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  • Why am I getting this error when overriding an inherited method?

    - by Sergio Tapia
    Here's my parent class: public abstract class BaseFile { public string Name { get; set; } public string FileType { get; set; } public long Size { get; set; } public DateTime CreationDate { get; set; } public DateTime ModificationDate { get; set; } public abstract void GetFileInformation(); public abstract void GetThumbnail(); } And here's the class that's inheriting it: public class Picture:BaseFile { public override void GetFileInformation(string filePath) { FileInfo fileInformation = new FileInfo(filePath); if (fileInformation.Exists) { Name = fileInformation.Name; FileType = fileInformation.Extension; Size = fileInformation.Length; CreationDate = fileInformation.CreationTime; ModificationDate = fileInformation.LastWriteTime; } } public override void GetThumbnail() { } } I thought when a method was overridden, I could do what I wanted with it. Any help please? :)

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  • Forget late static binding, I need late static __FILE__ ...

    - by bobthecow
    I'm looking for the get_called_class() equivalent for __FILE__ ... Maybe something like get_included_file()? I have a set of classes which would like to know what directory they exist in. Something like this: <?php class A { protected $baseDir; public function __construct() { $this->baseDir = dirname(__FILE__); } public function getBaseDir() { return $this->baseDir; } } ?> And in some other file, in some other folder... <?php class B extends A { // ... } class C extends B { // ... } $a = new A; echo $a->getBaseDir(); $b = new B; echo $b->getBaseDir(); $c = new C; echo $c->getBaseDir(); // Annnd... all three return the same base directory. ?> Now, I could do something ghetto, like adding $this->baseDir = dirname(__FILE__) to each and every extending class, but that seems a bit... ghetto. After all, we're talking about PHP 5.3, right? Isn't this supposed to be the future? Is there another way to get the path to the file where a class was declared?

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  • Cannot inherit from generic base class and specific interface using same type with generic constrain

    - by simendsjo
    Sorry about the strange title. I really have no idea how to express it any better... I get an error on the following snippet. I use the class Dummy everywhere. Doesn't the compiler understand the constraint I've added on DummyImplBase? Is this a compiler bug as it works if I use Dummy directly instead of setting it as a constraint? Error 1 'ConsoleApplication53.DummyImplBase' does not implement interface member 'ConsoleApplication53.IRequired.RequiredMethod()'. 'ConsoleApplication53.RequiredBase.RequiredMethod()' cannot implement 'ConsoleApplication53.IRequired.RequiredMethod()' because it does not have the matching return type of 'ConsoleApplication53.Dummy'. C:\Documents and Settings\simen\My Documents\Visual Studio 2008\Projects\ConsoleApplication53\ConsoleApplication53\Program.cs 37 27 ConsoleApplication53 public class Dummy { } public interface IRequired<T> { T RequiredMethod(); } public interface IDummyRequired : IRequired<Dummy> { void OtherMethod(); } public class RequiredBase<T> : IRequired<T> { public T RequiredMethod() { return default(T); } } public abstract class DummyImplBase<T> : RequiredBase<T>, IDummyRequired where T: Dummy { public void OtherMethod() { } }

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  • Using child visitor in C#

    - by Thomas Matthews
    I am setting up a testing component and trying to keep it generic. I want to use a generic Visitor class, but not sure about using descendant classes. Example: public interface Interface_Test_Case { void execute(); void accept(Interface_Test_Visitor v); } public interface Interface_Test_Visitor { void visit(Interface_Test_Case tc); } public interface Interface_Read_Test_Case : Interface_Test_Case { uint read_value(); } public class USB_Read_Test : Interface_Read_Test_Case { void execute() { Console.WriteLine("Executing USB Read Test Case."); } void accept(Interface_Test_Visitor v) { Console.WriteLine("Accepting visitor."); } uint read_value() { Console.WriteLine("Reading value from USB"); return 0; } } public class USB_Read_Visitor : Interface_Test_Visitor { void visit(Interface_Test_Case tc) { Console.WriteLine("Not supported Test Case."); } void visit(Interface_Read_Test_Case rtc) { Console.WriteLine("Not supported Read Test Case."); } void visit(USB_Read_Test urt) { Console.WriteLine("Yay, visiting USB Read Test case."); } } // Code fragment USB_Read_Test test_case; USB_Read_Visitor visitor; test_case.accept(visitor); What are the rules the C# compiler uses to determine which of the methods in USB_Read_Visitor will be executed by the code fragment? I'm trying to factor out dependencies of my testing component. Unfortunately, my current Visitor class contains visit methods for classes not related to the testing component. Am I trying to achieve the impossible?

