Qt 5.9 | Qt Quick | Qt Quick Demo - RSS News

Qt 5.9.9 Reference Documentation

# Qt Quick Demo - RSS News

RSS News demonstrates the following Qt Quick features:

- Using custom types to create screens and screen controls.
- Using list models and list elements to represent data.
- Using XML list models to download XML data.
- Using list views to display data.
- Using the Component type to create a footer for the news item list view.
- Using the Image type to create a button for closing the app.

## Running the Example

To run the example from Qt Creator, open the Welcome mode and select the example from Examples. For more information, visit Building and Running an Example.

## Using Custom Types

In the RSS News app, we use the following custom types that are each defined in a separate .qml file:

- `BusyIndicator.qml`
- `CategoryDelegate.qml`
- `NewsDelegate.qml`
- `RssFeeds.qml`
- `ScrollBar.qml`

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

      import "./content"

## Creating the Main Window

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

      Rectangle {
          id: window

          width: 800
          height: 480

          property string currentFeed: rssFeeds.get(0).feed
          property bool loading: feedModel.status === XmlListModel.Loading
          property bool isPortrait: Screen.primaryOrientation === Qt.PortraitOrientation

We will use the custom properties later for loading XML data and for adjusting the screen layout depending on its orientation.

## 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:

          RssFeeds { id: rssFeeds }

In RssFeeds.qml, we use a ListModel type with a ListElement type to create a category list where list elements represent feed categories:

      ListModel {
          ListElement { name: "Top Stories"; feed: "news.yahoo.com/rss/topstories"; image: "images/TopStories.jpg" }
          ListElement { name: "World"; feed: "news.yahoo.com/rss/world"; image: "images/World.jpg" }
          ListElement { name: "Europe"; feed: "news.yahoo.com/rss/europe"; image: "images/Europe.jpg" }
          ListElement { name: "Asia"; feed: "news.yahoo.com/rss/asia"; image: "images/Asia.jpg" }
          ListElement { name: "U.S. National"; feed: "news.yahoo.com/rss/us"; image: "images/USNational.jpg"  }
          ListElement { name: "Politics"; feed: "news.yahoo.com/rss/politics"; image: "images/Politics.jpg" }
          ListElement { name: "Business"; feed: "news.yahoo.com/rss/business"; image: "images/Business.jpg" }
          ListElement { name: "Technology"; feed: "news.yahoo.com/rss/tech"; image: "images/Technology.jpg" }
          ListElement { name: "Entertainment"; feed: "news.yahoo.com/rss/entertainment"; image: "images/Entertainment.jpg" }
          ListElement { name: "Health"; feed: "news.yahoo.com/rss/health"; image: "images/Health.jpg" }
          ListElement { name: "Science"; feed: "news.yahoo.com/rss/science"; image: "images/Science.jpg" }
          ListElement { name: "Sports"; feed: "news.yahoo.com/rss/sports"; image: "images/Sports.jpg" }
      }

List elements are defined like other QML types except that they contain a collection of 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 `name` role to specify the category name, the `feed` role to specify the URL to load the data from, and the `image` role to display an image for the category.

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

          ListView {
              id: categories
              property int itemWidth: 190

              width: isPortrait ? parent.width : itemWidth
              height: isPortrait ? itemWidth : parent.height
              orientation: isPortrait ? ListView.Horizontal : ListView.Vertical
              anchors.top: parent.top
              model: rssFeeds
              delegate: CategoryDelegate { itemSize: categories.itemWidth }
              spacing: 3
          }

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 `orientation` property. Based on the orientation, we bind either the width or the height of the list to a fixed value (`itemWidth`).

We use the `anchors.top` property to position the list view at the top of the screen in both orientations.

We use the `model` property to load XML data from the `rssFeeds` model, and `CategoryDelegate` as the delegate to instantiate each item in the list.

## Creating List Elements

In CategoryDelegate.qml, we use the Rectangle type with custom properties to create list elements:

      Rectangle {
          id: delegate

          property bool selected: ListView.isCurrentItem

We set the `selected` property to the `ListView.isCurrentItem` attached property to specify that `selected` is `true` if `delegate` is the current item.

We use the Image type `source` property to display the image, centered in the delegate, specified for the list element by the `image` role in the `rssFeeds` list model:

          Image {
              anchors.centerIn: parent
              source: image
          }

We use a Text type to add titles to list elements:

          Text {
              id: titleText

              anchors {
                  left: parent.left; leftMargin: 20
                  right: parent.right; rightMargin: 20
                  top: parent.top; topMargin: 20
              }

              font { pixelSize: 18; bold: true }
              text: name
              color: selected ? "#ffffff" : "#ebebdd"
              scale: selected ? 1.15 : 1.0
              Behavior on color { ColorAnimation { duration: 150 } }
              Behavior on scale { PropertyAnimation { duration: 300 } }

We use the `anchors` property to position the title at the top of the list element, with a 20-pixel margin. We use `font` properties to adjust font size and text formatting.

