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  • Why does Generic class signature requires specifying new() if type T needs instantiation ?

    - by this. __curious_geek
    I'm writing a Generic class as following. public class Foo<T> : where T : Bar, new() { public void MethodInFoo() { T _t = new T(); } } As you can see the object(_t) of type T is instantiated at run-time. To support instantiation of generic type T, language forces me to put new() in the class signature. I'd agree to this if Bar is an abstract class but why does it need to be so if Bar standard non-abstract class with public parameter-less constructor. compiler prompts following message if new() is not found. Cannot create an instance of the variable type 'T' because it does not have the new() constraint

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  • How do i get (is it possible to) a reference to the class that creates an instance of another class.

    - by Cadde
    Odd situation... I need to create a new instance of a class that needs a member of the calling class. But i can't pass a reference to the calling class through the constructor. The solution i am looking for is something like this: Public Class ChildClass Public Sub New(args) _MyMember = GetMemberFromCallingClass() ... ... End Sub End Class I want this to work without having to manually pass any references or variables from the calling class to the new instance of ChildClass. Is this possible and if so, what should i look at to make this part of my code.

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  • C++ Static Array Initialization - Memory Issue

    - by donalmg
    Hi, I have a header file which contains a member variable declaration of a static char array: class ABC { public: static char newArray[4]; // other variables / functions private: void setArray(int i, char * ptr); } In the CPP file, I have the array initialized to NULL: char ABC::newArray[4] = {0}; In the ABC constructor, I need to overwrite this value with a value constructed at runtime, such as the encoding of an integer: ABC::ABC() { int i; //some int value defined at runtime memset(newArray, 0, 4); // not sure if this is necessary setArray(i,newArray); } ... void setArray(int i, char * value) { // encoding i to set value[0] ... value [3] } When I return from this function, and print the modified newArray value, it prints out many more characters than the 4 specified in the array declaration. Any ideas why this is the case. I just want to set the char array to 4 characters and nothing further. Thanks...

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  • Getting Reference to Calling Activity from AsyncTask (NOT as an inner class)

    - by stormin986
    Is it at all possible, from within an AsyncTask that is NOT an inner class of the calling Activity class, to get a reference to the instance of Activity that initiated execution of the AsyncTask? I am aware of this thread, however it doesn't exactly address how to reference the calling Activity. Some suggest passing a reference to the Activity as a parameter to the AsyncTask constructor, however, it's reported that doing so will always result in a NullPointerException. So, I'm at a loss. My AsyncTask provides robust functionality, and I don't want to have to duplicate it as an inner class in every Activity that wants to use it. There must be an elegant solution.

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  • StructureMap DI on Model Assembly

    - by Dan dot net
    I’m new to Dependency Injection and had a question/need guidance. I had an application that used the repository pattern for data access. I used StructureMap to get the correct repository and all worked well. I have since broken out my model (including the repository logic) into its own assembly and added a service layer. In the interest of DI the service layer class takes an IRepository in its constructor. This seems wrong to me as now all consumers of my model need to know about the repository (at least configure their DI to know which one to use). I feel like that is getting into the guts of the model. What sounds wrong with this?

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  • Two phase Construction in C++

    - by tommieb75
    I have as part of assignment to look into a development kit that uses the "two-phase" construction for C++ classes: // Include Header class someFubar{ public: someFubar(); bool Construction(void); ~someFubar(); private: fooObject _fooObj; } In the source // someFubar.cpp someFubar::someFubar : _fooObj(null){ } bool someFubar::Construction(void){ bool rv = false; this->_fooObj = new fooObject(); if (this->_fooObj != null) rv = true; return rv; } someFubar::~someFubar(){ if (this->_fooObj != null) delete this->_fooObj; } Why would this "two-phase" be used and what benefits are there? Why not just instantiate the object initialization within the actual constructor?

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  • Hiding instantiated templates in shared library created with g++

    - by jchl
    I have a file that contains the following: #include <map> class A {}; void doSomething() { std::map<int, A> m; } When compiled into a shared library with g++, the library contains dynamic symbols for all the methods of std::map<int, A>. Since A is private to this file, there is no possibility that std::map will be instantiated in any other shared library with the same parameters, so I'd like to make the template instantiation hidden (for some of the reasons described in this document). I thought I should be able to do this by adding an explicit instantiation of the template class and marking it as hidden, like so: #include <map> class A {}; template class __attribute__((visibility ("hidden"))) std::map<int, A>; void doSomething() { std::map<int, A> m; } However, this has no effect: the symbols are still all exported. I even tried compiling with -fvisibility=hidden, but this also has no effect on the visibility of the methods of std::map<int, A> (although it does hide doSomething). The document I linked to above describes the use of export maps to restrict visibility, but that seems very tedious. Is there a way to do what I want in g++ (other than using export maps)? If so, what is it? If not, is there a good reason why these symbols must always be exported, or is this just a omission in g++?