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  • Rails 3 Abstract Class vs Inherited Class

    - by R. Yanchuleff
    In my rails 3 model, I have two classes: Product, Service. I want both to be of type InventoryItem because I have another model called Store and Store has_many :InventoryItems This is what I'm trying to get to, but I'm not sure how to model this in my InventoryItem model and my Product and Service models. Should InventoryItem just be a parent class that Product and Service inherit from, or should InventoryItem be modeled as a class abstract of which Product and Service extend from. Thanks in advance for the advice!

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  • Apples, oranges, and pointers to the most derived c++ class

    - by Matthew Lowe
    Suppose I have a bunch of fruit: class Fruit { ... }; class Apple : public Fruit { ... }; class Orange: public Fruit { ... }; And some polymorphic functions that operate on said fruit: void Eat(Fruit* f, Pesticide* p) { } void Eat(Apple* f, Pesticide* p) { ingest(f,p); } void Eat(Orange* f, Pesticide* p) { peel(f,p); ingest(f,p); } OK, wait. Stop right there. Note at this point that any sane person would make Eat() a virtual member function of the Fruit classes. But that's not an option, because I am not a sane person. Also, I don't want that Pesticide* in the header file for my fruit class. Sadly, what I want to be able to do next is exactly what member functions and dynamic binding allow: typedef list<Fruit*> Fruits; Fruits fs; ... for(Fruits::iterator i=fs.begin(), e=fs.end(); i!=e; ++i) Eat(*i); And obviously, the problem here is that the pointer we pass to Eat() will be a Fruit*, not an Apple* or an Orange*, therefore nothing will get eaten and we will all be very hungry. So what I really want to be able to do instead of this: Eat(*i); is this: Eat(MAGIC_CAST_TO_MOST_DERIVED_CLASS(*i)); But to my limited knowledge, such magic does not exist, except possibly in the form of a big nasty if-statement full of calls to dynamic_cast. So is there some run-time magic of which I am not aware? Or should I implement and maintain a big nasty if-statement full of dynamic_casts? Or should I suck it up, quit thinking about how I would implement this in Ruby, and allow a little Pesticide to make its way into my fruit header?

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  • Session is null when inherit from System.Web.UI.Page

    - by Andreas K.
    I want to extend the System.Web.UI.Page-class with some extra stuff. In the ctor I need the value of a session-variable. The problem is that the Session-object is null... public class ExtendedPage : System.Web.UI.Page { protected foo; public ExtendedPage() { this.foo = (int)HttpContext.Current.Session["foo"]; // NullReferenceException } } If I move the part with the session-object into the Load-Event everything works fine... public class ExtendedPage : System.Web.UI.Page { protected foo; public ExtendedPage() { this.Load += new EventHandler(ExtendedPage_Load); } void ExtendedPage_Load(object sender, EventArgs e) { this.foo = (int)HttpContext.Current.Session["foo"]; } } Why is the Session-object null in the first case??

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  • asp.net Can I force every page to inherit from a base page? Also should some of this logic be in my master page?

    - by Bex
    Hi! I have a web app that has a base page. Each page needs to inherit from this base page as it contains properties they all need as well as dealing with the login rights. My base page has some properties, eg: IsRole1, IsRole2, currentUserID, Role1Allowed, Role2Allowed. On the init of each page I set the properties "Role1Allowed" and "Role2Allowed" Private Sub Page_Init(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Init Role1Allowed = True Role2Allowed= False End Sub The basepage then decides if the user needs redirecting. 'Sample code so not exactly what is going to be, bug gives the idea Protected Overridable Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) If Role1Allowed And Not Role1 Then 'Redirect somewhere End If End Sub The page then must override this pageload if they need anything else in it, but making sure they call the base pageload first. Protected Overrides Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load MyBase.Page_Load(sender, e) If Not IsPostBack Then BindGrid() End If End Sub The other properties (IsRole1, IsRole, currentUserID) are also accessible by the page so it can be decided if certain things need doing based on the user. (I hope this makes sense) Ok so I have 2 questions Should this functionality be in the base page or should it somehow be in the master, and if so how would I get access to all the properties if it was? As there are multiple people working on this project and creating pages some are forgetting to inherit from this basepage, or call the base pageload when overriding it. Is there any way to force them to do this? Thanks for any help. bex

