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// Copyright (C) 2020 The Qt Company Ltd.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GFDL-1.3-no-invariants-only
/*!
\title Qt Quick Demo - RSS News
\examplecategory {Web Technologies}
\ingroup qtquickdemos
\example demos/rssnews
\meta {tag} {demo,quick,download,xml}
\brief A QML RSS news reader that uses XmlListModel and XmlListModelRole custom
QML types to download XML data, ListModel and ListElement to create a category list,
and ListView to display the data.
\image qtquick-demo-rssnews-small.png
{RSS News reader with category sidebar and news headlines}
\e{RSS News} demonstrates the following \l{Qt Quick} features:
\list
\li Using custom QML types.
\li Using list models and list elements to represent data.
\li Using XML list models to download XML data.
\li Using list views to display data.
\li Using the \l Component type to create a footer for the news item
list view.
\li Using the \l [QML] {Image} type to create a button for closing the
app.
\endlist
\include examples-run.qdocinc
\section1 Using Custom Types
In the RSS News app, we use the following custom types that are each defined
in a separate .qml file:
\list
\li \c BusyIndicator.qml
\li \c CategoryDelegate.qml
\li \c NewsDelegate.qml
\li \c RssFeeds.qml
\li \c ScrollBar.qml
\endlist
\section1 Creating the Main Window
In \c Main.qml, we use a \l{Rectangle} type with custom properties to
create the app main window:
\quotefromfile demos/rssnews/Main.qml
\skipto Rectangle
\printuntil isPortrait
We will use the custom properties later for loading XML data and for
adjusting the screen layout depending on its orientation.
\section1 Creating a Category List
In \c Main.qml, we use the \c RssFeeds custom type that we specify in
\c RssFeeds.qml to create a list of feed categories:
\skipto RssFeeds
\printuntil }
In \c RssFeeds.qml, we use a \l ListModel type with a \l ListElement type to
create a category list where list elements represent feed categories:
\quotefromfile demos/rssnews/content/RssFeeds.qml
\skipto ListModel
\printuntil /^\}/
List elements are defined like other QML types except that they contain a
collection of \e role definitions instead of properties. Roles both define
how the data is accessed and include the data itself.
For each list element, we use the \c name role to specify the category name,
the \c feed role to specify the URL to load the data from, and the \c image
role to display an image for the category.
In \c Main.qml, we use a \l ListView type to display the category list:
\quotefromfile demos/rssnews/Main.qml
\skipto ListView
\printuntil }
\printuntil }
To lay out the category list horizontally at the top of the window in
portrait orientation and vertically on the left side in landscape
orientation, we use the \c orientation property. Based on the orientation,
we bind either the width or the height of the list to a fixed value
(\c itemWidth).
We use the \c anchors.top property to position the list view at the top of
the screen in both orientations.
We use the \c model property to load XML data from the \c rssFeeds model,
and \c CategoryDelegate as the delegate to instantiate each item in the
list.
\section1 Creating List Elements
In \c CategoryDelegate.qml, we use the \l Rectangle type with custom
properties to create list elements:
\quotefromfile demos/rssnews/content/CategoryDelegate.qml
\skipto Rectangle
\printuntil selected
We use \c required to declare the properties that we expect from the model.
We set the \c selected property to the \c ListView.isCurrentItem attached
property to specify that \c selected is \c true if \c delegate is the
current item.
We use the \l [QML] {Image} type \c source property to display the image,
centered in the delegate, specified for the list element by the \c image
role in the \c rssFeeds list model:
\skipto Image
\printuntil }
We use a \l Text type to add titles to list elements:
\printuntil Behavior
\printuntil }
We use the \c anchors property to position the title at the top of the list
element, with a 20-pixel margin. We use \c font properties to adjust font
size and text formatting.
We use the \c color and \c scale properties to brighten the text and to
scale it slightly larger when the list item is the current item.
By applying a \l Behavior to the property, we animate the actions of
selecting and deselecting list items.
We use a \l MouseArea type to download XML data when users tap a category
list element:
\skipto MouseArea
\printuntil }
\printuntil }
The \c anchors.fill property is set to \c delegate to enable users to tap
anywhere within the list element.
To load the XML data for the category list on a \c clicked event, we set
the \c currentIndex of the \c ListView attached property and
emit the \c clicked signal() in \c onClicked.
\section1 Downloading XML Data
In \c Main.qml, we use an \l XmlListModel type as a data source for
\l ListView elements to display news items in the selected category:
\quotefromfile demos/rssnews/Main.qml
\skipto XmlListModel {
\printuntil query
We use the \c source property and the \c window.currentFeed custom property
to fetch news items for the selected category.
The \c query property specifies that the \l XmlListModel generates a model
item for each \c <item> in the XML document.
We use the \l XmlListModelRole type to specify the model item attributes.
Each model item has the \c title, \c content, \c link, and \c pubDate
attributes that match the values of the corresponding \c <item> in the
XML document:
\printuntil pubDate
\printuntil }
We use the \c feedModel model in a \l ListView type to display the data:
\skipuntil ScrollBar
\skipto ListView
\printuntil }
\printuntil }
To list the news items below the category list in portrait orientation and
to its right in landscape orientation, we use the \c isPortrait custom
property to anchor the top of the news items list to the left of \c window
and bottom of \c categories in portrait orientation and to the right of
\c categories and bottom of \c window in landscape orientation.
