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• What exactly is Two-way databinding in WPF ?

  - by blntechie

  I'm learning WPF with MVVM and for a starter, I viewed Jason Dolinger's video on MVVM . In that he mentioned, that one of the advantage of using MVVM with WPF is two-way data binding. My question is what does he mean by two-way data binding? Is that the feature of ability to 1) bind data from controls(View) to properties in VM and 2) any change in collections or properties are reflected in the view? If I'm wrong, can anyone please explain me in detail what it is and what are its advantages? This might be a very simple doubt, but I'm very new to WPF and it's terminologies and moving away from WinForms now.

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• generic function for extracting values from an array with one particular key in PHP

  - by Sabya

  Is it possible in PHP to extract values from an array with a particular key path and return an array of those values? I'll explain with an example: $user = array ( array( id => 1, email =>'[email protected]', project => array ('project_id' => 222, 'project_name' => 'design') ), array( id => 2, email =>'[email protected]', project => array ('project_id' => 333, 'project_name' => 'design') ) ); /** I have to write a function something like: */ $projectIds = extractValuesWithKey($user, array('project', 'project_id')); print_r($projectIds); Output: Array( [0] => 222, [1] => 333 )

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• Implementing sub fields in a PropertyGrid

  - by evolve

  Alright so my terminology when it comes to C# isn't great, so I'll attempt to explain this with a small example. If you create a class which you are using within a PropertyGrid and you have the following values: class Test { public Point example { get; set; } } This will produce a PropertyGrid which has an expandable object "example" which has fields X and Y in order to create a "Point". I'm attempting to create an object "name" which has fields "firstname" and "lastname", so I have: class Test { public Name example { get; set; } } public struct Name { public string firstname { get; set; } public string lastname { get; set; } } This however isn't working as intended. I think I need to override some method(s) in order to get this working, however since I don't really have the terminology down for PropertyGrids it is difficult for me to find a solution. Any help would be great.

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• PropelBundle database:create for postgres

  - by Karol85

  I've installed propel bundle for symfony2. my database configuration is: propel: dbal: driver: pgsql user: postgres password: postgres dsn: pgsql:host=localhost;port=5432;dbname=test_database options: {} attributes: {} When i wan to create this database from console (console propel: database:create) i have got strange error : Unable to open PDO connection [wrapped: SQLSTATE[08006] [7] FATAL: database "pgsql" does not exist. i created pgsql database on my localhost and everything was good. Database "test_database" was succesfull created. Can somebody explain me why i got this previous error? On mysql i've created database without any problems.

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• Request attributes in jsf / icefaces behaves strange (survive request end)

  - by hubertg

  I have the following code in a listener method: FacesContext.getCurrentInstance().getExternalContext().getRequestMap().put("time", new Date()); When a button is clicked the following code is executed System.out.println(FacesContext.getCurrentInstance().getExternalContext().getRequestMap().get("time")); One could except that "time" is null when the listener was not executed while processing the current request, but: it seems like the "time" object survives the request processing. So when "time" has been set sometimes in the past it stays there... can anybody explain this? Thanks.

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• Different behaviour of browsers while caching the same file.

  - by Amrita

  I am trying to implement mod_disk_caching. i wrote a php code as shown in the example of the tutorial i was following. i fired the following in the terminal a2enmod cache a2enmod disk_cache /etc/init.d/apache2 force-reload then in the php code "; ? now i tried running it using firefox. In the first execution i got the following timestamp. 1308643975 here, when i press refresh, the timestamp changes (as the file is reloaded from the server) and remains the same when i click the link again (as the file is retrieved from the cache). Now i am trying the same with IExplorer. As per my understanding, the timestamp should be the same as the subsequent request for the file will be retrieved only from the cache. But i got a different timestamp. Can anyone explain me the reason for this? Why is it giving separate timestamps when the browsers are different? Thanks and Regards, AMJ

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• Why calling ISet<dynamic>.Contains() compiles, but throws an exception at runtime?