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  • Java method: retrieve the inheriting type

    - by DrDro
    I have several classes that extend C and I would need a method that accepts any argument of type C. But in this method I would like to know if I'm dealing with A or B. * public A extends C public B extends C public void goForIt(C c)() If I cast how can I retrieve the type in a clean way (I just read using getClass or instanceof is often not the best way). *Sorry but I can't type closing braces

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  • Execute a function to affect different template class instances

    - by Samer Afach
    I have a complicated problem, and I need help. I have a base case, class ParamBase { string paramValue; //... } and a bunch of class templates with different template parameters. template <typename T> class Param : public ParamBase { T value; //... } Now, each instance of Param has different template parameter, double, int, string... etc. To make it easier, I have a vector to their base class pointers that contains all the instances that have been created: vector<ParamBase*> allParamsObjects; The question is: How can I run a single function (global or member or anything, your choice), that converts all of those different instances' strings paramValue with different templates arguments and save the conversion result to the appropriate type in Param::value. This has to be run over all objects that are saved in the vector allParamsObjects. So if the template argument of the first Param is double, paramValue has to be converted to double and saved in value; and if the second Param's argument is int, then the paramValue of the second has to be converted to int and saved in value... etc. I feel it's almost impossible... Any help would be highly appreciated :-)

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  • Generic calls to OnResetDevice() and OnLostDevice()

    - by bobobobo
    This is kind of a COM question to do with DirectX. So, both ID3DXSprite and ID3DXFont and a bunch of the other ID3DX* objects require you to call OnLostDevice() when the d3d device is lost AND OnResetDevice() when the device is reset. What I want to do is maintain an array of all ID3DX* objects and simply call OnResetDevice() and OnLostDevice() on each whenever the device is lost or reset. However I can't seem to find a BASE CLASS for the ID3DX* classes... they all seem to COM-ually inherit from IUnknown. Is there a way to do this or do I have to maintain separate arrays of ID3DXFont* pointers, ID3DXSprite* pointers, etc?

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  • Python:How to override inner class methods if the inner class is defined as a property of the top cl

    - by Maddy
    I have a code snippet like this class A(object): class b: def print_hello(self): print "Hello world" b = property(b) And I want to override the inner class 'b'(please dont worry about the lowercase name) behaviour. Say, I want to add a new method or I want to change an existing method, like: class C(A): class b(A.b): def print_hello(self): print "Inner Class: Hello world" b = property(b) Now if I create C's object as c = C(), and call c.b I get TypeError: 'property' object is not callable error. How would I get pass this and call print_hello of the extended inner class? Disclaimer: I dont want to change the code for A class.

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  • XSD: xs:sequence & xs:choice combination for xs:extension elements of a common base type?

    - by bguiz
    Hi, My question is about defining an XML schema that will validate the following XML: <rules> <other>...</other> <bool>...</bool> <other>...</other> <string>...</string> <other>...</other> </rules> The order of the child nodes does not matter. The cardinality of the child nodes is 0..unbounded. All the child elements of the rules node have a common base type, rule, like so: <xs:complexType name="booleanRule"> <xs:complexContent> <xs:extension base="rule"> ... </xs:extension> </xs:complexContent> </xs:complexType> <xs:complexType name="stringFilterRule"> <xs:complexContent> <xs:extension base="filterRule"> ... </xs:extension> </xs:complexContent> </xs:complexType> My current (feeble) attempt at defining the schema for the rules node is below. However, Can I nest xs:choice within xs:sequence? If, where do I specify the maxOccurs="unbounded" attribute? Is there a better way to do this, such as an xs:sequence which specifies only the base type of its child elements? <xs:element name="rules"> <xs:complexType> <xs:sequence> <xs:choice> <xs:element name="bool" type="booleanRule" /> <xs:element name="string" type="stringRule" /> <xs:element name="other" type="someOtherRule" /> </xs:choice> </xs:sequence> </xs:complexType> </xs:element>

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  • Problem overridding virtual function

    - by William
    Okay, I'm writing a game that has a vector of a pairent class (enemy) that s going to be filled with children classes (goomba, koopa, boss1) and I need to make it so when I call update it calls the childclasses respective update. I have managed to create a example of my problem. #include <stdio.h> class A{ public: virtual void print(){printf("Hello from A");} }; class B : public A{ public: void print(){printf("Hello from B");} }; int main(){ A ab = B(); ab.print(); while(true){} } Output wanted: "Hello from B" Output got: "Hello from A" How do I get it to call B's print function?