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  • .net: How do you feed a winform after clicking on a row of a datagridview of search form?

    - by odiseh
    I have a winform which is responsible for doing a search by some conditions that users enters and then selects the records from a Database. The search form has a data grid view which shows the result. After searching, user clikcs on a row of the datagridview and then another form (for example frmShowDetails) will be displayed. My question is when displaying frmShowDetails, what are your suggestions to send the id of selected row to frmShowDetails in order to feed it to show data in .net? Do you use form property or a private mariable which sets by only form constructor? Thank you

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  • How to Handle Console.log and error output in JavaScript.

    - by uber_n00b
    I have a constructor that has a series of classes and functions within it - in each function I check if the param is set to show the error and output if so. Like so using an inline if. The issue and question is short of keeping two versions is this approach not wise in that each IF has to be evaluated thus adding to the time it takes to perform? debugSlide = (bag.debug==1)? console.log("item id =" + bag.itemId) : 0; How do you do this? Any pointers on where I can find tips on this? Thanks in advance!

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  • I just don't get the C++ Pointer/Reference system.

    - by gnm
    I've never had problems with references as in Python (implicit) or PHP (explicit &). In PHP you write $p = &$myvar; and you have $p as a reference pointing to $myVar. So I know in C++ you can do this: void setToSomething( int& var ) { var = 123; } int myInt; setToSomething( myInt ); Myint is now 123, why? Doesn't & mean "memory address of" x in C++? What do I do then if var is only the adress to myInt and not a pointer? void setToSomething( int* var ) { var* = 123; } int myInt; int* myIntPtr = &myInt; setToSomething( myIntPtr ); Does the above work as expected? I don't understand the difference between * and & in C++ fully. They tell you & is used to get the adress of a variable, but why IN GODS NAME does that help you in functions etc. like in the first example?

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  • Is read-only auto-imlemented property possible?

    - by abatishchev
    Hello. I found a topic on MSDN that talks that yes, this is possible. I did a test that seems to break this statement: using System; namespace Test { class Program { static void Main(string[] args) { Foo f = new Foo("1"); Console.WriteLine(f.Bar); // prints 1 f.Test("2"); Console.WriteLine(f.Bar);// successfully prints 2 } } class Foo { public Foo(string b) { this.Bar = b; } public string Bar { get; private set; } public void Test(string b) { // this would be impossible for readonly field! // next error would be occur: CS0191 or CS0191 // A readonly field cannot be assigned to (except in a constructor or a variable initializer) this.Bar = b; } } } Where am I wrong?

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  • Visual C++ CreateThread Parameter Problem

    - by Vanwaril
    I have a class that contains a function that calls create thread, and needs to pass itself (this) as a parameter: DWORD threadId; HANDLE h = CreateThread( NULL, 0, runThread, this, 0, &threadId); My runThread definition is as follows: DWORD WINAPI runThread(LPVOID args) { Obj *t = (Obj*)args; t->funct(); return 0; } Unfortunately, the object t that I get in runThread() gets garbage. My Obj class has a function pointer attribute. Could that be the problem? class Obj{ void(*funct)(); and in the constructor: Obj(void(*f)()) { funct = f; } where is my mistake? The function pointer, the createThread itself, or type-casting? I tried whatever I could think of.

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  • Cannot understand the behaviour of C# compiler while instantiating a class thru interface

    - by Newbie
    I have a class that implements an interface. The interface is public interface IRiskFactory { void StartService(); void StopService(); } The class that implements the interface is public class RiskFactoryService : IRiskFactory { } Now I have a console application and one window service. From the console application if I write the following code static void Main(string[] args) { IRiskFactory objIRiskFactory = new RiskFactoryService(); objIRiskFactory.StartService(); Console.ReadLine(); objIRiskFactory.StopService(); } It is working fine. However, when I mwrite the same piece of code in Window service public partial class RiskFactoryService : ServiceBase { IRiskFactory objIRiskFactory = null; public RiskFactoryService() { InitializeComponent(); objIRiskFactory = new RiskFactoryService(); <- ERROR } /// <summary> /// Starts the service /// </summary> /// <param name="args"></param> protected override void OnStart(string[] args) { objIRiskFactory.StartService(); } /// <summary> /// Stops the service /// </summary> protected override void OnStop() { objIRiskFactory.StopService(); } } It throws error: Cannot implicitly convert type 'RiskFactoryService' to 'IRiskFactory'. An explicit conversion exists (are you missing a cast?) When I type cast to the interface type, it started working objIRiskFactory = (IRiskFactory)new RiskFactoryService(); My question is why so?