  - by Andrey Breslav

  Please, help me to explain the following behavior: dynamic d = 1; ISet<dynamic> s = new HashSet<dynamic>(); s.Contains(d); The code compiles with no errors/warnings, but at the last line I get the following exception: Unhandled Exception: Microsoft.CSharp.RuntimeBinder.RuntimeBinderException: 'System.Collections.Generic.ISet<object>' does not contain a definition for 'Contains' at CallSite.Target(Closure , CallSite , ISet`1 , Object ) at System.Dynamic.UpdateDelegates.UpdateAndExecuteVoid2[T0,T1](CallSite site, T0 arg0, T1 arg1) at FormulaToSimulation.Program.Main(String[] args) in As far as I can tell, this is related to dynamic overload resolution, but the strange things are (1) If the type of s is HashSet<dynamic>, no exception occurs. (2) If I use a non-generic interface with a method accepting a dynamic argument, no exception occurs. Thus, it looks like this problem is related particularly with generic interfaces, but I could not find out what exactly causes the problem. Is it a bug in the compiler/typesystem, or legitimate behavior?

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• Different return value of an overridden class

  - by Samer Afach

  I have a simple but confusing question here. Is it legal to have a different return value type for overridden methods than the abstact ones defined in the base class?? I did that and the compiler didn't complain... could someone please explain? class MyBaseClass { int value; public: virtual int getValue() = 0; }; class MyClass : public MyBaseClass { double value; public: virtual double getValue(); // here!!! return is double, not int }; double MyClass::getValue() { return this->value; } The compiler totally accepted something similar (MSVC und MinGW)... could anyone please exaplain to what extent this is legal?

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• CInternetSession::OpenURL exception if headers are defined. Works fine if not. Why?

  - by Jesse

  Trying to log the application version details in our weblogs using the headers: Should be a one liner..but for some reason whenever I specify anything but NULL for the headers it causes an exception (InternetOpenUrl() call returns NULL) - anyone able to explain why? CInternetSession internet; CHttpFile * pHttpFile; CString headers;// = APPLICATION_SUITE_NAME; DWORD dwHeadersLength = -1; headers.Format("%s %s %s\n",APPLICATION_SUITE_NAME,SHORT_APPLICATION_VERSION,BUILDNO_STR); pHttpFile =(CHttpFile *) internet.OpenURL(lpszURL, 1, INTERNET_FLAG_TRANSFER_ASCII|INTERNET_FLAG_DONT_CACHE, headers, dwHeadersLength); Without the headers, dwHeadersLength parameter (eg. pass in NULL,-1) then it goes through fine and I see the request come through to our website. But why does it fail if I pass in custom headers?

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• Nesting queries in SQL

  - by ZAX

  The goal of my query is to return the country name and its head of state if it's headofstate has a name starting with A, and the capital of the country has greater than 100,000 people utilizing a nested query. Here is my query: SELECT country.name as country, (SELECT country.headofstate from country where country.headofstate like 'A%') from country, city where city.population > 100000; I've tried reversing it, placing it in the where clause etc. I don't get nested queries. I'm just getting errors back, like subquery returns more than one row and such. If someone could help me out with how to order it, and explain why it needs to be a certain way, that'd be great.

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• Analyzing Python Code: Modulus Operator

  - by Bhubhu Hbuhdbus

  I was looking at some code in Python (I know nothing about Python) and I came across this portion: def do_req(body): global host, req data = "" s = socket.socket(socket.AF_INET, socket.SOCK_STREAM) s.connect((host, 80)) s.sendall(req % (len(body), body)) tmpdata = s.recv(8192) while len(tmpdata) > 0: data += tmpdata tmpdata = s.recv(8192) s.close() return data This is then called later on with body of huge size, as in over 500,000 bytes. This is sent to an Apache server that has the max request size on the default 8190 bytes. My question is what is happening at the "s.sendall()" part? Obviously the entire body cannot be sent at once and I'm guessing it is reduced by way of the modulus operator. I don't know how it works in Python, though. Can anyone explain? Thanks.

