Trouble with Connections

mrjj

Hi
Are you sure that syntax works when its a c++ signal ?
The docs says
"A Connections object creates a connection to a QML signal."

Anyway, I might just have over complicated it using the method
https://andrew-jones.com/blog/qml2-to-c-and-back-again-with-signals-and-slots/
section "Emitting a signal from C++ and listening to it from QML"

if "onUpdateTriggered:" can in fact auto bind, its much more elegant :)

Jpraccio

Hey, thanks for the response,

I got that from this doc and a few stack overflows:
http://doc.qt.io/qt-5/qtqml-cppintegration-contextproperties.html

Right at the bottom.

mrjj

Hi
You are right. it does say
"ApplicationData has a signal named dataChanged()"
and you even followed the naming exactly.

So i assume your code is very close to the sample except other names?

Jpraccio

Yes, just the names are different.

Jpraccio

Also, I can see using your method, but I have no clue how I would get to the QML object

mrjj

@Jpraccio
Hi
I just tested the sample project and it worked.. :)
So there must be something a little bit off some place in your code or something else.

Test project
https://www.dropbox.com/s/2ixu3sx172e97rm/untitled54.zip?dl=0

6thC

Have you registered it? For cpp instanced objects I register mine with:

qmlRegisterUncreatableType<T>

http://doc.qt.io/qt-5/qqmlengine.html#qmlRegisterUncreatableType

Jpraccio

I have it able to receive the signal if I put the connection in the top level Window qml. The qml object that needs the signal is nested a bit down in the hierarchy. Is this a know behavior?

Jpraccio

So it seems like nothing is received down the hierarchy from the main window. I have used the Connections inside my Window qml and it's triggered fine. Trying to pass a signal from the Window down to the Component using QML and a Connection object inside the Component fails.

So the components are inside a stack view. They are Component classes that contain a rectangle. The signal needs to happen within these components. Don't know if it matter, but these are not the initialItem of the StackView. I can get some code together if desired.

J.Hilk

@Jpraccio I think, my knowledge is limited here, that that behaviour depends heavly on how you marry your cpp class and your qml root file.

if for example you use qmlRegisterType<MyClass>("MyClass",1,0, "mClass"); than you can create an instande in each qml file you import myclass in, and can use Connect and signal slots there easily enough.

If you create it as a fixed class and register it as a rootContext() / ContextProperty than you should be able to access it everywhere in your qml files.

//main.cpp
MyClass mClass;
QQmlApplicationEngine engine;
engine.rootContext()->setContextProperty("MyClass", &mClass);

//any qml file
Connections{
    MyClass.onMySignal: console.log("SIGNAL!!!")
}
//The actual signal in MyClass is named: mySignal
//I believe the "on" prefix is needed

Jpraccio

I have the c++ class working at this point, I can send a signal to the window qml. Now trying to send a signal into the qml objects from the window. It seems these specific qml components just can't receive them. It looks like this:

// Window qml
Window {
    id: mainWindow
    signal mySig()
    Connections {
         target: myCpp
         onAction: {
              // this works
              mySig()
         }
    }

   StackView {
       initalItem: itemA
       ItemA {
          // this has a connection that works
       }

     ItemB {
         // this won't receive the above signal
     }
   }
}

// ItemB qml
Component {
     Rectangle {
         Connections {
             target: mainWindow
             onMySig: {
                  // nothing happens here
                  // regardles of using the cpp signal or the qml signal
              }
          }
     }

}

Jpraccio

I made some changes that forced the stack view to transition and got a new error:

QQmlEngine: Illegal attempt to connect to Chord(0x112847200) that is in a different thread than the QML engine QQmlApplicationEngine(0x7ffeefbfe1e0.

Is it possible this is a threading issue of some sort? I am not intentionally spawning any threads myself

Jpraccio

Solved by pushing ItemB onto the stack view.