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  • Atomic operations on several transactionless external systems

    - by simendsjo
    Say you have an application connecting 3 different external systems. You need to update something in all 3. In case of a failure, you need to roll back the operations. This is not a hard thing to implement, but say operation 3 fails, and when rolling back, the rollback for operation 1 fails! Now the first external system is in an invalid state... I'm thinking a possible solution is to shut down the application and forcing a manual fix of the external system, but then again... It might already have used this information (and perhaps that's why it failed), or we might not have sufficient access. Or it might not even be a good way to rollback the action! Are there some good ways of handling such cases? EDIT: Some application details.. It's a multi user web application. Most of the work is done with scheduled jobs (through Quartz.Net), so most operations is run in it's own thread. Some user actions should trigger jobs that update several systems though. The external systems are somewhat unstable. I Was thinking of changing the application to use the Command and Unit Of Work pattern

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  • Does it ever make sense to make a fundamental (non-pointer) parameter const?

    - by Scott Smith
    I recently had an exchange with another C++ developer about the following use of const: void Foo(const int bar); He felt that using const in this way was good practice. I argued that it does nothing for the caller of the function (since a copy of the argument was going to be passed, there is no additional guarantee of safety with regard to overwrite). In addition, doing this prevents the implementer of Foo from modifying their private copy of the argument. So, it both mandates and advertises an implementation detail. Not the end of the world, but certainly not something to be recommended as good practice. I'm curious as to what others think on this issue. Edit: OK, I didn't realize that const-ness of the arguments didn't factor into the signature of the function. So, it is possible to mark the arguments as const in the implementation (.cpp), and not in the header (.h) - and the compiler is fine with that. That being the case, I guess the policy should be the same for making local variables const. One could make the argument that having different looking signatures in the header and source file would confuse others (as it would have confused me). While I try to follow the Principle of Least Astonishment with whatever I write, I guess it's reasonable to expect developers to recognize this as legal and useful.

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  • Convincing why testing is good

    - by FireAphis
    Hello, In my team of real-time-embedded C/C++ developers, most people don't have any culture of testing their code beyond the casual manual sanity checks. I personally strongly believe in advantages of autonomous automatic tests, but when I try to convince I get some reappearing arguments like: We will spend more time on writing the tests than writing the code. It takes a lot of effort to maintain the tests. Our code is spaghetti; no way we can unit-test it. Our requirement are not sealed – we’ll have to rewrite all the tests every time the requirements are changed. Now, I'd gladly hear any convincing tips and advises, but what I am really looking for are references to researches, articles, books or serious surveys that show (preferably in numbers) how testing is worth the effort. Something like "We in IBM/Microsoft/Google, surveying 3475 active projects, found out that putting 50% more development time into testing decreased by 75% the time spent on fixing bugs" or "after half a year, the time needed to write code with test was only marginally longer than what used to take without tests". Any ideas? P.S.: I'm adding C++ tag too in case someone has a specific experience with convincing this, usually elitist, type of developers :-)

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  • Questions regarding detouring by modifying the virtual table

    - by Elliott Darfink
    I've been practicing detours using the same approach as Microsoft Detours (replace the first five bytes with a jmp and an address). More recently I've been reading about detouring by modifying the virtual table. I would appreciate if someone could shed some light on the subject by mentioning a few pros and cons with this method compared to the one previously mentioned! I'd also like to ask about patched vtables and objects on the stack. Consider the following situation: // Class definition struct Foo { virtual void Call(void) { std::cout << "FooCall\n"; } }; // If it's GCC, 'this' is passed as the first parameter void MyCall(Foo * object) { std::cout << "MyCall\n"; } // In some function Foo * foo = new Foo; // Allocated on the heap Foo foo2; // Created on the stack // Arguments: void ** vtable, uint offset, void * replacement PatchVTable(*reinterpret_cast<void***>(foo), 0, MyCall); // Call the methods foo->Call(); // Outputs: 'MyCall' foo2.Call(); // Outputs: 'FooCall' In this case foo->Call() would end up calling MyCall(Foo * object) whilst foo2.Call() call the original function (i.e Foo::Call(void) method). This is because the compiler will try to decide any virtual calls during compile time if possible (correct me if I'm wrong). Does that mean it does not matter if you patch the virtual table or not, as long as you use objects on the stack (not heap allocated)?

