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  • MS Access Interop - How to set print filename?

    - by Ryan
    Hi all, I'm using Delphi 2009 and the MS Access Interop COM API. I'm trying to figure out two things, but one is more important than the other right now. I need to know how to set the file name when sending the print job to the spooler. Right now it's defaulting to the Access DB's name, which can be something different than the file's name. I need to just ensure that when this is printed it enters the print spool using the same filename as the actual file itself - not the DB's name. My printer spool is actually a virtual print driver that converts documents to an image. That's my main issue. The second issue is how to specify which printer to use. This is less important at the moment because I'm just using the default printer for now. It would be nice if I could specify the printer to use, though. Does anyone know either of these two issues? Thank you in advance. I'll go ahead and paste my code: unit Converter.Handlers.Office.Access; interface uses sysutils, variants, Converter.Printer, Office_TLB, Access_TLB, UDC_TLB; procedure ToTiff(p_Printer: PrinterDriver; p_InputFile, p_OutputFile: String); implementation procedure ToTiff(p_Printer: PrinterDriver; p_InputFile, p_OutputFile: String); var AccessApp : AccessApplication; begin AccessApp := CoAccessApplication.Create; AccessApp.Visible := False; try AccessApp.OpenCurrentDatabase(p_InputFile, True, ''); AccessApp.RunCommand(acCmdQuickPrint); AccessApp.CloseCurrentDatabase; finally AccessApp.Quit(acQuitSaveNone); end; end; end.

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  • Is using SharePoint as a intranet/extranet portal a good idea?

    - by Rob
    I work for a fortune 500 company in IT and we have developed many systems/applications to do a variety of things. We are in need of some commonality of these applications and a better portal/dashboard/landing page for these applications. So, our customers and employees would log into this portal and see all the "things" that they can do which then link to their own application. This could maybe just iframe in each application inside of this portal to keep brand and navigation consistency. We are trying to decide whether to use SharePoint 2007 or 2010 for this or develop a portal/dashboard of sorts in house. We would like this portal to look and feel very branded to our needs and really not even feel like its using SharePoint (if needed). An example is to provide our own Menu control that drives the navigation if needed. Does anyone have any pros/cons for using SharePoint in such a way? Any advice on implementation (e.g. use 2010, much easier to customize design than 2007, etc)?

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  • How to reliably replace a library-defined error handler with my own?

    - by sharptooth
    On certain error cases ATL invokes AtlThrow() which is implemented as ATL::AtlThrowImpl() which in turn throws CAtlException. The latter is not very good - CAtlException is not even derived from std::exception and also we use our own exceptions hierarchy and now we will have to catch CAtlException separately here and there which is lots of extra code and error-prone. Looks like it is possible to replace ATL::AtlThrowImpl() with my own handler - define _ATL_CUSTOM_THROW and define AtlThrow() to be the custom handler before including atlbase.h - and ATL will call the custom handler. Not so easy. Some of ATL code is not in sources - it comes compiled as a library - either static or dynamic. We use the static - atls.lib. And... it is compiled in such way that it has ATL::ThrowImpl() inside and some code calling it. I used a static analysis tool - it clearly shows that there're paths on which the old default handler is called. To ensure I even tried to "reimplement" ATL::AtlThrowImpl() in my code. Now the linker says it sees two declarations of ATL::AtlThrowImpl() which I suppose confirms that there's another implementation that can be called by some code. How can I handle this? How do I replace the default handler completely and ensure that the default handler is never called?

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  • how useful is Turing completeness? are neural nets turing complete?

