to do.... This somewhat obnoxious blog entry hit the nail on the head for me though: Asynchronous IO for Grownups We're stuck using MySQL as well - I never knew how great PostgreSQL was until having had to work on a production OLTP system in MySQL instead - but that's another story. But if that monkey patch thing really works then wow. Just wow.

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• Java ReentrantReadWriteLocks - how to safely acquire write lock?

  - by Andrzej Doyle

  I am using in my code at the moment a ReentrantReadWriteLock to synchronize access over a tree-like structure. This structure is large, and read by many threads at once with occasional modifications to small parts of it - so it seems to fit the read-write idiom well. I understand that with this particular class, one cannot elevate a read lock to a write lock, so as per the Javadocs one must release the read lock before obtaining the write lock. I've used this pattern successfully in non-reentrant contexts before. What I'm finding however is that I cannot reliably acquire the write lock without blocking forever. Since the read lock is reentrant and I am actually using it as such, the simple code lock.getReadLock().unlock(); lock.getWriteLock().lock() can block if I have acquired the readlock reentrantly. Each call to unlock just reduces the hold count, and the lock is only actually released when the hold count hits zero. EDIT to clarify this, as I don't think I explained it too well initially - I am aware that there is no built-in lock escalation in this class, and that I have to simply release the read lock and obtain the write lock. My problem is/was that regardless of what other threads are doing, calling getReadLock().unlock() may not actually release this thread's hold on the lock if it acquired it reentrantly, in which case the call to getWriteLock().lock() will block forever as this thread still has a hold on the read lock and thus blocks itself. For example, this code snippet will never reach the println statement, even when run singlethreaded with no other threads accessing the lock: final ReadWriteLock lock = new ReentrantReadWriteLock(); lock.getReadLock().lock(); // In real code we would go call other methods that end up calling back and // thus locking again lock.getReadLock().lock(); // Now we do some stuff and realise we need to write so try to escalate the // lock as per the Javadocs and the above description lock.getReadLock().unlock(); // Does not actually release the lock lock.getWriteLock().lock(); // Blocks as some thread (this one!) holds read lock System.out.println("Will never get here"); So I ask, is there a nice idiom to handle this situation? Specifically, when a thread that holds a read lock (possibly reentrantly) discovers that it needs to do some writing, and thus wants to "suspend" its own read lock in order to pick up the write lock (blocking as required on other threads to release their holds on the read lock), and then "pick up" its hold on the read lock in the same state afterwards? Since this ReadWriteLock implementation was specifically designed to be reentrant, surely there is some sensible way to elevate a read lock to a write lock when the locks may be acquired reentrantly? This is the critical part that means the naive approach does not work.

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• Revisiting .NET, but what should I focus on?

  - by Wayne M

  After about a two-year hiatus, I'm brushing up on my .NET skills to find a .NET job (my previous two positions have very little development, or development using legacy technologies, so apart from a few very minor apps I have not touched .NET in close to two years). I'm aware of things like ASP.NET MVC, and I have previously read on things like NHibernate and DI/IOC, albeit I have yet to use them apart from very trivial "Hello World" type applications. I have a subscription to Rob Conery's Tekpub website and occasionally watch these videos when I have free time. My concern is this: I don't live in a very technical area. I would be surprised if any but the most tech-savvy companies have heard of, let alone use, ASP.NET MVC, NHibernate (or even LINQ/EF), or know about IoC. I would be willing to bet a large sum of money that 95% of the possible jobs I could obtain will use the following: Visual Source Safe, if any VCS at all ASP.NET 2.0 Webforms (3.5 if lucky) Raw ADO.NET on top of a very thin implementation of the Gateway pattern Stored Procedures in the database for most CRUD operations Gratuitous use of code-behind, with a Service layer if I'm lucky If I were extremely lucky, I might find a shop that has heard of ORMs and either uses one, or has wrote their own data abstraction. Also if I were lucky, the company would be using Model-View-Presenter. In light of this I'm not sure what I should focus on learning. Personally, I would prefer to be using the latest stuff - ASP.NET MVC, NHibernate, jQuery, WCF etc. Reality says I should go back to the basics, since it looks like most potential opportunities aren't going to be anywhere near the cutting edge, or anywhere close to it. And, as much as I would like to find a position and start to show the other developers the benefits, in my past experience this has usually resulted in my being fired for "not being a team player" and doing things the bad old way. So, I am curious how you would approach a situation like this? What should I focus on, in order to A) Reaquaint myself with .NET, and B) Prepare myself to obtain a .NET job again that is more than likely going to use techniques that I and most other knowledgeable developers will scoff at?

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• Get non-overlapping dates ranges for prices history data

