qt-everywhere-src-5.15.1/qtdoc/examples/demos/rssnews/doc/src/rssnews.qdoc

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/*!
    \title Qt Quick Demo - RSS News
    \ingroup qtquickdemos
    \example demos/rssnews
    \brief A QML RSS news reader that uses XmlListModel and XmlRole to download
    XML data, ListModel and ListElement to create a category list, and ListView
    to display the data.

    \image qtquick-demo-rssnews-small.png

    \e{RSS News} demonstrates the following \l{Qt Quick} features:

    \list
        \li Using custom types to create screens and screen controls.
        \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 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

    To use the custom types, we add an import statement to the main QML file,
    rssnews.qml that imports the folder called \c content where the types are
    located:

    \quotefromfile demos/rssnews/rssnews.qml
    \skipto content
    \printuntil "

    \section1 Creating the Main Window

    In rssnews.qml, we use a \l{Rectangle} type with custom properties to create
    the app main window:

    \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 rssnews.qml, we use the RssFeeds custom type that we specify in
    RssFeeds.qml to create a list of feed categories:

    \skipto RssFeeds
    \printuntil }

    In RssFeeds.qml, we use a ListModel type with a 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 rssnews.qml, we use a ListView type to display the category list:

    \quotefromfile demos/rssnews/rssnews.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 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 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 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 property 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 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.

    We use the \c onClicked signal handler to load the XML data for the category
    list. If the tapped category is already current, the \c reload() function
    is called to reload the data.

    \section1 Downloading XML Data

    In rssnews.qml, we use an XmlListModel type as a data source for ListView
    elements to display news items in the selected category:

    \quotefromfile demos/rssnews/rssnews.qml
    \skipto XmlListModel {
    \printuntil namespaceDeclarations

    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 XmlListModel generates a model item
    for each \c <item> in the XML document.

    We use the XmlRole type to specify the model item attributes. Each model
    item has the \c title, \c description, \c image, \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 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 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 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 Image type to display an image and apply a 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 BusyIndicator type from the
    \l {Qt Quick Controls} module.

    \section1 Creating Scroll Bars

    In rssnews.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 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/rssnews.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 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 NumberAnimation to the \c "opacity"
    property when the state changes from "visible" to the default state:

    \printuntil /^\}/

    \section1 Creating Footers

    In rssnews.qml, we use a \l Component type with a \l Rectangle type to
    create a footer for the news list view:

    \quotefromfile demos/rssnews/rssnews.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 of close button to align them when no news items are
    displayed.

    \section1 Creating Buttons

    In rssnews.qml, we use an \l 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 MouseArea to call the
    \c quit() function when users select the close button.

    \sa {QML Applications}
*/