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Qt Design Studio supports views, models, and delegates, so that when you add a Grid View, List View, or Path View component, the ListModel and the delegate component are added automatically.

However, the missing context of the application presents a challenge. Specific models defined in C++ are the most obvious case. Often, the context is missing simple properties, which are either defined in C++, or in other component files. A typical example is a component that uses the properties of its parent, such as parent.width.

Using Dummy Models

If you open a file in Form Editor that references a C++ model, you see nothing in it. If the data in the model is fetched from the internet, you have no control over it. To get reliable data, dummy data was introduced.

For example, the following code snippet describes the file example.qml that contains a ListView that in turn specifies a C++ model:

ListView {
    model: dataModel
    delegate: ContactDelegate {
        name: name
    }
}

Create a directory named dummydata in the root directory of the project, so that it is not deployed to the device. In the dummydata directory, create a file (.qml) that has the same name as the value of model:

qml/exampleapp/example.qml
dummydata/dataModel.qml

Then create the dataModel.qml file that contains the dummy data:

import QtQuick 2.0

ListModel {
     ListElement {
         name: "Ariane"
     }
     ListElement {
         name: "Bella"
     }
     ListElement {
         name: "Corinna"
     }
}

Creating Dummy Context

The following example presents a common pattern:

Item {
    width: parent.width
    height: parent.height
}

This works nicely for applications but Form Editor displays a zero-sized component. A parent for the opened file does not exist, because the context is missing. To get around the missing context, the idea of a dummy context is introduced. If you place a file with the same name as the application (here, example.qml) in the dummydata/context directory, you can fake a parent context:

import QtQuick 2.0
import QmlDesigner 1.0

DummyContextObject {
    parent: Item {
        width: 640
        height: 300
    }
}

Available under certain Qt licenses.
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