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  • Is there a design pattern to cut down on code duplication when subclassing Activities in Android?

    - by Daniel Lew
    I've got a common task that I do with some Activities - downloading data then displaying it. I've got the downloading part down pat; it is, of course, a little tricky due to the possibility of the user changing the orientation or cancelling the Activity before the download is complete, but the code is there. There is enough code handling these cases such that I don't want to have to copy/paste it to each Activity I have, so I thought to create an abstract subclass Activity itself such that it handles a single background download which then launches a method which fills the page with data. This all works. The issue is that, due to single inheritance, I am forced to recreate the exact same class for any other type of Activity - for example, I use Activity, ListActivity and MapActivity. To use the same technique for all three requires three duplicate classes, except each extends a different Activity. Is there a design pattern that can cut down on the code duplication? As it stands, I have saved much duplication already, but it pains me to see the exact same code in three classes just so that they each subclass a different type of Activity.

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  • C++ error message output format

    - by sub
    If I want to trigger an error in my interpreter I call this function: Error( ErrorType type, ErrorSeverity severity, const char* msg, int line ); However, with that I can only output Name error: Undefined variable in line 1 instead of Name error: Undefined variable 'someVariableName' in line 1 I'm working entirely with strings (except for the error messages as they all are constant at the moment), so sprintf won't work. What is the best way to create an efficient error function that can output a constant message combined with a string that describes which object, e.g.: a non-existing variable, triggered the error?

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  • How can I get my business objects layer to use the management layer in their methods?

    - by Tom Pickles
    I have a solution in VS2010 with several projects, each making up a layer within my application. I have business entities which are currently objects with no methods, and I have a management layer which references the business entities layer in it's project. I now think I have designed my application poorly and would like to move methods from helper classes (which are in another layer) into methods I'll create within the business entities themselves. For example I have a VirtualMachine object, which uses a helper class to call a Reboot() method on it which passes the request to the management layer. The static manager class talks to an API that reboots the VM. I want to move the Reboot() method into the VirtualMachine object, but I will need to reference the management layer: public void Reboot() { VMManager.Reboot(this.Name); } So if I add a reference to my management project in my entities project, I get the circular dependency error, which is how it should be. How can I sort this situation out? Do I need to an yet another layer between the entity layer and the management layer? Or, should I just forget it and leave it as it is. The application works ok now, but I am concerned my design isn't particularly OOP centric and I would like to correct this.

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  • Lazy loading? Better avoiding it?

    - by Charlie Pigarelli
    I just read about this design pattern: Lazy Load. And, since in the application i'm working on i have all the classes in one folder, i was wondering if this pattern could just make me avoiding the include() function for every class. I mean: It's nice to know that if i forgot to include a class, PHP, before falling into an error, trough an __autoload() function try to get it. But is it fine enough to just don't care about including classes and let PHP do it by your own every time? Or we should write __autoload() just in case it is needed?

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  • Is there a design pattern that expresses objects (an their operations) in various states?

    - by darren
    Hi I have a design question about the evolution of an object (and its state) after some sequence of methods complete. I'm having trouble articulating what I mean so I may need to clean up the question based on feedback. Consider an object called Classifier. It has the following methods: void initialise() void populateTrainingSet(TrainingSet t) void pupulateTestingSet(TestingSet t) void train() void test() Result predict(Instance i) My problem is that these methods need to be called in a certain order. Futher, some methods are invalid until a previous method is called, and some methods are invalid after a method has been called. For example, it would be invalid to call predict() before test() was called, and it would be invalid to call train() after test() was called. My approach so far has been to maintain a private enum that represents the current stateof the object: private static enum STATE{ NEW, TRAINED, TESTED, READY}; But this seems a bit cloogy. Is there a design pattern for such a problem type? Maybe something related to the template method.

