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• How does Play recognize a particular websocket message?

  - by noncom

  I am looking at the websocket-chat example. It unveils much, but I still cannot get something. I understand how messages are received, processed and sent on the web page side. However, Play captures websocket messages by means of the receive method of an Akka actor. In the websocket-chat, there are several cases in this method, but I don't get, how does it know which websocket message should be mapped to which case. In fact, I don't understand the path that a websocket message follows upon entering Play's domain, how is it processed and how can different message types/kinds be sent from the webpage. I have not find any info or sources related to this. Could please someone explain this or point to some kind of a good reference? UPDATE: The link to the original example.

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• How to save an image in it's original format?

  - by Patrick Klug

  I am trying to figure out how I can get the original format of an image so that I can store it with the same encoding. It seems that the only way to save an Image is by using a BitmapEncoder but I don't know how I can get the correct format from the image. Example: Clipboard.GetImage() returns a InteropBitmap which doesn't seem to contain any information about the original format. I also tried using an Extension method: public static void Save(this BitmapImage image, System.IO.Stream stream) { var decoder = BitmapDecoder.Create(image.StreamSource, BitmapCreateOptions.PreservePixelFormat, BitmapCacheOption.Default); var encoder = BitmapEncoder.Create(decoder.CodecInfo.ContainerFormat); foreach (var frame in decoder.Frames) { encoder.Frames.Add(BitmapFrame.Create(decoder.Frames[0])); } encoder.Save(stream); } but the problem is that a) the ImageSource is not always a BitmapImage (Clipboard.GetImage()) for example and b) the image.StreamSource can be null in some cases (seems to be when the image is loaded via a relative Uri)

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• What is the purpose of CS0161 when switching over an enum and how to work around it?

  - by Danvil

  Consider the following example of a simple enum and a switch over all possible enum values. enum State { Alpha, Beta, Gamma } State state = ...; switch(state) { case Alpha: ... break; case Beta: ... break; case Gamma: ... break; } Now I get error CS0161: not all code paths return a value. This seems rather pointless to me, because I would expect that other cases are not possible. So what is the purpose of this error, and how would one work around this in the most elegant way?

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• Why hasn't functional programming taken over yet?

  - by pankrax

  I've read some texts about declarative/functional programming (languages), tried out Haskell as well as written one myself. From what I've seen, functional programming has several advantages over the classical imperative style: Stateless programs; No side effects Concurrency; Plays extremely nice with the rising multi-core technology Programs are usually shorter and in some cases easier to read Productivity goes up (example: Erlang) Imperative programming is a very old paradigm (as far as I know) and possibly not suitable for the 21st century Why are companies using or programs written in functional languages still so "rare"? Why, when looking at the advantages of functional programming, are we still using imperative programming languages? Maybe it was too early for it in 1990, but today?

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• Android SDK: Create image on touch

  - by dagonal

  Hello, I'm a bit stumped here, I'm trying to make it so an image (already in the drawable folder) gets created everytime you touch the screen and removed when the finger is lifted. I have the touch part coded already, overriding the onTouch method with a couple switch cases that handle each type of action (down, up, move, etc). But I can't for the life of me figure out how to make the image appear and then disappear with the coordinates (matrix?) of where the finger is. Any help would be greatly appreciated!

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• C# wrapper for objects

  - by Haggai

  I'm looking for a way to create a generic wrapper for any object. The wrapper object will behave just like the class it wraps, but will be able to have more properties, variable, methods etc., for e.g. object counting, caching etc. Say the wrapper class be called Wrapper, and the class to be wrapped be called Square and has the constructor Square(double edge_len) and the properties/methods EdgeLength and Area, I would like to use it as follows: Wrapper<Square> mySquare = new Wrapper<Square>(2.5); /* or */ new Square(2.5); Console.Write("Edge {0} -> Area {1}", mySquare.EdgeLength, mySquare.Area); Obviously I can create such a wrapper class for each class I want to wrap, but I'm looking for a general solution, i.e. Wrapper<T> which can handle both primitive and compound types (although in my current situation I would be happy with just wrapping my own classes). Suggestions? Thanks.

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• NHibernate: What are child sessions and why and when should I use them?

