[Interest] QML required property in view delegate - bug?

[Benjamin Balga]

I agree with the doc for the "first level" of properties, but is it also by design even if the required properties are in a sub item, as in my 2nd example (where the delegate itself doesn't have any required properties)? It is this case that seems a bug to me.

--
Benjamin



> Le 13 mai 2022 à 14:42, Even Kristoffersen <Even.Kristoffersen at semcon.com> a écrit :
> 
> This behavior surprised me first time I encountered it as well, but it is not a bug as the behavior is documented here:
>  
> https://doc.qt.io/qt-5/qtquick-modelviewsdata-modelview.html <https://doc.qt.io/qt-5/qtquick-modelviewsdata-modelview.html>
> {required properties} can be used. If a delegate contains required properties, the named roles are not provided. Instead, the QML engine will check if the name of a required property matches that of a model role. If so, that property will be bound to the corresponding value from the model.
>  
> So if you have any “required” keyword in the delegate, the model won’t be attached.
> 
> 
> Even Kristoffersen
> even.kristoffersen at semcon.com <mailto:even.kristoffersen at semcon.com>		
> +4795223753
>  
> From: Interest <interest-bounces at qt-project.org> On Behalf Of Benjamin B (BBenj)
> Sent: fredag 13. mai 2022 14:11
> To: interest at qt-project.org
> Subject: [Interest] QML required property in view delegate - bug?
>  
> Hello,
>  
> I encountered a "friction point", and I think a bug, in QML with the "required" attribute for properties, when used in a view delegate.
> Here is an example hacked from the docs :
>  
> Item {
>     ListModel {
>         id: myModel
>         ListElement { type: "Dog"; age: 8; noise: "meow" }
>         ListElement { type: "Cat"; age: 5; noise: "woof" }
>     }
>     
>     component SomeDelegate: Item {
>         required property int age
>         property string text
>     }
>  
>     Repeater {
>         model: myModel
>         delegate: SomeDelegate {
>             text: model.noise
>         }
>     }
> }
>  
> Which raises the error "ReferenceError: model is not defined", as documented. Is there a way around this?
> I feel like this should be valid, as the delegate may not exactly match the model in every case. I would prefer not having this "auto-bind" feature and keep access to model/modelData/index.
>  
> But then, if I can't modify SomeDelegate (or want to keep the required property), how do I do?
> I tried various things to encapsulate SomeDelegate into something else, but I always get the same error. As soon as some child item has a required property, "model" is not available anymore.  This is a bug, right?
>  
> The following doesn't work for example (same error):
>  
> Item {
>     ListModel {
>         id: myModel
>         ListElement { type: "Dog"; age: 8; noise: "meow" }
>         ListElement { type: "Cat"; age: 5; noise: "woof" }
>     }
>     
>     component SomeDelegate: Item {
>         required property int age
>         property string text
>     }
>     
>     component AnotherDelegate: Item {
>         property int _age
>         property string _text
>         
>         SomeDelegate {
>             age: 0
>             text: ""
>         }
>     }
>  
>     Repeater {
>         model: myModel
>         delegate: AnotherDelegate {
>             _age: model.age
>             _text: model.noise
>         }
>     }
> }
>  
> (I'm testing with qml/qmlscene, Qt 6.3.0, Qt 5.15.2)
>  
>  
> Thank you,
>  
> --
> Benjamin
>  
>  
> 
> 
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