Vistas de lista

Una vista de lista le puede ayudar a mostrar fácilmente muchos componentes de forma dinámica.

Las Listviews le pueden ayudar a mostrar los objetos de un modelo de una forma atractiva. Para usar una vista de lista, debe seguir la pista de tres cosas:

El modelo, que contiene los datos que quiere que muestre la vista de lista
El delegado, que define cómo se muestran los elementos del modelo
La vista de lista, propiamente dicha, que mostrará la información del modelo como indica el delegado

Si necesita más aclaraciones, la documentación de Qt tiene una página informativa sobre este tema.

Lo esencial de modelos y vistas

Una vista de lista tiene dos propiedades esenciales a las que debemos prestar atención:

model, que acepta los datos o el id del objeto que contiene los datos
delegate, que acepta el componente que usaremos para mostrar los datos del modelo

The model is not visible, as it only contains data. Typically the delegate will be wrapped in a Component so that it is reusable: it serves as a blueprint for how to instantiate each delegate.

Here is an example that contains exactly one list view, one model and one delegate, using a Kirigami.SubtitleDelegate:

import QtQuick
import QtQuick.Controls as Controls
import org.kde.kirigami as Kirigami

Kirigami.ApplicationWindow {
    title: "List of Plasma products"
    width: 600
    height: 400
    pageStack.initialPage: Kirigami.ScrollablePage {
        ListView {
            anchors.fill: parent
            model: plasmaProductsModel
            delegate: listDelegate
        }
        ListModel {
            id: plasmaProductsModel
            ListElement { product: "Plasma Desktop"; target: "desktop" }
            ListElement { product: "Plasma Mobile";  target: "mobile" }
            ListElement { product: "Plasma Bigscreen"; target: "TVs" }
        }
        Component {
            id: listDelegate
            Controls.ItemDelegate {
                width: ListView.view.width
                text: `${model.product} is KDE software developed for ${model.target} stored at index ${model.index} of this list`
            }
        }
    }
}

And the exact same example, inline:

import QtQuick
import QtQuick.Controls as Controls
import org.kde.kirigami as Kirigami

Kirigami.ApplicationWindow {
    title: "List of Plasma products (inline)"
    width: 600
    height: 400
    pageStack.initialPage: Kirigami.ScrollablePage {
        ListView {
            anchors.fill: parent
            model: ListModel {
                id: plasmaProductsModel
                ListElement { product: "Plasma Desktop"; target: "desktop" }
                ListElement { product: "Plasma Mobile";  target: "mobile" }
                ListElement { product: "Plasma Bigscreen"; target: "TVs" }
            }
            delegate: Controls.ItemDelegate {
                width: ListView.view.width
                text: `${model.product} is KDE software developed for ${model.target} stored at index ${model.index} of this list`
            }
        }
    }
}

Entendiendo los modelos

The model contains the data that will be used to populate the list view. Different ways to use models have different ways to access the data:

MODO DE USO	CÓMO SE ACCEDE	CUÁNDO SE USA
Modelos de Qt con más de un rol	model.index, model.somerole	En la mayoría de casos
Modelos de Qt con un rol	model.index, model.somerole, model.modelData	In most cases, for prototyping
JavaScript array model	model.index, model.modelData	For prototyping
Integer model	model.index, model.modelData	For prototyping

You can read about other ways to use models in the Qt documentation.

In the table above, "Qt models" refers to both C++-specific models like QAbstractListModel and QML-specific models like ListModel. This tutorial page will only focus on QML-specific models. Farther ahead we provide a tutorial for Connecting C++ models to QML using QAbstractListModel.

The model.index property is made available to every model and contains the index (the position) of each delegate. It can be shortened to index for convenience.

The model.somerole property mentioned above is just a placeholder, it is not a specific property that comes from QML: somerole can be any role that is defined by the model. In the first code example of this page shown above the table, the plasmaProductsModel model has the product and target roles, which can be accessed with model.product and model.target, respectively.

