jpeg viewer

[jacek]

It could be needed to subclass it though, to handle a sequence of jpegs

The problem is that you can't subclass QMovie, because it has no virtual methods.

[wysota]

The problem is that you can't subclass QMovie, because it has no virtual methods.

Why not? You don't have to cast it to QMovie* to use it... Correct me if I'm wrong but I recall that virtual methods are only required if you want to call the subclass reimplementation from the superclass interface...

QMovie *m = new MyMovie();
m->start(); // will always call from QMovie
 
MyMovie *m = new MyMovie();
m->start(); // will call from MyMovie

QMovie *m = new MyMovie();
m->start(); // will always call from QMovie

MyMovie *m = new MyMovie();
m->start(); // will call from MyMovie

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[jacek]

Why not? You don't have to cast it to QMovie* to use it...

But you will have to implement every method, so there is no benefit in using QMovie.

#include <iostream>
 
class A
{
   public:
      void foo() { bar(); }
      void bar() { std::cerr << "A::bar()" << std::endl; }
};
 
class B : public A
{
   public:
      void bar() { std::cerr << "B::bar()" << std::endl; }
};
 
int main()
{
   B b;
   b.foo();
   b.bar();
   return 0;
}

#include <iostream>

class A
{
   public:
      void foo() { bar(); }
      void bar() { std::cerr << "A::bar()" << std::endl; }
};

class B : public A
{
   public:
      void bar() { std::cerr << "B::bar()" << std::endl; }
};

int main()
{
   B b;
   b.foo();
   b.bar();
   return 0;
}

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