    - by Albert
    While reading some papers about the Turing completeness of recurrent neural nets (for example: Turing computability with neural nets, Hava T. Siegelmann and Eduardo D. Sontag, 1991), I got the feeling that the proof which was given there was not really that practical. For example the referenced paper needs a neural network which neuron activity must be of infinity exactness (to reliable represent any rational number). Other proofs need a neural network of infinite size. Clearly, that is not really that practical. But I started to wonder now if it does make sense at all to ask for Turing completeness. By the strict definition, no computer system nowadays is Turing complete because none of them will be able to simulate the infinite tape. Interestingly, programming language specification leaves it most often open if they are turing complete or not. It all boils down to the question if they will always be able to allocate more memory and if the function call stack size is infinite. Most specification don't really specify this. Of course all available implementations are limited here, so all practical implementations of programming languages are not Turing complete. So, what you can say is that all computer systems are just equally powerful as finite state machines and not more. And that brings me to the question: How useful is the term Turing complete at all? And back to neural nets: For any practical implementation of a neural net (including our own brain), they will not be able to represent an infinite number of states, i.e. by the strict definition of Turing completeness, they are not Turing complete. So does the question if neural nets are Turing complete make sense at all? The question if they are as powerful as finite state machines was answered already much earlier (1954 by Minsky, the answer of course: yes) and also seems easier to answer. I.e., at least in theory, that was already the proof that they are as powerful as any computer.

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  • Colorbox with bxslider not working

    - by Bill K
    Hello I am trying to use bxslider with colorbox. My implementation of bxslider is like an example listed here. The difference is that I want only the pagers to be shown. Also when the user clicks one pager I want colorbox to open and have next and previous buttons. The problem is that I cant group the images with colorbox and next and previous button is not shown! The following code uses the rel option but with this way colorbox doesnt event start. What I have tried till now is: HTML <div class="slider_mini" style="position:relative;bottom:0px;"> <div id="bx-pager"> <a data-slide-index="0" href="image.jpg" class="imgz"><img style="width:130px;height:104px;" src="image.jpg"/></a> <a data-slide-index="1" href="image2.jpg" class="imgz"><img style="width:130px;height:104px;" src="image2.jpg"/></a> <a data-slide-index="2" href="image3.jpg" class="imgz"><img style="width:130px;height:104px;" src="image3.jpg"/></a> </div> </div> SCRIPT <script type="text/javascript"> $(document).ready(function(){ $('.imgz').colorbox({rel:'imgz'}); $('.bxslider.two').bxSlider({ pagerCustom: '#bx-pager' }); $('#bx-pager').bxSlider({ slideWidth: 130, minSlides: 2, maxSlides: 3, moveSlides: 1, slideMargin: 10 }); }); </script> Not working Fiddle. Feedback: The problem was in live website that I was calling colorbox before bxslider. I put the call after bxslider's and it works. Thank you.

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  • Good patterns for loose coupling in Java?

    - by Eye of Hell
    Hello. I'm new to java, and while reading documentation so far i can't find any good ways for programming with loose coupling between objects. For majority of languages i know (C++, C#, python, javascript) i can manage objects as having 'signals' (notification about something happens/something needed) and 'slots' (method that can be connected to signal and process notification/do some work). In all mentioned languages i can write something like this: Object1 = new Object1Class(); Object2 = new Object2Class(); Connect( Object1.ItemAdded, Object2.OnItemAdded ); Now if object1 calls/emits ItemAdded, the OnItemAdded method of Object2 will be called. Such loose coupling technique is often referred as 'delegates', 'signal-slot' or 'inversion of control'. Compared to interface pattern, technique mentioned don't need to group signals into some interfaces. Any object's methods can be connected to any delegate as long as signatures match ( C++Qt even extends this by allowing only partial signature match ). So i don't need to write additional interface code for each methods / groups of methods, provide default implementation for interface methods not used etc. And i can't see anything like this in Java :(. Maybe i'm looking a wrong way?