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  • Does "delegate" mean a type or an object?

    - by Michal Czardybon
    Reading from MSDN: "A delegate is a type that references a method. Once a delegate is assigned a method, it behaves exactly like that method." Does then "delegate" mean a type or an object?! ...It cannot be both. It seems to me that the single word is used in two different meanings: a type containing a reference to a method of some specified signature, an object of that type, which can be actually called like a method. I would prefer a more precise vocabulary and use "delegate type" for the first case. I have been recently reading a lot about events and delegates and that ambiguity was making me confused many times. Some other uses of "delegate" word in MSDN in the first meaning: "Custom event delegates are needed only when an event generates event data" "A delegate declaration defines a class that is derived from the class System.Delegate" Some other uses of "delegate" word in MSDN in the second meaning: "specify a delegate that will be called upon the occurrence of some event" "Delegates are objects that refer to methods. They are sometimes described as type-safe function pointers" What do you think? Why did people from Microsoft introduced this ambiguity? Am I the only person to have conceptual problems with different notions being referenced with the same word.

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  • Behavior difference between UIView.subviews and [NSView subviews]

    - by zpasternack
    I have a piece of code in an iPhone app, which removes all subviews from a UIView subclass. It looks like this: NSArray* subViews = self.subviews; for( UIView *aView in subViews ) { [aView removeFromSuperview]; } This works fine. In fact, I never really gave it much thought until I tried nearly the same thing in a Mac OS X app (from an NSView subclass): NSArray* subViews = [self subviews]; for( NSView *aView in subViews ) { [aView removeFromSuperview]; } That totally doesn’t work. Specifically, at runtime, I get this: *** Collection <NSCFArray: 0x1005208a0> was mutated while being enumerated. I ended up doing it like so: NSArray* subViews = [[self subviews] copy]; for( NSView *aView in subViews ) { [aView removeFromSuperview]; } [subViews release]; That's fine. What’s bugging me, though, is why does it work on the iPhone? subviews is a copy property: @property(nonatomic,readonly,copy) NSArray *subviews; My first thought was, maybe @synthesize’d getters return a copy when the copy attribute is specified. The doc is clear on the semantics of copy for setters, but doesn’t appear to say either way for getters (or at least, it’s not apparent to me). And actually, doing a few tests of my own, this clearly does not seem to be the case. Which is good, I think returning a copy would be problematic, for a few reasons. So the question is: how does the above code work on the iPhone? NSView is clearly returning a pointer to the actual array of subviews, and perhaps UIView isn’t. Perhaps it’s simply an implementation detail of UIView, and I shouldn’t get worked up about it. Can anyone offer any insight?

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  • How to capture strings using * or ? with groups in python regular expressions

    - by user1334085
    When the regular expression has a capturing group followed by "*" or "?", there is no value captured. Instead if you use "+" for the same string, you can see the capture. I need to be able to capture the same value using "?" >>> str1='This string has 29 characters' >>> re.search(r'(\d+)*', str1).group(0) '' >>> re.search(r'(\d+)*', str1).group(1) >>> >>> re.search(r'(\d+)+', str1).group(0) '29' >>> re.search(r'(\d+)+', str1).group(1) '29' More specific question is added below for clarity: I have str1 and str2 below, and I want to use just one regexp which will match both. In case of str1, I also want to be able to capture the number of QSFP ports >>> str1='''4 48 48-port and 6 QSFP 10GigE Linecard 7548S-LC''' >>> str2='''4 48 48-port 10GigE Linecard 7548S-LC''' >>> When I do not use a metacharacter, the capture works: >>> re.search(r'^4\s+48\s+.*(?:(\d+)\s+QSFP).*-LC', str1, re.I|re.M).group(1) '6' >>> It works even when I use the "+" to indicate one occurrence: >>> re.search(r'^4\s+48\s+.*(?:(\d+)\s+QSFP)+.*-LC', str1, re.I|re.M).group(1) '6' >>> But when I use "?" to match for 0 or 1 occurrence, the capture fails even for str1: >>> re.search(r'^4\s+48\s+.*(?:(\d+)\s+QSFP)?.*-LC', str1, re.I|re.M).group(1) >>>

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  • How can I get an NPC to move randomly in XNA?

