Call function when items are added or removed from a vector

I'm writing a widget kit for the Nano-X window system. In my base class view, I have a vector defined:

std::vector<RSMKit::View *> children;

Is it possible to call a function (GrReparentWindow in this case) when an item is开发者_开发百科 added or removed from the vector so that the newly added widget can be shown?

---

No, this is not possible. You also should not subclass std::vector to overwrite push_back and erase, because the class has not been designed for it. However, it would be simple to write your own container that would use std::vector for storage and expose Add and Remove functions with callbacks. Something along the following lines:

template<typename T>
class CallbackVector
{
public:

    typedef void (*Callback)();

private:

    std::vector<T> elements;
    Callback       OnAdd;
    Callback       OnRemove;

public:

    CallbackVector(Callback OnAdd, Callback OnRemove)
        : OnAdd    (OnAdd)
        , OnRemove (OnRemove)
    {
    }

    void Add(const T & element)
    {
        elements.push_back(element);
        OnAdd();
    }

    void Remove(int i)
    {
        elements.erase(elements.begin() + i);
        OnRemove();
    }
};

In practice, you would probably want a more complicated callback, using a function with a pointer parameter or using boost::function.

---

No. Do not inherit from std::vector. Just encapsulate it.

template<typename T> struct MyVector
{
private:
    std::vector<T> items;
public:
    void push_back (const T& x)
    {
        // Do something here
        items.push_back(x);
    }
    // etc
};

---

One possible solution is to subclass your vector class and add callbacks on the insertion and removal methods. With an stl vector this is not possible by default

---

There are two ways;

(1) Inherit std::vector and overload push_back() and pop_back() method:

template<typename T>
struct MyVector : std::vector<T>
{
  void push_back (const T& x)
  {
    GrReparentWindow ();
    vector<T>::push_back(x);
  }
  // same way pop_back()
};

Usage:

MyVector<RSMKit::View*> children;
children.push_back(new RSMKint::View);

(2) Another way is to push_back the items with custom overloaded operator or method; if you are allowed to edit RSMKit::View

class RSMKit::View
{
//...
public:
  RSMKit::View* get ()
  {
    GrReparentWindow ();
    return this;
  }
};

Usage:

MyVector<RSMKit::View*> children;
RSMKit::View *p = new RSMKint::View;
children.push_back(p->get());