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  • Why can't I create an abstract constructor on an abstract C# class?

    - by Anthony D
    I am creating an abstract class. I want each of my derived classes to be forced to implement a specific signature of constructor. As such, I did what I would have done has I wanted to force them to implement a method, I made an abstract one. public abstract class A { abstract A(int a, int b); } However I get a message saying the abstract modifier is invalid on this item. My goal was to force some code like this. public class B : A { public B(int a, int b) : base(a, b) { //Some other awesome code. } } This is all C# .NET code. Can anyone help me out? Update 1 I wanted to add some things. What I ended up with was this. private A() { } protected A(int a, int b) { //Code } That does what some folks are saying, default is private, and the class needs to implement a constructor. However that doesn't FORCE a constructor with the signature A(int a, int b). public abstract class A { protected abstract A(int a, int b) { } } Update 2 I should be clear, to work around this I made my default constructor private, and my other constructor protected. I am not really looking for a way to make my code work. I took care of that. I am looking to understand why C# does not let you do this.

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  • Nhibernate Common columns in base class

    - by sukh
    I want to design following scenario Base class (Id, Name, order, Value) 3 Derived classes derive1, derive2, derive3 inheriting properties from base There is no table for base class. And 1 table for each derived class. 3 tables have same columns. How can I create mapping file ignoring base class? Do I need to create 1 mapping file for each derived class? can I achieve this using only 1 mapping file?

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  • How to access the backing field of a base class using fluent nhibernate?

    - by Akk
    How do i set the Access Strategy in the mapping class to point to the base _photos field? public class Content { private IList<Photo> _photos; public Content() { _photos = new List<Photo>(); } public virtual IEnumerable<Photo> Photos { get { return _photos; } } public virtual void AddPhoto() {...} } public class Article : Content { public string Body {get; set;} } I am currently using the following to try and locate the backing field but an exception is thrown as it cannot be found. public class ArticleMap : ClassMap<Article> { HasManyToMany(x => x.Photos) .Access.CamelCaseField(Prefix.Underscore) //_photos //... } i tried moving the backing field _photos directly into the class and the access works. So how can i access the backing field of the base class?

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  • are there requirements for Struts setters beyond variable name matching?

    - by slk
    I have a model-driven Struts Web action: public class ModelDrivenAction<T extends Object> implements ModelDriven<T>, Preparable { protected Long id; protected T model; @Override public void prepare() {} public void setId(Long id) { this.id = id; } @Override public T getModel() { return model; } public void setModel(T model) { this.model = model; } } I have another action which is not currently model-driven: public class OtherAction implements Preparable { private ModelObj modelObj; private Long modelId; @Override public void prepare() { modelObj = repoService.retrieveModelById(modelId); } public void setModelId(Long modelId) { this.modelId = modelId; } } I wish to make it so, and would like to avoid having to track down all the instances in JavaScript where the action is passed a "modelId" parameter instead of "id" if at all possible. I thought this might work, so either modelId or id could be passed in: public class OtherAction extends ModelDrivenAction<ModelObj> { @Override public void prepare() { model = repoService.retrieveModelById(id); } public void setModelId(Long modelId) { this.id = modelId; } } However, server/path/to/other!method?modelId=123 is failing to set id. I thought so long as a setter matched a parameter name the Struts interceptor would call it on action invocation. Am I missing something here?

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  • Sorting NSTableColumn contents

    - by Yahoo
    Hey, I have a problem with sorting NSTableColumn contents. In my NSTableView there are three columns: File, Size, Path. The contents are stored in NSMutableArray. Each object in this array is a NSDictionary containing three keys: file, size and path - value for each is a NSString. In Interface Builder, in each Table Column's attributes I can choose sorting options: Selector: IB entered "compare:" which I think is ok, because I compare NSStrings. Sort Key - and that's the problem I think - I don't know what to enter here. Any clues? If you've got questions about my code, please ask.

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  • Reading a Text file in xcode

    - by Nicolaj Zefting
    First off, I'm a complete beginner. This might be a stupid question, but here it goes: I'm currently working on an App than contains Latin texts that the users can view and read. I'm using Xcode 4 with the storybord function. Theway the app is built: user selects author - then the book - then app shows the text. I am kind of confused because i need to have various text files, depending on the users choice.

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  • Should downcasting be avoided while using a class hierarchy in C++?

    - by neuviemeporte
    Let's say I'm writing an application which works with projects, and exposes different functionality depending on the type of the project. I have a hierarchy of classes for the different types of projects: class AbstractProject { }; class ProjectA : public AbstractProject { }; class ProjectB : public AbstractProject { }; class ProjectC : public AbstractProject { }; Now, I was planning to have an AbstractProject *_currentProject pointer as a member in the application's main class, pop up a dialog box on startup and based on the selection, do: _currentProject = new ProjectB(); // e.g. Later, I'll have to downcast the pointer to the specific type to utilize the functionality specific to different Project-s. Somehow this makes me feel uneasy. Is there a Better Way of doing this?