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  • Extension method using Reflection to Sort

    - by Xavier
    I implemented an extension "MyExtensionSortMethod" to sort collections (IEnumerate). This allows me to replace code such as 'entities.OrderBy( ... ).ThenByDescending( ...)' by 'entities.MyExtensionSortMethod()' (no parameter as well). Here is a sample of implementation: //test function function Test(IEnumerable<ClassA> entitiesA,IEnumerable<ClassB> entitiesB ) { //Sort entitiesA , based on ClassA MySort method var aSorted = entitiesA.MyExtensionSortMethod(); //Sort entitiesB , based on ClassB MySort method var bSorted = entitiesB.MyExtensionSortMethod(); } //Class A definition public classA: IMySort<classA> { .... public IEnumerable<classA> MySort(IEnumerable<classA> entities) { return entities.OrderBy( ... ).ThenBy( ...); } } public classB: IMySort<classB> { .... public IEnumerable<classB> MySort(IEnumerable<classB> entities) { return entities.OrderByDescending( ... ).ThenBy( ...).ThenBy( ... ); } } //extension method public static IEnumerable<T> MyExtensionSortMethod<T>(this IEnumerable<T> e) where T : IMySort<T>, new() { //the extension should call MySort of T Type t = typeof(T); var methodInfo = t.GetMethod("MySort"); //invoke MySort var result = methodInfo.Invoke(new T(), new object[] {e}); //Return return (IEnumerable < T >)result; } public interface IMySort<TEntity> where TEntity : class { IEnumerable<TEntity> MySort(IEnumerable<TEntity> entities); } However, it seems a bit complicated compared to what it does so I was wondering if they were another way of doing it?

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  • How to make a Global Array?

    - by Wayfarer
    So, I read this post, and it's pretty much exactly what I was looking for. However... it doesn't work. I guess I'm not going to go with the singleton object, but rather making the array in either a Global.h file, or insert it into the _Prefix file. Both times I do that though, I get the error: Expected specifier-qualifier-list before 'static' and it doesn't work. So... I'm not sure how to get it to work, I can remove extern and it works, but I feel like I need that to make it a constant. The end goal is to have this Mutable Array be accessible from any object or any file in my project. Help would be appreciated! This is the code for my Globals.h file: #import <Foundation/Foundation.h> @interface Globals : NSObject { static extern NSMutableArray * myGlobalArray; } @end I don't think I need anything in the implementation file. If I were to put that in the prefix file, the error was the same.

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  • Why does my ActivePerl program report 'Sorry. Ran out of threads'?

    - by Zaid
    Tom Christiansen's example code (à la perlthrtut) is a recursive, threaded implementation of finding and printing all prime numbers between 3 and 1000. Below is a mildly adapted version of the script #!/usr/bin/perl # adapted from prime-pthread, courtesy of Tom Christiansen use strict; use warnings; use threads; use Thread::Queue; sub check_prime { my ($upstream,$cur_prime) = @_; my $child; my $downstream = Thread::Queue->new; while (my $num = $upstream->dequeue) { next unless ($num % $cur_prime); if ($child) { $downstream->enqueue($num); } else { $child = threads->create(\&check_prime, $downstream, $num); if ($child) { print "This is thread ",$child->tid,". Found prime: $num\n"; } else { warn "Sorry. Ran out of threads.\n"; last; } } } if ($child) { $downstream->enqueue(undef); $child->join; } } my $stream = Thread::Queue->new(3..shift,undef); check_prime($stream,2); When run on my machine (under ActiveState & Win32), the code was capable of spawning only 118 threads (last prime number found: 653) before terminating with a 'Sorry. Ran out of threads' warning. In trying to figure out why I was limited to the number of threads I could create, I replaced the use threads; line with use threads (stack_size => 1);. The resultant code happily dealt with churning out 2000+ threads. Can anyone explain this behavior?

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  • Why is python decode replacing more than the invalid bytes from an encoded string?

