abstract-class

问题 I'm following a tutorial where a ViewModel extends an abstract class in order to use coroutines, this is the class that extends: abstract class BaseViewModel(application: Application) : AndroidViewModel(application), CoroutineScope { private val job = Job() override val coroutineContext: CoroutineContext get() = job + Dispatchers.Main override fun onCleared() { super.onCleared() job.cancel() }} And this is the ViewModel: class ViewModel(application: Application) : BaseViewModel(application) {

问题 I have abstract class A abstract class A{ def this(obj:Object){ this() obj match{ case s:String => stringMethod(s) case n:Int => intMethod(n) } def stringMethod(s:String) def intMethod(n:Int) } and I have a class that extends this class class B(obj:Object) extends A(obj){ var s:String = null def stringMethod(s:String){ this.s = s } def intMethod(n:Int){ this.s = n.toString } } The point of this class is to instantiate an object and its variables depending on the class type of the object used

问题 I have abstract class A abstract class A{ def this(obj:Object){ this() obj match{ case s:String => stringMethod(s) case n:Int => intMethod(n) } def stringMethod(s:String) def intMethod(n:Int) } and I have a class that extends this class class B(obj:Object) extends A(obj){ var s:String = null def stringMethod(s:String){ this.s = s } def intMethod(n:Int){ this.s = n.toString } } The point of this class is to instantiate an object and its variables depending on the class type of the object used

问题 I have an abstract base class in C++ and need to create an array to store objects which are subclasses of it. I use pointers to the subclasses since each member of the array needs to be of the same size. Currently I am declaring and initializing my array like this: BaseClass *array[]; ... array = { &SubClass1(...), &SubClass2(...), ... &SubClass3(...) }; This is giving me the following when I try to compile: warning: taking address of temporary error: too many initializers for ‘BaseClass* [0]

问题 In Bjarne Stroustrup's book "The C++ Programming Language", it is stated that a derived class from a super class in a class hierarchy, in many case, gets access to the data of the super class. The book suggests this is a problem, because the sharing between " two related, but different, sets of data is asking for trouble. Sooner or later someone will get them out of sync. Also, experience shows that novice programmers tend to mess with protected data in ways that are unnecessary and that

问题 I have event declared in abstract class: public abstract class AbstractClass { public event Action ActionEvent; } public class MyClass : AbstractClass { private void SomeMethod() { //Want to access ActionEvent-- Not able to do so if (ActionEvent != null) { } } } I wanted to access this base class event in derived. Further I wanted to access this event in some other derived class of MyClass: MyClass.ActionEvent += DerivedMethod() Please help me understand how to work with event defined in

问题 I have event declared in abstract class: public abstract class AbstractClass { public event Action ActionEvent; } public class MyClass : AbstractClass { private void SomeMethod() { //Want to access ActionEvent-- Not able to do so if (ActionEvent != null) { } } } I wanted to access this base class event in derived. Further I wanted to access this event in some other derived class of MyClass: MyClass.ActionEvent += DerivedMethod() Please help me understand how to work with event defined in

问题 I have event declared in abstract class: public abstract class AbstractClass { public event Action ActionEvent; } public class MyClass : AbstractClass { private void SomeMethod() { //Want to access ActionEvent-- Not able to do so if (ActionEvent != null) { } } } I wanted to access this base class event in derived. Further I wanted to access this event in some other derived class of MyClass: MyClass.ActionEvent += DerivedMethod() Please help me understand how to work with event defined in

问题 I have the following error in my code: error: allocating an object of abstract class type 'Material' I don't know how to handle this case. I'm aware that std::make_unique performs an allocation, so it can't allocate the object of type Material , but I don't know how to correct it. #include <iostream> #include <memory> struct Material { Material() = default; virtual int get_color() const = 0; }; struct Basic : public Material { Basic() = default; virtual int get_color() const override { return

问题 I have the following error in my code: error: allocating an object of abstract class type 'Material' I don't know how to handle this case. I'm aware that std::make_unique performs an allocation, so it can't allocate the object of type Material , but I don't know how to correct it. #include <iostream> #include <memory> struct Material { Material() = default; virtual int get_color() const = 0; }; struct Basic : public Material { Basic() = default; virtual int get_color() const override { return