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  • Calling base class constructor

    - by The Void
    In the program below, is the line Derived(double y): Base(), y_(y) correct/allowed? That is, does it follow ANSI rules? #include <iostream> class Base { public: Base(): x_(0) { std::cout << "Base default constructor called" << std::endl; } Base(int x): x_(x) { std::cout << "Base constructor called with x = " << x << std::endl; } void display() const { std::cout << x_ << std::endl; } protected: int x_; }; class Derived: public Base { public: Derived(): Base(1), y_(1.2) { std::cout << "Derived default constructor called" << std::endl; } Derived(double y): Base(), y_(y) { std::cout << "Derived constructor called with y = " << y << std::endl; } void display() const { std::cout << Base::x_ << ", " << y_ << std::endl; } private: double y_; }; int main() { Base b1; b1.display(); Derived d1; d1.display(); std::cout << std::endl; Base b2(-9); b2.display(); Derived d2(-8.7); d2.display(); return 0; }

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  • Base form controls not visible in child form

    - by Kildareflare
    Hello I'm using C#.Net and have a base form that is inherited by several forms. Until yesterday, when the child (derived) form was opened in the designer the base forms controls would be displayed and shown as locked. Now, however the form is simply blank. None of the base forms controls are visible in the designer. Everything compiles, builds and runs OK. Has anyone else seen this? I've tried placing a call to the base forms InitializeComponent method in the derived forms OnLoad method but to no avail.

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  • Are private members inherited in C#?

    - by Petr
    Just seen one tutorial saying that: Class Dog { private string Name; } Class SuperDog:Dog { private string Mood; } Then there was an UML displaying that SuperDog will inherit Name as well. I have tried but to me it seems that only public members are inherited. At least I could not access Name unless it was declared as public.

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  • Calling base Text method on custom TextBox

    - by The Demigeek
    I'm trying to create a CurrencyTextBox that inherits from TextBox. I'm seeing some really weird behavior that I just don't understand. After lots of testing, I think I can summarize as follows: In the class code, when I access base.Text (to get the textbox's text), I'm actually getting the return value of my overridden Text property. I thought the base keyword would ensure that the underlying object's methods get called. To demonstrate: public class cTestTextBox : System.Windows.Forms.TextBox { string strText = ""; public cTestTextBox() { SetVal("AAA"); base.Text = "TEST"; } public override string Text { get { string s = strText; s = "++" + s + "++"; return s; } } public void SetVal(string val) { strText = val; } } Place this control on a form and set a breakpoint on the constructor. Run the app. Hover your mouse over the base.Text expression. Note that the tooltip shows you the value of the overridden property, not the base property. Execute the SetVal() statement and again hover your mouse over the base.Text expression. Note that the tooltop shows you the value of the overridden property, not the base property. How do I reliably access the Text property of the textbox from which I'm inheriting?

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  • scala: defining a tratit and referencing the corresponding companion object

    - by opensas
    I'm trying to define a trait that uses the corresponding companion object, that is, the componion object of the class using the trait. for example, I have: :paste class Parent { def callMyCompanion = print(Parent.salute) } object Parent { def salute = "Hello from Parent companion object" } class Child extends Parent { } object Child { def salute = "Hello from Child companion object" } And then I create a parent object: scala> val p = new Parent() p: Parent = Parent@1ecf669 scala> p.callMyCompanion Hello from Parent companion object But with a child: scala> val c = new Child() c: Child = Child@4fd986 scala> c.callMyCompanion Hello from Parent companion object I'd like to get: Hello from Child companion object How can I achieve it???

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  • Having troubles inheriting base class

    - by Nick
    When I inherit the base class, it's telling me there is no such class This is enhanced.h: class enhanced: public changeDispenser // <--------where error is occuring { public: void changeStatus(); // Function: Lets the user know how much of each coin is in the machine enhanced(int); // Constructor // Sets the Dollar amount to what the User wants void changeLoad(int); // Function: Loads what change the user requests into the Coin Machine int dispenseChange(int); // Function: Takes the users amount of cents requests and dispenses it to the user private: int dollar; }; This is enhanced.cpp: #include "enhanced.h" #include <iostream> using namespace std; enhanced::enhanced(int dol) { dollar = dol; } void enhanced::changeStatus() { cout << dollar << " dollars, "; changeDispenser::changeStatus(); } void enhanced::changeLoad(int d) { dollar = dollar + d; //changeDispenser::changeLoad; } This is changeDispenser.h: class changeDispenser { public: void changeStatus(); // Function: Lets the user know how much of each coin is in the machine changeDispenser(int, int, int, int); // Constructor // Sets the Quarters, Dimes, Nickels, and Pennies to what the User wants void changeLoad(int, int, int, int); // Function: Loads what change the user requests into the Coin Machine int dispenseChange(int); // Function: Takes the users amount of cents requests and dispenses it to the user private: int quarter; int dime; int nickel; int penny; }; I didn't include the driver file or the changeDispenser imp file, but in the driver, these are included #include "changeDispenser.h" #include "enhanced.h"