    - by Fishwaffles
    I basically want a character to walk in one direction for a while, stop, then go in another random direction. Right now my sprites look but don't move, randomly very quickly in all directions then wait and have another seizure. I will post the code I have so far in case that is useful. class NPC: Mover { int movementTimer = 0; public override Vector2 direction { get { Random rand = new Random(); int randDirection = rand.Next(8); Vector2 inputDirection = Vector2.Zero; if (movementTimer >= 50) { if (randDirection == 4) { inputDirection.X -= 1; movingLeft = true; } else movingLeft = false; if (randDirection == 1) { inputDirection.X += 1; movingRight = true; } else movingRight = false; if (randDirection == 2) { inputDirection.Y -= 1; movingUp = true; } else movingUp = false; if (randDirection == 3) { inputDirection.Y += 25; movingDown = true; } else movingDown = false; if (movementTimer >= 100) { movementTimer = 0; } } return inputDirection * speed; } } public NPC(Texture2D textureImage, Vector2 position, Point frameSize, int collisionOffset, Point currentFrame, Point sheetSize, Vector2 speed) : base(textureImage, position, frameSize, collisionOffset, currentFrame, sheetSize, speed) { } public NPC(Texture2D textureImage, Vector2 position, Point frameSize, int collisionOffset, Point currentFrame, Point sheetSize, Vector2 speed, int millisecondsPerframe) : base(textureImage, position, frameSize, collisionOffset, currentFrame, sheetSize, speed, millisecondsPerframe) { } public override void Update(GameTime gameTime, Rectangle clientBounds) { movementTimer++; position += direction; if (position.X < 0) position.X = 0; if (position.Y < 0) position.Y = 0; if (position.X > clientBounds.Width - frameSize.X) position.X = clientBounds.Width - frameSize.X; if (position.Y > clientBounds.Height - frameSize.Y) position.Y = clientBounds.Height - frameSize.Y; base.Update(gameTime, clientBounds); } }

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  • The use of getters and setters for different programming languages [closed]

    - by leonhart88
    So I know there are a lot of questions on getters and setters in general, but I couldn't find something exactly like my question. I was wondering if people change the use of get/set depending on different languages. I started learning with C++ and was taught to use getters and setters. This is what I understand: In C++ (and Java?), a variable can either be public or private, but we cannot have a mix. For example, I can't have a read-only variable that can still be changed inside the class. It's either all public (can read and change it), or all private (can't read and can only change inside the class). Because of this (and possibly other reasons), we use getters and setters. In MATLAB, I can control the "setaccess" and "getaccess" properties of variables, so that I can make things read-only (can directly access the property, but can't overwrite it). In this case, I don't feel like I need a getter because I can just do class.property. Also, in Python it is considered "Pythonic" to not use getters/setters and to only put things into properties if needed. I don't really understand why its OK to have all public variables in Python, because that's opposite of what I learned when I started with C++. I'm just curious what other people's thoughts are on this. Would you use getters and setters for all languages? Would you only use it for C++/Java and do direct access in MATLAB and Python (which is what I am currently doing)? Is the second option considered bad? For my purposes, I am only referring to simple getters and setters (just return/set the value and do not do anything else). Thanks!

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  • Large ListView containing images in Android

    - by Marco W.
    For various Android applications, I need large ListViews, i.e. such views with 100-300 entries. All entries must be loaded in bulk when the application is started, as some sorting and processing is necessary and the application cannot know which items to display first, otherwise. So far, I've been loading the images for all items in bulk as well, which are then saved in an ArrayList<CustomType> together with the rest of the data for each entry. But of course, this is not a good practice, as you're very likely to have an OutOfMemoryException then: The references to all images in the ArrayList prevent the garbage collector from working. So the best solution is, obviously, to load only the text data in bulk whereas the images are then loaded as needed, right? The Google Play application does this, for example: You can see that images are loaded as you scroll to them, i.e. they are probably loaded in the adapter's getView() method. But with Google Play, this is a different problem, anyway, as the images must be loaded from the Internet, which is not the case for me. My problem is not that loading the images takes too long, but storing them requires too much memory. So what should I do with the images? Load in getView(), when they are really needed? Would make scrolling sluggish. So calling an AsyncTask then? Or just a normal Thread? Parametrize it? I could save the images that are already loaded into a HashMap<String,Bitmap>, so that they don't need to be loaded again in getView(). But if this is done, you have the memory problem again: The HashMap stores references to all images, so in the end, you could have the OutOfMemoryException again. I know that there are already lots of questions here that discuss "Lazy loading" of images. But they mainly cover the problem of slow loading, not too much memory consumption.