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  • Accessing the "super of this" in Java

    - by gerdemb
    This is what I'm doing now. Is there a better way to access the super class? public class SearchWidget { private void addWishlistButton() { final SearchWidget thisWidget = this; button.addClickHandler(new ClickHandler() { public void onClick(ClickEvent event) { // A better way to access the super class? // something like "this.super" ...? workWithWidget(thisWidget); } } } } I'm programming with Google Web Toolkit, but I think this is really a generic Java question.

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  • Magic Method __set() on a Instantiated Object

    - by streetparade
    Ok i have a problem, sorry if i cant explaint it clear but the code speaks for its self. i have a class which generates objects from a given class name; Say we say the class is Modules: public function name($name) { $this->includeModule($name); try { $module = new ReflectionClass($name); $instance = $module->isInstantiable() ? $module->newInstance() : "Err"; $this->addDelegate($instance); } catch(Exception $e) { Modules::Name("Logger")->log($e->getMessage()); } return $this; } The AddDelegate Method: protected function addDelegate($delegate) { $this->aDelegates[] = $delegate; } The __call Method public function __call($methodName, $parameters) { $delegated = false; foreach ($this->aDelegates as $delegate) { if(class_exists(get_class($delegate))) { if(method_exists($delegate,$methodName)) { $method = new ReflectionMethod(get_class($delegate), $methodName); $function = array($delegate, $methodName); return call_user_func_array($function, $parameters); } } } The __get Method public function __get($property) { foreach($this->aDelegates as $delegate) { if ($delegate->$property !== false) { return $delegate->$property; } } } All this works fine expect the function __set public function __set($property,$value) { //print_r($this->aDelegates); foreach($this->aDelegates as $k=>$delegate) { //print_r($k); //print_r($delegate); if (property_exists($delegate, $property)) { $delegate->$property = $value; } } //$this->addDelegate($delegate); print_r($this->aDelegates); } class tester { public function __set($name,$value) { self::$module->name(self::$name)->__set($name,$value); } } Module::test("logger")->log("test"); // this logs, it works echo Module::test("logger")->path; //prints /home/bla/test/ this is also correct But i cant set any value to class log like this Module::tester("logger")->path ="/home/bla/test/log/"; The path property of class logger is public so its not a problem of protected or private property access. How can i solve this issue? I hope i could explain my problem clear.

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  • What is the best way to create a debugging web page for a computation in Java?

    - by Shooshpanchick
    I'm developing a website that uses some complex computations (NLP-related). My customer wants to have "debugging" webpages for some of these computations where he can run them with arbitrary input and see all the intermediate results that occur during computation. Before this request all of the computations were encapsulated in beans and intermediate results were logged into general log. What is the best way to capture all these results on Java level to render them as webpage?

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  • C++ Singleton design pattern.

    - by Artem Barger
    Recently I've bumped into realization/implementation of Singleton design pattern for C++. It has looked in the following way (I have adopted it from real life example): // a lot of methods is omitted here class Singleton { public: static Singleton* getInstance( ); ~Singleton( ); private: Singleton( ); static Singleton* instance; }; From this declaration I can deduce that instance field is initiated on the heap, that means there is a memory allocation. That is completely unclear for me is when does exactly memory is going to be deallocated? Or there is a bug and memory leak? It seems like there is a problem in implementation. PS. And main question how to implement it in the right way?

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  • Find recipes that can be cooked from provided ingridients

    - by skaurus
    Sorry for bad English :( Suppose i can preliminary organize recipes and ingredients data in any way. How can i effectively conduct search of recipes by user-provided ingredients, preferably sorted by max match - so, first going recipes that use maximum of provided ingridients and do not contain any other ingrs, after them recipes that uses less of provided set and still not any other ingrs, after them recipes with minimum additional requirements and so on? All i can think about is represent recipe ingridients like bitmasks, and compare required bitmask with all recipes, but it is obviously a bad way to go. And related things like Levenstein distance i don't see how to use here. I believe it should be quite common task...

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  • What are the best practices for writing maintainable CSS?

