Prevent Firing Signals in Qt

Question

We have a QCheckBox object, when user checks it or removes check we want to call a function so we connect our function to stateChanged ( int state )

Answer 1

While learning Qt, I ran into this problem with a set of interconnected widgets that I wanted to update "atomically". I liked @cjhuitt's solution, but found that it goes even better with a bit of syntactic sugar based on proxy objects. Here's the approach that I used...

First, I defined a class template for a blocker proxy object. Like Caleb's, this blocks the signals on construction, and then restores their previous state on destruction. However, it also overloads the -> operator to return a pointer to the blocked object:

template class Blocker {
    T *blocked;
    bool previous;
public:
    Blocker(T *blocked)
        : blocked(blocked),
          previous(blocked->blockSignals(true)) {}
    ~Blocker() { blocked->blockSignals(previous); }
    T *operator->() { return blocked; }
};

Next, I defined a small template function to construct and return a Blocker:

template inline Blocker whileBlocking(T *blocked) {
    return Blocker(blocked);
}

Putting this all together, I'd use it like this:

whileBlocking(checkBox)->setChecked(true);

or

whileBlocking(xyzzySpin)->setValue(50);

This gets me all the benefits of RAII, with automatically paired blocking and restore around the method call, but I don't need to name any wrapper or state flags. It's nice, easy, and pretty darn foolproof.