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  • Class lookup structure array in C++

    - by wyatt
    I'm trying to create a structure array which links input strings to classes as follows: struct {string command; CommandPath cPath;} cPathLookup[] = { {"set an alarm", AlarmCommandPath}, {"send an email", EmailCommandPath}, {"", NULL} }; which will be used as follows: CommandPath *cPath = NULL; string input; getline(cin, input); for(int i = 0; cPathLookup[i] != ""; i++) { if(cPathLookup[i].command == input) cPath = new cPathLookup[i].cPath; } Obviously, this code is meaningless, but I think my intention is apparent - depending on input, I'd like cPath to be initialized as either a new AlarmCommandPath or a new EmailCommandPath. I could handle it with a function returning an instance depending on input, but a whole sequence of ifs just seems inelegant. I should also note that, in case it's not apparent and important, that AlarmCommandPath and EmailCommandPath are derived from CommandPath, and CommandPath is an abstract class. Thanks for any help you can offer. EDIT: I just noticed that, in spite of CommandPath being abstract, I have a declaration: CommandPath *cPath = NULL; in working code. Why does that compile?

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  • C++ Dynamic object construction

    - by Rajesh Subramanian
    I have a base class, class Msg { ParseMsg() { ParseMsgData(); ParseTrailer(); } virtual void ParseMsgData() = 0; ParseTrailer(); }; and derived classes, class InitiateMsg { void ParseMsgData() { ... } }; class ReadOperationMsg { void ParseMsgData() { ... } }; class WriteOperationMsg { void ParseMsgData() { ... } }; and the scenario is below, void UsageFunction(string data) { Msg* msg = ParseHeader(data); ParseMsg } Msg* ParseHeader(string data) { Msg *msg = NULL; .... switch() { case 1: msg = new InitiateMsg(); break; case 2: msg = new ReadOperationMsg{(); break; case 3: msg = new WriteOperationMsg{(); break; .... } return msg; } based on the data ParseHeader method will decide which object has to be created, So I have implemented ParseHeader function outside the class where I am using. How can I make the ParseHeader function inside the Msg class and then use it? In C# the same is achieved by defining ParseHeader method as static with in class and use it from outside,

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  • Agile web development with Rails 4 interface difficulties

    - by Luke Annison
    I've been following along with the examples in the book in making a online catalog and am having a couple of discouraging difficulties in Chapter 8 task C: Catalog display. I have input the code for the stylesheets as instructed but it has created a slightly skewed result as compared to what is shown in the book. Whilst minor and aesthetic in nature its a little shock to my confidence and slightly irritating when trying to carry on through the book. I have too little rep to post a pic, but heres the link: http://s11.postimage.org/3pwlzfiwj/Screen_Shot_2012_10_08_at_22_29_56.png) As you can see the boarder seems a little confused and the image at the top is covering the header text. I've been through the code time and time again but can't seem find out where I've gone wrong. Could anybody give me some clues?

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  • Need to interface to a C++ DLL

    - by Pedro
    Hi, I need to call a C++ API from C#. I have been able to call the API, but the char[] parameters do not seem to be marshalling correctly. Here's the C++ signature: Create2ptModel(double modelPowers[2], double modelDacs[2], int pclRange[2], double targetPowers[32], double *dacAdjustFactor, unsigned short powerRampFactors[32], BOOL bPCLDacAdjusted[32], char calibrationModel[32], char errMsg[1024]) and this is how I am trying to call it from C# [DllImport("AlgorithmsLib.dll", EntryPoint = "_Create2ptModel@36", ExactSpelling = true, CallingConvention = CallingConvention.StdCall, CharSet = CharSet.Auto)] private static extern AlgorithmStatus Create2ptModel( double[] modelPowers, double[] modelDacs, int[] pclRange, double[] targetPowers, ref double dacAdjustFactor, ushort[] powerRampFactors, bool[] bPCLDacAdjusted, /**/char[] calibrationModel, char[] errMsg/**/); Any idea of how I can marshall it correctly? Thanks in advance!