    - by dangra
    Trying to decode an invalid encoded utf-8 html page gives different results in python, firefox and chrome. The invalid encoded fragment from test page looks like 'PREFIX\xe3\xabSUFFIX' >>> fragment = 'PREFIX\xe3\xabSUFFIX' >>> fragment.decode('utf-8', 'strict') ... UnicodeDecodeError: 'utf8' codec can't decode bytes in position 6-8: invalid data What follows is the summary of replacement policies used to handle decoding errors by python, firefox and chrome. Note how the three differs, and specially how python builtin removes the valid S (plus the invalid sequence of bytes). by Python The builtin replace error handler replaces the invalid \xe3\xab plus the S from SUFFIX by U+FFFD >>> fragment.decode('utf-8', 'replace') u'PREFIX\ufffdUFFIX' >>> print _ PREFIX?UFFIX The python implementation builtin replace error handler looks like: >>> python_replace = lambda exc: (u'\ufffd', exc.end) As expected, trying this gives same result than builtin: >>> codecs.register_error('python_replace', python_replace) >>> fragment.decode('utf-8', 'python_replace') u'PREFIX\ufffdUFFIX' >>> print _ PREFIX?UFFIX by Firefox Firefox replaces each invalid byte by U+FFFD >>> firefox_replace = lambda exc: (u'\ufffd', exc.start+1) >>> codecs.register_error('firefox_replace', firefox_replace) >>> test_string.decode('utf-8', 'firefox_replace') u'PREFIX\ufffd\ufffdSUFFIX' >>> print _ PREFIX??SUFFIX by Chrome Chrome replaces each invalid sequence of bytes by U+FFFD >>> chrome_replace = lambda exc: (u'\ufffd', exc.end-1) >>> codecs.register_error('chrome_replace', chrome_replace) >>> fragment.decode('utf-8', 'chrome_replace') u'PREFIX\ufffdSUFFIX' >>> print _ PREFIX?SUFFIX The main question is why builtin replace error handler for str.decode is removing the S from SUFFIX. Also, is there any unicode's official recommended way for handling decoding replacements?

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  • Threads, Sockets, and Designing Low-Latency, High Concurrency Servers

    - by lazyconfabulator
    I've been thinking a lot lately about low-latency, high concurrency servers. Specifically, http servers. http servers (fast ones, anyway) can serve thousands of users simultaneously, with very little latency. So how do they do it? As near as I can tell, they all use events. Cherokee and Lighttpd use libevent. Nginx uses it's own event library performing much the same function of libevent, that is, picking a platform optimal strategy for polling events (like kqueue on *bsd, epoll on linux, /dev/poll on Solaris, etc). They all also seem to employ a strategy of multiprocess or multithread once the connection is made - using worker threads to handle the more cpu intensive tasks while another thread continues to listen and handle connections (via events). This is the extent of my understanding and ability to grok the thousand line sources of these applications. What I really want are finer details about how this all works. In examples of using events I've seen (and written) the events are handling both input and output. To this end, do the workers employ some sort of input/output queue to the event handling thread? Or are these worker threads handling their own input and output? I imagine a fixed amount of worker threads are spawned, and connections are lined up and served on demand, but how does the event thread feed these connections to the workers? I've read about FIFO queues and circular buffers, but I've yet to see any implementations to work from. Are there any? Do any use compare-and-swap instructions to avoid locking or is locking less detrimental to event polling than I think? Or have I misread the design entirely? Ultimately, I'd like to take enough away to improve some of my own event-driven network services. Bonus points to anyone providing solid implementation details (especially for stuff like low-latency queues) in C, as that's the language my network services are written in.

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  • Qt - no such signal error

    - by bullettime
    I'm trying to trigger a signal when a double click happens in one of the draggable widgets on the fridge magnets example. Here's the changes I made to the example source: DragLabel: class DragLabel : public QLabel { public: DragLabel(const QString &text, QWidget *parent); QString labelText() const; public slots: void testSlot(){qDebug()<<"testSlot";} //<-- implemented this slot protected: void mouseDoubleClickEvent(QMouseEvent *ev){emit testSignal();} //<-- overriden this method private: QString m_labelText; signals: void testSignal(); //<-- added this signal }; The only thing I changed in the implementation file is adding connect(this,SIGNAL(testSignal()),this,SLOT(testSlot())); to DragLabel's constructor. Trying to compile the project resulted in 'undefined reference to `DragLabel::testSignal()' and 'collect2: ld returned 1 exit status' errors. When I comment out the call to the signal, it compiles and runs, but gives off 'Object::connect: No such signal QLabel::testSignal() in draglabel.cpp' warning in the application output. Apparently testSignal() isn't being recognized as a signal. What am I missing?