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  • Constructor Overload Problem in C++ Inherrentance

    - by metdos
    Here my code snippet: class Request { public: Request(void); ……….. } Request::Request(void) { qDebug()<<"Request: "<<"Hello World"; } class LoginRequest :public Request { public: LoginRequest(void); LoginRequest(QDomDocument); …………… } LoginRequest::LoginRequest(void) { qDebug()<<"LoginRequest: "<<"Hello World"; requestType=LOGIN; requestId=-1; } LoginRequest::LoginRequest(QDomDocument doc){ qDebug()<<"LoginRequest: "<<"Hello World with QDomDocument"; LoginRequest::LoginRequest(); xmlDoc_=doc; } When call constructor of Overrided LoginRequest LoginRequest *test=new LoginRequest(doc); I came up with this result: Request: Hello World LoginRequest: Hello World with QDomDocument Request: Hello World LoginRequest: Hello World Obviously both constructor of LoginRequest called REquest constructor. Is there any way to cape with this situation? I can construct another function that does the job I want to do and have both constructors call that function. But I wonder is there any solution?

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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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  • Using enums or a set of classes when I know I have a finite set of different options?

    - by devoured elysium
    Let's say I have defined the following class: public abstract class Event { public DateTime Time { get; protected set; } protected Event(DateTime time) { Time = time; } } What would you prefer between this: public class AsleepEvent : Event { public AsleepEvent(DateTime time) : base(time) { } } public class AwakeEvent : Event { public AwakeEvent(DateTime time) : base(time) { } } and this: public enum StateEventType { NowAwake, NowAsleep } public class StateEvent : Event { protected StateEventType stateType; public MealEvent(DateTime time, StateEventType stateType) : base(time) { stateType = stateType; } } and why? I am generally more inclined to the first option, but I can't explain why. Is it totally the same or are any advantages in using one instead of the other? Maybe with the first method its easier to add more "states", altough in this case I am 100% sure I will only want two states: now awake, and now asleep (they signal the moments when one awakes and one falls asleep).

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  • ActiveRecord Validations for Models with has_many, belongs_to associations and STI

    - by keruilin
    I have four models: User Award Badge GameWeek The associations are as follows: User has many awards. Award belongs to user. Badge has many awards. Award belongs to badge. User has many game_weeks. GameWeek belongs to user. GameWeek has many awards. Award belongs to game_week. Thus, user_id, badge_id and game_week_id are foreign keys in awards table. Badge implements an STI model. Let's just say it has the following subclasses: BadgeA and BadgeB. Some rules to note: The game_week_id fk can be nil for BadgeA, but can't be nil for BadgeB. Here are my questions: For BadgeA, how do I write a validation that it can only be awarded one time? That is, the user can't have more than one -- ever. For BadgeB, how do I write a validation that it can only be awarded one time per game week?

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  • Me As Child Type In General Function

    - by Steven
    I have a MustInherit Parent class with two Child classes which Inherit from the Parent. How can I use (or Cast) Me in a Parent function as the the child type of that instance? EDIT: My actual goal is to be able to serialize (BinaryFormatter.Serialize(Stream, Object)) either of my child classes. However, "repeating the code" in each child "seems" wrong. EDIT2: This is my Serialize function. Where should I implement this function? Copying and pasting to each child doesn't seem right, but casting the parent to a child doesn't seem right either. Public Function Serialize() As Byte() Dim bFmt As New BinaryFormatter() Dim mStr As New MemoryStream() bFmt.Serialize(mStr, Me) Return mStr.ToArray() End Function

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  • Python, invoke super constructor

    - by Mike
    class A: def __init__(self): print "world" class B(A): def __init__(self): print "hello" B() hello In all other languages I've worked with the super constructor is invoked implicitly. How does one invoke it in Python? I would expect super(self) but this doesn't work

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