We use the `color` property to brighten the text and to scale it slightly larger when the list item is the current item. By applying a 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:

          MouseArea {
              anchors.fill: delegate
              onClicked: {
                  delegate.ListView.view.currentIndex = index
                  if (window.currentFeed == feed)
                      feedModel.reload()
                  else
                      window.currentFeed = feed
              }
          }

The `anchors.fill` property is set to `delegate` to enable users to tap anywhere within the list element.

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

## 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:

          XmlListModel {
              id: feedModel

              source: "http://" + window.currentFeed
              query: "/rss/channel/item[child::media:content]"
              namespaceDeclarations: "declare namespace media = 'http://search.yahoo.com/mrss/';"

We use the `source` property and the `window.currentFeed` custom property to fetch news items for the selected category.

The `query` property specifies that the XmlListModel generates a model item for each `<item>` in the XML document.

We use the XmlRole type to specify the model item attributes. Each model item has the `title`, `description`, `image`, `link`, and `pubDate` attributes that match the values of the corresponding `<item>` in the XML document:

              XmlRole { name: "title"; query: "title/string()" }
              // Remove any links from the description
              XmlRole { name: "description"; query: "fn:replace(description/string(), '\&lt;a href=.*\/a\&gt;', '')" }
              XmlRole { name: "image"; query: "media:content/@url/string()" }
              XmlRole { name: "link"; query: "link/string()" }
              XmlRole { name: "pubDate"; query: "pubDate/string()" }
          }

We use the `feedModel` model in a ListView type to display the data:

          ListView {
              id: list

              anchors.left: isPortrait ? window.left : categories.right
              anchors.right: closeButton.left
              anchors.top: isPortrait ? categories.bottom : window.top
              anchors.bottom: window.bottom
              anchors.leftMargin: 30
              anchors.rightMargin: 4
              clip: isPortrait
              model: feedModel
              footer: footerText
              delegate: NewsDelegate {}
          }

To list the news items below the category list in portrait orientation and to its right in landscape orientation, we use the `isPortrait` custom property to anchor the top of the news items list to the left of `window` and bottom of `categories` in portrait orientation and to the right of `categories` and bottom of `window` in landscape orientation.

We use the `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 `model` property to load XML data from the `feedModel` model, and use `NewsDelegate` as the delegate to instantiate each item in the list.

In NewsDelegate.qml, we use a Column type to lay out the XML data:

      Column {
          id: delegate
          width: delegate.ListView.view.width
          spacing: 8

Within the column, we use a Row and another column to position images and title text:

          Row {
              width: parent.width
              spacing: 8

              Column {
                  Item {
                      width: 4
                      height: titleText.font.pixelSize / 4
                  }

                  Image {
                      id: titleImage
                      source: image
                  }
              }

              Text {
                  id: titleText

                  text: title
                  width: delegate.width - titleImage.width
                  wrapMode: Text.WordWrap
                  font.pixelSize: 26
                  font.bold: true
              }
          }

We generate a textual representation of how long ago the item was posted using the `timeSinceEvent()` JavaScript function:

          Text {
              width: delegate.width
              font.pixelSize: 12
              textFormat: Text.RichText
              font.italic: true
              text: timeSinceEvent(pubDate) + " (<a href=\"" + link + "\">Link</a>)"
              onLinkActivated: {
                  Qt.openUrlExternally(link)
              }
          }

We use the `onLinkActivated` signal handler to open the URL in an external browser when users select the link.

## Providing Feedback to Users

In CategoryDelegate.qml, we use the `BusyIndicator` custom type to indicate activity while the XML data is being loaded:

          BusyIndicator {
              scale: 0.8
              visible: delegate.ListView.isCurrentItem && window.loading
              anchors.centerIn: parent
          }

We use the `scale` property to reduce the indicator size to `0.8`. We bind the `visible` property to the `isCurrentItem` attached property of the `delegate` list view and `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 `BusyIndicator` type in `BusyIndicator.qml`. We use an Image type to display an image and apply a NumberAnimation to its `rotation` property to rotate the image in an infinite loop:

      Image {
          id: container

          source: "images/busy.png";

          NumberAnimation on rotation {
              running: container.visible
              from: 0; to: 360;
              loops: Animation.Infinite;
              duration: 1200
          }
      }

In your apps, you can also use the BusyIndicator type from the Qt Quick Controls module.

