How to connect two separate classes using signal/slots.

[rocklionmba]

@Wieland That's a good point. Currently I have it where MainWindow is dealing with the front end, so things like user input and all of that, while Interior_Paint is dealing with the calculations and other stuff,using signals and slots to talk in between each other to pass information. Could there be a problem like this?

[kshegunov]

If Interior_Paint has a private member, then it is private. That's the purpose - not to expose something that's not part of the interface. So your question boils down to: "how can I gut my class and expose its internals", well you can do it, but you really shouldn't. Instead you should expose a method of your Interior_Paint class that does what you want and only through Interior_Paint's interface you'd modify/access it's internal private member object.

[rocklionmba]

@kshegunov could you maybe show an example of what you mean? I get the gist of what your saying, but I wouldn't know how exactly I would implement it.

[kshegunov]

class A : public QObject
{
    Q_OBJECT
    // ...
signals:
     void signalFromAtoC();
};

class C
{
public:
    void methodToBeCalledFromA();
};

class B : public QObject
{
    Q_OBJECT
    // ...
public slots:
     void delegateToCSlot()
     {
         privateMember.methodToBeCalledFromA(); //< Delegate the call
     }

private:
     C privateMember;
}

then you use as before:

A a;
B b;

QObject::connect(&a, &A::signalFromAtoC, &b, &B::delegateToCSlot);

If all classes are QObjects then you can also directly forward the signal to another signal in B, which you can connect to a slot in C.

[rocklionmba]

@kshegunov What exactly does

privateMember.methodToBeCalledFromA(); 

do? I haven't seen anything like it before.

[kshegunov]

It's a method call, you should've seen it while learning C++.

[rocklionmba]

@kshegunov I still am. I'm a second year CS/CE student.

[mrjj]

@rocklionmba
Hi
Its just non pointer syntax for calling a method/access member.

C privateMemberVAR;
privateMemberVAR.methodToBeCalledFromA();

in contrast to
C *privateMemberVAR = new C;
privateMemberVAR->methodToBeCalledFromA();

[rocklionmba]

@mrjj so it would be """ interior_paint:: privatememberVAR.somefunction(){ //code here }""" ?

[mrjj]

@rocklionmba

Hi
Where ?
In the slot ?

The main trick here is that, the slot calls the private member. Not directly from outside.
Its triggered via the signal.

Maybe show how interior_paint looks like.

and it will end up in something like
void interior_paint::TheNewSlot() {
privatememberVAR.somefunction();
}

[rocklionmba]

@mrjj so in terms that I'm using, class A would be MainWindow, B is the extra class to handle info, and C is interior_paint?

[mrjj]

@rocklionmba
Well B is the interior_paint that has the private member you want to call a method on
and A is mainwin.
C is the private member class (inside interior_paint )

The mainwindow will fire its new signal signalFromAtoC and that will call
delegateToCSlot that call its private class and its function.

[Amogh]

you can do it by sending signals from both the classes and catch in a slot

[rocklionmba]

@mrjj Hey, so I finally had the chance to try it out today and I noticed a problem with it. I'm using a dynamic array, so it naturally has to be a pointer for it to work. Also, a and b in the example are together, while in the actual code both are made in their constructors. Would the pointer make a problem? and would I have to move the location of where the variables are made for it to work?

[mrjj]

@rocklionmba said in How to connect two separate classes using signal/slots.:

Would the pointer make a problem?

Not at all. Just make sure they are initialized before any of the slots can be triggered.