  - by Anonymouse

  Hello, Let's assume that I have the following table: CREATE TABLE [dbo].[PricesHist]( [Product] varchar NOT NULL, [Price] [float] NOT NULL, [StartDate] [datetime] NOT NULL, [EndDate] [datetime] NOT NULL ) INSERT [dbo].[PricesHist] ([Product], [Price], [StartDate], [EndDate]) VALUES (N'Apples', 4.9, CAST(0x00009D2C00000000 AS DateTime), CAST(0x00009D2C00000000 AS DateTime)) INSERT [dbo].[PricesHist] ([Product], [Price], [StartDate], [EndDate]) VALUES (N'Apples', 4.9, CAST(0x00009D2D00000000 AS DateTime), CAST(0x00009D2D00000000 AS DateTime)) INSERT [dbo].[PricesHist] ([Product], [Price], [StartDate], [EndDate]) VALUES (N'Apples', 2.5, CAST(0x00009D2E00000000 AS DateTime), CAST(0x00009D2E00000000 AS DateTime)) INSERT [dbo].[PricesHist] ([Product], [Price], [StartDate], [EndDate]) VALUES (N'Apples', 4.9, CAST(0x00009D3000000000 AS DateTime), CAST(0x00009D3000000000 AS DateTime)) INSERT [dbo].[PricesHist] ([Product], [Price], [StartDate], [EndDate]) VALUES (N'Apples', 4.9, CAST(0x00009D3100000000 AS DateTime), CAST(0x00009D3100000000 AS DateTime)) INSERT [dbo].[PricesHist] ([Product], [Price], [StartDate], [EndDate]) VALUES (N'Apples', 4.9, CAST(0x00009D3400000000 AS DateTime), CAST(0x00009D3400000000 AS DateTime)) INSERT [dbo].[PricesHist] ([Product], [Price], [StartDate], [EndDate]) VALUES (N'Apples', 2.5, CAST(0x00009D3500000000 AS DateTime), CAST(0x00009D3500000000 AS DateTime)) INSERT [dbo].[PricesHist] ([Product], [Price], [StartDate], [EndDate]) VALUES (N'Apples', 4.9, CAST(0x00009D3600000000 AS DateTime), CAST(0x00009D3600000000 AS DateTime)) INSERT [dbo].[PricesHist] ([Product], [Price], [StartDate], [EndDate]) VALUES (N'Apples', 4.9, CAST(0x00009D3700000000 AS DateTime), CAST(0x00009D3700000000 AS DateTime)) INSERT [dbo].[PricesHist] ([Product], [Price], [StartDate], [EndDate]) VALUES (N'Apples', 4.9, CAST(0x00009D3800000000 AS DateTime), CAST(0x00009D3800000000 AS DateTime)) INSERT [dbo].[PricesHist] ([Product], [Price], [StartDate], [EndDate]) VALUES (N'Apples', 4.9, CAST(0x00009D3A00000000 AS DateTime), CAST(0x00009D3A00000000 AS DateTime)) INSERT [dbo].[PricesHist] ([Product], [Price], [StartDate], [EndDate]) VALUES (N'Apples', 4.9, CAST(0x00009D3B00000000 AS DateTime), CAST(0x00009D3B00000000 AS DateTime)) INSERT [dbo].[PricesHist] ([Product], [Price], [StartDate], [EndDate]) VALUES (N'Apples', 2.5, CAST(0x00009D3C00000000 AS DateTime), CAST(0x00009D3C00000000 AS DateTime)) INSERT [dbo].[PricesHist] ([Product], [Price], [StartDate], [EndDate]) VALUES (N'Apples', 4.9, CAST(0x00009D3D00000000 AS DateTime), CAST(0x00009D3D00000000 AS DateTime)) INSERT [dbo].[PricesHist] ([Product], [Price], [StartDate], [EndDate]) VALUES (N'Apples', 4.9, CAST(0x00009D3E00000000 AS DateTime), CAST(0x00009D3E00000000 AS DateTime)) INSERT [dbo].[PricesHist] ([Product], [Price], [StartDate], [EndDate]) VALUES (N'Apples', 4.9, CAST(0x00009D3F00000000 AS DateTime), CAST(0x00009D3F00000000 AS DateTime)) INSERT [dbo].[PricesHist] ([Product], [Price], [StartDate], [EndDate]) VALUES (N'Apples', 4.9, CAST(0x00009D4100000000 AS DateTime), CAST(0x00009D4100000000 AS DateTime)) INSERT [dbo].[PricesHist] ([Product], [Price], [StartDate], [EndDate]) VALUES (N'Apples', 4.9, CAST(0x00009D4200000000 AS DateTime), CAST(0x00009D4200000000 AS DateTime)) INSERT [dbo].[PricesHist] ([Product], [Price], [StartDate], [EndDate]) VALUES (N'Apples', 2.5, CAST(0x00009D4300000000 AS DateTime), CAST(0x00009D4300000000 AS DateTime)) INSERT [dbo].[PricesHist] ([Product], [Price], [StartDate], [EndDate]) VALUES (N'Apples', 4.9, CAST(0x00009D4400000000 AS DateTime), CAST(0x00009D4400000000 AS DateTime)) INSERT [dbo].[PricesHist] ([Product], [Price], [StartDate], [EndDate]) VALUES (N'Apples', 4.9, CAST(0x00009D4500000000 AS DateTime), CAST(0x00009D4500000000 AS DateTime)) INSERT [dbo].[PricesHist] ([Product], [Price], [StartDate], [EndDate]) VALUES (N'Apples', 4.9, CAST(0x00009D4600000000 AS DateTime), CAST(0x00009D4600000000 AS DateTime)) INSERT [dbo].[PricesHist] ([Product], [Price], [StartDate], [EndDate]) VALUES (N'Apples', 4.9, CAST(0x00009D4800000000 AS DateTime), CAST(0x00009D4800000000 AS DateTime)) INSERT [dbo].[PricesHist] ([Product], [Price], [StartDate], [EndDate]) VALUES (N'Apples', 2.5, CAST(0x00009D4A00000000 AS DateTime), CAST(0x00009D4A00000000 AS DateTime)) As you can see, there are two prices on that month for Apples. 4.90 and 2.50. In order to tidy this table up, I need to get this information as a date range rather than a row per day as it currently is. I can obviously do this with Min and Max aggregates easily but the ranges overlap and other business code expect non-overlapping ranges. I also tried to achieve this with self joins and row_number(), but without much success... Here is what I'm trying to achieve as the output: Product | StartDate | EndDate | Price ------------------------------------------- Apples | 01 Mar 2010 | 02 Mar 2010 | 4.90 Apples | 03 Mar 2010 | 03 Mar 2010 | 2.50 Apples | 05 Mar 2010 | 09 Mar 2010 | 4.90 Apples | 10 Mar 2010 | 10 Mar 2010 | 2.50 Apples | 11 Mar 2010 | 16 Mar 2010 | 4.90 Apples | 17 Mar 2010 | 17 Mar 2010 | 2.50 Apples | 18 Mar 2010 | 23 Mar 2010 | 4.90 Apples | 24 Mar 2010 | 24 Mar 2010 | 2.50 Apples | 25 Mar 2010 | 30 Mar 2010 | 4.90 Apples | 31 Mar 2010 | 31 Mar 2010 | 2.50 What would please be the best approach to get this done? Thanks a lot in advance,

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• Properly clean up excel interop objects revisited: Wrapper objects