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  • Where do you take mocking - immediate dependencies, or do you grow the boundaries...?

    - by Peter Mounce
    So, I'm reasonably new to both unit testing and mocking in C# and .NET; I'm using xUnit.net and Rhino Mocks respectively. I'm a convert, and I'm focussing on writing behaviour specifications, I guess, instead of being purely TDD. Bah, semantics; I want an automated safety net to work above, essentially. A thought struck me though. I get programming against interfaces, and the benefits as far as breaking apart dependencies goes there. Sold. However, in my behaviour verification suite (aka unit tests ;-) ), I'm asserting behaviour one interface at a time. As in, one implementation of an interface at a time, with all of its dependencies mocked out and expectations set up. The approach seems to be that if we verify that a class behaves as it should against its collaborating dependencies, and in turn relies on each of those collaborating dependencies to have signed that same quality contract, we're golden. Seems reasonable enough. Back to the thought, though. Is there any value in semi-integration tests, where a test-fixture is asserting against a unit of concrete implementations that are wired together, and we're testing its internal behaviour against mocked dependencies? I just re-read that and I think I could probably have worded it better. Obviously, there's going to be a certain amount of "well, if it adds value for you, keep doing it", I suppose - but has anyone else thought about doing that, and reaped benefits from it outweighing the costs?

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  • AJAX - querying a search engine and returning the number of results

    - by Moddy
    Right, so basically I need to query a selection of search engines in an AJAX app. As there is a number of different search engines - there's no search engine specific API I can use either. My main problem is getting the number of results returned by the search. So far, I have decided it is probably best to use a regexp from the returned search query HTML, and then convert the string of characters to an integer. However, this method just doesn't feel.. clean to me. It seems a bit rough around the edges and I think it could do with improving! I guess not being 100% confident with regular expressions doesn't help; but it just feels like it could be improved. Any ideas on how to implement this would be great cheers! It doesn't seem like that an exotic thing to do, so I was wondering if perhaps any of you guys have done this before and would have a few tips? Note: This is an AJAX app at the moment, but I may be re-writing this functionality in a different app soon - which won't be AJAX. I'm confident I can transfer any AJAX implementation to the other language though.

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  • Problem with SQLite related nUnit-tests after upgrade to VS2010 and Re#5

    - by stiank81
    After converting to Visual Studio 2010 with ReSharper5 some of my unit tests started failing. More specifically this applies to all unit tests that use NHibernate with SQLite. The problem seem to be related to SQLite somehow. The unit tests that does not involve NHibernate and SQLite are still running fine. The exception is as follows: NHibernate.HibernateException : Could not create the driver from NHibernate.Driver.SQLite20Driver, NHibernate, Version=2.1.2.4000, Culture=neutral, PublicKeyToken=aa95f207798dfdb4. ----> System.Reflection.TargetInvocationException : Exception has been thrown by the target of an invocation. ----> NHibernate.HibernateException : The IDbCommand and IDbConnection implementation in the assembly System.Data.SQLite could not be found. Ensure that the assembly System.Data.SQLite is located in the application directory or in the Global Assembly Cache. If the assembly is in the GAC, use <qualifyAssembly/> element in the application configuration file to specify the full name of the assembly. TearDown : System.NullReferenceException : Object reference not set to an instance of an object. The exception is the NullReferenceException on TearDown when cleaning up NHibernate objects that wasn't successfully created, but the problem seem to be related to SQLite somehow. I run my unit tests through ReSharper, but I get the same exception when running them directly through the NUnit.exe application. However, running them through the x86 variant (NUnit-x86.exe) all tests run fine. Can it be related to some mixing of 64bit and 32bit dlls? It still runs fine through VS2008 + ReSharper4.5. Note that the target framework of my projects still is .NET3.5. Anyone seen this problem before?