## Creating Scroll Bars

In rssnews.qml, we use our own custom `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 Qt Quick Controls module.

First, we create a scroll bar in the category list view. We bind the `orientation` property to the `isPortrait` property and to the `Horizontal` value of the `Qt::Orientation` enum type to display a horizontal scroll bar in portrait orientation and to the `Vertical` value to display a vertical scroll bar in landscape orientation:

          ScrollBar {
              id: listScrollBar

              orientation: isPortrait ? Qt.Horizontal : Qt.Vertical
              height: isPortrait ? 8 : categories.height;
              width: isPortrait ? categories.width : 8
              scrollArea: categories;
              anchors.right: categories.right
          }

Same as with the `categories` list view, we adjust the width and height of the scroll bar based on the `isPortrait` property.

We use the `scrollArea` property to display the scroll bar in the `categories` list view.

We use the `anchors.right` property to anchor the scroll bar to the right side of the category list.

          ScrollBar {
              scrollArea: list
              width: 8
              anchors.right: window.right
              anchors.top: isPortrait ? categories.bottom : window.top
              anchors.bottom: window.bottom
          }

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 `width` property to `8` and bind the `anchors.right` property to the `window.right` property. We use the `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 `anchors.bottom` property to anchor the scroll bar bottom to the list view bottom in both orientations.

We define the `ScrollBar` type in `ScrollBar.qml`. We use an Item type with custom properties to create a container for the scroll bar:

      Item {
          id: container

          property variant scrollArea
          property int orientation: Qt.Vertical

          opacity: 0

We use a BorderImage type to display the scroll bar thumb at the x and y position that we calculate by using the `position()` function:

          BorderImage {
              source: "images/scrollbar.png"
              border { left: 1; right: 1; top: 1; bottom: 1 }
              x: container.orientation == Qt.Vertical ? 2 : position()
              y: container.orientation == Qt.Vertical ? position() : 2
              width: container.orientation == Qt.Vertical ? container.width - 4 : size()
              height: container.orientation == Qt.Vertical ? size() : container.height - 4
          }

We use the `size` function to calculate the thumb width and height depending on the screen orientation.

We use `states` to make the scroll bar visible when the users move the scroll area:

          states: State {
              name: "visible"
              when: container.orientation == Qt.Vertical ?
                        scrollArea.movingVertically :
                        scrollArea.movingHorizontally
              PropertyChanges { target: container; opacity: 1.0 }
          }

We use `transitions` to apply a NumberAnimation to the `"opacity"` property when the state changes from "visible" to the default state:

          transitions: Transition {
              from: "visible"; to: ""
              NumberAnimation { properties: "opacity"; duration: 600 }
          }
      }

## Creating Footers

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

          Component {
              id: footerText

              Rectangle {
                  width: parent.width
                  height: closeButton.height
                  color: "lightgray"

                  Text {
                      text: "RSS Feed from Yahoo News"
                      anchors.centerIn: parent
                      font.pixelSize: 14
                  }
              }
          }

We bind the `width` of the footer to the width of the component and the `height` to the of close button to align them when no news items are displayed.

## Creating Buttons

In rssnews.qml, we use an Image type to create a simple push button that users can tap to close the app:

          Image {
              id: closeButton
              source: "content/images/btn_close.png"
              scale: 0.8
              anchors.top: parent.top
              anchors.right: parent.right
              anchors.margins: 4
              opacity: (isPortrait && categories.moving) ? 0.2 : 1.0
              Behavior on opacity {
                  NumberAnimation { duration: 300; easing.type: Easing.OutSine }
              }

              MouseArea {
                  anchors.fill: parent
                  onClicked: {
                      Qt.quit()
                  }
              }
          }

We use `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 `opacity` property to make the button almost fully transparent when users are scrolling the category list.

We use the `onClicked` signal handler within a MouseArea to call the `quit()` function when users select the close button.

Files:

- demos/rssnews/rssnews.qml
- demos/rssnews/content/BusyIndicator.qml
- demos/rssnews/content/CategoryDelegate.qml
- demos/rssnews/content/NewsDelegate.qml
- demos/rssnews/content/RssFeeds.qml
- demos/rssnews/content/ScrollBar.qml
- demos/rssnews/main.cpp
- demos/rssnews/rssnews.pro
- demos/rssnews/rssnews.qmlproject
- demos/rssnews/rssnews.qrc

See also QML Applications.