Qt - modify slot's parameter of previous connected signal using lambda function

Question

I'm trying to reconnect a signal to the same slot but with a different parameter. This would work if I just wanted to reconnect the same signal to a diferent slot without using parameters or lambda functions but I need to do it this way.

At first I tried something like this:

connect(remove_btn,&QPushButton::clicked,[this, id] {function1(varA);});
connect(remove_btn,&QPushButton::clicked,[this, id] {function1(varB);});

function1 receives varA and never varB.

I found a way to do this by keeping a list of the connections and when I wanted to modify the parameter I would just disconnect the old one and make a new connection.

What I'd like to know is if is there a way to make this modification without the need of keeping track of all the connections and go through the discconnect/connect process.

Answer 1

Two solutions come to my mind:

1. Capture var by reference and change it instead of reconnecting:

   class Foo : public QWidget {
     Q_OBJECT
     int remove_btn_var;
     int varA = 10, varB = 20;
     QPushButton remove_btn;
     void function1(int);
   public:
     Foo() {
       remove_btn_var = varA;
       connect(&remove_btn, &QPushButton::clicked, [&] { function1(remove_btn_var); });
     }
     void switch() {
       remove_btn_var = varB;
     }
   };
   

2. Add a property to the button that you can modify:

   static const char k_function1_var[] = "function1_var";
   class Foo : public QWidget {
     Q_OBJECT
     int varA, varB;
     QPushButton remove_btn;
     void function1(int);
   public:
     Foo() {
       remove_btn.setProperty(k_function1_var, varA);
       connect(&remove_btn, &QPushButton::clicked, [this] { 
         function1(remove_btn.property(k_function1_var).toInt())
       });
     }
     void switch() {
       remove_btn.setProperty(k_function1_var, varB);
     }
   };