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  • Android Custom View Constructor

    - by Mitch
    I'm learning about using Custom Views from the following: http://developer.android.com/guide/topics/ui/custom-components.html#modifying The description says: Class Initialization As always, the super is called first. Furthermore, this is not a default constructor, but a parameterized one. The EditText is created with these parameters when it is inflated from an XML layout file, thus, our constructor needs to both take them and pass them to the superclass constructor as well. Is there a better description? I've been trying to figure out what the constructor(s) should look like and I've come up with 4 possible choices (see example at end of post). I'm not sure what these 4 choices do (or don't do), why I should implement them, or what the parameters mean. Is there a description of these? Thanks. Mitch public MyCustomView() { super(); } public MyCustomView(Context context) { super(context); } public MyCustomView(Context context, AttributeSet attrs) { super(context, attrs); } public MyCustomView(Context context, AttributeSet attrs, Map params) { super(context, attrs, params); }

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  • Boost Python : How to only expose the constructor of a class with virtual (pure & impure) methods

    - by fallino
    Hello, I'm a newbie with Boost::Python but I tried to search on the web to do so I want to expose a 3rd party library to Python. One of the class of the library (.hpp) is composed of a public constructor with arguments a protected constructor and functions various regular functions various pure virtual functions various non pure virtual functions First, I did not succeed in building it without having errors about this protected constructor. I finally commented it. A first question would be : Is there a way to exclude these protected functions since I don't want to expose them ? (I know it's possible and easy with Py++, but I started without using it) Then I tried to expose all of my functions, beginning with the pure virtual ones (commenting them all except one), which wasn't a success too So I finally decided not to expose these virtual functions (which in fact seems logical...), but, here again, I didn't manage building it with a simple constructor with arguments (without no_init). So my second question is : Is there a way to exclude these virtual functions since I don't want to expose them ? Sorry if it seems trivial but I didn't find anything explicit on the web and I need something rather explicit :). Thanks in advance

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  • Swig: No Constructor defined

    - by wheaties
    I added %allowexcept to my *.i file when building a Python <-- C++ bridge using Swig. Then I removed that preprocessing directive. Now I can't get the Python produced code to recognize the constructor of a C++ class. Here's the class file: #include <exception> class Swig_Foo{ public: Swig_Foo(){} virtual ~Swig_Foo(){} virtual getInt() =0; virtual throwException() { throw std::exception(); } }; And here's the code Swig produces from it: class Swig_Foo: __swig_setmethods__ = {} __setattr__ = lambda self, name, value: _swig_setattr(self, Swig_Foo, name, value) __swig_getmethods__ = {} __getattr__ = lambda self, name: _swig_getattr(self, Swig_Foo, name) def __init__(self): raise AttributeError, "No constructor defined" __repr__ = _swig_repr __swig_destroy__ = _foo.delete_Swig_Foo __del__ = lambda self : None; def getInt(*args): return apply(_foo.Swig_Foo_getInt, args) def throwOut(*args): return apply(_foo.Swig_Foo_throwOut, args) Swig_Foo_swigregister = _foo.Swig_Foo_swigregister Swig_Foo_swigregister(Swig_Foo) The problem is the def __init__self): raise AttributeError, "No constructor defined" portion. It never did this before I added the %allowexception and now that I've removed it, I can't get it to create a real constructor. All the other classes have actual constructors. Quite baffled. Anyone know how I can get it to stop doing this?

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  • Constructor and Destructors in C++ [Not a question] [closed]

    - by Jack
    I am using gcc. Please tell me if I am wrong - Lets say I have two classes A & B class A { public: A(){cout<<"A constructor"<<endl;} ~A(){cout<<"A destructor"<<endl;} }; class B:public A { public: B(){cout<<"B constructor"<<endl;} ~B(){cout<<"B destructor"<<endl;} }; 1) The first line in B's constructor should be a call to A's constructor ( I assume compiler automatically inserts it). Also the last line in B's destructor will be a call to A's destructor (compiler does it again). Why was it built this way? 2) When I say A * a = new B(); compiler creates a new B object and checks to see if A is a base class of B and if it is it allows 'a' to point to the newly created object. I guess that is why we don't need any virtual constructors. ( with help from @Tyler McHenry , @Konrad Rudolph) 3) When I write delete a compiler sees that a is an object of type A so it calls A's destructor leading to a problem which is solved by making A's destructor virtual. As user - Little Bobby Tables pointed out to me all destructors have the same name destroy() in memory so we can implement virtual destructors and now the call is made to B's destructor and all is well in C++ land. Please comment.

