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  • Abstract class reference

    - by AlgoMan
    Can i have a class Class Room{ ~Room(); virtual cost() =0; } Class Hotel{ map rooms; /* */ }; will my hotel become abstract ? Can it hold the list of concrete Room objects that are derived from Room ?

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  • C# Drag and Drop - e.Data.GetData using a base class

    - by Dustin Brooks
    C# Winforms 3.5 I have a list of user controls all derived from one base class. These controls can be added to various panels and I'm trying to implement the drag-drop functionality, the problem I'm running in to is on the DragDrop event. The DragEventArgs: e.Data.GetData(typeof(baseClass)) doesn't work. It wants: e.Data.GetData(typeof(derivedClass1)) e.Data.GetData(typeof(derivedClass2)) etc... Is there a way I can get around this, or a better way to architect it?

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  • Style guide for database metadata naming

    - by Nulldevice
    We want to establish some database metadata naming rules in our new project. For example: tables are named as nouns in a plural form (courses, books, lessons) if present, an adjective goes before a noun in a table name and is separated by an underscore (red_books, new_lessons) table index column is always named "id" foreign key names are derived from a table name with suffix _id (book_id, red_book_id) so on Does someone know any guide like this?

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  • Crazy interview question

    - by benjamin button
    I was asked this crazy question. I was out of my wits. Can a method in base class which is declared as virtual be called using the base class pointer which is pointing to a derived class object? Is this possible?

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  • Is this not downcasting?

    - by cambr
    If I do double d = 34.56; int i = (int)d; Am I not "downcasting"? OR Is this term only used in terms of classes and objects? I am confused because in this case we are "downcasting" from a bigger double to a smaller int, but in case of classes, we "downcast" from a smaller base class to a bigger derived class. Aren't these two conventions, in some sense, opposite?

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  • What means slicing in C++?

    - by George2
    Hello everyone, It is mentioned in C++ FAQ site -- "larger derived class objects get sliced when passed by value as a base class object", what does slicing mean? Any sample to demonstrate? http://www.parashift.com/c++-faq-lite/value-vs-ref-semantics.html#faq-31.8 I am using VSTS 2008 + native C++ as my development environment. thanks in advance, George

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  • How can we set authorization for a whole area in ASP.NET MVC?

    - by CodingTales
    I've an Admin area and I want only Admins to enter the area. I considered adding the Authorized attribute to every controller in the Admin area. Isn't there an elegant solution or is this feature not there in the framework itself? EDIT: I'm sorry, I should to have mentioned this before. I'm using a custom AuthorizedAttribute derived from AuthorizeAttribute.

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  • What does slicing mean in C++?

    - by George2
    Hello everyone, It is mentioned in C++ FAQ site -- "larger derived class objects get sliced when passed by value as a base class object", what does slicing mean? Any sample to demonstrate? http://www.parashift.com/c++-faq-lite/value-vs-ref-semantics.html#faq-31.8 I am using VSTS 2008 + native C++ as my development environment. thanks in advance, George

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  • Servlet Exception + Class Cast Exception + Glassfish + Netbeans + JPA Entities + Vaadin

    - by Random Joe
    Hi all, I get this error: StandardWrapperValve[Vaadin Servlet]: PWC1406: Servlet.service() for servlet Vaadin Servlet threw exception java.lang.ClassCastException: com.delhi.entities.Category cannot be cast to com.delhi.entities.Category when I try to run my webapps on glassfish v2. Category is a JPA entity object the offending code according to the server log is: for (Category c : categories) { mymethod(); } categories is derived from: List<Category> categories = q.getResultList(); Any idea what went wrong?

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  • C++ type-checking at compile-time

    - by Masterofpsi
    Hi, all. I'm pretty new to C++, and I'm writing a small library (mostly for my own projects) in C++. In the process of designing a type hierarchy, I've run into the problem of defining the assignment operator. I've taken the basic approach that was eventually reached in this article, which is that for every class MyClass in a hierarchy derived from a class Base you define two assignment operators like so: class MyClass: public Base { public: MyClass& operator =(MyClass const& rhs); virtual MyClass& operator =(Base const& rhs); }; // automatically gets defined, so we make it call the virtual function below MyClass& MyClass::operator =(MyClass const& rhs); { return (*this = static_cast<Base const&>(rhs)); } MyClass& MyClass::operator =(Base const& rhs); { assert(typeid(rhs) == typeid(*this)); // assigning to different types is a logical error MyClass const& casted_rhs = dynamic_cast<MyClass const&>(rhs); try { // allocate new variables Base::operator =(rhs); } catch(...) { // delete the allocated variables throw; } // assign to member variables } The part I'm concerned with is the assertion for type equality. Since I'm writing a library, where assertions will presumably be compiled out of the final result, this has led me to go with a scheme that looks more like this: class MyClass: public Base { public: operator =(MyClass const& rhs); // etc virtual inline MyClass& operator =(Base const& rhs) { assert(typeid(rhs) == typeid(*this)); return this->set(static_cast<Base const&>(rhs)); } private: MyClass& set(Base const& rhs); // same basic thing }; But I've been wondering if I could check the types at compile-time. I looked into Boost.TypeTraits, and I came close by doing BOOST_MPL_ASSERT((boost::is_same<BOOST_TYPEOF(*this), BOOST_TYPEOF(rhs)>));, but since rhs is declared as a reference to the parent class and not the derived class, it choked. Now that I think about it, my reasoning seems silly -- I was hoping that since the function was inline, it would be able to check the actual parameters themselves, but of course the preprocessor always gets run before the compiler. But I was wondering if anyone knew of any other way I could enforce this kind of check at compile-time.