  - by chiccodoro

  Hi all, Excel 2007 Hangs When Closing via .NET How to properly clean up Excel interop objects in C# How to properly clean up interop objects in C# All of these struggle with the problem that C# does not release the Excel COM objects properly after using them. There are mainly two directions of working around this issue: Kill the Excel process when Excel is not used anymore. Take care to assign each COM object used explicitly to a variable and to Marshal.ReleaseComObject all of these. Some have stated that 2 is too tedious and there is always some uncertainty whether you forget to stick to this rule at some places in the code. Still 1 seems dirty and dangerous to me, also I could imagine that in an environment with restricted access killing processes is not allowed. So I've been thinking about solving 2 by creating another proxy object model which mimics the Excel object model (for me, it would suffice to implement the objects I actually need). The principle would look as follows: Each Excel Interop class has its proxy which wraps an object of that class. The proxy releases the COM object in its destructor. The proxy mimics the interface of the Interop class (maybe by inheriting it). Any methods that usually return another COM object return a proxy instead. The other methods simply delegate the implementation to the inner COM object. This is a rough sketch of the code: public class Application : Microsoft.Office.Interop.Excel.Application { private Microsoft.Office.Interop.Excel.Application innerApplication = new Microsoft.Office.Interop.Excel.Application innerApplication(); ~Application() { Marshal.ReleaseCOMObject(innerApplication); } public Workbooks Workbooks { get { return new Workbooks(innerApplication.Workbooks); } } } public class Workbooks { private Microsoft.Office.Interop.Excel.Workbooks innerWorkbooks; Workbooks(Microsoft.Office.Interop.Excel.Workbooks innerWorkbooks) { this.innerWorkbooks = innerWorkbooks; } ~Workbooks() { Marshal.ReleaseCOMObject(innerWorkbooks); } } My questions to you are in particular: Who finds this a bad idea and why? Who finds this a gread idea? If so, why hasn't anybody implemented/published such a model yet? Just due to the effort, or am I missing a killing problem with that idea? Is it impossible/bad/dangerous to do the ReleaseCOMObject in the destructor? (I've only seen proposals to put it in a Dispose() rather than in a destructor - why?) If the approach makes sense, any suggestions to improve it?

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• UIViewAnimation done by a UIViewController belonging to a UINavigationController?

  - by RickiG

  Hi I have an UINavigationController which the user navigates with. When pushing a specific UIViewController onto the navigation stack, a "settings" button appear in the navigationBar. When the user clicks this button I would like to flip the current view/controller, i.e. everything on screen, including the navigationBar, over to a settings view. So I have a SettingsViewController which I would like to flip to from my CurrentViewController that lives on a navigationController stack. I get all kinds of strange behavior trying to do this, the UIViews belonging to the SettingsViewController will start to animate, sliding into place, the navigationButtons moves around, nothing acts as I would think. -(void)settingsHandler { SettingViewController *settingsView = [[SettingViewController alloc] init]; [UIView beginAnimations:nil context:nil]; [UIView setAnimationDuration:1.0]; [UIView setAnimationTransition:UIViewAnimationTransitionFlipFromRight forView:self.navigationController.view cache:YES]; [self.navigationController.view addSubview:settingsView.view]; [UIView commitAnimations]; } The above results in the views flipping correctly, but the subviews of the SettingsViewController are all positioned in (0, 0) and after the transition, they 'snap' into place? Is it because I instantiate and add my subviews in viewDidLoad, like this? - (void)viewDidLoad { UIImageView *imageBg = [[UIImageView alloc] initWithFrame:CGRectMake(0.0f, 0.0f, 320.0f, 460.0f)]; [imageBg setImage:[UIImage imageNamed:@"background.png"]]; [self.view addSubview:imageBg]; [imageBg release]; SettingsSubview *switchView = [[SettingsSubview alloc] initWithFrame:CGRectMake(0.0f, 0.0f, 320.0f, 460.0f)]; [self.view addSubview:switchView]; [switchView release]; [super viewDidLoad]; } 1: How should I correctly do the "flip" transition, from within the UIViewController in the UINavigationController, to a new UIViewController and subsequently from the new UIViewController and back to the "original" UIViewController residing on the UINavigationControllers stack? 2: Should I use a different approach, than the "viewDidLoad" method, when instantiating and adding subviews to a UIViewController? -question 2 is more of a "best practice" thing. I have seen different ways of doing it and I am having trouble either finding or understanding the life-cycle documentation and the different threads and posts on the subject. I am missing the "best practice" examples. Thank You very much for any help given:)

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• ANTLR: using stringTemplate

  - by Kevin Won

  (I'm a Noob with Antlr)... I'm having difficulties getting my grammar with StringTemplates. Basically I'm trying to write a little DSL. I can get my grammar the way I want (it parses correctly), but I can't get the generation of the target code to work with templates. So here's a snippet of my grammar: grammar Pfig; options { output=template; language=CSharp2; } conf : globalName ; globalName : 'GlobalName:' ID -> localConf(name ={$ID.text}) ; I simplified it quite a bit just to get the essence across. Basically, when the lex/parse comes across `GlobalName: Foo' I want it to spit out text based on the StringTemplate called 'localConf'. Super straightforward. So now, let's fire up the parser in a test app and have it process an input file. // C# processing a file with the lex/parser. // the 'app.pfig' file just has one line that reads 'GlobalName: Bla' using (FileStream fs = File.OpenRead("c:\\app.pfig")) { PfigParser parser = new PfigParser(new CommonTokenStream( new PfigLexer(new ANTLRInputStream(fs)))); using (TextReader tr = File.OpenText("./Pfig.stg")) { parser.TemplateLib = new StringTemplateGroup(tr); } var parseResult = parser.conf(); string code = parseResult.Template.ToString(); // Fail: template is null } I can step through the parser code and see that it correctly identifies my text and applies the stringTemplate correctly. The problem is that since this 'globalName' rule is a subrule of 'conf' it doesn't get executed directly--the method just finds it and returns. But the calling 'Conf' method does not keep the return value from the subrule--it goes to thin air. This means that my resultant template on the last line is null. If I get rid of the 'conf' rule in my grammar and call 'globalName' directly, it will work (since it's the only rule on the stack). But I obviously want more than one rule. I've generated the parser in Java and it does the same thing: // antlr generated parser code public PfigParser.conf_return conf() // throws RecognitionException [1] { PfigParser.conf_return retval = new PfigParser.conf_return(); try { { PushFollow(FOLLOW_globalName_in_conf30); globalName(); // <- it calls globalName() but doesn't keep the return. state.followingStackPointer--; } retval.Stop = input.LT(-1); } // snip It's simple to see I don't get some basic concept with how the Template approach is supposed to work with Antlr. I'm quite sure this is my problem but I'm a loggerheads to know what I'm doing wrong... the examples I've seen don't really show real-world template emission of code.

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• How do you get Matlab to write the BOM (byte order markers) for UTF-16 text files?