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  • PHP - Find a string in file then show it's line number

    - by xZero
    I have an application which needs to open the file, then find string in it, and print a line number where is string found. For example, file example.txt contains few hashes: APLF2J51 1a79a4d60de6718e8e5b326e338ae533 EEQJE2YX 66b375b08fc869632935c9e6a9c7f8da O87IGF8R c458fb5edb84c54f4dc42804622aa0c5 APLF2J51 B7TSW1ZE 1e9eea56686511e9052e6578b56ae018 EEQJE2YX affb23b07576b88d1e9fea50719fb3b7 So, I want to PHP search for "1e9eea56686511e9052e6578b56ae018" and print out its line number, in this case 4. Please note that there are will not be multiple hashes in file. I found a few codes over Internet, but none seem to work. I tried this one: <?PHP $string = "1e9eea56686511e9052e6578b56ae018"; $data = file_get_contents("example.txt"); $data = explode("\n", $data); for ($line = 0; $line < count($data); $line++) { if (strpos($data[$line], $string) >= 0) { die("String $string found at line number: $line"); } } ?> It just says that string is found at line 0.... Which is not correct.... Final application is much more complex than that... After it founds line number, it should replace string which something else, and save changes to file, then goes further processing.... Thanks in advance :)

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  • Dealing with Expression Blend's lack of support for C++/CLI projects

    - by Brian Ensink
    I have a WPF C# project that references a C++/CLI mixed mode project. I'm having trouble using the WPF project in Expression Blend 3. I'm new to Blend so perhaps this is obvious, but it won't display the xaml designer properly until it builds the project. In my case it complains that my custom commands are not "recognized or accessible" and the solution is to build the project in Blend. But I can't build the project because it references a C++/CLI mixed mode project which Blend won't load. The WPF project is pure C# it just happens to reference a C++/CLI mixed mode project but I'm not asking Blend to do anything with the mixed-mode assembly. How can I work around this problem? Edit: I was able to get it to build by removing the reference to the C++/CLI mixed mode project and replacing it with a reference to the actual assembly. However this is not ideal because in my past experience Visual Studio will not always be able to resolve the reference when switching between release and debug configurations.

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  • What's the most efficient way to load data from a file to a collection on-demand?

    - by Dan
    I'm working on a java project that will allows users to parse multiple files with potentially thousands of lines. The information parsed will be stored in different objects, which then will be added to a collection. Since the GUI won't require to load ALL these objects at once and keep them in memory, I'm looking for an efficient way to load/unload data from files, so that data is only loaded into the collection when a user requests it. I'm just evaluation options right now. I've also thought of the case where, after loading a subset of the data into the collection, and presenting it on the GUI, the best way to reload the previously observed data. Re-run the parser/Populate collection/Populate GUI? or probably find a way to keep the collection into memory, or serialize/deserialize the collection itself? I know that loading/unloading subsets of data can get tricky if some sort of data filtering is performed. Let's say that I filter on ID, so my new subset will contain data from two previous analyzed subsets. This would be no problem is I keep a master copy of the whole data in memory. I've read that google-collections are good and efficient when handling big amounts of data, and offer methods that simplify lots of things so this might offer an alternative to allow me to keep the collection in memory. This is just general talking. The question on what collection to use is a separate and complex thing. Do you know what's the general recommendation on this type of task? I'd like to hear what you've done with similar scenarios. I can provide more specifics if needed.

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  • Codeigniter/mySQL question. Checking if several inserts are possible before actual insertion.