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  • Printing contents of a div

    - by Hulk
    The contents of the following div re derived dynamically. i.e, A table is added dynamically to this div with some button .My question is how to print the content of this div(window.print) and not other things in the page <div id="newdiv" name="newdiv"></div> Thanks..............

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  • Interface in a dynamic language?

    - by Bryan
    Interface (or an abstract class with all the methods abstract) is a powerful weapon in a static language. It allows different derived types to be used in a uniformed way. However, in a dynamic language, all objects can be used in a uniformed way as long as they define certain methods. Does interface exist in dynamic languages? It seems unnecessary to me.

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  • Adding NavigationControl to a TabBar Application containing UITableViews

    - by kungfuslippers
    Hi, I'm new to iPhone dev and wanted to get advice on the general design pattern / guide for putting a certain kind of app together. I'm trying to build a TabBar type application. One of the tabs needs to display a TableView and selecting a cell from within the table view will do something else - maybe show another table view or a web page. I need a Navigation Bar to be able to take me back from the table view/web page. The approach I've taken so far is to: Create an app based around UITabBarController as the rootcontroller i.e. @interface MyAppDelegate : NSObject <UIApplicationDelegate> { IBOutlet UIWindow *window; IBOutlet UITabBarController *rootController; } Create a load of UIViewController derived classes and associated NIBs and wire everything up in IB so when I run the app I get the basic tabs working. I then take the UIViewController derived class and modify it to the following: @interface MyViewController : UIViewController<UITableViewDataSource, UITableViewDelegate> { } and I add the delegate methods to the implementation of MyViewController - (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section { return 2; } - (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath { static NSString *CellIdentifier = @"Cell"; UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier]; if (cell == nil) { cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:CellIdentifier] autorelease]; } if (indexPath.row == 0) { cell.textLabel.text = @"Mummy"; } else { cell.textLabel.text = @"Daddy"; } return cell; } Go back to IB , open MyViewController.xib and drop a UITableView onto it. Set the Files Owner to be MyViewController and then set the delegate and datasource of the UITableView to be MyViewController. If I run the app now, I get the table view appearing with mummy and daddy working nicely. So far so good. The question is how do I go about incorporating a Navigation Bar into my current code for when I implement: - (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath() { // get row selected NSUInteger row = [indexPath row]; if (row == 0) { // Show another table } else if (row == 1) { // Show a web view } } Do I drop a NavigationBar UI control onto MyControllerView.xib ? Should I create it programmatically? Should I be using a UINavigationController somewhere ? I've tried dropping a NavigationBar onto my MyControllerView.xib in IB but its not shown when I run the app, only the TableView is displayed.

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  • Getting all the fields and properties of a custom attribute from a specific instance

    - by Gbps
    I have a custom attribute PackerAttrib which takes no data, simply marking a field or property, which will be used to mark a property or field of a class inherited from Panel in order to serialize it later on. How would I take an instance of any object derived from Panel and get a Directory<string s, object o> where s is the name of the field or property and o is the current value of said field or property from the instance. Thank you, don't be afraid to ask me to clarify!

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  • How do I get tooltips to work in MFC for menus?

    - by frungash
    I have a dlg box as the main window. After a few searches on the we I tried downloading and running the sample the source here: http://msdn.microsoft.com/en-us/magazine/cc164067.aspx I get a compile error: error C2440: 'static_cast' : cannot convert from 'UINT (__thiscall CStaticLink::* )(CPoint)' to 'LRESULT (__thiscall CWnd::* )(CPoint)' 1 Cast from base to derived requires dynamic_cast or static_cast (VS 2008) The tooltips functionality seems to be a bit of a challenge. Any suggestions on how to get this working are much appreciated.

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  • Base class pointer vs inherited class pointer?

    - by Goose Bumper
    Suppose I have a class Dog that inherits from a class Animal. What is the difference between these two lines of code? Animal *a = new Dog(); Dog *d = new Dog(); In one, the pointer is for the base class, and in the other, the pointer is for the derived class. But when would this distinction become important? For polymorphism, either one would work exactly the same, right?

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  • How can I specify resources in an MVVM view model?