  - by Richard Povinelli

  I am creating UTF16 text files with Matlab, which I am later reading in using Java. In Matlab, I open a file called fileName and write to it as follows: fid = fopen(fileName, 'w','n','UTF16-LE'); fprintf(fid,"Some stuff."); In Java, I can read the text file using the following code: FileInputStream fileInputStream = new FileInputStream(fileName); Scanner scanner = new Scanner(fileInputStream, "UTF-16LE"); String s = scanner.nextLine(); Here is the hex output: Offset(h) 00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F 10 11 12 13 00000000 73 00 6F 00 6D 00 65 00 20 00 73 00 74 00 75 00 66 00 66 00 s.o.m.e. .s.t.u.f.f. The above approach works fine. But, I want to be able to write out the file using UTF16 with a BOM to give me more flexibility so that I don't have to worry about big or little endian. In Matlab, I've coded: fid = fopen(fileName, 'w','n','UTF16'); fprintf(fid,"Some stuff."); In Java, I change the code to: FileInputStream fileInputStream = new FileInputStream(fileName); Scanner scanner = new Scanner(fileInputStream, "UTF-16"); String s = scanner.nextLine(); In this case, the string s is garbled, because Matlab is not writing the BOM. I can get the Java code to work just fine if I add the BOM manually. With the added BOM, the following file works fine. Offset(h) 00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F 10 11 12 13 14 15 00000000 FF FE 73 00 6F 00 6D 00 65 00 20 00 73 00 74 00 75 00 66 00 66 00 ÿþs.o.m.e. .s.t.u.f.f. How can I get Matlab to write out the BOM? I know I could write the BOM out separately, but I'd rather have Matlab do it automatically. Addendum I selected the answer below from Amro because it exactly solves the question I posed. One key discovery for me was the difference between the Unicode Standard and a UTF (Unicode transformation format) (see http://unicode.org/faq/utf_bom.html). The Unicode Standard provides unique identifiers (code points) for characters. UTFs provide mappings of every code point "to a unique byte sequence." Since all but a handful of the characters I am using are in the first 128 code points, I'm going to switch to using UTF-8 as Romeo suggests. UTF-8 is supported by Matlab (The warning shown below won't need to be suppressed.) and Java, and for my application will generate smaller text files. I suppress the Matlab warning Warning: The encoding 'UTF-16LE' is not supported. with warning off MATLAB:iofun:UnsupportedEncoding;

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• Unable to rename file with c# ftp methods when current user directory is different from root

  - by Agata

  Hello everyone, Remark: due to spam prevention mechanizm I was forced to replace the beginning of the Uris from ftp:// to ftp. I've got following problem. I have to upload file with C# ftp method and afterwards rename it. Easy, right? :) Ok, let's say my ftp host is like this: ftp.contoso.com and after logging in, current directory is set to: users/name So, what I'm trying to achieve is to log in, upload file to current directory as file.ext.tmp and after upload is successful, rename the file to file.ext The whole difficulty is, as I guess, to properly set the request Uri for FtpWebRequest. MSDN states: The URI may be relative or absolute. If the URI is of the form "ftp://contoso.com/%2fpath" (%2f is an escaped '/'), then the URI is absolute, and the current directory is /path. If, however, the URI is of the form "ftp://contoso.com/path", first the .NET Framework logs into the FTP server (using the user name and password set by the Credentials property), then the current directory is set to UserLoginDirectory/path. Ok, so I upload file with the following URI: ftp.contoso.com/file.ext.tmp Great, the file lands where I wanted it to be: in directory "users/name" Now, I want to rename the file, so I create web request with following Uri: ftp.contoso.com/file.ext.tmp and specify rename to parameter as: file.ext and this gives me 550 error: file not found, no permissions, etc. I traced this in Microsoft Network Monitor and it gave me: Command: RNFR, Rename from CommandParameter: /file.ext.tmp Ftp: Response to Port 53724, '550 File /file.ext.tmp not found' as if it was looking for the file in the root directory - not in the current directory. I renamed the file manually using Total Commander and the only difference was that CommandParameter was without the first slash: CommandParameter: file.ext.tmp I'm able to successfully rename the file by supplying following absolute URI: ftp.contoso.com/%2fusers/%2fname/file.ext.tmp but I don't like this approach, since I would have to know the name of current user's directory. It can probably be done by using WebRequestMethods.Ftp.PrintWorkingDirectory, but it adds extra complexity (calling this method to retrieve directory name, then combining the paths to form proper URI). What I don't understand is why the URI ftp.contoso.com/file.ext.tmp is good for upload and not for rename? Am I missing something here? The project is set to .NET 4.0, coded in Visual Studio 2010.

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• Lots of questions about file I/O (reading/writing message strings)

  - by Nazgulled

  Hi, For this university project I'm doing (for which I've made a couple of posts in the past), which is some sort of social network, it's required the ability for the users to exchange messages. At first, I designed my data structures to hold ALL messages in a linked list, limiting the message size to 256 chars. However, I think my instructors will prefer if I save the messages on disk and read them only when I need them. Of course, they won't say what they prefer, I need to make a choice and justify the best I can why I went that route. One thing to keep in mind is that I only need to save the latest 20 messages from each user, no more. Right now I have an Hash Table that will act as inbox, this will be inside the user profile. This Hash Table will be indexed by name (the user that sent the message). The value for each element will be a data structure holding an array of size_t with 20 elements (20 messages like I said above). The idea is to keep track of the disk file offsets and bytes written. Then, when I need to read a message, I just need to use fseek() and read the necessary bytes. I think this could work nicely... I could use just one single file to hold all messages from all users in the network. I'm saying one single file because a colleague asked an instructor about saving the messages from each user independently which he replied that it might not be the best approach cause the file system has it's limits. That's why I'm thinking of going the single file route. However, this presents a problem... Since I only need to save the latest 20 messages, I need to discard the older ones when I reach this limit. I have no idea how to do this... All I know is about fread() and fwrite() to read/write bytes from/to files. How can I go to a file offset and say "hey, delete the following X bytes"? Even if I could do that, there's another problem... All offsets below that one will be completely different and I would have to process all users mailboxes to fix the problem. Which would be a pain... So, any suggestions to solve my problems? What do you suggest?

