Retrieve differents Qmap in a single variable

Question

I am working on a game in Qt. My characters/objects are stored in my model Class (I try to follow the MVC model).

I created a QMap containing for each of the object :

QMap<int, Safe*> *safes;
QMap<int, Mushroom*> *mushroom;
QMap<int, Floor*> *floors;

But then I would like to retrieve all theses QMap in my Controller and send it to the paintEvent() class of my View from the controller. Is there a way to store the QMap in a QList like this :

QList<QMap<int, void*>>

And then cast it ? I am searching for a way to acces to theses QMap from a single object.

Thank you for your help !

unrelated, but why pointers to qmap? – UmNyobe Oct 15 '15 at 08:33 — UmNyobe, Oct 15 '15 at 08:33
because I modify them in my controller – ltheron Oct 15 '15 at 08:42 — ltheron, Oct 15 '15 at 08:42

Mohamad Elghawi · Accepted Answer · 2015-10-15T08:47:17.387

3

You could use a struct to bundle them up inside one object:

struct Maps
{
    QMap<int, Safe*> *safes;
    QMap<int, Mushroom*> *mushroom;
    QMap<int, Floor*> *floors;
};

Although it's valid to have a pointer to QMap, if you don't need to hold a pointer to it then I would advise against it.

struct Maps
{
    QMap<int, Safe*> safes;
    QMap<int, Mushroom*> mushroom;
    QMap<int, Floor*> floors;
};

That way you don't have to worry about heap allocations/deallocations.

If you have a compiler that supports C++11 then you can use std::tuple to group items together.

std::tuple<QMap, QMap, QMap> maps (safes, mushroom, floors);

edited Oct 15 '15 at 08:47

answered Oct 15 '15 at 08:34

Mohamad Elghawi

2,071
10
14

Perhaps using a class would be better. I assume that if he wants to group them somehow he will want to apply operations. Having a class would probably be better for this reason no? +1 for the pointer to QMap – LBes Oct 15 '15 at 08:36
By the way, there's something called `std::tuple` if you want to be lightweight and convenient :) – yzn-pku Oct 15 '15 at 08:40
1

@LBesancon As you know in C++ the only difference between a struct and a class is their default access specifiers and the way they are inherited. So you could have methods in your struct if you wanted to. I do however tend to use structs when I need to group some data together without any methods but it's completely down to you. – Mohamad Elghawi Oct 15 '15 at 08:42
@yzn-pku You're absolutely right. I will update my answer. – Mohamad Elghawi Oct 15 '15 at 08:43
@MohamadElghawi sure you can have methods in your struct. It is more a matter of what you're used to do. Basically I tend to create classes whenever the need arises but you're right. Did not downvote your answer anyway for that ;) – LBes Oct 15 '15 at 08:46

bkausbk · Answer 2 · 2015-10-15T08:43:58.927

First, yes you can use a QList for this purpose, however I would suggest to create an interface class first and use this in your QMap.

struct GameObjectInterface {
};

class Safe : public GameObjectInterface {};
class Mushroom : public GameObjectInterface {};
class Floor : public GameObjectInterface {};

QMap<int, GameObjectInterface*> _GameObjects;

// Is game object with ID `n` a `Safe`?

Safe* s = dynamic_cast<Safe*>(_GameObjects[n]);
if (s != nullptr) {
    // Yes it is a safe
}

Another possibility:

QList<QMap<int, GameObjectInterface*>> _GameObjects;

And if you want you can capsule everything into one struct as hinted by other responders.

struct MyGameObject {
    QMap<int, Safe*> Safes;
    QMap<int, Mushrooms*> Mushrooms;
    QMap<int, Floor*> Floors;
};

QList<MyGameObject> _GameObjects;

If each are related (same key for all objects) it could be simplified like:

struct MyGameObject {
    Safe* _Safe;
    Mushrooms* _Mushroom;
    Floor* _Floor;
};
QMap<int, MyGameObject*> _GameObjects;

score 0 · Answer 3 · answered Oct 15 '15 at 08:36

0

You could keep pointer to base class for all your specific objects:

QMap<int, MyBaseClass*> allObjects;

answered Oct 15 '15 at 08:36

AnatolyS

4,249
18
28

Retrieve differents Qmap in a single variable

3 Answers3