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  • Obj-C: ++variable is increasing by two instead of one

    - by Eli Garfinkel
    I am writing a program that asks users yes/no questions to help them decide how to vote in an election. I have a variable representing the question number called questionnumber. Each time I go through the switch-break loop, I add 1 to the questionnumber variable so that the next question will be displayed. This works fine for the first two questions. But then it skips the third question and moves on to the fourth. When I have more questions in the list, it skips every other question. Somewhere, for some reasons, the questionnumber variable is increasing when I don't want it to. Please look at the code below and tell me what I'm doing wrong. Thank you! Eli import "MainView.h" import @implementation MainView @synthesize Question; @synthesize mispar; int conservative = 0; int liberal = 0; int questionnumber = 1; (IBAction)agreebutton:(id)sender { ++liberal; } (IBAction)disagreebutton:(id)sender { ++conservative; } (IBAction)nextbutton:(id)sender { ++questionnumber; switch (questionnumber) { case 2: Question.text = @"Congress should pass a law that would ban Americans from earning more than one hundred million dollars in any given year."; break; case 3: Question.text = @"It is not fair to admit people to a university or employ them on the basis of merit alone. Factors such as race, gender, class, and sexual orientation must also be considered."; break; case 4: Question.text = @"There are two Americas - one for the rich and one for the poor."; break; case 5: Question.text = @"Top quality health care should be free for all."; break; default: break; } } @end

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  • Behavior of retained property while holder is retained

    - by Aurélien Vallée
    Hello everyone, I am a beginner ObjectiveC programmer, coming from the C++ world. I find it very difficult to understand the memory management offered by NSObject :/ Say I have the following class: @interface User : NSObject { NSString* name; } @property (nonatomic,retain) NSString* name; - (id) initWithName: (NSString*) theName; - (void) release; @end @implementation User @synthesize name - (id) initWithName: (NSString*) theName { if ( self = [super init] ) { [self setName:theName]; } return self; } - (void) release { [name release]; [super release]; } @end No considering the following code, I can't understand the retain count results: NSString* name = [[NSString alloc] initWithCString:/*C string from sqlite3*/]; // (1) name retainCount = 1 User* user = [[User alloc] initWithName:name]; // (2) name retainCount = 2 [whateverMutableArray addObject:user]; // (3) name retainCount = 2 [user release]; // (4) name retainCount = 1 [name release]; // (5) name retainCount = 0 At (4), the retain count of name decreased from 2 to 1. But that's not correct, there is still the instance of user inside the array that points to name ! The retain count of a variable should only decrease when the retain count of a referring variable is 0, that is, when it is dealloced, not released.

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  • Unittesting aspect-oriented features.

    - by Tomas Brambora
    Hi, I'd like to know what would you propose as the best way to unit test aspect-oriented application features (well, perhaps that's not the best name, but it's the best I was able to come up with :-) ) such as logging or security? These things are sort of omni-present in the application, so how to test them properly? E.g. say that I'm writing a Cherrypy web server in Python. I can use a decorator to check whether the logged-in user has the permission to access a given page. But then I'd need to write a test for every page to see whether it works oK (or more like to see that I had not forgotten to check security perms for that page). This could maybe (emphasis on maybe) be bearable if logging and/or security were implemented during the web server "normal business implementation". However, security and logging usually tend to be added to the app as an afterthough (or maybe that's just my experience, I'm usually given a server and then asked to implement security model :-) ). Any thoughts on this are very welcome. I have currently 'solved' this issue by, well - not testing this at all. Thanks.

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  • Java - Class type from inside static initialization block

    - by DutrowLLC
    Is it possible to get the class type from inside the static initialization block? This is a simplified version of what I currently have:: class Person extends SuperClass { String firstName; static{ // This function is on the "SuperClass": // I'd for this function to be able to get "Person.class" without me // having to explicitly type it in but "this.class" does not work in // a static context. doSomeReflectionStuff(Person.class); // IN "SuperClass" } } This is closer to what I am doing, which is to initialize a data structure that holds information about the object and its annotations, etc... Perhaps I am using the wrong pattern? public abstract SuperClass{ static void doSomeReflectionStuff( Class<?> classType, List<FieldData> fieldDataList ){ Field[] fields = classType.getDeclaredFields(); for( Field field : fields ){ // Initialize fieldDataList } } } public abstract class Person { @SomeAnnotation String firstName; // Holds information on each of the fields, I used a Map<String, FieldData> // in my actual implementation to map strings to the field information, but that // seemed a little wordy for this example static List<FieldData> fieldDataList = new List<FieldData>(); static{ // Again, it seems dangerous to have to type in the "Person.class" // (or Address.class, PhoneNumber.class, etc...) every time. // Ideally, I'd liken to eliminate all this code from the Sub class // since now I have to copy and paste it into each Sub class. doSomeReflectionStuff(Person.class, fieldDataList); } }