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  • Dependency Properties, change notification and setting values in the constructor

    - by stefan.at.wpf
    Hello, I have a clas with 3 dependency properties A,B,C. The values of these properties are set by the constructor and every time one of the properties A, B or C changes, the method recalculate() is called. Now during execution of the constructor these method is called 3 times, because the 3 properties A, B, C are changed. Hoewever this isn't necessary as the method recalculate() can't do anything really useful without all 3 properties set. So what's the best way for property change notification but circumventing this change notification in the constructor? I thought about adding the property changed notification in the constructor, but then each object of the DPChangeSample class would always add more and more change notifications. Thanks for any hint! class DPChangeSample : DependencyObject { public static DependencyProperty AProperty = DependencyProperty.Register("A", typeof(int), typeof(DPChangeSample), new PropertyMetadata(propertyChanged)); public static DependencyProperty BProperty = DependencyProperty.Register("B", typeof(int), typeof(DPChangeSample), new PropertyMetadata(propertyChanged)); public static DependencyProperty CProperty = DependencyProperty.Register("C", typeof(int), typeof(DPChangeSample), new PropertyMetadata(propertyChanged)); private static void propertyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e) { ((DPChangeSample)d).recalculate(); } private void recalculate() { // Using A, B, C do some cpu intensive caluclations } public DPChangeSample(int a, int b, int c) { SetValue(AProperty, a); SetValue(BProperty, b); SetValue(CProperty, c); } }

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  • Attaching methods to prototype from within constructor function

    - by Matthew Taylor
    Here is the textbook standard way of describing a 'class' or constructor function in JavaScript, straight from the Definitive Guide to JavaScript: function Rectangle(w,h) { this.width = w; this.height = h; } Rectangle.prototype.area = function() { return this.width * this.height; }; I don't like the dangling prototype manipulation here, so I was trying to think of a way to encapsulate the function definition for area inside the constructor. I came up with this, which I did not expect to work: function Rectangle(w,h) { this.width = w; this.height = h; this.constructor.prototype.area = function() { return this.width * this.height; }; } I didn't expect this to work because the this reference inside the area function should be pointing to the area function itself, so I wouldn't have access to width and height from this. But it turns out I do! var rect = new Rectangle(2,3); var area = rect.area(); // great scott! it is 6 Some further testing confirmed that the this reference inside the area function actually was a reference to the object under construction, not the area function itself. function Rectangle(w,h) { this.width = w; this.height = h; var me = this; this.constructor.prototype.whatever = function() { if (this === me) { alert ('this is not what you think');} }; } Turns out the alert pops up, and this is exactly the object under construction. So what is going on here? Why is this not the this I expect it to be?

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  • Constructor and Destructors in C++ work?

    - by Jack
    I am using gcc. Please tell me if I am wrong - Lets say I have two classes A & B class A { public: A(){cout<<"A constructor"<<endl;} ~A(){cout<<"A destructor"<<endl;} }; class B:public A { public: B(){cout<<"B constructor"<<endl;} ~B(){cout<<"B destructor"<<endl;} }; 1) The first line in B's constructor should be a call to A's constructor ( I assume compiler automatically inserts it). Also the last line in B's destructor will be a call to A's destructor (compiler does it again). Why was it built this way? 2) When I say A * a = new B(); compiler creates a new B object and checks to see if A is a base class of B and if it is it allows 'a' to point to the newly created object. I guess that is why we don't need any virtual constructors. ( with help from @Tyler McHenry , @Konrad Rudolph) 3) When I write delete a compiler sees that a is an object of type A so it calls A's destructor leading to a problem which is solved by making A's destructor virtual. As user - Little Bobby Tables pointed out to me all destructors have the same name destroy() in memory so we can implement virtual destructors and now the call is made to B's destructor and all is well in C++ land. Please comment.

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  • Calling a constructor from method within the same class