  - by stefando

  In the comments for the ayende's blog about the auditing in NHibernate there is a mention about the need to use a child session:session.GetSession(EntityMode.Poco). As far as I understand it, it has something to do with the order of the SQL operation which session.Flush will emit. (For example: If I wanted to perform some delete operation in the pre-insert event but the session was already done with deleting operations, I would need some way to inject them in.) However I did not find documentation about this feature and behavior. Questions: Is my understanding of child sessions correct? How and in which scenarios should I use them? Are they documented somewhere? Could they be used for session "scoping"? (For example: I open the master session which will hold some data and then I create 2 child-sessions from the master one. I'd expect that the two child-scopes will be separated but the will share objects from the master session cache. Is this the case?) Are they first class citizens in NHibernate or are they just hack to support some edge-case scenarios? Thanks in advance for any info.

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• How do you make your Java application memory efficient?

  - by Boune

  How do you optimize the heap size usage of an application that has a lot (millions) of long-lived objects? (big cache, loading lots of records from a db) Use the right data type Avoid java.lang.String to represent other data types Avoid duplicated objects Use enums if the values are known in advance Use object pools String.intern() (good idea?) Load/keep only the objects you need I am looking for general programming or Java specific answers. No funky compiler switch. Edit: Optimize the memory representation of a POJO that can appear millions of times in the heap. Use cases Load a huge csv file in memory (converted into POJOs) Use hibernate to retrieve million of records from a database Resume of answers: Use flyweight pattern Copy on write Instead of loading 10M objects with 3 properties, is it more efficient to have 3 arrays (or other data structure) of size 10M? (Could be a pain to manipulate data but if you are really short on memory...)

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• How to update SQL Server database from multiple data sources for ASP.Net MVC 4 application

  - by shaz

  I have 10+ SQL Server databases, from where I would use one table from each database to display information using the application that I am creating. For instance, DB1, DB2....DB10. NewDB (Account, Country, Costcenter....etc.). I have started with creating a new database which would contain all the information from all those 10+ databases. However, I am confused in many cases. First of all what process should I follow? Shall I create a table (in new database) with the same structure as the actual data source and insert data from actual data source to new database? Should I be doing this on the DBMS? If so, is it some scripting? (hint expected since very new to this) I am creating a report generation application which has 10+ data sources. I need some hint which way should I proceed? Thanks for advice/help in advance.

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• What is the standard way to add an icon to a link with CSS?

  - by ewernli

  I'm used to use padding + background-image to place an icon next to a link. There are many example of this approach. Here is one from here: <a class="external" href="http://www.othersite.com/">link</a> a.external { padding-right: 15px; background: transparent url(images/external-link-icon.gif) no-repeat top right; } But most browser don't print background image, which is annoying. What is the standard to place icon next to links which is semantically correct and works in all cases? (I couldn't find an exact similar question. If there is one, just close this one as duplicate)

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• How do I find the current virtual terminal

  - by camh

  I am working around a problem in Ubuntu 10.04 where after resume, the mouse cursor disappears. This can be "fixed" by running chvt 1; chvt 7 in a script in /etc/pm/sleep.d, such that those commands run on thaw and resume. However, the X console is not always vt #7, so chvt 7 is wrong in those cases. What I would like to do is find out the current vt in the fix-up script and make sure I change back to that vt. How can I find the current vt? (tty(1) just reports "not a tty")

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• Need some testcases on solving this problem

  - by user285825

  I am trying to solve the minesweeper problem of acm problemset archive, http://uva,onlinejudge,org/index,php?option=com_onlinejudge&Itemid=8&category=13&page=show_problem&problem=1130 I tested with all the possible cases that I can imagine of: 1, minimum 1 1 , 1 1 # 2, maximum upto 100 upto 100 repeat until 100 3, for each position I test for mine 4 4 ,,, ,,,, ,,,, 4 4 ,#,, ,,,, ,,,, ,,,, lastly 4 4 ,,,, ,,,, ,,,, ,,,# 4, for each postion I put a ',' and surround it with mines 4 4 ,### # # # 4 4 , # # # lastly 4 4 # # # , I thought that these are reasonable and representative sets of testcases, But still Wrong answer, I am not sure what else could I test for, I would be glad if someone throw some light on further strategy to test this thing,

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• Designing an API with compile-time option to remove first parameter to most functions and use a glob