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  • Converting C# class to JavaScript

    - by AgileMeansDoAsLittleAsPossible
    Take a look at this basic class: namespace AcmeWeb { public string FirstName { get; set; } public class Person { public Person(string firstName, string lastName) { if (String.IsNullOrEmpty(firstName)) { throw new ArgumentNullException(firstName); } this.FirstName = firstName; } } } What's the best translation of this into JavaScript? This is what I'm thinking: (function(namespace) { namespace.Person = function(firstName, lastName) { // Constructor (function() { if (!firstName) { throw "'firstName' argument cannot be null or empty"; } })(); // Private memberts var _ = { firstName: firstName }; // Public members this.firstName = function(value) { if (typeof(value) === "undefined") { return _.firstName; } else { _.firstName = value; return this; } }; }; })(AcmeWeb);

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  • How to initialize static const char array for ASCII codes [C++]

    - by Janney
    I want to initialize a static const char array with ASCII codes in a constructor, here's my code: class Card { public: Suit(void) { static const char *Suit[4] = {0x03, 0x04, 0x05, 0x06}; // here's the problem static const string *Rank[ 13 ] = {'A', '2', '3', '4', '5', '6', '7', '8', '9', '10', 'J', 'Q', 'K'}; // and here. } However i got a whole lot of errors stating that 'initializing' : cannot convert from 'char' to 'const std::string *' 'initializing' : cannot convert from 'int' to 'const std::string *' please help me! Thank you so much.

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  • javascript - Google Chrome cluttering Array generated from .split()

    - by patrick
    Given the following string: var str = "one,two,three"; If I split the string on the commas, I normally get an array, as expected: var arr = str.split(/\s*,\s*/); Trouble is that in Google Chrome (for Mac), it appends extra properties to the array. Output from Chrome's debugger: arr: Array 0: one 1: two 2: three constructor: function Array() index: undefined input: undefined length: 3 So if I iterate over the array with a for/in loop, it iterates over the new properties. Specifically the input and index properties. Using hasOwnProperty doesn't seem to help. A fix would be to do a for loop based on the length of the Array. Still I'm wondering if anyone has insight into why Chrome behaves this way. Firefox and Safari don't have this issue.

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  • array of objects of a class

    - by anurag18294
    #include class test{ int a; char b; public: test() { cout<<"\n\nDefault constructor being called"; } test(int i,char j) { a=i; b=j; cout<<"\n\nConstructor with arguments called"; } }; int main() { test tarray[5]; test newobj(31,'z'); }; In the above code snippet can we intialize values to tarray[5].

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  • ViewDidLoad not being called with my custom UIViewController

    - by user1060500
    I have created a custom UIViewController class that creates a ScrollView at runtime that it loads into the view. See code here in the constructor of my custom UIViewController. initControl(id, canEdit); _controllers = new NSMutableArray(0); //required to keep view controllers around _scrollView = new UIScrollView(); _scrollView.BackgroundColor = UIColor.Green; this.View = _scrollView; ViewDidAppear and ViewWillAppear are called normally. ViewDidLoad is not called which I am not sure why as the view is showing up on the screen just fine. Any ideas?

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  • WPF + MvvM + Prism

    - by 2Fast4YouBR
    Hi all, I am new in the Wpf & Mvvm world , but I have found a couple of examples and just found that there is some different way to instantiate the model. I would like to know the best/correct way to do it. both ways are using Unity What I've foud: var navigatorView = new MainView(); navigatorView.DataContext = m_Container.Resolve<INavigatorViewModel>(); m_RegionManager.Regions["NavigatorRegion"].Add(navigatorView); What I did: var navigatorView = m_Container.Resolve<MainView>; m_RegionManager.Regions["NavigatorRegion"].Add(navigatorView); and I changed the constructor to receive viewmodel so I can point the datacontext to it: public MainView(NavigatorViewModel navigatorViewModel) { this.DataContext = navigatorViewModel; } Other examples I've found another way like: ...vm = new viewmodel ...m = new model v.model = vm; get/set DataContext cheers