    - by Nathan
    I'm new to java and I'm learning about creating object classes. One of my homework assignment requires that I call the constructor at least once within a method of the same object class. I'm getting an error that says The method DoubleMatrix(double[][]) is undefined for the type DoubleMatrix Here's my constructor: public DoubleMatrix(double[][] tempArray) { // Declaration int flag = 0; int cnt; // Statement // check to see if doubArray isn't null and has more than 0 rows if(tempArray == null || tempArray.length < 0) { flag++; } // check to see if each row has the same length if(flag == 0) { for(cnt = 0; cnt <= tempArray.length - 1 || flag != 1; cnt++) { if(tempArray[cnt + 1].length != tempArray[0].length) { flag++; } } } else if(flag == 1) { makeDoubMatrix(1, 1);// call makeDoubMatrix method } }// end constructor 2 Here's the method where I try and call the constructor: public double[][] addMatrix(double[][] tempDoub) { // Declaration double[][] newMatrix; int rCnt, cCnt; //Statement // checking to see if both are of same dimension if(doubMatrix.length == tempDoub.length && doubMatrix[0].length == tempDoub[0].length) { newMatrix = new double[doubMatrix.length][doubMatrix[0].length]; // for loop to add matrix to a new one for(rCnt = 0; rCnt <= doubMatrix.length; rCnt++) { for(cCnt = 0; cCnt <= doubMatrix.length; cCnt++) { newMatrix[rCnt][cCnt] = doubMatrix[rCnt][cCnt] + tempDoub[rCnt][cCnt]; } } } else { newMatrix = new double[0][0]; DoubleMatrix(newMatrix) } return newMatrix; }// end addMatrix method Can someone point me to the right direction and explain why I'm getting an error?

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  • c# copy constructor generator

    - by Shawn Mclean
    I want to copy values from one object to another object. Something similiar to pass by value but with assignment. Eg. PushPin newValPushPin = oldPushPin; //I want to break the reference here. I was told to write a copy constructor for this. But this class has alot of properties, it will probably take an hour to write a copy constructor by hand. Is there a better way to assign an object to another object by value? If not, is there a copy constructor generator?

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  • Constructor in a Interface?

    - by Sebi
    I know its not possible to define a constructor in a interface. But im wondering why, because i think i could be very useful. So you could be sure that some fields in a class are defined for every implementaiton of this interface. For example consider the following message class: public class MyMessage { public MyMessage(String receiver) { this.receiver = receiver; } private String receiver; public void send() { //some implementation for sending the mssage to the receiver } } If a define a Interface for this class so that i can have more classes which implement the message interface, i can only define the send method and not the constructor. So how can i assure that every implementation of this class really has an receiver setted? If i use a method like setReceiver(String receiver) i can't be sure that this method is really called. In the constructor i could assure it.

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  • FxCop giving a warning on private constructor CA1823 and CA1053

    - by Luis Sánchez
    I have a class that looks like the following: Public Class Utilities Public Shared Function blah(userCode As String) As String 'doing some stuff End Function End Class I'm running FxCop 10 on it and it says: "Because type 'Utilities' contains only 'static' ( 'Shared' in Visual Basic) members, add a default private constructor to prevent the compiler from adding a default public constructor." Ok, you're right Mr. FxCop, I'll add a private constructor: Private Utilities() Now I'm having: "It appears that field 'Utilities.Utilities' is never used or is only ever assigned to. Use this field or remove it." Any ideas of what should I do to get rid of both warnings?

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  • C# Constructor & List Question

    - by ShonnaE
    Ohk, I am doing a c-sharp program, and I get everything but this, I just can't understand what it is asking. I know how to create a list.. and how to create a constructor.. but this is where i get confused.. its probably way simple but i am missing it. I created 2 lists .. now i should create a constructor here is one my lists List<Person> organize = new List<Person>(); THIS PART --- *The constructor should also initialize the two event lists to new empty lists. *

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  • javascript constructor reset: What is it ?

    - by Sake
    I came across this slide: http://www.slideshare.net/stoyan/javascript-patterns#postComment at page 35: Option 5 + super + constructor reset function inherit(C, P) { var F = function(){}; F.prototype = P.prototype; C.prototype = new F(); C.uber = P.prototype; C.prototype.constructor = C; // WHY ??? } I don't get it. Can anybody please explain what the last line for ? C.prototype.constructor = C; // WHY ??? Thanks

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  • How to initialise a STL vector/list with a class without invoking the copy constructor

    - by Warpspace
    I have a C++ program that uses a std::list containing instances of a class. If I call e.g. myList.push_back(MyClass(variable)); it goes through the process of creating a temporary variable, and then immediately copies it to the vector, and afterwards deletes the temporary variable. This is not nearly as efficient as I want, and sucks when you need a deep copy. I would love to have the constructor of my class new something and not have to implement a copy constructor just to allocate my memory for the second time and waste runtime. I'd also rather not have to immediately find the class instance from the vector/list and then manually allocate the memory (or do something horrible like allocate the memory in the copy constructor itself). Is there any way around this (I'm not using Visual Studio BTW)?