    - by Art
    I am just starting to explore this area and wonder what are the best practices when it comes to production of clean, well-structured and maintainable CSSes. There seems to be few different approaches to structuring CSS rules. One of the most commonly encountered ones I saw was throwing everything together in one rule, i.e. margins, borders, typefaces, backgrounds, something like this: .my-class { border-top:1px solid #c9d7f1; font-size:1px; font-weight:normal; height:0; position:absolute; top:24px; width:100%; } Another approach I noticed employed grouping of properties, say text-related properties like font-size, typeface, emphasis etc goes into one rule, backgrounds go into other, borders/margins go into yet another one: .my-class { border-top:1px solid #c9d7f1; } .my-class { font-size:1px; font-weight:normal; } .my-class { height:0; top:24px; width:100%; position:absolute; } I guess I am looking for a silver bullet here which I know I am not going to get, bet nevertheless - what are the best practices in this space?

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  • Beginner Design pattern question (Web Services involved)

    - by zombie
    Hi all ! I am a noob to web services world. I need to develop a login validator module and expose it as a service. I want it to be service independent, i.e I should have the option of exposing it as a SOAP service or REST service in the future. What pattern should I follow ? Sorry if I am unclear in my requirements, I can clarify as per need. Thanks !! Edit : I am using Eclipse as an IDE and Jersey libraries. I am not into any framework, simply using the MVC pattern. I find a lot of difference between SOAP ann REST methods, so I want my methods to be implementation independent - i.e I should be easily able to use my method through a SOAP or REST service call as per need. What should I do for maximum flexibility ?

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  • Should I use a modified singleton design pattern that only allows one reference to its instance?

    - by Graham
    Hi, I have a class that would normally just generate factory objects, however this class should only used once throughout the program in once specifix place. What is the best design pattern to use in this instance? I throught that having a modified singleton design which only allows one reference to instance throughout the program would be the correct way to go. So only the first call to getInstance() returns the factory library. Is this a good or bad idea? Have I missed out another fundermental design pattern for solving this problem? Thanks for your help.

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  • What elegant method callback design should be used ?

    - by ereOn
    Hi, I'm surprised this question wasn't asked before on SO (well, at least I couldn't find it). Have you ever designed a method-callback pattern (something like a "pointer" to a class method) in C++ and, if so, how did you do it ? I know a method is just a regular function with some hidden this parameter to serve as a context and I have a pretty simple design in mind. However, since things are often more complex than they seem to, I wonder how our C++ gurus would implement this, preferably in an elegant and standard way. All suggestions are welcome !

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  • Using Remote Web Page to Initialize iPhone App

    - by Chris_K
    My iPhone app relies on a vendor's XML feed to provide data. But that feed is not locked down. The vendor could change the format of the XML at any time, although so far they've promised not to. Since I might want to tell my app to use a different URL for its data source, I'd like to set up a single "Command Central" Web page, on my own server, to direct the app to the correct data source. In other words, each time my app starts, in the background and unseen by the user, it would visit "http://www.myserver.com/iphoneapp_data_sources.xml" to retrieve the URL for retrieving data from my vendor. That way, if my vendor suddenly changes the exact URL or the XML feed that the app needs, I can update that Web page and ensure that all installations of the app are using the correct XML feed. Does anyone have any advice or examples showing this kind of approach? It seems as if this must be a common problem, but so far I haven't found a well-established design pattern that fits it.