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  • How can I improve this design?

    - by klausbyskov
    Let's assume that our system can perform actions, and that an action requires some parameters to do its work. I have defined the following base class for all actions (simplified for your reading pleasure): public abstract class BaseBusinessAction<TActionParameters> : where TActionParameters : IActionParameters { protected BaseBusinessAction(TActionParameters actionParameters) { if (actionParameters == null) throw new ArgumentNullException("actionParameters"); this.Parameters = actionParameters; if (!ParametersAreValid()) throw new ArgumentException("Valid parameters must be supplied", "actionParameters"); } protected TActionParameters Parameters { get; private set; } protected abstract bool ParametersAreValid(); public void CommonMethod() { ... } } Only a concrete implementation of BaseBusinessAction knows how to validate that the parameters passed to it are valid, and therefore the ParametersAreValid is an abstract function. However, I want the base class constructor to enforce that the parameters passed are always valid, so I've added a call to ParametersAreValid to the constructor and I throw an exception when the function returns false. So far so good, right? Well, no. Code analysis is telling me to "not call overridable methods in constructors" which actually makes a lot of sense because when the base class's constructor is called the child class's constructor has not yet been called, and therefore the ParametersAreValid method may not have access to some critical member variable that the child class's constructor would set. So the question is this: How do I improve this design? Do I add a Func<bool, TActionParameters> parameter to the base class constructor? If I did: public class MyAction<MyParameters> { public MyAction(MyParameters actionParameters, bool something) : base(actionParameters, ValidateIt) { this.something = something; } private bool something; public static bool ValidateIt() { return something; } } This would work because ValidateIt is static, but I don't know... Is there a better way? Comments are very welcome.

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  • Pong: How does the paddle know where the ball will hit?

    - by Roflcoptr
    After implementing Pacman and Snake I'm implementing the next very very classic game: Pong. The implementation is really simple, but I just have one little problem remaining. When one of the paddle (I'm not sure if it is called paddle) is controlled by the computer, I have trouble to position it at the correct position. The ball has a current position, a speed (which for now is constant) and a direction angle. So I could calculate the position where it will hit the side of the computer controlled paddle. And so Icould position the paddle right there. But however in the real game, there is a probability that the computer's paddle will miss the ball. How can I implement this probability? If I only use a probability of lets say 0.5 that the computer's paddle will hit the ball, the problem is solved, but I think it isn't that simple. From the original game I think the probability depends on the distance between the current paddle position and the position the ball will hit the border. Does anybody have any hints how exactly this is calculated?

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  • How to avoid using this in a constructor

    - by Paralife
    I have this situation: interface MessageListener { void onMessageReceipt(Message message); } class MessageReceiver { MessageListener listener; public MessageReceiver(MessageListener listener, other arguments...) { this.listener = listener; } loop() { Message message = nextMessage(); listener.onMessageReceipt(message); } } and I want to avoid the following pattern: (Using the this in the Client constructor) class Client implements MessageListener { MessageReceiver receiver; MessageSender sender; public Client(...) { receiver = new MessageReceiver(this, other arguments...); sender = new Sender(...); } . . . @Override public void onMessageReceipt(Message message) { if(Message.isGood()) sender.send("Congrtulations"); else sender.send("Boooooooo"); } } The reason why i need the above functionality is because i want to call the sender inside the onMessageReceipt() function, for example to send a reply. But I dont want to pass the sender into a listener, so the only way I can think of is containing the sender in a class that implements the listener, hence the above resulting Client implementation. Is there a way to achive this without the use of 'this' in the constructor? It feels bizare and i dont like it, since i am passing myself to an object(MessageReceiver) before I am fully constructed. On the other hand, the MessageReceiver is not passed from outside, it is constructed inside, but does this 'purifies' the bizarre pattern? I am seeking for an alternative or an assurance of some kind that this is safe, or situations on which it might backfire on me.

