Why use a QtObject to define properties rather than directly declaring properties?

Diracsbracket

Hello,

The QtObject documentation shows the following example code:

import QtQuick 2.0

Item {
    QtObject {
        id: attributes
        property string name
        property int size
        property variant attributes
    }

    Text { text: attributes.name }
}

When/why use the above over directly declaring properties as shown below:

Item {
    id: item
    property string name
    property int size
    property variant attributes

    Text { text: item.name }
}

Thanks~!

sierdzio

First, to make it clear - both approaches are good & correct.

When/why use the above over directly declaring properties as shown below:

I'll give you a few reasons, but as stated above - it's not in any way a requirement, just a "makes sense" recommendation:

if you embed QtObject inside your Item, the properties of QtObject will not be visible outside of Item. So it is a way of declaring private properties in QML. They are not really private... but kind of ;-)
since QtObject is lighter (less memory etc.) than an Item, in some cases it might be a good idea to use a QtObject as a container for frequently used properties, accessed by many components within a file or project (think of it as a "style definition" file, holding default margins, colours etc. in your app), especially if you also declare these properties as readonly

Diracsbracket

Thanks, @sierdzio

@sierdzio said in Why use a QtObject to define properties rather than directly declaring properties?:

in some cases it might be a good idea to use a QtObject as a container for frequently used properties, accessed by many components within a file or project

In that case, those properties could also simply be added to the top-level element, and accessed where needed, no? How does using a QtObject instead save any memory then?

sierdzio

@Diracsbracket said in Why use a QtObject to define properties rather than directly declaring properties?:

Thanks, @sierdzio

@sierdzio said in Why use a QtObject to define properties rather than directly declaring properties?:

in some cases it might be a good idea to use a QtObject as a container for frequently used properties, accessed by many components within a file or project

In that case, those properties could also simply be added to the top-level element, and accessed where needed, no?

I meant creating a separate component out of it, shared between multiple files. Now that I think about it, though, I am not entirely sure it is allowed to have QtObject as a top-level component in a file.

How does using a QtObject instead save any memory then?

It doesn't, in the case you described. You're right.

fcarney

This article explains one use of QtObject in QML:
https://qml.guide/using-the-qtobject-element/

Diracsbracket

Thanks, @fcarney,
The bit about the default property of the QtObject was interesting.

@sierdzio said in Why use a QtObject to define properties rather than directly declaring properties?:

Now that I think about it, though, I am not entirely sure it is allowed to have QtObject as a top-level component in a file.

The example mentioned by @fcarney shows that it is possible indeed.

What I will take away from this is that QtObject is mainly to keep certain things private by embedding them into a child object, and that it is more "lightweight" than an Item for achieving this.

Cheers!