Component objects cannot declare new properties

[pingal]

If I don't use Button element in the Component, it doesn't give me the above error.

e.g. This works fine

Component {

  Row {
        Rectangle {..}
        Rectangle {..}
        Rectangle {..}
        Rectangle {..}
   }
}

But if I add Button element as below, it gives me the mentioned error in the application output

Component {
      id: itemDelegate
      Button { .. }
      Row {
            Rectangle {..}
            Rectangle {..}
            Rectangle {..}
            Rectangle {..}
       }
}

I'm using the Component as a delegate

[KroMignon]

@pingal said in Component objects cannot declare new properties:

But if I add Button element as below, it gives me the mentioned error in the application output

AFAIK, Component can hold only 1 root object (eg. Item, Rectangle, Row ect.). It is same a creating a QML file for a component (cf. https://doc.qt.io/qt-5/qml-qtqml-component.html)
You should change your code to:

Component {
    id: itemDelegate
    Item {
        Button { .. }
        Row {
            Rectangle {..}
            Rectangle {..}
            Rectangle {..}
            Rectangle {..}
        }
  }
}