Списки

Панель перегляду списку може спростити для вас динамічний показ багатьох компонентів.

Панелі списків можуть допомогти у показі об'єктів на основі моделі у привабливий спосіб. Щоб правильно користуватися панеллю списку, вам слід стежити за трьома речима:

  1. Моделлю, яка містить дані, які має бути показано на вашій панелі списку
  2. Делегата, який визначає, як буде показано кожне з елементів моделі
  3. Самої панелі списку, на якій буде показано відомості щодо моделі, відповідно до параметрів делегата

Якщо вам потрібні додаткові пояснення, у документації Qt є інформативна сторінка щодо цього питання.

Essentials of models and views

У панелі списку є дві ключові властивості, на які нам слід звернути увагу:

  • model, яка приймає дані або id об'єкта, який містить дані
  • delegate, яка приймає компонент, якими ми скористаємося для показу даних у моделі

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`
            }
        }
    }
}

Розбираємося із моделями

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:

СПОСІБ ВИКОРИСТАННЯДОСТУПУМОВИ ВИКОРИСТАННЯ
Qt models with more than one rolemodel.index, model.someroleIn most cases
Qt models with one rolemodel.index, model.somerole, model.modelDataIn most cases, for prototyping
JavaScript array modelmodel.index, model.modelDataFor prototyping
Integer modelmodel.index, model.modelDataFor 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}`
            }
        }
    }
}

Розбираємося із переглядами і делегатами

Let's go back to the original example:

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:

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.

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:

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.