    - by Ethan
    Hey SO, So I'm trying to perform a couple inserts at once that are kind of co-dependent on each other. Let's say I'm doing a dog rating website. Anyone can add a dog to my database, but in doing so they also need to add a preliminary rating of the dog. Other people can then rate the dog afterwards. The dogs to ratings is a many to one relationship: a dog has many ratings. This means for my preliminary add, since I have the person both rate and add the dog, I need to take the rating, and set a foreign key to the dog's primary key. As far as I know, this means I have to actually add the dog, then check what that new addition's primary key is, and then put that in my rating before insertion. Now suppose something were to go wrong with the rating's insert, be it a string that's too long, or something that I've overlooked somehow. If the rating's failed, the dog has already been inserted, but the rating has not. In this case, I'd like the dog to not have been added in the first place. Does this mean I have to write code that says "if the rating fails, do a remove for the dog," or is there a way to predict what the key will be for the dog should everything go as planned. Is there a way to say "hold that spot," and then if everything works, add it? Any help would be greatly appreciated. Thanks!!

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  • GUID or int entity key with SQL Compact/EF4?

    - by David Veeneman
    This is a follow-up to an earlier question I posted on EF4 entity keys with SQL Compact. SQL Compact doesn't allow server-generated identity keys, so I am left with creating my own keys as objects are added to the ObjectContext. My first choice would be an integer key, and the previous answer linked to a blog post that shows an extension method that uses the Max operator with a selector expression to find the next available key: public static TResult NextId<TSource, TResult>(this ObjectSet<TSource> table, Expression<Func<TSource, TResult>> selector) where TSource : class { TResult lastId = table.Any() ? table.Max(selector) : default(TResult); if (lastId is int) { lastId = (TResult)(object)(((int)(object)lastId) + 1); } return lastId; } Here's my take on the extension method: It will work fine if the ObjectContext that I am working with has an unfiltered entity set. In that case, the ObjectContext will contain all rows from the data table, and I will get an accurate result. But if the entity set is the result of a query filter, the method will return the last entity key in the filtered entity set, which will not necessarily be the last key in the data table. So I think the extension method won't really work. At this point, the obvious solution seems to be to simply use a GUID as the entity key. That way, I only need to call Guid.NewGuid() method to set the ID property before I add a new entity to my ObjectContext. Here is my question: Is there a simple way of getting the last primary key in the data store from EF4 (without having to create a second ObjectContext for that purpose)? Any other reason not to take the easy way out and simply use a GUID? Thanks for your help.

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  • How to write a JOIN statement to combine data from disparate tables

    - by Amarundo
    I have the following 2 procedures that I use as my source for a report. As of now, I'm presenting 2 different tables in my SQL Server Reporting Services 2008 R2 report, because it doesn't let me put them together as they belong to 2 different data sets. I want to present them in a single table, but I have not been successful trying to use JOIN here. How do I do that? NOTE: cName in IAgentQueueStats corresponds to UserId in AgentActivityLog. /*** Aggregate values for Call Center Agents for calls, talk and hold time ***/ /*** The detail/row values is per 30-minute interval ***/ ALTER PROCEDURE [dbo].[sp_IAgentQueueStats_OnlyCalls_Grouped] @p_StartDate datetime, @p_EndDate datetime, @p_Agents varchar(8000) AS SELECT [cName] ,sum([nAnswered]) SumNAnswered ,sum([nAnsweredAcd]) SumNAnsweredAcd ,sum([tTalkAcd]) SumTTalkAcd ,sum([nHoldAcd]) SumNHoldAcd ,sum([tHoldAcd]) SumTHoldAcd ,sum([tAcw]) SumTAcw FROM [I3_IC].[dbo].[IAgentQueueStats] WHERE dIntervalStart between @p_StartDate and DATEADD(s, 86400-1, @p_EndDate) AND CHARINDEX ( cName ,@p_Agents)> 0 AND cReportGroup <> '*' AND cHKey3 = '*' and cHKey4 ='*' AND nEnteredAcd > 0 AND cReportGroup <> 'CCFax Email' GROUP BY cName And here is the second one: /*** Aggregate values for Call Center Agents for status/activity time ***/ /*** The detail/row values is per start-time/end-time ***/ ALTER PROCEDURE [dbo].[sp_AgentActivity_Grouped] @p_StartDate datetime, @p_EndDate datetime, @p_Agents varchar(8000) AS SELECT [UserId],[StatusCategory],SUM([StateDuration]) [StatusDuration] FROM ( SELECT [UserId] ,[StatusGroup] ,[StatusKey] , CASE [StatusKey] WHEN 'Available' THEN 'Productive' WHEN 'Follow Up' THEN 'Productive' WHEN 'Campaign Call' THEN 'Productive' WHEN 'Awaiting Callback' THEN 'Productive' WHEN 'In a Meeting' THEN 'Not Your Fault' WHEN 'Project Work' THEN 'Not Your Fault' WHEN 'At a Training Session'THEN 'Not Your Fault' WHEN 'System Issues' THEN 'Not Your Fault' WHEN 'Test' THEN 'Not Your Fault' WHEN 'At Lunch' THEN 'Non Productive' WHEN 'Available, Forward' THEN 'Non Productive' WHEN 'Available, Follow-Me' THEN 'Non Productive' WHEN 'At Play' THEN 'Non Productive' WHEN 'AcdAgentNotAnswering' THEN 'Non Productive' WHEN 'Do Not Disturb' THEN 'Non Productive' WHEN 'Available, No ACD' THEN 'Non Productive' WHEN 'Away from desk' THEN 'Non Productive' ELSE [StatusKey] END StatusCategory ,stateduration FROM [I3_IC].[dbo].[AgentActivityLog] WHERE [StatusDateTime] between @p_StartDate and DATEADD(s, 86400-1, @p_EndDate) AND CHARINDEX ( [UserId] ,@p_Agents)> 0 AND [StatusKey] not in ('Gone Home','Out of the Office','On Vacation','Out of Town') ) a GROUP BY [UserId],[StatusCategory] ORDER BY [UserId], [StatusCategory] desc BTW, if I take some time to comment/reply on your posts, it's not lack of interest, but of understanding...