    - by gix
    Suppose I want to show list of objects where each object should have a name and a suitable image (for example MenuItems with Icons, or buttons with text and image). All examples and programs exposed the image in the viewmodel as a path to a PNG file and then bound the Source of an Image to that. But what if I want to use vector images (for example as a DrawingImage in a local ResourceDictionary)? Exposing the DrawingImage from the view model seems bad because I would have to store a reference to the application/window/user control/... (and it is advised to not expose such XAML objects from view models). So a better approach would be to use a string identifier in the view model and then somehow select the appropriate resource. If that identifier is the resource key this snippet looks tempting but does not work: <Image Source="{StaticResource {Binding Icon}}"/> I found two workarounds for that though they did not work for me. The first one was using a normal binding to the icon with a converter that looked up the resource in Application.Current. This does not work if the resource is stored somewhere else I think (and the situation where I initially bumped into this problem had no Application running yet since it was a Window choosing the Application to launch!). The second workaround was using a markup extension derived from StaticResourceExtension that fetched its ResourceKey from the passed binding: <Image Source="{local:BindableStaticResource {Binding Icon}"/> This one looks really neat because it could use local resources, also be used for other things. But when using it I always got an exception ("Resource named {FooIcon} could not be found.", showing the correct XAML file and position of the extension). Even an empty resource extension derived from StaticResourceExtension that just passed the resource key to the base constructor did not work and I cannot explain why. Just using StaticResourceExtension worked just fine. Any ideas how I could fix the second approach, or even better solutions? Edit I noticed that it does work when used directly like this: <Window> <Window.Resources> <DrawingImage x:Key="SomeIcon"/> </Window.Resources> <Image Source="{BindableStaticResource {Binding Icon}}"/> </Window> but fails for example in a DataTemplate. Though a normal StaticResourceExtension works on both occasions so I am puzzled what is going wrong.

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  • SerialVersionUID with "private static final long" still gets InvalidClassException

    - by Buggieboy
    I have compiled and jarred the various projects in my Java application, generating serialVersionUIDs automatically through Eclipse for all my classes derived from Serializable. I read the answers to this question, and verified that serialVersionUids are all private static final long. Nevertheless, I get an error like this when I try to run: java.io.InvalidClassException: com.acme.product.Widget; local class incompatible: stream classdesc serialVersionUID = 5226096973188250357, local class serialVersionUID = -5432967318654384362 What am I missing?

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  • What do you choose, protected or internal?

    - by brickner
    If I have a class with a method I want protected and internal. I want that only derived classes in the assembly would be able to call it. Since protected internal means protected or internal, you have to make a choice. What do you choose in this case - protected or internal?

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  • How expose the properties of an component created in an activex form

    - by Salvador
    You can publish the properties of an control that is inside a activex form? example I have a form with an TAdoconnection component, I wish the properties of this component can be modified by the user when he loads my activex control. UPDATE @TOndrej gives me a very nice sample, but this sample only works for components derived from an activex control, how can accomplish this same efffect with an VCL component like an Timage or TMemo? is possible publish all the properties without rewrite each property to expose manually?

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  • Using boost::iterator

    - by Neil G
    I wrote a sparse vector class (see #1, #2.) I would like to provide two kinds of iterators: The first set, the regular iterators, can point any element, whether set or unset. If they are read from, they return either the set value or value_type(), if they are written to, they create the element and return the lvalue reference. Thus, they are: Random Access Traversal Iterator and Readable and Writable Iterator The second set, the sparse iterators, iterate over only the set elements. Since they don't need to lazily create elements that are written to, they are: Random Access Traversal Iterator and Readable and Writable and Lvalue Iterator I also need const versions of both, which are not writable. I can fill in the blanks, but not sure how to use boost::iterator_adaptor to start out. Here's what I have so far: template<typename T> class sparse_vector { public: typedef size_t size_type; typedef T value_type; private: typedef T& true_reference; typedef const T* const_pointer; typedef sparse_vector<T> self_type; struct ElementType { ElementType(size_type i, T const& t): index(i), value(t) {} ElementType(size_type i, T&& t): index(i), value(t) {} ElementType(size_type i): index(i) {} ElementType(ElementType const&) = default; size_type index; value_type value; }; typedef vector<ElementType> array_type; public: typedef T* pointer; typedef T& reference; typedef const T& const_reference; private: size_type size_; mutable typename array_type::size_type sorted_filled_; mutable array_type data_; // lots of code for various algorithms... public: class sparse_iterator : public boost::iterator_adaptor< sparse_iterator // Derived , array_type::iterator // Base (the internal array) (this paramater does not compile! -- says expected a type, got 'std::vector::iterator'???) , boost::use_default // Value , boost::random_access_traversal_tag? // CategoryOrTraversal > class iterator_proxy { ??? }; class iterator : public boost::iterator_facade< iterator // Derived , ????? // Base , ????? // Value , boost::?????? // CategoryOrTraversal > { }; };

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