How to assign model roles to delegates

[ustulation]

Is there any way i can specify the role name accessible to the delegate of Repeaters and ListViews at run time? For instance i have the following GenericRepeater {} that I want to reuse. I have lot of QAbstractListModel derived classes in C++. Many of them have different rolenames and different number of roles (if they all had just one role I could have accessed it by mentioning modelData, but moment there are more than one, modelData is no longer provided by Repeaters/ListViews to their delegates).

Here is the Repeater code:

//GenericRepeater.qml

Column {
 property alias m_refModel: objRepeater.model
 
 Repeater {
    id: objRepeater
 
    delegate: Rectangle {
       height: 40; width: 200
       color: "#000000"
       Text {
          color: "#ffffff"
          anchors.fill: parent
          text: model.genericRole  //-----(1) What can I write here
       }
    }
 }
}

Column {
 property alias m_refModel: objRepeater.model
 
 Repeater {
    id: objRepeater

    delegate: Rectangle {
       height: 40; width: 200
       color: "#000000"
       Text {
          color: "#ffffff"
          anchors.fill: parent
          text: model.genericRole  //-----(1) What can I write here
       }
    }
 }
}

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I want to use it in many places as:
//SomeFile.qml

GenericRepeater { m_refModel: myCppClass0 }
GenericRepeater { m_refModel: myCppClass1 }

GenericRepeater { m_refModel: myCppClass0 }
GenericRepeater { m_refModel: myCppClass1 }

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//SomeOtherFile.qml

GenericRepeater { m_refModel: myCppClass2 }

GenericRepeater { m_refModel: myCppClass2 }

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where myCppClass<n> are objects of classes derived from QAbstractListModel and each of those classes can have any number of roles each arbitarily named. Ofcourse the code will fail at (1) above. How do I use GenericRepeater in SomeFile.qml etc ? Just like I assign various models to GenericRepeater {} can I assign the roles too ? If no, then is there an alternate way to realize this ?

[wysota]

You can have a proxy model that does custom mapping of model roles.

[aamer4yu]

Have a look at QAbstractItemModel::setRoleNames
Oops,, Sorry I seem to have overlooked the problem in hurry. You can go with as Wysota said

[ustulation]

Hi,
I've found one solution to letting the user input the role at runtime but i don't know if it's a standard way and should be used.

The roles are usually accessed as:

text: model.someRole

text: model.someRole

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But as stated this is like hard-coding the role. If instead I want the user to input the role via line-edit and show that instead, there is no way I can do it here
but this seems to be equivalent:

text: model["someRole"]

text: model["someRole"]

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Bingo!
Now that since it is a string, the user can easily input it during the runtime. But is this a standard way or it just happens to work?

[anda_skoa]

I think that is just fine.

As wysota said, a proxy model might even allow to keep the traditional syntax, by doing the mapping internally.

Cheers,
_

[ustulation]

I think that is just fine.

<1> So why isn't it documented? Seems very important to me - Hard-coding vs freedom, you choose.

a proxy model might even allow to keep the traditional syntax, by doing the mapping internally

I'm guilty of not being able to wrap my head around that

<2> What exactly does that mean? My code is the file GenericRepeater.qml. People using my code will write files such as SomeFile.qml and SomeOtherFile.qml (refer to the 1st post in this thread). How should the structure of GenericRepeater.qml be?

Here is an attempt at the public interface:

Column {
 //--- begin public interface ---
 property var m_refModel      //this is what the user will supply
 property string m_roleToUse //this is what the user will supply
 //--- end public interface --- 
 
 Repeater {
    id: objRepeater
 
    model: //--------------(1) what should I give here?
 
    delegate: Rectangle {
       height: 40; width: 200
       color: "#000000"
       Text {
          color: "#ffffff"
          anchors.fill: parent
          text: //--------------(2) What role should i give here?
       }
    }
 }
}

Column {
 //--- begin public interface ---
 property var m_refModel      //this is what the user will supply
 property string m_roleToUse //this is what the user will supply
 //--- end public interface --- 

 Repeater {
    id: objRepeater
 
    model: //--------------(1) what should I give here?

    delegate: Rectangle {
       height: 40; width: 200
       color: "#000000"
       Text {
          color: "#ffffff"
          anchors.fill: parent
          text: //--------------(2) What role should i give here?
       }
    }
 }
}

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Questions and comments are inlined.

Can you pls answer those?

[wysota]

<1> So why isn't it documented?

It is documented. It is part of Javascript specification where object.property is equivalent to object["property"]. Which also implies by the way that if you have a function "fun" in object "object" you can call it via object.fun() or object["fun"]().

Ad 2.: m_refModel and modelData[m_roleToUse]

[ustulation]

It is documented. It is part of Javascript specification where object.property is equivalent to object["property"]. Which also implies by the way that if you have a function "fun" in object "object" you can call it via object.fun() or object["fun"]().

ooo that was subtle for me. I's too busy thinking of QML syntax that i forgot it's javascript working. Thanks a lot for that !

m_refModel and modelData[m_roleToUse]

ya that's what i mentioned in #4. That is clear. What was not clear was your original proposal to use a proxying model somewhere in between (if i understood correctly) m_refModel and Repeater::model which would continue to allow me to use the

tradational syntax

as anda_skoa said.

[wysota]

You put a proxy model between a base model and a view. That proxy model can take care of mapping roles based on the base model data and its own role specification.