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  • Assigning two strings together getting Access Read Violation

    - by Jay Bell
    I am trying to pass a string to a class mutator and set the private member to that string here is the code that is sending the string void parseTradePairs(Exchange::Currency *curr, std::string *response, int begin, int exit) { int start; int end; string temp; string dataResponse; CURL *tempCurl; initializeCurl(tempCurl); int location = response->find("marketid", begin); if(location <= exit) { start = location + 11; begin = response->find("label", start); end = begin - start - 3; findStrings(start, end, temp, response); getMarketInfo(tempCurl, temp, dataResponse); curr->_coin->setExch(temp); // here is the line of code that is sending the string dataResponse >> *(curr->_coin); curr->_next = new Exchange::Currency(curr, curr->_position + 1); parseTradePairs(curr->_next, response, begin, exit); } } and here is the mutator within the coin class that is receiving the string and assigning it to _exch void Coin::setExch(string exch) { _exch = exch; } I have stepped through it and made sure that exch has the string in it. "105" but soon as it hits _exch = exch; I get the reading violation. I tried passing as pointer as well. I do not believe it should go out of scope. and the string variable in the class is initialized to zero in the default constructor but again that should matter unless I am trying to read from it instead of writing to it. /* defualt constructor */ Coin::Coin() { _id = ""; _label = ""; _code= ""; _name = ""; _marketCoin = ""; _volume = 0; _last = 0; _exch = ""; } Exchange::Exchange(std::string str) { _exch = str; _currencies = new Currency; std::string pair; std::string response; CURL *curl; initializeCurl(curl); getTradePairs(curl, response); int exit = response.find_last_of("marketid"); parseTradePairs(_currencies, &response, 0, exit); } int main(void) { CURL *curl; string str; string id; Coin coin1; initializeCurl(curl); Exchange ex("cryptsy"); curl_easy_cleanup(curl); system("pause"); return 0; } class Exchange { public: typedef struct Currency { Currency(Coin *coin, Currency *next, Currency *prev, int position) : _coin(coin), _next(next), _prev(prev), _position(position) {} Currency(Currency *prev, int position) : _prev(prev), _position(position), _next(NULL), _coin(&Coin()){} Currency() : _next(NULL), _prev(NULL), _position(0) {} Coin *_coin; Currency *_next; Currency *_prev; int _position; }; /* constructor and destructor */ Exchange(); Exchange(std::string str); ~Exchange(); /* Assignment operator */ Exchange& operator =(const Exchange& copyExchange); /* Parse Cryptsy Pairs */ friend void parseTradePairs(Currency *curr, std::string *response, int begin, int exit); private: std::string _exch; Currency *_currencies; }; here is what i changed it to to fix it. typedef struct Currency { Currency(Coin *coin, Currency *next, Currency *prev, int position) : _coin(coin), _next(next), _prev(prev), _position(position) {} Currency(Currency *prev, int position) : _prev(prev), _position(position), _next(NULL), _coin(&Coin()){} Currency() { _next = NULL; _prev = NULL; _position = 0; _coin = new Coin(); } Coin *_coin; Currency *_next; Currency *_prev; int _position; };

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  • C++ parent class alignment

    - by aaa
    hello. Is it possible to specify alignment of parent class? for example something like (which does not compiled): template<size_t n> class Vector : public boost::array<double,n> __attribute__ ((aligned(16))) { thanks

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  • Visual Studio code generated when choosing to explicitly implement interface

    - by fearofawhackplanet
    Sorry for the vague title, but I'm not sure what this is called. Say I add IDisposable to my class, Visual Studio can create the method stub for me. But it creates the stub like: void IDisposable.Dispose() I don't follow what this syntax is doing. Why do it like this instead of public void Dispose()? And with the first syntax, I couldn't work out how to call Dispose() from within my class (in my destructor).

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  • are Hierarchical SIngletons in Java possible?

    - by Zach H
    I've been toying with an interesting idea (No idea if I'll include it in any code, but it's fun to think about) Let's say we have a program that requires a large number of classes, all of a certain subclass. And those classes all need to be singletons. Now, we could write the singleton pattern for each of those classes, but it seems wasteful to write the same code over and over, and we already have a common base class. It would be really nice to create a getSingleton method of A that when called from a subclass, returns a singleton of the B class (cast to class A for simplicity) class A{ public A getSingleton(){ //Wizardry } } class B extends A{ } A blargh = B.getSingleton() A gish = B.getSingleton() if(A == B) System.out.println("It works!") It seems to me that the way to do this would be to recognize and call B's default constructor (assuming we don't need to pass anything in.) I know a little of the black magic of reflection in Java, but i'm not sure if this can be done. Anyone interested in puzzling over this?

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  • Does string inherits from Object in Javascript?

    - by Morgan Cheng
    Is Object the base class of all objects in Javascript, just like other language such as Java & C#? I tried below code in Firefox with Firebug installed. var t = new Object(); var s1 = new String('str'); var s2 = 'str'; console.log(typeof t); console.log(typeof s1); console.log(typeof s2); The console output is object object string So, s1 and s2 are of diffeent type?

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