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• String intern puzzles

  - by Yob

  On this blog I found interesting String puzzles: --- Quote --- String te = "te", st = "st"; //"test".length(); String username = te + st; username.intern(); System.out.println("String object the same is: " + (username == "test")); prints String object the same is: true but uncomment the "test".length(); line and it prints String object the same is: false --- EoQ --- Being honest I don't understand why the outputs are different. Could you please explain me what's the cause of such behaviour?

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• Why first arg to execve() must be path to executable

  - by EBM

  I understand that execve() and family require the first argument of its argument array to be the same as the executable that is also pointed to by its first argument. That is, in this: execve(prog, args, env); args[0] will usually be the same as prog. But I can't seem to find information as to why this is. I also understand that executables (er, at least shell scripts) always have their calling path as the first argument when running, but I would think that the shell would do the work to put it there, and execve() would just call the executable using the path given in its first argument ("prog" from above), then passing the argument array ("args" from above) as one would on the command line.... i.e., I don't call scripts on the command line with a duplicate executable path in the args list.... /bin/ls /bin/ls /home/john Can someone explain?

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• GQL, Aggregation and Order By

  - by Koran

  Hi, How can GQL support ORDER BY when it does not support aggregation? The question is - if say the result of the query is more than 1000, does ORDER BY return fully ordered list or only the first 1000 items which is then ordered? To explain the question more: is conceptually MIN() same as query.orderby('asc').fetch(1)? If it is properly ordering the list, then how can it not provide COUNT(), since to properly order the list, GQL possibly has to parse through the whole list - in which case, COUNT() is not an issue at all? Or is item indexed and kept in some type of tree so that it does not need to parse it all the time?

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• Rails: unexpected behavior updating a shared instance

  - by Pascal Lindelauf

  I have a User object, that is related to a Post object via two different association paths: Post --(has_many)-- comments --(belongs to)-- writer (of type User) Post --(belongs to)-- writer (of type User) Say the following hold: user1.name == "Bill" post1.comments[1].writer == user1 post1.writer == user1 Now when I retrieve the post1 and its comments from the database and I update post1.comments[1].writer like so: post1.comments[1].writer.name = "John" I would expect post1.writer to equal "John" too. But it doesn't! It still equals "Bill". So there seems to be some caching going on, but the kind I would not expect. I would expect Rails to be clever enough to load exactly one instance of the user with name "Bill"; instead is appears to load two individual ones: one for each association path. Can someone explain how this works exactly and how I am to handle these types of situations the "Rails way"?

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• How extension methods work in background ?

  - by Freshblood

  I am just cuirous about behind of extension method mechanism.Some questions and answer appear in my mind. MyClass.OrderBy(x=>x.a).OrderBy(x=>x.b); I was guessing that mechanism was first orderby method works and order them by a member then returns sorted items in IEnumarable interface then next Orderby method of IEnumarable Order them for b paramater.But i am wrong when i look at this linq query. MyClass.Orderby(x=>x.a).ThenOrderBy(x=>x.b); this is slightly different and tells me that i am wrong.Because this is not ordering by a then b and not possible to have such result if i was right.This get me confuse enough... Similiar structure is possible to write withot extension methods as first query but second is not possible.This prove i am wrong . Can u explain it ?

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• Question regarding C++ Templates

  - by Isuru

  I used a simple class for a test program about templates, this is what I did: template <typename T> class test { public: test<T>::test(); T out(); }; template <typename T> test<T>::test() { } T test<T>::out() { } int main() { //test<int> t; } But when I try to compile it says 'T' : undeclared identifier and use of class template requires template argument list , pointing to the same line, where I have implemented the method out() . Can anyone please explain what the problem is?? I'm using visual studio 2008.

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• Why are difference lists more efficient than regular concatenation?