Just as model.index can be shortened to index, each model.somerole property can be shorted to just somerole (like product) for convenience, but it is recommended that they be turned into required properties:

import QtQuick
import QtQuick.Controls as Controls
import org.kde.kirigami as Kirigami

Kirigami.ApplicationWindow {
    title: "List of Plasma products (shortened with required properties)"
    width: 600
    height: 400
    pageStack.initialPage: Kirigami.ScrollablePage {
        ListView {
            anchors.fill: parent
            model: plasmaProductsModel
            delegate: listDelegate
        }
        ListModel {
            id: plasmaProductsModel
            ListElement { product: "Plasma Desktop"; target: "desktop" }
            ListElement { product: "Plasma Mobile";  target: "mobile" }
            ListElement { product: "Plasma Bigscreen"; target: "TVs" }
        }
        Component {
            id: listDelegate
            Controls.ItemDelegate {
                width: ListView.view.width
                required property string product
                required property string target
                required property int index
                text: `${product} is KDE software developed for ${target} stored at index ${index} of this list`
            }
        }
    }
}

Additionally, if the model contains only one role or has no role at all, its data can also be accessed with the property model.modelData, which can also be shortened to modelData (and as such would also need to be a required property):

import QtQuick
import QtQuick.Controls as Controls
import org.kde.kirigami as Kirigami


Kirigami.ApplicationWindow {
    title: "List of KDE software"
    width: 400
    height: 400
    pageStack.initialPage: Kirigami.ScrollablePage {
        ListView {
            anchors.fill: parent
            model: kdeSoftwareModel
            delegate: listDelegate
        }
        ListModel {
            id: kdeSoftwareModel
            ListElement { software: "Dolphin" }
            ListElement { software: "Discover" }
            ListElement { software: "KHelpCenter" }
            ListElement { software: "KCalc" }
            ListElement { software: "Ark" }
        }
        Component {
            id: listDelegate
            Controls.ItemDelegate {
                width: ListView.view.width
                required property string modelData
                text: modelData // This matches model.software
            }
        }
    }
}

For comparison, here is how the above code would look like with a JavaScript array, with no role:

import QtQuick
import QtQuick.Controls as Controls
import org.kde.kirigami as Kirigami

Kirigami.ApplicationWindow {
    title: "List of KDE software (as JS array)"
    width: 400
    height: 400
    pageStack.initialPage: Kirigami.ScrollablePage {
        ListView {
            anchors.fill: parent
            model: ["Dolphin", "Discover", "KHelpCenter", "KCalc", "Ark"]
            delegate: listDelegate
        }
        Component {
            id: listDelegate
            Controls.ItemDelegate {
                width: ListView.view.width
                required property string modelData
                text: modelData
            }
        }
    }
}

Using an integer for the model can be useful for very specific cases, namely prototyping and tests:

import QtQuick
import QtQuick.Controls as Controls
import org.kde.kirigami as Kirigami

Kirigami.ApplicationWindow {
    title: "Simple list of indexes"
    width: 400
    height: 400
    pageStack.initialPage: Kirigami.ScrollablePage {
        ListView {
            anchors.fill: parent
            model: 30
            delegate: listDelegate
        }
        Component {
            id: listDelegate
            Controls.ItemDelegate {
                width: ListView.view.width
                required property string modelData
                text: `This delegate's index is: ${modelData}`
            }
        }
    }
}

Entendiendo las vistas y los delegados

Volvamos al ejemplo original:

import QtQuick
import QtQuick.Controls as Controls
import org.kde.kirigami as Kirigami

Kirigami.ApplicationWindow {
    title: "List of Plasma products"
    width: 600
    height: 400
    pageStack.initialPage: Kirigami.ScrollablePage {
        ListView {
            // anchors.fill: parent
            model: plasmaProductsModel
            delegate: listDelegate
        }
        ListModel {
            id: plasmaProductsModel
            ListElement { product: "Plasma Desktop"; target: "desktop" }
            ListElement { product: "Plasma Mobile";  target: "mobile" }
            ListElement { product: "Plasma Bigscreen"; target: "TVs" }
        }
        Component {
            id: listDelegate
            Controls.ItemDelegate {
                width: ListView.view.width
                text: `${model.product} is KDE software developed for ${model.target} stored at index ${model.index} of this list`
            }
        }
    }
}

Unlike the model (which merely contains data) and a delegate Component (which only appears when instantiated), the view is a visual component immediately instantiated and so it needs to either have its dimensions set or use anchors or Layouts.

