Passing model data from delegate Loader to component in TableView object.

jebediahcrunk

Hi,

Firstly, I hope that this post conforms to the rules of this forum as this is my first post. I have a QAbstractTableModel that I am passing into my qml file. To then visualise this object (with a 2d grid), I am using a delegate loader and attempting to pass in the model from the loader to the component although i cant even manage to pass in model.gateType (just a QString) with the following code:

TableView {
                id: circuitGrid
    //this is where i pass in the model 
                model: qgui && qgui.gateModel ? qgui.gateModel : null

                Component {
                    id: gateDelegate
                    GateIcon {
                        gateType : delegateLoader.type
       
                        implicitWidth: 40
                        implicitHeight: 40
                }

                delegate: Item {
                    implicitWidth: 40
                    implicitHeight: 40

                    Loader {
                        id: delegateLoader
                        anchors.fill: parent
                        property string type : model.gateType
                        sourceComponent: gateDelegate
                        
                    }
                }
            }

I am sure there is a much simpler/better way to do this but i have been trying for a while now. The code gives the following error:

ReferenceError: delegateLoader is not defined

JoeCFD

Can you try:
gateType : model.gateType

be aware of id: delegateLoader is same for all delegates and not unique.

jebediahcrunk

Hi thanks,

Unfortunately that still gives
ReferenceError: model is not defined

JoeCFD

@jebediahcrunk Is } for GateIcon missing?

                Component {
                    id: gateDelegate
                    GateIcon {
                        gateType : delegateLoader.type
       
                        implicitWidth: 40
                        implicitHeight: 40
                    }
              }

jebediahcrunk

Sorry, i took some parts out of my actual code to make it a bit more readable so accidentally deleted that in the process. That is not the issue though.

JoeCFD

@jebediahcrunk I did similar thing.
model is visible for component and gateType : model.gateType should work.

Bob64

I do something like this in my application. Loader introduces some not necessarily intuitive behaviour about scoping of properties. I think you have accounted for this by introducing your type property at the loader level as a means of passing the model's gateType to your loaded component.

However, in my code at least, I do not refer to the loader in my loaded component (I do not even give the loader an ID). Instead I simply access the properties that are defined at the loader level because these now exist in the scope of the loaded component.

In your case, that would mean changing to this:

GateIcon {
    gateType : type // this is the property defined in `Loader`
    ...
}

GrecKo

@jebediahcrunk : is the Loader needed here?

What is discussed here is sharing data via context properties, a system that is not recommended anymore.

Bob64

@GrecKo said in Passing model data from delegate Loader to component in TableView object.:

@jebediahcrunk : is the Loader needed here?

What is discussed here is sharing data via context properties, a system that is not recommended anymore.

That's interesting. What would be recommended now?

I use Loader for a case where I have heterogeneous components shown in a ListView. I am aware of DelegateChooser as another way of doing this in theory, but I saw some weird behaviour when I tried to use it. I forget the details - I need to have another go sometime - but things like properties such as the model index that should have been accessible were sometimes not available in the delegates. Also, the documentation is unclear as to whether it should even be expected to work with a ListView. (Is ListView "internally based on a DelegateModel"? How am I supposed to know this?)

GrecKo

That's interesting. What would be recommended now?

DelegateChooser

Is ListView "internally based on a DelegateModel"? How am I supposed to know this?

Yes. Good question 😬 reading the code can answer that but that's hardly practical.
In practice view taking QAbstractItemModel but also QList, JS arrays are based on DelegateModel.
This is the case for ListView, TableView, Repeater, ...

Bob64

@GrecKo OK, thanks. I did actually want to switch to DelegateChooser so I will try it again. And good to know about its applicability.

jebediahcrunk

@Bob64 Thank you, just using 'type' worked! I knew it would be something simple like this. And @GrecKo thanks for the tip, that looks like a better solution so ill definitely look into it.