  - by Craig Innes

  I am currently working my way through the Learn you a haskell book online, and have come to a chapter where the author is explaining that some list concatenations can be ineffiecient: For example ((((a ++ b) ++ c) ++ d) ++ e) ++ f Is supposedly inefficient. The solution the author comes up with is to use 'difference lists' defined as newtype DiffList a = DiffList {getDiffList :: [a] -> [a] } instance Monoid (DiffList a) where mempty = DiffList (\xs -> [] ++ xs) (DiffList f) `mappend` (DiffList g) = DiffList (\xs -> f (g xs)) I am struggling to understand why DiffList is more computationally efficient than a simple concatenation in some cases. Could someone explain to me in simple terms why the above example is so inefficient, and in what way the DiffList solves this problem?

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• Is it a good idea to work on header files only, just at the start of the project?

  - by m4design

  To explain my point further, I'm a beginner in programming, and I'm working on a small project. Instead of separating the .cpp file from the header file, I'm implementing the code in the header files, and making one .cpp file for testing. I do this to have less files, hence easier navigation. Then later I'll separate the code as it should be. Will this cause any problems? should I continue doing that? Thanks.

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• What is this event?

  - by Shawn Mclean

  Could someone explain what this C# code is doing? // launch the camera capture when the user touch the screen this.MouseLeftButtonUp += (s, e) => new CameraCaptureTask().Show(); // this static event is raised when a task completes its job ChooserListener.ChooserCompleted += (s, e) => { //some code here }; I know that CameraCaptureTask is a class and has a public method Show(). What kind of event is this? what is (s, e)?

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• Question About Abstract Classes?

  - by IbrarMumtaz

  URL: Link (1) According to this wesbite .. you cannot implement Abstract classes but derive from them. This makes sense and I have read this many times. Like an interface, you cannot implement an instance of an abstract class, however you can implement methods, fields, and properties in the abstract class that can be used by the child class. But on MSDN URL: TextWriter CLass on MSDN TextWriter is an abstract class but it has two constructors defined ... and according to the MS 70-536 book, the following statement is valid: TextWriter tw = new File.CreateText("myFile.Txt") The static file class and it's CreateText method is fine by me as I have studied it on MSDN but can somebody explain this little contradiction I have found? Surely I am not the first? Why is instantaion of base abstract classes possible????

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• What type of websites does memcached speed up

  - by Saif Bechan

  I have read this article about 400% boost of your website. This is done by a combination of nginx and memcached. The how-to part of this website is quite good, but i mis the part where it says to what types of websites this applies. I know nginx is a http engine, I need no explanation for that. I thought memcached had something to do with caching database result. However i don't understand what this has to do with the http request, can someone please explain that to me. Another question I have is for what types of websites is this used. I have a website where the important part of the website consist of data that changes often. Often being minutes. Will this method still apply to me, or should I just stick with the basic boring setup of apache and nothing else.

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• What is the Software Development Lifecycle?

  - by j-t-s

  Our investor wants a SDLC. I've never written one before, and I don't have enough time to go and buy a book, or spend much time learning about them. From what I've been told about them, they consist of requirements (what needs to be done), and a list is done. Is this correct? Update: I have found this article which really helps to explain things in simple terms and very quickly. Not that I think an SDLC should be done quickly. In my case, I have no other option.

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• Pattern for null settings

  - by user21243

  Hi, I would like to hear your thoughts and ideas about this one. in my application i have controls that are binded to objects properties. but.. the controls always looks like that: a check box, label that explain the settings and then the edited control (for ex: text box) when unchecking the checkbox i disable the text box (using binding) when the checkbox is unchecked i want the property to contain null, and when it is checked i would like the property to contain the text box's text. Of course text box can be NumericUpDown, ComboBox, DatePicker etc.. Do you have any smart way of doing it using binding or do i have to do everything on code; I really would like to a build a control that supports that and re-use it all over Ideas? Thanks,

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• Why make anything internal?

  - by c-charp N00b

  I don't really see the point of making methods or classes internal. In my very limited understanding, all it does is make working with your code very difficult for other programmers. Say I write Big_Important_Class for Project A and make said class internal. Then Bob, working on Project B needs to use my class to have project B work with Project A, but since its internal he can't. As of now this is the only thing I have seen internals do, make things really complicated for the guy working on Project B. I know there has to be a good reason to use internals, but I don't see any. Could someone please explain how they can be a good thing?

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