How to achieve exclusive (e.g. Radio Button) type behavior with QGraphicObject? - qt

Question

I'm working with Qt (v 5.3) again after sometime away. As a learning exercise I am prototyping a module using QGraphicView in order to understand better how to use it.
The functionality is simple: I have several QGraphicObjects which function like buttons with states and behaviors:
OFF - image panel hidden; default button art
ON - image panel
displayed; highlight button art
At startup all buttons are in an OFF state
A clicked button will toggle it's state (non-Exclusive)
If a different button is already in an ON state, it must be turned off (Exclusive)
Everything is data driven and created dynamically at runtime.
So that is my little learning exercise. What I am trying to sort out is an efficient messaging mechanism to handle the "radio button sometimes" exclusive behavior and sending a message to a group of objects without strongly coupling them.
I've looked at signals and slots but that gets tedious if there are many connections to make.
QSignalMapper which seems somewhat better
QEvent is probably the most solid approach but I've had trouble finding good learning examples.
I am making this more complicated than need be but as I say, it's a learning exercise to get used to Qt again.
So my question (finally): is there an approach I am overlooking or one of these mentioned which would be better (e.g most flexible, maintainable, scalable). Not looking for code per se, but an understanding of how to go about coding something like this using the Qt framework.
Here's an image of the thing:

Answer 1

Signal and slots is the method I would use here. However, rather than connect each button to every other button, you can create an intermediate, Controller class.
The Controller class can either aggregate, or be a parent to all of the buttons.
When a button is created, it connects signals to the controller to inform it of being pressed. The receiving slot in the Controller class is then responsible for turning off any other buttons.
Skeleton code: -
class ButtonController : public QGraphicsObject
{
public slots:
void ButtonPressed();
private:
QList<MyButton*> m_buttonList;
};
void ButtonController::ButtonPressed()
{
foreach(MyButton* pButton, m_buttonList)
{
if(pButton != sender())
{
pButton->Off();
}
}
}
In the constructor of MyButton, assuming the controller is the parent: -
MyButton::MyButton(ButtonController* parent)
: QGraphicsObject(parent);
{
connect(this, &MyButton::pressed(), parent, &ButtonController::ButtonPressed());
...
}
Alternatively, the controller may just hold a list of the buttons, in which case you can do this: -
MyButton::MyButton(QObject* parent, ButtonController* pButtonController)
: QGraphicsObject(parent);
{
connect(this, &MyButton::pressed(), pButtonController, &ButtonController::ButtonPressed());
...
}
In the case of not being able to change the constructor of the buttons, the controller may simply have an AddButton function, in which it creates the connection when the button is added under its control.

Answer 2

Subclass QGraphicsScene
Reimplement mousePressEvent and check is left mouse button pressed.
If so, then get position of mouse by pos() method and get current graphics object under arrow by itemAt() method.
Try to cast it into your needed object, if it was successfully, then change background and other.
Store your graphics objects in vector, in this case you can check every object and decide which object should be turned off.
Fully working example:
header:
#ifndef GRAPHICSSCENE_H
#define GRAPHICSSCENE_H
#include <QGraphicsScene>
#include <QPoint>
#include <QMouseEvent>
class GraphicsScene : public QGraphicsScene
{
Q_OBJECT
public:
explicit GraphicsScene(QObject *parent = 0);
signals:
protected:
void mousePressEvent(QGraphicsSceneMouseEvent *mouseEvent);
public slots:
private:
QVector<QGraphicsEllipseItem * > vec;
};
#endif // GRAPHICSSCENE_H
cpp:
#include "graphicsscene.h"
#include <QDebug>
#include <QGraphicsSceneMouseEvent>
#include <QGraphicsItem>
GraphicsScene::GraphicsScene(QObject *parent) :
QGraphicsScene(parent)
{
//set circles in different positions.
vec.push_back(addEllipse(0,0,50,50,QPen(Qt::red),QBrush(Qt::blue)));
vec.push_back(addEllipse(0+100,0+100,50,50,QPen(Qt::red),QBrush(Qt::blue)));
vec.push_back(addEllipse(0+150,0+150,50,50,QPen(Qt::red),QBrush(Qt::blue)));
}
void GraphicsScene::mousePressEvent(QGraphicsSceneMouseEvent *mouseEvent)
{
//qDebug() << "in";
if (mouseEvent->button() == Qt::LeftButton)
{
QGraphicsItem *item = itemAt(mouseEvent->scenePos(), QTransform());
QGraphicsEllipseItem *ell = qgraphicsitem_cast<QGraphicsEllipseItem *>(item);
if(ell)
{
for(int i = 0; i < vec.size(); i++)
{
if(vec.at(i) != ell)
{
vec.at(i)->setBrush(QBrush(Qt::blue));//disable all other bettons
}
}
ell->setBrush(QBrush(Qt::black));//to chosen circle
qDebug() << "good";
}
else
qDebug() << "not ell" << mouseEvent->scenePos();
}
}
Usage:
GraphicsScene *scene = new GraphicsScene(this);
ui->graphicsView->setScene(scene);
With this case, your circles will be similar to radioButtons. If you want save state of all buttons you can use:
for(int i = 0; i < vec.size(); i++)
vec.at(i)->setData(0,false);
And get state with
if(!ell->data(0).toBool())
//do