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  • Multiple exports with MEF does some really heinous stuff -- why, and why is it allowed?

    - by Dave
    I have an interesting situation where I need to do something like this: [Export[typeof(ICandy1)] [Export[typeof(ICandy2)] public class Candy : ICandy2 { ... } where public interface ICandy1 { ... } public interface ICandy2 : ICandy1 { ... } I couldn't find any posts anywhere regarding using multiple [Export] attributes, so I figured, what the hell, might as well try it. At first glance, it actually seemed to work. I have a couple of methods that call into both interfaces of a Candy instance, and it was fine. However, as I started to test the app, I saw that the behavior wasn't right, and when looking at the Output window, I saw that I was getting tons of COMExceptions. I couldn't track down where they were all coming from, but they always occurred when a worker thread was sleeping. I figured that it had to be from the main thread, then, but didn't know how to debug this at all. Nothing should have been going on in the GUI, and I disabled my DispatchTimers just in case -- same thing. Even more strange than the COMExceptions was the really, really erratic behavior when stepping through code. About 30% of the time, when I single stepped, it would pop out of the method, or it would single step over two lines of code! Totally weird stuff that I am not used to seeing. The only thing that changed between working and non-working code was the introduction of MEF through my plugin loading code. So as a test, I changed my plugin assembly to only export one interface, and I hardcoded everything in the app that relied on the other (now not-implemented) interface. And now the COMExceptions are gone, and the weird debugging behavior is gone. Is this something people here have seen before? If MEF is not expected to allow a class to Export multiple interfaces, then shouldn't a CompositionException get raised when composing the parts? Can anyone explain why MEF would cause these weird problems???

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  • Is it possible to install into Program Files with limited privileges?

    - by Marek
    I have an application that will be deployed as MSI package (authored in WiX). I am deciding whether to specify elevated or limited privileges as required for the installer. The application does not include anything requiring elevated privileges besides the default install location, which is under Program Files. Now the problem: If I specify elevated privileges, then the user is prompted by UAC for administrator password during the installation. This is not required and prevents non-admin users from installing. If I specify limited privileges, then the user is presented with a dialog to select install location with Program Files being default. In case they do not change the install location (95 % of end users probably won't), then the installer will fail with a message that they should contact the Administrator or run the application as administrator. If they launch the installer as Administrator then they can install into Program Files without problem - but most of the users won't probably know how to launch an installer as administrator. I can potentially set the default install location to e.g. C:\Company name\Program\, but this seems nonstandard to me and majority of users will not probably like this (they are probably used to installing into Program Files). How do you solve this problem with installing applications under limited user accounts?