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• Loading a Page into a jQuery Dialog

  - by Dave

  I tend to follow a fairly "modular" approach to building applications and I recently started working with jQuery. The application I'm working on is going to be fairly large so I'm trying to break pieces out into separate files/modules when possible. One example of this is a "User Settings" dialog. This dialog has a form, a few tabs, and quite a good number of input fields so I want to develop it in a separate HTML file (PHP actually, but it can be considered HTML for the purposes of this example). It's an entire page in and of itself with all the tags you would expect such as: <html><head></head><body></body></html> So I can now develop, what I want to be, the dialog separate from the base application. This dialog has it's own Javascript (A LOT of Javascript, in fact) in the head as well, with jQuery $(document).ready(){} capturing, etc. Everything works flawlessly in isolation. However, when I attempt to load the jQuery modal dialog with the page (inside of the main application page), as one might expect, trouble ensues. Here's a brief, very simple, example of what it looks like: editUserDialog.load ("editUser.php", {id : $('#userList').val(), popup : "true"}, function () { editUserDialog.dialog ("option", "title" , "Edit User"); editUserDialog.dialog ('open'); }); (I'm passing in a "popup" flag to the page so that the page can determine its context -- i.e. as a page or inside of the jQuery dialog). Question 1: When I moved the code from the "head" into "body" (in the editUser.php page) it actually worked for the most part. It seemed that jQuery was calling the $(document).ready() function in the context of the body of the loaded file and not the head. Is this a bad idea? Question 2: Is my process for building this application just totally flawed to begin with? I've scoured the net to attempt to find a "best practices" sort of document to building reasonably large applications using jQuery/PHP without a lot of success so maybe there's something out there someone else is aware of that I've somehow missed. Thanks for bearing with me while I attempt to describe the issues I've encountered and I hope I've accurately described the problem.

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• Lambda Expression to be used in Select() query

  - by jameschinnock

  Hi, I am trying to build a lambda expression, containing two assignments (as shown further down), that I can then pass to a Queryable.Select() method. I am trying to pass a string variable into a method and then use that variable to build up the lambda expression so that I can use it in a LINQ Select query. My reasoning behind it is that I have a SQL Server datasource with many column names, I am creating a charting application that will allow the user to select, say by typing in the column name, the actual column of data they want to view in the y-axis of my chart, with the x-axis always being the DateTime. Therefore, they can essentially choose what data they chart against the DateTime value (it’s a data warehouse type app). I have, for example, a class to store the retrieved data in, and hence use as the chart source of: public class AnalysisChartSource { public DateTime Invoicedate { get; set; } public Decimal yValue { get; set; } } I have (purely experimentaly) built an expression tree for the Where clause using the String value and that works fine: public void GetData(String yAxis) { using (DataClasses1DataContext db = new DataClasses1DataContext()) { var data = this.FunctionOne().AsQueryable<AnalysisChartSource>(); //just to get some temp data in.... ParameterExpression pe = Expression.Parameter(typeof(AnalysisChartSource), "p"); Expression left = Expression.MakeMemberAccess(pe, typeof(AnalysisChartSource).GetProperty(yAxis)); Expression right = Expression.Constant((Decimal)16); Expression e2 = Expression.LessThan(left, right); Expression expNew = Expression.New(typeof(AnalysisChartSource)); LambdaExpression le = Expression.Lambda(left, pe); MethodCallExpression whereCall = Expression.Call( typeof(Queryable), "Where", new Type[] { data.ElementType }, data.Expression, Expression.Lambda<Func<AnalysisChartSource, bool>>(e2, new ParameterExpression[] { pe })); } } However……I have tried a similar approach for the Select statement, but just can’t get it to work as I need the Select() to populate both X and Y values of the AnalysisChartSource class, like this: .Select(c => new AnalysisChartSource { Invoicedate = c.Invoicedate, yValue = c.yValue}).AsEnumerable(); How on earth can I build such an expression tree….or….possibly more to the point…..is there an easier way that I have missed entirely?

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• XmlReader throws on an RSS feed, when the RSS document includes an embedded <script> block.

  - by Cheeso

  The code: using (XmlReader xmlr = XmlReader.Create(new StringReader(allXml))) { var items = from item in SyndicationFeed.Load(xmlr).Items select item; } The exception: Exception: System.Xml.XmlException: Unexpected node type Element. ReadElementString method can only be called on elements with simple or empty content. Line 11, position 25. at System.Xml.XmlReader.ReadElementString() at System.ServiceModel.Syndication.Rss20FeedFormatter.ReadXml(XmlReader reader, SyndicationFeed result) at System.ServiceModel.Syndication.Rss20FeedFormatter.ReadFeed(XmlReader reader) at System.ServiceModel.Syndication.Rss20FeedFormatter.ReadFrom(XmlReader reader) at System.ServiceModel.Syndication.SyndicationFeed.Load[TSyndicationFeed](XmlReader reader) at System.ServiceModel.Syndication.SyndicationFeed.Load(XmlReader reader) at Ionic.ToolsAndTests.ReadRss.Run() in c:\dev\dotnet\ReadRss.cs:line 90 The XML content: <?xml version="1.0" encoding="utf-8"?> <?xml-stylesheet type="text/xsl" href="https://www.ibm.com/developerworks/mydeveloperworks/blogs/roller-ui/styles/rss.xsl" media="screen"?><rss version="2.0" xmlns:dc="http://purl.org/dc/elements/1.1/" xmlns:atom="http://www.w3.org/2005/Atom" > <channel> <title>Software architecture, software engineering, and Renaissance Jazz</title> <link>https://www.ibm.com/developerworks/mydeveloperworks/blogs/gradybooch</link> <atom:link rel="self" type="application/rss+xml" href="https://www.ibm.com/developerworks/mydeveloperworks/blogs/gradybooch/feed/entries/rss?lang=en" /> <description>Software architecture, software engineering, and Renaissance Jazz</description> <language>en-us</language> <copyright>Copyright <script type='text/javascript'> document.write(blogsDate.date.localize (1273534889181));</script></copyright> <lastBuildDate>Mon, 10 May 2010 19:41:29 -0400</lastBuildDate> As you can see, on line 11, at position 25, there's a script block inside the <copyright> element. Other people have reported similar errors with other XML documents. The way I worked around this was to do a StreamReader.ReadToEnd, then do Regex.Replace on the result of that to yank out the script block, before passing the modified string to XmlReader.Create(). Feels like a hack. Has anyone got a better approach? I don't like this because I have to read in a 125k string into memory. Is it valid rss to include "complex content" like that - a script block inside an element? Thanks.

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• How to best design a date/geographic proximity query on GAE?