As views are commonly lists of content the user would want to scroll through, when they are added to a Kirigami.ScrollablePage, views become the main content with little padding around them, and there is no need to make it fill the page. When the view is added to a simple Kirigami.Page, it will require to set its dimensions properly before it will show up. In other words: in the scrollable page above, anchors.fill: parent is not required; if a simple page was used, it would be required.

There are multiple views APIs can be used, some from Qt and some from Kirigami. Here are the most commonly used ones:

ListView de Qt
GridView de Qt
TableView de Qt
TreeView de Qt
CardsListView de Kirigami
ColumnView de Kirigami

The delegate on the other hand always need to have its dimensions set. Generally its dimensions are set to use only the full width of the view.

Errores comunes

The above means that delegates should not have bottom anchors, since the delegate doesn't need to have the same height as the view. In other words, you will probably never want to use anchors.fill: parent.

Additionally, while it is possible to set its dimensions using the parent and anchors, which is usually the view's contentItem, like so:

Controls.ItemDelegate {
    anchors.left: parent.left
    anchors.right: parent.right
    text: // ...
}

It is not guaranteed that the delegate's parent will be a view, and so it should be avoided. Instead, use the ListView.view attached property to point to the delegate's parent view:

Controls.ItemDelegate {
    width: ListView.view.width
    text: // ...
}

The most common use of a delegate is within a Component, which does not instantiate the delegate immediately. When a view is constructed, the delegate is then used as a blueprint to make each item in the view.

While you can make your own custom components to be used as delegates without delegate-specific Qt APIs (for example, a Layout containing a few Items), QtQuick Controls does provide delegate APIs that are simpler to use:

ItemDelegate (delegates with only text)
CheckDelegate (delegates with a checkbox)
RadioDelegate (delegates with a radio)
SwitchDelegate (delegates with a switch)
SwipeDelegate (delegates that can be swiped)

You should prefer using the upstream Qt delegates where possible.

On top of these Qt delegates, Kirigami provides its own equivalents, with the added functionality of subtitles and icons:

The API ending with "Delegate" can be set as a direct delegate of the view, just like the previous examples that used Controls.ItemDelegate:

import QtQuick
import QtQuick.Controls as Controls
import org.kde.kirigami as Kirigami
import org.kde.kirigami.delegates as KD

Kirigami.ApplicationWindow {
    title: "List of Plasma products"
    width: 600
    height: 400
    pageStack.initialPage: Kirigami.ScrollablePage {
        ListView {
            model: plasmaProductsModel
            delegate: listDelegate
        }
        ListModel {
            id: plasmaProductsModel
            ListElement { product: "Plasma Desktop"; target: "desktop" }
            ListElement { product: "Plasma Mobile";  target: "mobile" }
            ListElement { product: "Plasma Bigscreen"; target: "TVs" }
        }
        Component {
            id: listDelegate
            KD.CheckSubtitleDelegate {
                width: ListView.view.width
                text: `${model.product} is KDE software developed for ${model.target}.`
                subtitle: `This delegate is stored at index ${model.index} of this list`
                icon.name: "kde"
            }
        }
    }
}

Both TitleSubtitle and IconTitleSubtitle are expected to be used to override a Qt delegate's contentItem, for example:

import QtQuick
import QtQuick.Controls as Controls
import org.kde.kirigami as Kirigami
import org.kde.kirigami.delegates as KD

Kirigami.ApplicationWindow {
    title: "List of Plasma products"
    width: 600
    height: 400
    pageStack.initialPage: Kirigami.ScrollablePage {
        ListView {
            // anchors.fill: parent
            model: plasmaProductsModel
            delegate: listDelegate
        }
        ListModel {
            id: plasmaProductsModel
            ListElement { product: "Plasma Desktop"; target: "desktop" }
            ListElement { product: "Plasma Mobile";  target: "mobile" }
            ListElement { product: "Plasma Bigscreen"; target: "TVs" }
        }
        Component {
            id: listDelegate
            Controls.ItemDelegate {
                width: ListView.view.width
                text: `${model.product} is KDE software developed for ${model.target}.`
                contentItem: KD.IconTitleSubtitle {
                    title: parent.text
                    subtitle: `This delegate is stored at index ${model.index} of this list`
                    icon.name: "kde"
                }
            }
        }
    }
}

A practical example of using Kirigami delegates can be seen in the ListItemTest file in the Kirigami Repository.

Barras de avance e indicadores

Entendiendo CMakeLists