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  • Exceptions in constructors

    - by FredOverflow
    In C++, the lifetime of an object begins when the constructor finishes successfully. Inside the constructor, the object does not exist yet. Q: What does emitting an exception from a constructor mean? A: It means that construction has failed, the object never existed, its lifetime never began. [source] My question is: Does the same hold true for Java? What happens, for example, if I hand this to another object, and then my constructor fails? Foo() { Bar.remember(this); throw new IllegalStateException(); } Is this well-defined? Does Bar now have a reference to a non-object?

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  • How to inherit constructors with arguments in .NET?

    - by Soumya92
    I have a "MustInherit" .NET class which declares a constructor with an integer parameter. However, Visual Studio gives me an error when I create any derived class stating that there is no constructor that can be called without any arguments. Is it possible to inherit the constructor with arguments? Right now, I have to use Public Sub New(ByVal A As Integer) MyBase.New(A) End Sub in the derived classes. Is there any way to avoid this?

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  • Do you put a super() call a the beginning of your constructors?

    - by sleske
    This is a question about coding style and recommended practices: As explained in the answers to the question unnecessary to put super() in constructor?, if you write a constructor for a class that is supposed to use the default (no-arg) constructor from the superclass, you may call super() at the beginning of your constructor: public MyClass(int parm){ super(); // leaving this out makes no difference // do stuff... } but you can also omit the call; the compiler will in both cases act as if the super() call were there. So then, do you put the call into your constructors or not? On the one hand, one might argue that including the super() makes things more explicit. OTOH, I always dislike writing redundant code, so personally I tend to leave it out; I do however regularly see it in code from others. What are your experiences? Did you have problems with one or the other approach? Do you have coding guidelines which prescribe one approach?

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  • Multiple constructors definitions with same name but different signatures (C++)

    - by PuRe_ChAoS12
    With the following code, I keep getting error C2535 when I compile. It's complaining that a member function already defined or declared. Rationnel.h ... class Rationnel { public: Rationnel(int); //Constructor Rationnel(int,int); //Constructor void add(const Rationnel); ... Rationnel.cpp ... //Constructor Rationnel::Rationnel(int n = 1) { numerateur = n; denominateur = 1; } //Constructor Rationnel::Rationnel(int n = 1, int d = 1) { numerateur = n; denominateur = d; } ... Any idea what could be causing the error? Thanks for your time.

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  • my asp.net mvc 2.0 application fails with error "No parameterless constructor defined for this objec

    - by loviji
    Hello, i'm new in asp.net mvc 2. I'm trying to list all data from one table(ms sql server table). as ORM I use Entity Framework. now, I'm tried to write something to do this: Model: private uqsEntities _uqsEntity; public permissionRepository(uqsEntities uqsEntity) { _uqsEntity = uqsEntity; } public IEnumerable<userPermissions> getAllData() { return _uqsEntity.userPermissions; } controller: private DataManager _dataManager; public ManagePermissionsController(DataManager datamanager) { _dataManager = datamanager; } public ActionResult Index() { return RedirectToAction("List"); } [AcceptVerbs(HttpVerbs.Get)] public ActionResult List() { return List(null); } [AcceptVerbs(HttpVerbs.Post)] public ActionResult List(int? userID) { return View(_dataManager.Permission.getAllData().ToList()); } Route: routes.MapRoute( "ManagePerm", // Route name "{controller}/{action}/{id}", // URL with parameters new { controller = "ManagePermissions", action = "Index"}, new string[] { "uqs.Controllers" } // Parameter defaults ); and View automatically generated by Visual Studio(in action mouse right-click). when I run app. , my app. fails. No parameterless constructor defined for this object. Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code. Exception Details: System.MissingMethodException: No parameterless constructor defined for this object. Source Error: An unhandled exception was generated during the execution of the current web request. Information regarding the origin and location of the exception can be identified using the exception stack trace below. Stack Trace: [MissingMethodException: No parameterless constructor defined for this object.] System.RuntimeTypeHandle.CreateInstance(RuntimeType type, Boolean publicOnly, Boolean noCheck, Boolean& canBeCached, RuntimeMethodHandle& ctor, Boolean& bNeedSecurityCheck) +0 System.RuntimeType.CreateInstanceSlow(Boolean publicOnly, Boolean fillCache) +86 System.RuntimeType.CreateInstanceImpl(Boolean publicOnly, Boolean skipVisibilityChecks, Boolean fillCache) +230 System.Activator.CreateInstance(Type type, Boolean nonPublic) +67 System.Web.Mvc.DefaultControllerFactory.GetControllerInstance(RequestContext requestContext, Type controllerType) +80 [InvalidOperationException: An error occurred when trying to create a controller of type 'uqs.Controllers.ManagePermissionsController'. Make sure that the controller has a parameterless public constructor.] System.Web.Mvc.DefaultControllerFactory.GetControllerInstance(RequestContext requestContext, Type controllerType) +190 System.Web.Mvc.DefaultControllerFactory.CreateController(RequestContext requestContext, String controllerName) +68 System.Web.Mvc.MvcHandler.ProcessRequestInit(HttpContextBase httpContext, IController& controller, IControllerFactory& factory) +118 System.Web.Mvc.MvcHandler.BeginProcessRequest(HttpContextBase httpContext, AsyncCallback callback, Object state) +46 System.Web.Mvc.MvcHandler.BeginProcessRequest(HttpContext httpContext, AsyncCallback callback, Object state) +63 System.Web.Mvc.MvcHandler.System.Web.IHttpAsyncHandler.BeginProcessRequest(HttpContext context, AsyncCallback cb, Object extraData) +13 System.Web.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +8679186 System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +155 please, somebody, help me to catch problem.