  - by Dane

  Hi all, I'm building a directory for finding athletic tournaments on GAE with web2py and a Flex front end. The user selects a location, a radius, and a maximum date from a set of choices. I have a basic version of this query implemented, but it's inefficient and slow. One way I know I can improve it is by condensing the many individual queries I'm using to assemble the objects into bulk queries. I just learned that was possible. But I'm also thinking about a more extensive redesign that utilizes memcache. The main problem is that I can't query the datastore by location because GAE won't allow multiple numerical comparison statements (<,<=,=,) in one query. I'm already using one for date, and I'd need TWO to check both latitude and longitude, so it's a no go. Currently, my algorithm looks like this: 1.) Query by date and select 2.) Use destination function from geopy's distance module to find the max and min latitude and longitudes for supplied distance 3.) Loop through results and remove all with lat/lng outside max/min 4.) Loop through again and use distance function to check exact distance, because step 2 will include some areas outside the radius. Remove results outside supplied distance (is this 2/3/4 combination inefficent?) 5.) Assemble many-to-many lists and attach to objects (this is where I need to switch to bulk operations) 6.) Return to client Here's my plan for using memcache.. let me know if I'm way out in left field on this as I have no prior experience with memcache or server caching in general. -Keep a list in the cache filled with "geo objects" that represent all my data. These have five properties: latitude, longitude, event_id, event_type (in anticipation of expanding beyond tournaments), and start_date. This list will be sorted by date. -Also keep a dict of pointers in the cache which represent the start and end indices in the cache for all the date ranges my app uses (next week, 2 weeks, month, 3 months, 6 months, year, 2 years). -Have a scheduled task that updates the pointers daily at 12am. -Add new inserts to the cache as well as the datastore; update pointers. Using this design, the algorithm would now look like: 1.) Use pointers to slice off appropriate chunk of list based on supplied date. 2-4.) Same as above algorithm, except with geo objects 5.) Use bulk operation to select full tournaments using remaining geo objects' event_ids 6.) Assemble many-to-manys 7.) Return to client Thoughts on this approach? Many thanks for reading and any advice you can give. -Dane

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• Programmatically specifying Django model attributes

  - by mojbro

  Hi! I would like to add attributes to a Django models programmatically, at run time. For instance, lets say I have a Car model class and want to add one price attribute (database column) per currency, given a list of currencies. What is the best way to do this? I had an approach that I thought would work, but it didn't exactly. This is how I tried doing it, using the car example above: from django.db import models class Car(models.Model): name = models.CharField(max_length=50) currencies = ['EUR', 'USD'] for currency in currencies: Car.add_to_class('price_%s' % currency.lower(), models.IntegerField()) This does seem to work pretty well at first sight: $ ./manage.py syncdb Creating table shop_car $ ./manage.py dbshell shop=# \d shop_car Table "public.shop_car" Column | Type | Modifiers -----------+-----------------------+------------------------------------------------------- id | integer | not null default nextval('shop_car_id_seq'::regclass) name | character varying(50) | not null price_eur | integer | not null price_usd | integer | not null Indexes: "shop_car_pkey" PRIMARY KEY, btree (id) But when I try to create a new Car, it doesn't really work anymore: >>> from shop.models import Car >>> mycar = Car(name='VW Jetta', price_eur=100, price_usd=130) >>> mycar <Car: Car object> >>> mycar.save() Traceback (most recent call last): File "<console>", line 1, in <module> File "/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/site-packages/django/db/models/base.py", line 410, in save self.save_base(force_insert=force_insert, force_update=force_update) File "/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/site-packages/django/db/models/base.py", line 495, in save_base result = manager._insert(values, return_id=update_pk) File "/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/site-packages/django/db/models/manager.py", line 177, in _insert return insert_query(self.model, values, **kwargs) File "/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/site-packages/django/db/models/query.py", line 1087, in insert_query return query.execute_sql(return_id) File "/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/site-packages/django/db/models/sql/subqueries.py", line 320, in execute_sql cursor = super(InsertQuery, self).execute_sql(None) File "/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/site-packages/django/db/models/sql/query.py", line 2369, in execute_sql cursor.execute(sql, params) File "/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/site-packages/django/db/backends/util.py", line 19, in execute return self.cursor.execute(sql, params) ProgrammingError: column "price_eur" specified more than once LINE 1: ...NTO "shop_car" ("name", "price_eur", "price_usd", "price_eur... ^

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• Any one like me who still believes in AspNet Web forms? Or has evryone switched to MVC

  - by The_AlienCoder

  After years mastering Aspnet webforms I recently decided to try out ASpnet MVC. Naturally my first action was to google 'Aspnet webforms vs Aspnet MVC'. I hoped to get an honest comparison of the two development techniques and guidelines on when to use which one. ..But I was completely turned off by the MVC proponents. In almost every post on the net comparing the two 'platforms' the MVC camp is simply bashing webform developers like me. They go on and on about how wrong and stupid using webforms is. As if what we have been doing the past decade has been pointless - all those websites built(& still running), all those clever controls, the mighty gridview..ALL POINTLESS ! Karl Seguin especially with his stupid webforms rant really turned me off. If his intention was to convert people like me he did the oposite and made me defensive. If anything I am now convinced that the webforms approach is better. consider the following All the critical shortcomings of aspnet webforms have now been Addressed in visual studio 2010 with Aspnet 4.0.- Cleaner html, cleaner control IDs, friendly urls, leaner viewstate etc Why would any one want to implement the mighty gridview and other wonderful controls from scratch ? In MVC you have to do this yourself because ABSTRACTION IS PLAIN STUPID- Instead of writing loops why not just code using 1s and 0s then? A stateless web is a WEAKNESS so why would anyone want to get rid of viewstate? Everyone would like a better implementation but getting rid of it is a step backwards not forward. Unit testing is great but not a critical requirement for most web projects. I thought inline codes were dead with asp. But now they are back and fashionable - Thanks to MVC. I dont know about you people but codebehind was REVOLUTIONARY. Ive had the Ajax Update panel do so many wonderful things without writing a line of code so why demonise it? Ive succesfully implemented a chat client, IM client and Status bar using nothing but the update panel and script manager.Ofcourse you cant use it for everything but most of the time its appropriate. And finally the last word from JQUERY - 'Write less do more !' - That's what webforms is all about ! So Am I the only who still believes in webforms(and it getting better as Aspnet 4.0 has shown) or will it be dead and gone a few years from now like asp? I mean if inline coding is 'the future' why not just switch to PHP !

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• Visitor pattern and compiler code generation, how to get children attributes?