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  • c# wpf command pattern

    - by evan
    I have a wpf gui which displays a list of information in separate window and in a separate thread from the main application. As the user performs actions in the main window the side window is updated. (For example if you clicked page down in the main window a listbox in the side window would page down). Right now the architecture for this application feels very messy and I'm sure there is a cleaner way to do it. It looks like this: Main Window contains a singleton SideWindowControl which communicates with an instance of the SideWindowDisplay using events - so, for example, the pagedown button would work like: 1) the event handler of the button on the main window calls SideWindowControl.PageDown() 2) in the PageDown() function a event is created and thrown. 3) finally the gui, ShowSideWindowDisplay is subscribing to the SideWindowControl.Actions event handles the event and actually scrolls the listbox down - note because it is in a different thread it has to do that by running the command via Dispatcher.Invoke() This just seems like a very messy way to this and there must be a clearer way (The only part that can't change is that the main window and the side window must be on different threads). Perhaps using WPF commands? I'd really appreciate any suggestions!! Thanks

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  • Protocol specification in XML

    - by Mathijs
    Is there a way to specify a packet-based protocol in XML, so (de)serialization can happen automatically? The context is as follows. I have a device that communicates through a serial port. It sends and receives a byte stream consisting of 'packets'. A packet is a collection of elementary data types and (sometimes) other packets. Some elements of packets are conditional; their inclusion depends on earlier elements. I have a C# application that communicates with this device. Naturally, I don't want to work on a byte-level throughout my application; I want to separate the protocol from my application code. Therefore I need to translate the byte stream to structures (classes). Currently I have implemented the protocol in C# by defining a class for each packet. These classes define the order and type of elements for each packet. Making class members conditional is difficult, so protocol information ends up in functions. I imagine XML that looks like this (note that my experience designing XML is limited): <packet> <field name="Author" type="int32" /> <field name="Nickname" type="bytes" size="4"> <condition type="range"> <field>Author</field> <min>3</min> <max>6</min> </condition> </field> </packet> .NET has something called a 'binary serializer', but I don't think that's what I'm looking for. Is there a way to separate protocol and code, even if packets 'include' other packets and have conditional elements?

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  • Function chaining depending on boolean result

    - by Markive
    This is just an efficiency question really.. I'm interested to know if there is a more efficient or logical way that people use to handle this sort of scenario. In my asp.net application I am running a script to generate a new project my code at the top level looks like this: Dim ok As Boolean = True ok = createFolderStructure() If ok Then ok = createMDB() If ok Then ok = createProjectConfig() If ok Then ok = updateCompanyConfig() I create a boolean and each function returns a boolean result, the next function in this chain will only run if the previous one was successful. I do this because an asp.net application will continue to run through the page life cycle unless there is an unhandled exception and I don't want my whole application to be screwed up if something in the chain goes wrong (there is a lot of copying and deleting of files etc.. in this example). I was just wondering how other people handle this scenario? the vb.net single line if statement is quite succinct but I'm wondering if there is a better way?

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  • C# Design Reduce a Long List of Methods

    - by guazz
    I have a simple application that loads data from an XML file to a database. public class EmployeeLoader() { public void LoadEmpoyees() {...} public void LoadSalaries() {...} public void LoadRegistrationData() {...} public void LoadTaxData() {...} } Is it a good idea to have multiple "Load" methods as this looks like a code smell as I have about tweney Load methods? If so, how do I make my code more readable? Each Load method loads data to the corresponding table in the database via a repository?

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  • What pattern to use in this scenario?

    - by jess
    Hi, We have got many forms(windows app C#) in our application.We have similar steps in most of them - user adds a new object(in a grid),fills values and save.On,save,we validate,and save if everything ok,else show message.Now,adding of object usually means we add a new row with some default values.

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  • How can I use Object Oriented Javascript to interact with HTML Objects

    - by Steve
    I am very new to object orientated javascript, with experience writing gui's in python and java. I am trying to create html tables that I can place in locations throughout a webpage. Each html table would have two css layouts that control if it is selected or not. I can write all of the interaction if I only have one table. It gets confusing when I have multiple tables. I am wondering how to place these tables throughout a blank webpage and then access the tables individually. I think I am having trouble understanding how inheritance and hierarchy works in javascript/html. NOTE: I am not asking how to make a table. I am trying to dynamically create multiple tables and place them throughout a webpage. Then access their css independently and change it (move them to different locations or change the way the look, independently of the other tables).

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