  - by tomlogic

  I'm trying to design a portable API in ANSI C89/ISO C90 to access a wireless networking device on a serial interface. The library will have multiple network layers, and various versions need to run on embedded devices as small as an 8-bit micro with 32K of code and 2K of data, on up to embedded devices with a megabyte or more of code and data. In most cases, the target processor will have a single network interface and I'll want to use a single global structure with all state information for that device. I don't want to pass a pointer to that structure through the network layers. In a few cases (e.g., device with more resources that needs to live on two networks) I will interface to multiple devices, each with their own global state, and will need to pass a pointer to that state (or an index to a state array) through the layers. I came up with two possible solutions, but neither one is particularly pretty. Keep in mind that the full driver will potentially be 20,000 lines or more, cover multiple files, and contain hundreds of functions. The first solution requires a macro that discards the first parameter for every function that needs to access the global state: // network.h typedef struct dev_t { int var; long othervar; char name[20]; } dev_t; #ifdef IF_MULTI #define foo_function( x, a, b, c) _foo_function( x, a, b, c) #define bar_function( x) _bar_function( x) #else extern dev_t DEV; #define IFACE (&DEV) #define foo_function( x, a, b, c) _foo_function( a, b, c) #define bar_function( x) _bar_function( ) #endif int bar_function( dev_t *IFACE); int foo_function( dev_t *IFACE, int a, long b, char *c); // network.c #ifndef IF_MULTI dev_t DEV; #endif int bar_function( dev_t *IFACE) { memset( IFACE, 0, sizeof *IFACE); return 0; } int foo_function( dev_t *IFACE, int a, long b, char *c) { bar_function( IFACE); IFACE->var = a; IFACE->othervar = b; strcpy( IFACE->name, c); return 0; } The second solution defines macros to use in the function declarations: // network.h typedef struct dev_t { int var; long othervar; char name[20]; } dev_t; #ifdef IF_MULTI #define DEV_PARAM_ONLY dev_t *IFACE #define DEV_PARAM DEV_PARAM_ONLY, #else extern dev_t DEV; #define IFACE (&DEV) #define DEV_PARAM_ONLY void #define DEV_PARAM #endif int bar_function( DEV_PARAM_ONLY); // I don't like the missing comma between DEV_PARAM and arg2... int foo_function( DEV_PARAM int a, long b, char *c); // network.c #ifndef IF_MULTI dev_t DEV; #endif int bar_function( DEV_PARAM_ONLY) { memset( IFACE, 0, sizeof *IFACE); return 0; } int foo_function( DEV_PARAM int a, long b, char *c) { bar_function( IFACE); IFACE->var = a; IFACE->othervar = b; strcpy( IFACE->name, c); return 0; } The C code to access either method remains the same: // multi.c - example of multiple interfaces #define IF_MULTI #include "network.h" dev_t if0, if1; int main() { foo_function( &if0, -1, 3.1415926, "public"); foo_function( &if1, 42, 3.1415926, "private"); return 0; } // single.c - example of a single interface #include "network.h" int main() { foo_function( 11, 1.0, "network"); return 0; } Is there a cleaner method that I haven't figured out? I lean toward the second since it should be easier to maintain, and it's clearer that there's some macro magic in the parameters to the function. Also, the first method requires prefixing the function names with "_" when I want to use them as function pointers. I really do want to remove the parameter in the "single interface" case to eliminate unnecessary code to push the parameter onto the stack, and to allow the function to access the first "real" parameter in a register instead of loading it from the stack. And, if at all possible, I don't want to have to maintain two separate codebases. Thoughts? Ideas? Examples of something similar in existing code? (Note that using C++ isn't an option, since some of the planned targets don't have a C++ compiler available.)

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• check if a tree is complete standard ml

  - by aizen92

  I want to make a function in standard ml that checks if a tree is complete or not, the function somehow works, but its giving me the wrong type and a warning of non-exhaustive cases The tree code: datatype 'data tree = EMPTY | NODE of 'data tree * 'data * 'data tree; fun isComplete EMPTY = true | isComplete (NODE(x, y, z)) = if (x = EMPTY andalso z <> EMPTY) orelse (x <> EMPTY andalso z = EMPTY) then false else true; Now the above function's type is: ''a tree -> bool but the required type is 'a tree -> bool The warning I'm having is: stdIn:169.8 Warning: calling polyEqual stdIn:169.26 Warning: calling polyEqual stdIn:169.45-169.47 Warning: calling polyEqual stdIn:169.64-169.66 Warning: calling polyEqual stdIn:124.1-169.94 Warning: match nonexhaustive NODE (x,y,z) => ... What is the problem I'm having?

