Why does calling setValue in my Customer Slider Class cause the program to crash?

Sailanarmo

Kind of a follow up from my last post. However not related in context (at least I don't think they are).

This is going to seem a little silly but please follow me if you can:

class Slider : public QSlider
{
    Q_OBJECT
public:
    Slider(QWidget *parent = nullptr);

    void updateValue(int value) { setValue(value);}
    int get() const { return value(); }
};

Simply put, I am just trying to update the value of the custom slider via a controller (I know, I can do this with slots by doing ui->horizontalSlider->setValue(int);).

I have a Controller<T....> controller(t&...), which takes an arbitrary number of Classes and allows me to set their values and get their values, for example:

Controller<CustomSlider,CustomSpinBox,MyClass> controller(*ui->horizontalSlider,*ui->spinBox,myClass);

So what I do with the slot, is tell the controller to update all of the values like so:

void MainWindow::on_horizontalSlider_valueChanged(int value)
{
    controller.setValues(value);
    getValues();
}

getValues() simply outputs to the console to tell me that they have indeed all updated.

setValues(int) calls the function updateValue(int) which calls each classes setter function. It should be a straight forward update, however whenever I try to move the slider the program crashes and the debugger doesn't really give me anything useful other than crashing on qabstractslider.cpp line 531 Q_D(QAbstractSlider). So I don't really know what is going on with this. Does anyone have any suggestions?

EDIT: Forgot to mention that ui->horizontalSlider has been promoted to Slider.

EDIT 2: Here is the header file I have been using:

#ifndef CONTROLLER_HPP
#define CONTROLLER_HPP

#include <functional>
#include <vector>
#include <iostream>
#include <utility>

template<typename...Classes>
class Controller
{
  public:
    Controller(Classes&...objects) : objects(objects...){}
    Controller(std::tuple<Classes&...> tup) : objects(tup){}

    void setValues(int value)
    {
      std::apply([&](auto&...x) { (x.updateValue(value),...);}, objects);
    }

    void getValues(std::vector<int> &values) const
    {
      std::apply([&](auto&...x) { (values.push_back(x.get()),...);}, objects);
    }

    std::tuple<Classes&...> getObjects() const
    {
      return objects;
    }

  private:
    std::tuple<Classes&...> objects;
};

template<typename...ClassesL, typename...ClassesR>
auto operator+(const Controller<ClassesL...>& lhs, const Controller<ClassesR...>& rhs)
{
  return Controller(std::tuple_cat(lhs.getObjects(),rhs.getObjects()));
}

template<typename...ClassesL, typename ClassesR>
auto operator+(const Controller<ClassesL...> &lhs, ClassesR rhs)
{
  Controller<ClassesR> makeController(rhs);
  return Controller(std::tuple_cat(lhs.getObjects(),makeController.getObjects()));
}

template<typename ClassesL, typename...ClassesR>
auto operator+(ClassesL lhs, const Controller<ClassesR...> &rhs)
{
  Controller<ClassesL> makeController(lhs);
  return Controller(std::tuple_cat(makeController.getObjects(),rhs.getObjects()));
}

#endif // CONTROLLER_HPP

Pl45m4

@Sailanarmo

What exactly IS in line 531?

You said updateValue from your custom slider will call the setValue from QSlider, but in your code you call setValue(value) directly...

Passing *ui->slider looks wrong too. AFAIK are ui-elements already pointers to the object.

Sailanarmo

@Pl45m4 Line 531 is what I posted Q_D(QAbstractSlider), that is line 531 in qabstractslider.cpp.

Am I not supposed to call setValue(value) directly? This has no problem running if I do:

Slider mySlider;
SpinBox mySpinBox;
MyClass myClass;

controller(mySlider,mySpinBox,myClass);
controller.setValues(20);

However, mySlider and mySpinBox are not ui->horizontalSlider or ui->spinBox. But the calls should be the same right?

aha_1980

@Sailanarmo run your program in a debugger and on crash, inspect the stack trace. you're likely accessing an invalid pointer.

Sailanarmo

@aha_1980 If I am accessing an invalid pointer, where would be the best place to fix it? I'll edit the post and show the controller header file.

aha_1980

@Sailanarmo said in Why does calling setValue in my Customer Slider Class cause the program to crash?:

where would be the best place to fix it

Of course at the place where you create the crash.

As said, inspect the backtrace. Everything else is guessing.