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  • Is there really such a thing as "being good at math"?

    - by thezhaba
    Aside from gifted individuals able to perform complex calculations in their head, I'm wondering if proficiency in mathematics, namely calculus and algebra, has really got to do with one's natural inclination towards sciences, if you can put it that way. A number of students in my calculus course pick up material in seemingly no time whereas I, personally, have to spend time thinking about and understanding most concepts. Even then, if a question that requires a bit more 'imagination' comes up I don't always recognize the concepts behind it, as is the case with calculus proofs, for instance. Nevertheless, I refuse to believe that I'm simply not made for it. I do very well in programming and software engineering courses where a lot of students struggle. At first I could not grasp what they found to be so difficult, but eventually I realized that having previous programming experience is a great asset -- once I've seen and made practical use of the programming concepts learning about them in depth in an academic setting became much easier as I have then already seen their use "in the wild". I suppose I'm hoping that something similar happens with mathematics -- perhaps once the practical idea behind a concept (which authors of textbooks sure do a great job of concealing..) is evident, understanding the seemingly dry and symbolic ideas and proofs would be more obvious? I'm really not sure. All I'm sure of is I'd like to get better at calculus, but I don't yet understand why some of us pick it up easily while others have to spend considerable amounts of time on it and still not have complete understanding if an unusual problem is given.

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  • How to detect .NET WPF memory leak or GC long run?

    - by Néstor Sánchez A.
    I have the next very strange situation and problem: .NET 4.0 application for diagram editing (WPF). Runs ok in my PC: 8GM RAM, 3.0GHz, i7 quad-core. While creating objects (mostly diagram nodes and connectors, plus all the undo/redo information) the TaskManager show, as expected, some memory usage "jumps" (up and down). These mem-usage "jumps" also remains executing AFTER user interaction ended. Maybe this is the GC cleaning/regorganizing memory? To see what is going on, I've used the Ants mem profiler, but somewhat it prevents those "jumps" to happen after user interaction. PROBLEM: It Freezes/Hangs after seconds or minutes of usage in some slow/weak laptos/netbooks of my beta testers (under 2GHz of speed and under 2GB of RAM). I was thinking of a memory leak, but... EDIT: Also, there is the case that the memory usage grows and grows until collapse (only in slow machines). In a Windows XP Mode machine (VM in Win 7) with only 512MB of RAM Assigned it works fine without mem-usage "jumps" after user interaction (no GC cleaning?!). So, I really have a big trouble because I cannot reproduce the error, only see these strange behaviour (mem jumps), and the tool supposed to show me what is happening is hiding the problem (like the "observer's paradox"). Any ideas on what's happening and how to solve it?

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  • Stopping work from one thread using another thread

    - by 113483626144458436514
    Not sure if my title is worded well, but whatever :) I have two threads: the main thread with the work that needs to be done, and a worker thread that contains a form with a progress bar and a cancel button. In normal code, it would be the other way around, but I can't do that in this case. When the user clicks the cancel button, a prompt is displayed asking if he wants to really cancel the work. The problem is that work continues on the main thread. I can get the main thread to stop work and such, but I would like for it to stop doing work when he clicks "Yes" on the prompt. Example: // Main thread work starts here t1 = new Thread(new ThreadStart(progressForm_Start)); t1.Start(); // Working for (i = 0; i <= 10000; i++) { semaphore.WaitOne(); if (pBar.Running) bgworker_ProgressChanged(i); semaphore.Release(); if (pBar.IsCancelled) break; } t1.Abort(); // Main thread work ends here // Start progress bar form in another thread void progressForm_Start() { pBar.Status("Starting"); pBar.ShowDialog(); } I could theoretically include a prompt in the cancelWatch() function, but then I would have to do that everywhere I'm implementing this class.

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  • How to design authentication in a thick client, to be fail safe?