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• Opencv video frame not showing Sobel output

  - by user1016950

  This is a continuation question from Opencv video frame giving me an error I think I closed it off, Im new to Stackoverflow. I have code below that Im trying to see its Sobel edge image. However the program runs but the output is just a grey screen where if I mouseover the cursor disappears. Does anyone see the error? or is it a misunderstanding about the data structures Im using IplImage *frame, *frame_copy = 0; // capture frames from video CvCapture *capture = cvCaptureFromFile( "lightinbox1.avi"); //Allows Access to video propertys cvQueryFrame(capture); //Get the number of frames int nframe=(int) cvGetCaptureProperty(capture,CV_CAP_PROP_FRAME_COUNT); //Name window cvNamedWindow( "video:", 1 ); //start loop for(int i=0;i<nframe;i++){ //prepare capture frame extraction cvGrabFrame(capture); cout<<"We are on frame "<<i<<"\n"; //Get this frame frame = cvRetrieveFrame( capture ); con2txt(frame); frame_copy = cvCreateImage(cvSize(frame->width,frame->height),IPL_DEPTH_8U,frame->nChannels ); //show and destroy frame cvCvtColor( frame,frame,CV_RGB2GRAY); //Create Sobel output frame_copy1 = cvCreateImage(cvSize(frame->width,frame->height),IPL_DEPTH_16S,1 ); cvSobel(frame_copy,frame_copy1,2,2,3); cvShowImage("video:",frame_copy1); cvWaitKey(33);} cvReleaseCapture(&capture);

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• When does it make sense to use a map?

  - by kiwicptn

  I am trying to round up cases when it makes sense to use a map (set of key-value entries). So far I have two categories (see below). Assuming more exist, what are they? Please limit each answer to one unique category and put up an example. Property values (like a bean) age -> 30 sex -> male loc -> calgary Presence, with O(1) performance peter -> 1 john -> 1 paul -> 1

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• A btter way to represent Same value given multiple values(C#3.0)

  - by Newbie

  I have a situation for which I am looking for a more elegant solution. Consider the below cases "BKP","bkp","book-to-price" (will represent) BOOK-TO-PRICE "aop","aspect oriented program" (will represent) ASPECT-ORIENTED-PROGRAM i.e. if the user enter BKP or bkp or book-to-price , the program should treat that as BOOK-TO-PRICE. The same holds good for the second example(ASPECT-ORIENTED-PROGRAM). I have the below solution: Solution: if (str == "BKP" || str == "bkp" || str == "book-to-price" ) return "BOOK-TO-PRICE". But I think that there can be many other better solutions . Could you people please give some suggestion.(with an example will be better) I am using C#3.0 and dotnet framework 3.5

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• Efficient multiple services exposed over c# .NET remoting using more channels or end points?

  - by wb

  I am using remoting over TCP for a prototype distributed server application where I want to have varying multiple services exposed from each remoting server process. In some cases I want the services running from the same process but I don't want whatever is using the service to care about that. I am wondering is it more efficient to have multiple services in the same process going over the same remoting channel distinguished by endpoint URI/URL or should I be creating new channels on different ports for each service in the same process? Using up ports isn't so much of a problem as the number of services will be low and the network and machine configuration is completely controlled. Also its not clear to me if remoting sends the URI string for every single message or just at connection time, and whether if the remoting framework is intelligent enough to reduce work if calls are made on the same machine and even the same process? Thanks in advance.

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• Identifying all types with some attribute

  - by Tom W

  Hello SO; I have an issue with .Net reflection. The concept is fairly new to me and I'm exploring it with some test cases to see what works and what doesn't. I'm constructing an example wherein I populate a set of menus dynamically by scanning through my Types' attributes. Basically, I want to find every type in my main namespace that declares 'SomeAttribute' (doesn't matter what it is, it doesn't have any members at present). What I've done is: For Each itemtype As Type In Reflection.Assembly.GetExecutingAssembly().GetTypes If itemtype.IsDefined(Type.GetType("SomeAttribute"), False) Then 'do something with the type End If Next This crashes the application on startup - the first type it identifies is MyApplication which is fairly obviously not what I want. Is there a right and proper way to look for all the 'real' 'sensible' types - i.e. classes that I've defined - within the current assembly?

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• AES Key encoded byte[] to String and back to byte[]

  - by Tom Brito

  In the similar question "Conversion of byte[] into a String and then back to a byte[]" is said to not to do the byte[] to String and back conversion, what looks like apply to most cases, mainly when you don't know the encoding used. But, in my case I'm trying to save to a DB the javax.crypto.SecretKey data, and recoverd it after. The interface provide a method getEncoded() which returns the key data encoded as byte[], and with another class I can use this byte[] to recover the key. So, the question is, how do I write the key bytes as String, and later get back the byte[] to regenerate the key?