We use the \c anchors.bottom property to anchor the bottom of the list view
to the bottom of the window in both orientations.
In portrait orientation, we clip the painting of the news items to the
bounding rectangle of the list view to avoid graphical artifacts when news
items are scrolled over other items. In landscape, this is not required,
because the list spans the entire screen vertically.
We use the \c model property to load XML data from the \c feedModel model,
and use \c NewsDelegate as the delegate to instantiate each item in the
list.
In \c NewsDelegate.qml, we use a \l Column type to lay out the XML data:
\quotefromfile demos/rssnews/content/NewsDelegate.qml
\skipto Column
\printuntil spacing
Within the column, we use a \l Row and another column to position images and
title text:
\skipto Row
\printuntil font.bold
\printuntil }
\printuntil }
We generate a textual representation of how long ago the item was posted
using the \c timeSinceEvent() JavaScript function:
\printuntil }
\printuntil }
We use the \c onLinkActivated signal handler to open the URL in an external
browser when users select the link.
\section1 Providing Feedback to Users
In \c CategoryDelegate.qml, we use the \c BusyIndicator custom type to
indicate activity while the XML data is being loaded:
\quotefromfile demos/rssnews/content/CategoryDelegate.qml
\skipto BusyIndicator
\printuntil }
We use the \c scale property to reduce the indicator size to \c 0.8. We bind
the \c visible property to the \c isCurrentItem attached property of the
\c delegate list view and \c loading property of the main window to display
the indicator image when a category list item is the current item and XML
data is being loaded.
We define the \c BusyIndicator type in \c BusyIndicator.qml. We use an
\l [QML] {Image} type to display an image and apply a \l NumberAnimation to
its \c rotation property to rotate the image in an infinite loop:
\quotefromfile demos/rssnews/content/BusyIndicator.qml
\skipto Image
\printuntil }
\printuntil }
In your apps, you can also use the \l BusyIndicator type from the
\l {Qt Quick Controls} module.
\section1 Creating Scroll Bars
In \c Main.qml, we use our own custom \c ScrollBar type to create scroll
bars in the category and news item list views. In your apps, you can also
use the \l ScrollView type from the \l {Qt Quick Controls} module.
First, we create a scroll bar in the category list view. We bind the
\c orientation property to the \c isPortrait property and to the
\c Horizontal value of the \c Qt::Orientation enum type to display a
horizontal scroll bar in portrait orientation and to the \c Vertical value
to display a vertical scroll bar in landscape orientation:
\quotefromfile demos/rssnews/Main.qml
\skipto ScrollBar
\printuntil }
Same as with the \c categories list view, we adjust the width and height of
the scroll bar based on the \c isPortrait property.
We use the \c scrollArea property to display the scroll bar in the
\c categories list view.
We use the \c anchors.right property to anchor the scroll bar to the right
side of the category list.
\skipto ScrollBar
\printuntil }
Second, we create another scroll bar in the news item list view. We want a
vertical scroll bar to appear on the right side of the view regardless of
screen orientation, so we can set the \c width property to \c 8 and bind the
\c anchors.right property to the \c window.right property. We use the
\c anchors.top property to anchor the scroll bar top to the bottom of the
category list in portrait orientation and to the top of the news item list
in landscape orientation. We use the \c anchors.bottom property to anchor
the scroll bar bottom to the list view bottom in both orientations.
We define the \c ScrollBar type in \c ScrollBar.qml. We use an \l Item type
with custom properties to create a container for the scroll bar:
\quotefromfile demos/rssnews/content/ScrollBar.qml
\skipto Item
\printuntil opacity
We use a \l BorderImage type to display the scroll bar thumb at the x and y
position that we calculate by using the \c position() function:
\skipto BorderImage
\printuntil height
\printuntil }
We use the \c size function to calculate the thumb width and height
depending on the screen orientation.
We use \c states to make the scroll bar visible when the users move the
scroll area:
\printuntil }
\printuntil }
We use \c transitions to apply a \l NumberAnimation to the \c opacity
property when the state changes from \c "visible" to the default state:
\printuntil /^\}/
\section1 Creating Footers
In \c Main.qml, we use a \l Component type with a \l Rectangle type to
create a footer for the news list view:
\quotefromfile demos/rssnews/Main.qml
\skipto Component
\printuntil }
\printuntil }
\printuntil }
We bind the \c width of the footer to the width of the component and the
\c height to the height of close button to align them when no news items are
displayed.
\section1 Creating Buttons
In \c Main.qml, we use an \l [QML] {Image} type to create a simple push
button that users can tap to close the app:
\printuntil Qt.quit()
\printuntil }
\printuntil }
\printuntil }
We use \c anchors to position the close button in the top right corner of
the news list view, with 4-pixel margins. Because the close button overlaps
the category list in portrait orientation, we animate the \c opacity
property to make the button almost fully transparent when users are
scrolling the category list.
We use the \c onClicked signal handler within a \l MouseArea to call the
\c quit() function when users select the close button.
\sa {QML Applications}
*/