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Qt QML: Get reference to object emitting a signal


Qt QML: Get reference to object emitting a signal

By : Ryanirob
Date : November 20 2020, 03:01 PM
fixed the issue. Will look into that further I have a screen with some rectangles which can contain text. The text content of these rectangles should be allowed to change through clicking on buttons in the screen where this component is used. The problem I am having is how to know in the screen which uses this component which instance is selected. I thought about solving this via emitting a signal, which transmits the id of the instance as reference, but it seems this does not work. How could this be accomplished? Here my custom rectangle component
code :
root.sendId(root.id)
root.sendId(root)
signal sendId(Item item)
        MyRectangle {               
            onSendId: tempNumber.setSelected(item)
        }
// Rect.qml
Rectangle {
  width: 50
  height: 50
  color: manager.selected === this ? "red" : "blue"
  MouseArea {
    anchors.fill: parent
    onClicked: manager.selected = parent
  }
}

// main.qml
Window {
  id: manager

  visible: true
  width: 600
  height: 300

  property Item selected: null

  Row {
    spacing: 2
    Repeater {
      model: 10
      delegate: Rect {}
    }
  }
}


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Is emitting a disconnected signal bad?

Is emitting a disconnected signal bad?


By : user2160279
Date : March 29 2020, 07:55 AM
fixed the issue. Will look into that further The class that emits the signal shouldn't care if anybody listens or not. Users of the class connect to the signals if they need to, or not. Maybe they just need to connect to some of them. There is no harm to a signal nobody is connected to, the call itself is cheap. It's like with every other part of the API: signals are part of the interface design, a service provided by the class to the users, who might use this part of the API, or not, which is their own business.
selective D-BUS signal emitting from ObServer (unicast signal)

selective D-BUS signal emitting from ObServer (unicast signal)


By : Andrey Leonidovich
Date : March 29 2020, 07:55 AM
this one helps. You can't. Signals are received by all clients that have registered for that signal on a DBus interface.
You can either add a parameter to the OnNotify signal, and handle it in the client, or create separate signals for each client. However, if you want this component to be dynamic (add clients at runtime), you have to go with the first approach (parameter to OnNotify).
code :
dbus_bool_t dbus_message_set_destination (DBusMessage  *message, const char *destination)
DBusMessage *QDBusMessagePrivate::toDBusMessage(const QDBusMessage &message, QDBusError *error)
qt emitting a signal across threads by moving the object to

qt emitting a signal across threads by moving the object to


By : jsellers
Date : October 28 2020, 04:01 PM
This might help you According to the doc:
code :
r = new Receiver{};
t = new QThread();
r->moveToThread(t);
connect(this, &MessageGenerator::messageCompleted, r, &Receiver::onNewMessage);
t->start();
Qt not emitting signal

Qt not emitting signal


By : Federico Pinna
Date : March 29 2020, 07:55 AM
hop of those help? In connect function, no need to mention parameter names. just declare on argument type. Connect like this:-
code :
connect(keyboard,SIGNAL(keyboard_respoense(QString)),this,SLOT(send_to_MBU(QString))); 
Emitting QVector reference in Qt signal results in copy

Emitting QVector reference in Qt signal results in copy


By : eNoahRaja
Date : March 29 2020, 07:55 AM
may help you . Copies will be made in this case both because you are passing by value and because signals across thread boundaries are queued. That's fine though, because implicit-sharing means they are shallow copies. There's practically no overhead to copying if both the original and the copy are only used for reading.
Unfortunately, that's not actually the case in your program. Your forever loop will modify the vector when it loops back around after signal emission. In this example, it won't actually change anything in the vector since you're always just assigning 1,2,3,4, but calling the non-const operator[] is enough to trigger the deep copy.
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