**Course Title:** QML Application Development **Section Title:** Models and Views **Topic:** Introduction to models: ListModel, XmlListModel, and Custom Models **Introduction** ---------------- In QML, models are used to manage and provide data to views, such as ListView and GridView. In this topic, we will explore the different types of models available in QML, including ListModel, XmlListModel, and custom models. **ListModel** ------------ ListModel is a basic model that can hold a list of data. It is commonly used when you need to display a simple list of items, such as a list of strings or objects. **Example: Using ListModel** ```qml import QtQuick 2.12 import QtQuick.Window 2.12 Window { visible: true width: 400 height: 200 ListModel { id: fruitModel ListElement { name: "Apple" } ListElement { name: "Banana" } ListElement { name: "Orange" } } ListView { anchors.fill: parent model: fruitModel delegate: Text { text: "Fruit: " + name } } } ``` In this example, we create a ListModel called `fruitModel` and populate it with three ListElements, each containing a `name` property. We then create a ListView and set its `model` property to `fruitModel`. Finally, we define a delegate that displays the `name` property of each ListElement. **XmlListModel** ---------------- XmlListModel is a model that can parse XML data and provide it to views. It is commonly used when you need to display data from an XML file or a web service that returns XML data. **Example: Using XmlListModel** ```qml import QtQuick 2.12 import QtQuick.Window 2.12 Window { visible: true width: 400 height: 200 XmlListModel { id: fruitModel source: "fruits.xml" query: "/fruits/fruit" XmlRole { name: "name"; query: "name/string()" } } ListView { anchors.fill: parent model: fruitModel delegate: Text { text: "Fruit: " + name } } } ``` In this example, we create an XmlListModel called `fruitModel` and set its `source` property to an XML file called `fruits.xml`. We then define an `XmlRole` that extracts the `name` property from each `fruit` element in the XML file. Finally, we create a ListView and set its `model` property to `fruitModel`. **Custom Models** ----------------- Custom models are models that you create yourself to manage and provide data to views. They are commonly used when you need to display complex data that requires custom logic to manage. **Example: Creating a custom model** ```qml import QtQuick 2.12 import QtQuick.Window 2.12 Window { visible: true width: 400 height: 200 ListModel { id: fruitModel // custom logic to populate the model function addFruit(name) { append({ name: name }) } function removeFruit(index) { remove(index) } } ListView { anchors.fill: parent model: fruitModel delegate: Text { text: "Fruit: " + name } } // example usage: Component.onCompleted: { fruitModel.addFruit("Apple") fruitModel.addFruit("Banana") fruitModel.addFruit("Orange") } } ``` In this example, we create a ListModel called `fruitModel` and define two custom functions, `addFruit` and `removeFruit`, to manage the data in the model. We then create a ListView and set its `model` property to `fruitModel`. **Best Practices** ------------------ * Use ListModel when you need to display a simple list of data. * Use XmlListModel when you need to display data from an XML file or a web service that returns XML data. * Use custom models when you need to display complex data that requires custom logic to manage. * Always define a delegate that displays the data in the model. **Conclusion** ---------- In this topic, we have explored the different types of models available in QML, including ListModel, XmlListModel, and custom models. We have also seen examples of how to use each type of model to display data in a ListView. By following the best practices outlined in this topic, you can create effective and efficient models to display data in your QML applications. **What to do next** ------------------ * Experiment with different types of models to display data in a ListView. * Create a custom model to manage complex data. * Use the XmlListModel to display data from an XML file or a web service. **Leave a comment or ask for help** --------------------------------- If you have any questions or need help with any of the concepts covered in this topic, please leave a comment below. We will be happy to assist you. **Proceed to the next topic** ------------------------------ * [Displaying data in ListView and GridView](https://www.qt.io/qt-for-qt-quick-developers.html#displaying-data-in-listview-and-gridview)