Method onClicked

src/fl/ui/button.h:84–92

    }

    int onClicked(function<void()> callback) FL_NOEXCEPT {
        int id = mCallbacks.add([callback](UIButton &btn) {
            if (btn.clicked()) {
                callback();
            }
        });
        mListener.addToEngineEventsOnce();
        return id;
    }

    int onPressed(function<void()> callback) FL_NOEXCEPT {
        int id = mPressCallbacks.add(callback);