  - by LeleDumbo

  I'd like to modify my compiler's code generator to use visitor pattern since the current approach must use multiple conditional statement to check the real type of a child before generating the corresponding code. However, I have problems to get children attributes after they're visited. For instance, in binary expression I use this: LHSCode := GenerateExpressionCode(LHSNode); RHSCode := GenerateExpressionCode(RHSNode); CreateBinaryExpression(Self,LHS,RHS); In visitor pattern the visit method is usually void, so I can't get the expression code from LHS and RHS. Keeping shared global variables isn't an option since expression code generation is recursive thus could erase previous values kept in the variables. I'll just show the binary expression as this is the most complicated part (for now): function TLLVMCodeGenerator.GenerateExpressionCode( Expr: TASTExpression): TLLVMValue; var BinExpr: TASTBinaryExpression; UnExpr: TASTUnaryExpression; LHSCode, RHSCode, ExprCode: TLLVMValue; VarExpr: TASTVariableExpression; begin if Expr is TASTBinaryExpression then begin BinExpr := Expr as TASTBinaryExpression; LHSCode := GenerateExpressionCode(BinExpr.LHS); RHSCode := GenerateExpressionCode(BinExpr.RHS); case BinExpr.Op of '<': Result := FBuilder.CreateICmp(ccSLT, LHSCode, RHSCode); '<=': Result := FBuilder.CreateICmp(ccSLE, LHSCode, RHSCode); '>': Result := FBuilder.CreateICmp(ccSGT, LHSCode, RHSCode); '>=': Result := FBuilder.CreateICmp(ccSGE, LHSCode, RHSCode); '==': Result := FBuilder.CreateICmp(ccEQ, LHSCode, RHSCode); '<>': Result := FBuilder.CreateICmp(ccNE, LHSCode, RHSCode); '/\': Result := FBuilder.CreateAnd(LHSCode, RHSCode); '\/': Result := FBuilder.CreateOr(LHSCode, RHSCode); '+': Result := FBuilder.CreateAdd(LHSCode, RHSCode); '-': Result := FBuilder.CreateSub(LHSCode, RHSCode); '*': Result := FBuilder.CreateMul(LHSCode, RHSCode); '/': Result := FBuilder.CreateSDiv(LHSCode, RHSCode); end; end else if Expr is TASTPrimaryExpression then if Expr is TASTBooleanConstant then with Expr as TASTBooleanConstant do Result := FBuilder.CreateConstant(Ord(Value), ltI1) else if Expr is TASTIntegerConstant then with Expr as TASTIntegerConstant do Result := FBuilder.CreateConstant(Value, ltI32) else if Expr is TASTUnaryExpression then begin UnExpr := Expr as TASTUnaryExpression; ExprCode := GenerateExpressionCode(UnExpr.Expr); case UnExpr.Op of '~': Result := FBuilder.CreateXor( FBuilder.CreateConstant(1, ltI1), ExprCode); '-': Result := FBuilder.CreateSub( FBuilder.CreateConstant(0, ltI32), ExprCode); end; end else if Expr is TASTVariableExpression then begin VarExpr := Expr as TASTVariableExpression; with VarExpr.VarDecl do Result := FBuilder.CreateVar(Ident, BaseTypeLLVMTypeMap[BaseType]); end; end; Hope you understand it :)

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• Rails - embedded polymorphic comment list + add comment form - example?

  - by odigity

  Hey, all. Working on my first Rails app. I've searched all around - read a bunch of tutorials, articles, and forum posts, watched some screencasts, and I've found a few examples that come close to what I'm trying to do (notably http://railscasts.com/episodes/154-polymorphic-association and ep 196 about nested model forms), but not exactly. I have two models (Podcast and BlogPost) that need to be commentable, and I have a Comment model that is polymorphically related to both. The railscasts above had a very similar example (ep 154), but Ryan used a full set of nested routes, so there were specific templates for adding and editing comments. What I want to do is show the list of comments right on the Podcast or BlogPost page, along with an Add Comment form at the bottom. I don't need a separate add template/route, and I don't need the ability to edit, only delete. This is a pretty common design on the web, but I can't find a Rails example specifically about this pattern. Here's my current understanding: I need routes for the create and delete actions, of course, but there are no templates associated with those. I'm also guessing that the right approach is to create a partial that can be included at the bottom of both the Podcast and BlogPost show template. The logical name for the partial seems to me to be something like _comments.html.haml. I know it's a common convention to have the object passed to the partial be named after the template, but calling the object 'comments' seems to not match my use case, since what I really need to pass is the commentable object (Podcast or BlogPost). So, I guess I'd use the locals option for the render partial call? (:commentable = @podcast). Inside the partial, I could call commentable.comments to get the comments collection, render that with a second partial (this time with the conventional use case, calling the partial _comment.html.haml), then create a form that submits to... what? REST-wise, it should be a POST to the collection, which would be /podcast|blogpost/:id/comments, and I think the helper for that is podcast_comments_path(podcast) if it were a podcast - not sure what to do though, since I'm using polymorphic comments. That would trigger the Comment.create action, which would then need to redirect back to the podcast|blogpost path /podcast|blogpost/:id. It's all a bit overwhelming, which is why I was really hoping to find a screencast or example that specifically implements this design.

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• C# Design Questions

  - by guazz

  How to approach unit testing of private methods? I have a class that loads Employee data into a database. Here is a sample: public class EmployeeFacade { public Employees EmployeeRepository = new Employees(); public TaxDatas TaxRepository = new TaxDatas(); public Accounts AccountRepository = new Accounts(); //and so on for about 20 more repositories etc. public bool LoadAllEmployeeData(Employee employee) { if (employee == null) throw new Exception("..."); EmployeeRepository emps = new EmployeeRepository(); bool exists = emps.FetchExisting(emps.Id); if (!exists) { emps.AddNew(); } try { emps.Id = employee.Id; emps.Name = employee.EmployeeDetails.PersonalDetails.Active.Names.FirstName; emps.SomeOtherAttribute; } catch() {} try { emps.Save(); } catch(){} try { LoadorUpdateTaxData(employee.TaxData); } catch() {} try { LoadorUpdateAccountData(employee.AccountData); } catch() {} ... etc. for about 20 more other employee objects } private bool LoadorUpdateTaxData(employeeId, TaxData taxData) { if (taxData == null) throw new Exception("..."); ...same format as above but using AccountRepository } private bool LoadorUpdateAccountData(employee.TaxData) { ...same format as above but using TaxRepository } } I am writing an application to take serialised objects(e.g. Employee above) and load the data to the database. I have a few design question that I would like opinions on: A - I am calling this class "EmployeeFacade" because I am (attempting?) to use the facade pattern. Is it good practace to name the pattern on the class name? B - Is it good to call the concrete entities of my DAL layer classes "Repositories" e.g. "EmployeeRepository" ? C - Is using the repositories in this way sensible or should I create a method on the repository itself to take, say, the Employee and then load the data from there e.g. EmployeeRepository.LoadAllEmployeeData(Employee employee)? I am aim for cohesive class and but this will requrie the repository to have knowledge of the Employee object which may not be good? D - Is there any nice way around of not having to check if an object is null at the begining of each method? E - I have a EmployeeRepository, TaxRepository, AccountRepository declared as public for unit testing purpose. These are really private enities but I need to be able to substitute these with stubs so that the won't write to my database(I overload the save() method to do nothing). Is there anyway around this or do I have to expose them? F - How can I test the private methods - or is this done (something tells me it's not)? G- "emps.Name = employee.EmployeeDetails.PersonalDetails.Active.Names.FirstName;" this breaks the Law of Demeter but how do I adjust my objects to abide by the law?

