Connecting a signal from a QGraphicsItem inside QGraphicsView

lansing

In my main window, I have called a subclass of QGraphicsView. And inside my custom QGraphicsView class, I have added a subclass of QGraphicsItem. In the custom QGraphicsItem class, I have a function that emits a signal. I want to catch this signal back in my main window, but I don't know how to connect to it. I tried using the graphicsView object as the signal sender but it doesn't work.

main_window.cpp

MyGraphicsView myView = new MyGraphicsView();

connect(m_ui.myView, &MyGraphicsView::mySignal, this, &MyMainWindow::mySlot)

MyGraphicsView .cpp

class MyGraphicsView : public QGraphicsView
{
...
    scene = new QGraphicsScene(this);
    myItem = new MyGraphicsItem();
    scene->addItem(myItem);
}

MyGraphicsItem.cpp

class MyGraphicsItem: public QGraphicsItem
{
    Q_OBJECT
...
    void myFunction() {
        emit mySignal();
    }
}

I'm getting the error "no member named mySignal in MyGraphicsView". I don't know how to point to the graphicsItem as the signal sender from the main window.

SGaist

Hi,
@lansing said in Connecting a signal from a QGraphicsItem inside QGraphicsView:

MyGraphicsView myView = new MyGraphicsView();

connect(m_ui.myView, &MyGraphicsView::mySignal, this, &MyMainWindow::mySlot)

myView and m_ui.myView are not the same object and likely not from the same class.

lansing

@SGaist said in Connecting a signal from a QGraphicsItem inside QGraphicsView:

Hi,
@lansing said in Connecting a signal from a QGraphicsItem inside QGraphicsView:

MyGraphicsView myView = new MyGraphicsView();

connect(m_ui.myView, &MyGraphicsView::mySignal, this, &MyMainWindow::mySlot)

myView and m_ui.myView are not the same object and likely not from the same class.

Hi they are the same, I just removed all the other extra stuff to simplify my problem. In my project, myView was promoted to MyGraphicsView class in the ui instead of declaring it in the main_window.cpp

lansing

Hi I figured it out.

First I should subclass QGraphicsObject for my item instead of QGraphicsItem, because it was made specifically for use of signal and slots inside graphicsitem.

Then when the item object fired a signal, catch it in the graphicsView object and then forward it to the main_window at the top. Just create a signal with the same name for each of the item and view class.

MyGraphicsItem.cpp

class MyGraphicsItem: public QGraphicsObject
{
    Q_OBJECT
    ...
    void myFunction() {
        emit mySignal();
    }    
}

MyGraphicsView .cpp

class MyGraphicsView : public QGraphicsView
{
    ...
    scene = new QGraphicsScene(this);    
    myItem = new MyGraphicsItem();    
    scene->addItem(myItem);

    connect(myItem, &MyGraphicsItem::mySignal, this, &MyGraphicsView::mySignal);
}

main_window.cpp

connect(m_ui.myView, &MyGraphicsView::mySignal, this, &MyMainWindow::mySlot)