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  • Objective C, Linking Error with extern variable..

    - by LCYSoft
    I have a very simple java code like this. I don't have any idea how to do this in Objective C. Especially, the static part which calls the getLocalAddress() method and assign it into the static string variable. I know how to set a static variable and a static method in Objective but I dont know how to implement that static { } part in java. Thanks in advance... public class Address { public static String localIpAddress; static { localIpAddress = getLocalIpAddress(); } public Address() { } static String getLocalIpAddress() { //do something to get local ip address } } I added this in my .h file #import <Foundation/Foundation.h> extern NSString *localIpAddress; @class WifiAddrss; @interface Address : NSObject { } @end And my .m file looks like #import "Address.h" #import "WifiAddress.h" @implementation Address +(void)initialize{ if(self == [Address class]){ localIpAddress = [self getLocalIpAddress]; } } +(NSString *)getLocalIpAddress{ return address here } -(id)init{ self = [super init]; if (self == nil){ NSLog(@"init error"); } return self; } @end And Now I am getting a linking error and it complains about "extern NSString *localIpAddress" part. If I change the extern to static, it works fine. But what I wanted to do is that I want make the scope of "localIpAddress" variable as grobal. Since if I put "static" in front of a variable in Objective-C then the variable is only visible in the class. But this time, I want to make that as a grobal variable. So my question is how to make "localIpAddress" variable as a grobal variable which is initialized once when the first time Address class is created.. Thanks in advance...

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  • Dependency Injection and decoupling of software layers

    - by cs31415
    I am trying to implement Dependency Injection to make my app tester friendly. I have a rather basic doubt. Data layer uses SqlConnection object to connect to a SQL server database. SqlConnection object is a dependency for data access layer. In accordance with the laws of dependency injection, we must not new() dependent objects, but rather accept them through constructor arguments. Not wanting to upset the DI gods, I dutifully create a constructor in my DAL that takes in SqlConnection. Business layer calls DAL. Business layer must therefore, pass in SqlConnection. Presentation layer calls Business layer. Hence it too, must pass in SqlConnection to business layer. This is great for class isolation and testability. But didn't we just couple the UI and Business layers to a specific implementation of the data layer which happens to use a relational database? Why do the Presentation and Business layers need to know that the underlying data store is SQL? What if the app needs to support multiple data sources other than SQL server (such as XML files, Comma delimited files etc.) Furthermore, what if I add another object upon which my data layer is dependent on (say, a second database). Now, I have to modify the upper layers to pass in this new object. How can I avoid this merry-go-round and reap all the benefits of DI without the pain?

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  • Quickly determine if a number is prime in Python for numbers < 1 billion

    - by Frór
    Hi, My current algorithm to check the primality of numbers in python is way to slow for numbers between 10 million and 1 billion. I want it to be improved knowing that I will never get numbers bigger than 1 billion. The context is that I can't get an implementation that is quick enough for solving problem 60 of project Euler: I'm getting the answer to the problem in 75 seconds where I need it in 60 seconds. http://projecteuler.net/index.php?section=problems&id=60 I have very few memory at my disposal so I can't store all the prime numbers below 1 billion. I'm currently using the standard trial division tuned with 6k±1. Is there anything better than this? Do I already need to get the Rabin-Miller method for numbers that are this large. primes_under_100 = [2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97] def isprime(n): if n <= 100: return n in primes_under_100 if n % 2 == 0 or n % 3 == 0: return False for f in range(5, int(n ** .5), 6): if n % f == 0 or n % (f + 2) == 0: return False return True How can I improve this algorithm?

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