Pass custom object in signal from QML

yeckel

Hi,

I would like to send manually crafted object defined in c++ header file from onClick method in QML into legacy C++ code. I can make it working with basic types like QString, int, but is it possible with custom classes like MyMessage here:

class MyClass : public QObject
{
    Q_OBJECT
public slots:
    void addMessage(const MyMessage &msg) {
        qDebug() << "Called the C++ slot with message:" << msg.author();
    }
}; 
...
struct MyMessage : public QObject
{
     Q_OBJECT
    MyMessage(QString author):author(author){}
    QString author;
}
...
engine.rootContext()->setContextProperty("MyClass",&myClass);

I need code like this to be working:

Button {
 text: "SendMessage"
  onClicked: {
  var message = MyMessage("Karel") // here i would like to set more attributes
  MyClass.addMessage(MyMessage(message))
 }
}

Thanks for any suggestion!

p3c0

Hi@yeckel,
You can do it in following way

Register the class using qmlRegisterType
qmlRegisterType<MyMessage>("MyMessage", 1, 0, "MyMessage")
Import that type it in QML
import MyMessage 1.0
Instantiate it
```
 MyMessage {
    id: myMessage
 }
```
Use it using its id
myMessage.myMethod()

It would be better to add some properties defined using Q_PROPERTY in MyMessage class so that they can be directly accessible from QML. Add accessor and mutator to it so as to access the data from other class.
So for eg. if you have a property like
Q_PROPERTY(QString quote READ quote WRITE setQuote NOTIFY quoteChanged)
From QML you can just do this:

MyMessage {
   id: myMessage
}
myMessage.quote = "Some Quote"

Then you can send this object to MyClass using the id

MyClass.addMessage(myMessage)

More info here.

yeckel

Thanks! To instantiate that object that I was missing. One more point: the slot has to accept pointer not reference:

class MyClass : public QObject
{
    Q_OBJECT
public slots:
    void addMessage(MyMessage *msg) {
        qDebug() << "Called the C++ slot with message:" << msg->author();
    }
};

Without that i was getting an error: Error: Unknown method parameter type: MyMessage

p3c0

@yeckel Right. Forgot to mention it here. You can mark the post as solved