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  • Wpf usercontrol with parameterised constructor

    - by Miral
    Hi, We are using Microsoft Unity and we are using dependency injection and so we have parametrised constructor. So now how to call such a usercontrol in the main window. I see the below error when i added the usercontrol in xaml. "It does not define a public parameterless constructor or a type converter" I have added the usercontrol in XAML as below xmlns:usrRefundArrivalProcessor="Ttl.Refunds.Wpf.Dashboad.Application.Usercontrols;assembly=Ttl.Refunds.Wpf.Dashboad.Application"

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  • Java: why does extending need an empty constructor?

    - by HH
    I have classes SearchToUser and getFilesToWord. GetFilesToWord must inherit SearchToUser fields. Extending works if an empty construction in SearchToUser-class, otherwise: cannot find symbol symbol : constructor SearchToUser() location: class SearchToUser public class GetFilesToWord extends SearchToUser{ ^ 1 error make: *** [all] Error 1 I cannot understand why the empty constructor is required for extending.

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  • Define Default constructor Structuremap in a Generic Repository

    - by Ricky
    Hello guys, I have a generic IRepository that has 2 constructors, one have none parameters, other has the datacontext as parameter. I want to define to structuremap to aways in this case use the parameterless constructor. I want a way to create a parameterless contructor, other solutions that I have seen, they create a new Datacontext and pass it to the constructor that has parameters.

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  • Virtual member call in a constructor when assigning value to property

    - by comecme
    I have an Abstract class and a Derived class. The abstract class defines an abstract property named Message. In the derived class, the property is implemented by overriding the abstract property. The constructor of the derived class takes a string argument and assigns it to its Message property. In Resharper, this assignment leads to a warning "Virtual member call in constructor". The AbstractClass has this definition: public abstract class AbstractClass { public abstract string Message { get; set; } protected AbstractClass() { } public abstract void PrintMessage(); } And the DerivedClass is as follows: using System; public class DerivedClass : AbstractClass { private string _message; public override string Message { get { return _message; } set { _message = value; } } public DerivedClass(string message) { Message = message; // Warning: Virtual member call in a constructor } public DerivedClass() : this("Default DerivedClass message") {} public override void PrintMessage() { Console.WriteLine("DerivedClass PrintMessage(): " + Message); } } I did find some other questions about this warning, but in those situations there is an actual call to a method. For instance, in this question, the answer by Matt Howels contains some sample code. I'll repeat it here for easy reference. class Parent { public Parent() { DoSomething(); } protected virtual void DoSomething() {}; } class Child : Parent { private string foo; public Child() { foo = "HELLO"; } protected override void DoSomething() { Console.WriteLine(foo.ToLower()); } } Matt doesn't describe on what error the warning would appear, but I'm assuming it will be on the call to DoSomething in the Parent constructor. In this example, I understand what is meant by a virtual member being called. The member call occurs in the base class, in which only a virtual method exists. In my situation however, I don't see why assigning a value to Message would be calling a virtual member. Both the call to and the implementation of the Message property are defined in the derived class. Although I can get rid of the error by making my Derived Class sealed, I would like to understand why this situation is resulting in the warning.

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  • IoC.Resolve vs Constructor Injection

    - by Omu
    I heard a lot of people saying that it is a bad practice to use IoC.Resolve(), but I never heard a good reason why (if it's all about testing than you can just mock the container, and you're done). now the advantages of using Resolve instead of Constructor Injection is that you don't need to create classes that have 5 parameters in the constructor, and whenever you are going to create a instance of that class you're not gonna need to provide it with anything

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