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• Saving a single entity instead of the entire context - revisited

  - by nite

  I’m looking for a way to have fine grained control over what is saved using Entity Framework, rather than the whole ObjectContext.SaveChanges(). My scenario is pretty straight forward, and I’m quite amazed not catered for in EF – pretty basic in NHibernate and all other data access paradigms I’ve seen. I’m generating a bunch of data (in a WPF UI) and allowing the user to fine tune what is proposed and choose what is actually committed to the database. For the proposed entities I’m: getting a bunch of reference entities (eg languages) via my objectcontext, creating the proposed entities and assigning these reference entities to them (as navigation properties), so by virtue of their relationship to the reference entities they’re implicitly added to the objectconext Trying to create & save individual entites based on the proposed entities. I figure this should be really simple & trivial but everything I’ve tried I’ve hit a brick wall, either I set up another objectcontext & add just the entity I need (it then tries to add the whole graph and fails as it’s on another objectcontext). I’ve tried MergeOptions = NoTracking on my reference entities to try to get the Attach/AddObject not to navigate through these to create a graph, no avail. I've removed the navigation properties from the reference entities. I've tried AcceptAllChanges, that works but pretty useless in practice as I do still want to track & save other entities. In a simple test, I can create 2 of my proposed entities, AddObject the one I want to save and then Detach the one I dont then call SaveChanges, this works but again not great in practice. Following are a few links to some of the nifty ideas which in the end don’t help in the end but illustrate the complexity of EF for something so simple. I’m really looking for a SaveSingle/SaveAtomic method, and think it’s a pretty reasonable & basic ask for any DAL, letalone a cutting edge ORM. http://stackoverflow.com/questions/1301460/saving-a-single-entity-instead-of-the-entire-context www.codeproject.com/KB/architecture/attachobjectgraph.aspx?fid=1534536&df=90&mpp=25&noise=3&sort=Position&view=Quick&select=3071122&fr=1 bernhardelbl.spaces.live.com/blog/cns!DB54AE2C5D84DB78!238.entry

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• Setting ownership/permissions for symfony2 and other web projects

  - by Handonam

  I've been very confused as to how to set permissions and user/groups for my sites. It is particularly one of my weakest suits My curent problem is that I often find myself running into a situation where if i view a particular page, it won't have permissions to write to cache or logs. At this point I'll set the ownership towards apache. Then, in other cases, if i try to run internal scripts, for example, I can't write to these cache/log files because i set them for apache. Currently, my symfony2 files are all registered to me as a part of staff (Handonam:Staff). I've seen various people creating groups such as www-data, apache, etc, and using users such as theirselves (e.g. Handonam) or www as a part of those groups. So my question is: For symfony2 and other web projects, what's generally the best setup for user/group setup so that both apache and myself can interact with these files, while maintaining decent security?

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• What good practices, if any, has the agile movement lost?

  - by clarke ching

  I am a long time agile advocated but one of the things that bothers me about Agile is that a lot of agile practitioners, especially the younger ones, have thrown out or are missing a whole lot of good (non Scrum, non XP) practices. Alistair Cockburn's style of writing Use Cases springs to mind; orthogonal arrays (pairwise testing) is another. I hope this is an okay forum to ask this, but since I read mostly Agile related books and articles and work with mostly Agile folk ... is there anything I'm missing? Thanks for all your help. StackOverlow is a fantastic resource.

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• Why is TargetInvocationException treated as uncaught by the IDE?

  - by Jason Coyne

  I have some code that is using reflection to pull property values from an object. In some cases the properties may throw exceptions, because they have null references etc. try { child.Target = propertyInfo.GetValue(target, null); } catch (TargetInvocationException ex) { child.Target = ex.InnerException.Message; } catch (Exception ex) { child.Target = ex.Message; } Ultimately the code works correctly, however when I am running under the debugger : When the property throws an exception, the IDE drops into the debugger as if the exception was uncaught. If I just hit run, the program flows through and the exception comes out as a TargetInvocationException with the real exception in the InnerException property. How can I stop this from happening?

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• flash.media.Sound.play takes long time to return

  - by Fire Lancer

  I'm trying to play some sounds in my flash project through action script. However for some reason in my code the call to Sound.play takes from 40ms to over 100ms in extreme cases, which is obviously more than enough to be very noticeable whenever a sound is played. This happens every time a sound is played, not just when that sound is first played, so I dont think its because the Sound object is still loading data or anything like that... At the start I have this to load the sound: class MyClass { [Embed(source='data/test_snd.mp3')] private var TestSound:Class; private var testSound:Sound;//flash.media.Sound public function MyClass() { testSound = new TestSound(); } Then im just using the play method of the sound object to play it later on. testSound.play();//seems to take a long time to return This as far as I can tell is following the same process as other Flash programs I found, however none of them seem to have this problem. Is there something that I've missed that would cause the play() method to be so slow?

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