    - by Jay
    Here's a use case: I have a desktop application (built using Eclipse RCP) which on start, pops open a dialog box with 'UserName' and 'Password' fields in it. Once the end user, inputs his UserName and Password, a server is contacted (a spring remote-servlet, with the client side being a spring httpclient: similar to the approaches here.), and authentication is performed on the server side. A few questions related to the above mentioned scenario: If said this authentication service were to go down, what would be the best way to handle further proceedings? Authentication is something that I cannot do away with. Would running the desktop client in a "limited" mode be a good idea? For instance, important features/menus/views will be disabled, rest of the application will be accessible? Should I have a back up authentication service running on a different machine, working as a backup? What are the general best-practices in this scenario? I remember reading about google gears and how it would let you edit and do stuff offline - should something like this be designed? Please let me know your design/architectural comments/suggestions. Appreciate your help.

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  • How do I stop a page from unloading (navigating away) in JS?

    - by Natalie Downe
    Does anyone know how to stop a page from reloading or navigating away? jQuery(function($) { /* global on unload notification */ warning = true; if(warning) { $(window).bind("unload", function() { if (confirm("Do you want to leave this page") == true) { //they pressed OK alert('ok'); } else { // they pressed Cancel alert('cancel'); return false; } }); } }); I am working on an e-commerce site at the moment, the page that displays your future orders has the ability to alter the quantities of items ordered using +/- buttons. Changing the quantities this way this doesn't actually change the order itself, they have to press confirm and therefore committing a positive action to change the order. However if they have changed the quantities and navigate away from the page I would like to warn them they are doing so in case this is an accident, as the changed quantities will be lost if they navigate away or refresh the page. In the code above I am using a global variable which will be false by default (its only true for testing), when a quantity is changed I will update this variable to be true, and when they confirm the changes I will set it to false. If warning is true and the page is unloaded, I offer them a confirmation box, if they say no they would like to stay on this page I need to stop it from unloading. return false isn't working, it still lets the user navigate away (the alerts are there for debugging only) Any ideas?

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  • Is it rude to add "TODO: wtf?" in source code?

    - by mafutrct
    I encountered something ... well, you know TDWTF... something like that in an international project I'm working on. The code was written by a team mate. For a second I was tempted to add // TODO: wtf? to the infringing code but restrained myself. The project is indeed on a professional level, but for internal conversation, more colloquial language is used - but still no "bad" words as in "wtf". Usually, I'd surely not add such a comment, but I believe there are a few factors that allow consideration still: 1. It is not visible except as a comment in the source code (of course). 2. It is internal to our team - other developers may happen see it but it is not their code. 3. Comments in source code are usually accepted to be more colloquial, since it is "kept between us developers". Would you totally advise to never add such a comment? Or do you regard it as an edge case? Did you possibly add something similar yourself?

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  • HTML Helper/Text Box validation

    - by slandau
    I have this input on the view: <%= Html.TextBoxCurrentDateWithoutPermission("EffectiveDate", Model.EffectiveDate.HasValue ? Model.EffectiveDate.Value.ToString("dd-MMM-yyyy") : "", new string[] { PERMISSIONS.hasICAdvanced }, new { @class = "economicTextBox", propertyName = "EffectiveDate", onchange = "parseAndSetDt(this); ", dataType = "Date" })%> Here is the custom HTML Helper: public static MvcHtmlString TextBoxCurrentDateWithoutPermission( this HtmlHelper htmlHelper, string name, object value, string[] permissions, object htmlAttributes ) { foreach (string permission in permissions) { if (Chatham.Web.UI.Extranet.SessionManager.DisplayUser.IsInRole(permission)) { // the user has the permission => render the textbox return htmlHelper.TextBox(name, value, htmlAttributes); } } // the user has no permission => render a readonly checkbox var mergedHtmlAttributes = new RouteValueDictionary(htmlAttributes); mergedHtmlAttributes["disabled"] = "disabled"; return htmlHelper.TextBox(name, value == "" ? DateTime.Now : value, mergedHtmlAttributes); } The way this works now is, when a user does NOT have the permission passed in, the box is disabled. The way it needs to be -- if the user does NOT have the permission passed in, it needs to be enabled, however the only dates it can accept are todays date AND dates in the future. So I need JQuery validation (or just plain JS), for this textbox on the page for the following case: If the textbox is enabled AND the user does not have the permission, allow the user to input the current date or future dates ONLY.

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