Slint Application Architecture

[Murmele]

Hi,

I created a small application to test rust with slint Multimeter Control and I have some architecture design questions.
I have a mainwindow which is able to show multiple multimeter controls at the same time. They can be added dynamically by clicking a button. Once I click the button I will pick up the model and add new multimeter data

let app = app_weak.unwrap();
let model = app.get_dmm_data();
let model = model.as_any().downcast_ref::<VecModel<DmmData>>().unwrap();
model.push(DmmData { id, ip, connected: true, result: 0.0, terminal: Terminal::Front, mode: Mode::VoltageDc});

(https://gitlab.com/Murmele/multimetercontrol/-/blob/main/src/lib.rs?ref_type=heads#L30-L32)

dmm_data is an array in the AppWindow: in property <[DmmData]> dmm_data: [];

struct DmmData {
    ip: string,
}

When the model changes, in slint new objects get created. That means that all previous Dmm objects get deleted and all are recreated?

https://gitlab.com/Murmele/multimetercontrol/-/blob/main/ui/dmm-control.slint?ref_type=heads#L32-L43
AppWindow:

for dmm in dmm_data: Dmm {
	...
}

export component Dmm inherits Rectangle {
    in property <string> ip <=> ip-text.text;
	
	HorizontalLayout {
		ip-text:= Text {
			text: "<IP>";
		}
	}
}

Then I assign data to that Dmm object. So the ip is stored once in the model dmm_data and in the Dmm object and at least also in the ip-text object or am I wrong?
Is there a better way to handle the data so that there exist less number of copies?

[hunger]

Whether the old values get deleted or not depends on what you do: They do get replaced when you replace the entire model (even if most entries contain the same data). They are not replaced when you add a new element into the current model. You seem to be doing the latter, but that is hard to tell with just a few snippets of code.

The ip in Dmm is a two-way binding to ip-text.text. So they are effectively references to the same memory, sharing the storage space. We do not yet support two-way bindings to fields in a struct or data in a model, so you will have one real copy there. Extending two-way bindings is work in progress, I hope we get that for struct fields and model fields soon.

[Murmele]

Thanks for the hint about the two-way binding that they are references. So that means I have only 2 copies instead of 3.

If I push another DmmData to model as shown above, in the AppWindow my loop over dmm_data will be called for the complete vector or only for the added element?

for dmm in dmm_data: Dmm {
	ip: dmm.ip;
}

[hunger]

It should only create components for the new entries in the model and keep the old ones around.