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• How to make custom WCF error handler return JSON response with non-OK http code?

  - by John

  I'm implementing a RESTful web service using WCF and the WebHttpBinding. Currently I'm working on the error handling logic, implementing a custom error handler (IErrorHandler); the aim is to have it catch any uncaught exceptions thrown by operations and then return a JSON error object (including say an error code and error message - e.g. { "errorCode": 123, "errorMessage": "bla" }) back to the browser user along with an an HTTP code such as BadRequest, InteralServerError or whatever (anything other than 'OK' really). Here is the code I am using inside the ProvideFault method of my error handler: fault = Message.CreateMessage(version, "", errorObject, new DataContractJsonSerializer(typeof(ErrorMessage))); var wbf = new WebBodyFormatMessageProperty(WebContentFormat.Json); fault.Properties.Add(WebBodyFormatMessageProperty.Name, wbf); var rmp = new HttpResponseMessageProperty(); rmp.StatusCode = System.Net.HttpStatusCode.InternalServerError; rmp.Headers.Add(HttpRequestHeader.ContentType, "application/json"); fault.Properties.Add(HttpResponseMessageProperty.Name, rmp); -- This returns with Content-Type: application/json, however the status code is 'OK' instead of 'InternalServerError'. fault = Message.CreateMessage(version, "", errorObject, new DataContractJsonSerializer(typeof(ErrorMessage))); var wbf = new WebBodyFormatMessageProperty(WebContentFormat.Json); fault.Properties.Add(WebBodyFormatMessageProperty.Name, wbf); var rmp = new HttpResponseMessageProperty(); rmp.StatusCode = System.Net.HttpStatusCode.InternalServerError; //rmp.Headers.Add(HttpRequestHeader.ContentType, "application/json"); fault.Properties.Add(HttpResponseMessageProperty.Name, rmp); -- This returns with the correct status code, however the content-type is now XML. fault = Message.CreateMessage(version, "", errorObject, new DataContractJsonSerializer(typeof(ErrorMessage))); var wbf = new WebBodyFormatMessageProperty(WebContentFormat.Json); fault.Properties.Add(WebBodyFormatMessageProperty.Name, wbf); var response = WebOperationContext.Current.OutgoingResponse; response.ContentType = "application/json"; response.StatusCode = HttpStatusCode.InternalServerError; -- This returns with the correct status code and the correct content-type! The problem is that the http body now has the text 'Failed to load source for: http://localhost:7000/bla..' instead of the actual JSON data.. Any ideas? I'm considering using the last approach and just sticking the JSON in the HTTP StatusMessage header field instead of in the body, but this doesn't seem quite as nice?

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• How to load entities into private collections using the entity framework

  - by Anton P

  I have a POCO domain model which is wired up to the entity framework using the new ObjectContext class. public class Product { private ICollection<Photo> _photos; public Product() { _photos = new Collection<Photo>(); } public int Id { get; set; } public string Name { get; set; } public virtual IEnumerable<Photo> Photos { get { return _photos; } } public void AddPhoto(Photo photo) { //Some biz logic //... _photos.Add(photo); } } In the above example i have set the Photos collection type to IEnumerable as this will make it read only. The only way to add/remove photos is through the public methods. The problem with this is that the Entity Framework cannot load the Photo entities into the IEnumerable collection as it's not of type ICollection. By changing the type to ICollection will allow callers to call the Add mentod on the collection itself which is not good. What are my options? Edit: I could refactor the code so it does not expose a public property for Photos: public class Product { public Product() { Photos = new Collection<Photo>(); } public int Id { get; set; } public string Name { get; set; } private Collection<Photo> Photos {get; set; } public IEnumerable<Photo> GetPhotos() { return Photos; } public void AddPhoto(Photo photo) { //Some biz logic //... Photos.Add(photo); } } And use the GetPhotos() to return the collection. The other problem with the approach is that I will loose the change tracking abilities as I cannot mark the collection as Virtual - It is not possible to mark a property as private virtual. In NHibernate I believe it's possible to map the proxy class to the private collection via configuration. I hope that this will become a feature of EF4. Currently i don't like the inability to have any control over the collection!

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• Strategy pattern and "action" classes explosion

  - by devoured elysium

  Is it bad policy to have lots of "work" classes(such as Strategy classes), that only do one thing? Let's assume I want to make a Monster class. Instead of just defining everything I want about the monster in one class, I will try to identify what are its main features, so I can define them in interfaces. That will allow to: Seal the class if I want. Later, other users can just create a new class and still have polymorphism by means of the interfaces I've defined. I don't have to worry how people (or myself) might want to change/add features to the base class in the future. All classes inherit from Object and they implement inheritance through interfaces, not from mother classes. Reuse the strategies I'm using with this monster for other members of my game world. Con: This model is rigid. Sometimes we would like to define something that is not easily achieved by just trying to put together this "building blocks". public class AlienMonster : IWalk, IRun, ISwim, IGrowl { IWalkStrategy _walkStrategy; IRunStrategy _runStrategy; ISwimStrategy _swimStrategy; IGrowlStrategy _growlStrategy; public Monster() { _walkStrategy = new FourFootWalkStrategy(); ...etc } public void Walk() { _walkStrategy.Walk(); } ...etc } My idea would be next to make a series of different Strategies that could be used by different monsters. On the other side, some of them could also be used for totally different purposes (i.e., I could have a tank that also "swims"). The only problem I see with this approach is that it could lead to a explosion of pure "method" classes, i.e., Strategy classes that have as only purpose make this or that other action. In the other hand, this kind of "modularity" would allow for high reuse of stratagies, sometimes even in totally different contexts. What is your opinion on this matter? Is this a valid reasoning? Is this over-engineering? Also, assuming we'd make the proper adjustments to the example I gave above, would it be better to define IWalk as: interface IWalk { void Walk(); } or interface IWalk { IWalkStrategy WalkStrategy { get; set; } //or something that ressembles this } being that doing this I wouldn't need to define the methods on Monster itself, I'd just have public getters for IWalkStrategy (this seems to go against the idea that you should encapsulate everything as much as you can!) Why? Thanks

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