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  • Template Syntax in C++

    - by Crystal
    I don't understand templates really and was trying to run a simple find the minimum for ints, doubles, chars. First question, why is template<typename T> sometimes used, and other times template<>? Second question, I do not know what I am doing wrong with the following code below: #include <iostream> template <typename T> T minimum(T arg1, T arg2) { return arg1 < arg2 ? arg1 : arg2; } template <typename T> // first I tried template <> instd of above, but wasn't sure the difference T minimum<const char *>(const char *arg1, const char *arg2) { return strcmp(arg1, arg2) ? arg2 : arg1; } int main() { std::cout << minimum<int>(4, 2) << '\n'; std::cout << minimum<double>(2.2, -56.7) << '\n'; std::cout << minimum(2.2, 2) << '\n'; } Compile Errors: error C2768: 'minimum' : illegal use of explicit template arguments error C2783: 'T minimum(const char *,const char *)' : could not deduce template argument for 'T' : see declaration of 'minimum' : error C2782: 'T minimum(T,T)' : template parameter 'T' is ambiguous : see declaration of 'minimum' Third, in getting familiar with separating .h and .cpp files, if I wanted this minimum() function to be a static function of my class, but it was the only function in that class, would I have to have a template class as well? I originally tried doing it that way instead of having it all in one file and I got some compile errors as well that I can't remember right now and was unsure how I would do that. Thanks!

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  • Override existing AS3 classes

    - by purga
    For a custom derived class "Vector2" from flash.geom.Point, when trying to override the clone() method (similar to add(), subtract() methods that will return the type itself), it will always complain about incompatible overriding 'cuz the return type has been altered from "Point" to "Vector2". import flash.geom.Point; public class Vector2 extends Point { //Constructor is good public function Vector2(x:Number = 0, y:Number = 0) { super(x,y); } // Error: Incompatible overriding override public function clone():Vector2 //return type has to be "Point" { return new Vector2(this.x , this.y); } } How can we correctly reuse/override the methods provided by the super classes as supposed to create our own one (e.g. : a new clone1() method), or simply we just can't? Thanks.

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  • Cannot create an array of LinkedLists in Java...?

    - by kchau
    I'm working on a sparse matrix class that needs to use an array of LinkedLists to store the values of a matrix. Each element of the array (i.e. each LinkedList) represents a row of the matrix. And, each element in the LinkedLists represents a column and the stored value. In my class, I have a declaration of the array as: private LinkedList<IntegerNode>[] myMatrix; And, in my constructor for the SparseMatrix, I try to define: myMatrix = new LinkedList<IntegerNode>[numRows]; The error I end up getting is "Cannot create a generic array of LinkedList<IntegerNode>." So, I have two issues with this, 1) What am I doing wrong, and 2) Why is the type acceptable in the declaration for the array if it can't be created? Edit: IntegerNode is a class that I have created. And, all of my class files are packaged together.

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  • Dynamic memory allocation with default values

    - by viswanathan
    class A { private: int m_nValue; public: A() { m_nValue = 0; } A(int nValue) { m_nValue = nValue); ~A() {} } Now in main if i call A a(2);// 2 will be assigned for m_nValue of object A. Now how do we do this if i want to define an array of objects. Also how do we do this if i dynamically create objects using operator new like A *pA; pA = new A[5];// while creating the object i want the parameterised constructor to be //called I hope the question is clear. Do let me know if more explanation is needed

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  • C# - Silverlight - Custom control or UserControl ?

    - by cmaduro
    I need a button that is visually completely customizable, but has custom logic to publish events and manage it's visual state based on events it has registered for. When I say visually customizable, I mean I should be able to both create the button in xaml and set it's style by binding to the supplied style. Or I can create an instance of the button and set the style by passing a parameter to an alternate constructor. Or by calling a method on the button class to set the style. I do not plan on substituting the controls template, it should be a button. Can anyone point me to some code samples of this?

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  • Subtle C++ mistake, can you spot it?

    - by aaa
    I ran into a subtle C++ gotcha, took me while to resolve it. Can you spot it? class synchronized_container { boost::mutex mutex_; std::vector <T> container_; void push_back(const T &value) { boost::scoped_lock(mutex_); // raii mutex lock container_.push_back(value); } ... }; scoped lock is a raii mutex lock, obtains lock on constructor, release lock in destructor. The program will work as expected in serial, but will may occasionally produce weird stuff with more than one thread.

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