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examples/network/rsslisting/doc/src/rsslisting.qdoc

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-// Copyright (C) 2023 The Qt Company Ltd.
-// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GFDL-1.3-no-invariants-only
-
-/*!
-    \example serialization/rsslisting
-    \examplecategory {Networking}
-    \meta tag {serialization}
-    \title A minimal RSS listing application
-
-    \brief A demonstration of how to fetch and display a network resource.
-
-    This example shows how to fetch a resource the user has requested and
-    display data contained in the response, illustrated by an RSS listing
-    application. (RDF Site Summary, or Really Simple Syndication, is a standard
-    format for communicating updates to web sites. See
-    https://www.rssboard.org/rss-specification for details.) The user inferface
-    in the illustration is simple, as the focus of this example is on how to use
-    networking, but naturally a more sophisticated interface would be wanted for
-    a serious RSS reader.
-
-    The example also illustrates how to do asynchronous parsing of data as it is
-    received, preserving state in member variables so that an incremental parser
-    can consume chunks of data as they arrive over the network. Constituents of
-    the parsed content may start in one chunk of data but not be completed until
-    a later chunk, requiring the parser to retain state between calls.
-
-    \image rsslisting.png
-
-    The main program is fairly minimal. It simply instantiates a \l QApplication
-    and the \c RSSListing widget, shows the latter and hands over control to the
-    former. For the sake of illustration, it gives the widget the Qt blog's URL
-    as default value for the resource to check.
-
-    \snippet serialization/rsslisting/main.cpp 0
-
-    \section1 The RSSListing class
-
-    \snippet serialization/rsslisting/rsslisting.h 0
-
-    The widget itself provides a simple user interface for specifying the URL to
-    fetch and, once available updates are displayed, controlling the downloading
-    of updated items. A \l QLineEdit provides for input of the URL, and a
-    \l QTreeWidget for display of the results once fetched.
-
-    The widget downloads and parses the RSS (a form of XML) asynchronously,
-    feeding the data to an XML reader as it arrives. This supports reading of
-    very large data sources. Because the data is streamed from the network
-    through the XML reader, there is no need to retain the full text of the XML
-    in memory. In other context, a similar approach can allow the user to
-    interrupt such incremental loading.
-
-    \section2 Construction
-
-    \snippet serialization/rsslisting/rsslisting.cpp setup
-
-    The constructor sets up the assorted components of the widget and connects
-    their various signals to the slots it shall use to handle them.
-
-    The user interface consists of a line edit, a push button, and a list view
-    widget. The line edit is used for entering the URL to fetch; the push button
-    starts the process of fetching updates. The line edit is empty by default,
-    but the constructor's caller can override that, as our \c main() has done.
-    In any case, the user can replace the default with the URL of another RSS
-    feed.
-
-    The list view shows the updated items reported in the RSS feed.
-    Double-clicking on one of these sends its URL to the user's browser or other
-    user agent using \l QDesktopServices::openUrl().
-
-    \section2 The slots
-
-    \snippet serialization/rsslisting/rsslisting.cpp slots
-
-    All slots are kept simple by delegating any hard work to private methods.
-
-    When the user completes input of a URL, either by clicking the "Fetch"
-    button or by pressing the return key in the line edit, the \c fetch() slot
-    disables the "Fetch" button and disables further editing of the line edit.
-    It clears the display of available updates and delegates to \c get() the
-    initiating of an HTTP GET request.
-
-    When data is received, the network reply triggers its \l {QNetworkReply::}
-    {readyRead()} signal, which \c get() connects to the \c consumeData()
-    slot. This checks the response got a successful status code and, if it did,
-    calls \c parseXml() to consume the data.
-
-    If the network reply gets an error, this is delivered to the \c error()
-    slot, which reports the error, clears the XML stream reader then disconnects
-    from the reply and deletes it.
-
-    On completion (whether successful or otherwise) of a network reply, the \c
-    finished() slot restores the UI to be ready to accept a new URL to fetch by
-    re-enabling the line edit and "Fetch" button.
-
-    \section2 The get() method
-
-    \snippet serialization/rsslisting/rsslisting.cpp get
-
-    The private \c get() method is used by the \c fetch() slot to initiate an
-    HTTP GET request. It first clears the XML stream reader and, if a reply is
-    currently active, disconnects and deletes it. If the URL it has been passed
-    is valid, it asks the network access manager to GET it. It connects its
-    relevant slots to signals of the resulting reply (if any) and sets up its
-    XML stream reader to read data from the reply - a network reply object is
-    also a \c QIODevice, from which data can be read.
-
-    \section2 The parseXml() method
-
-    \snippet serialization/rsslisting/rsslisting.cpp parse
-
-    When data is received, and thus made available to the XML stream reader, \c
-    parseXml() reads from the XML stream, checking for \c item elements and,
-    within them, \c title and \c link elements. It will use the \c{rss:about}
-    attribute of an \c item as URL in the Link column of the tree-view, failing
-    that the content of its \c link element; and it uses the content of the \c
-    title element in the Title column of the tree-view. As each \c item element
-    closes, its details are turned into a new row in the tree widget, with the
-    extracted title and URL in the Title and Link columns.
-
-    The variables that keep track of the parsing state - \c linkString, \c
-    titleString and \c currentTag - are member variables of the \c RSSListing
-    class, even though they are only accessed from this method, because this
-    method may be called repeatedly, as new data arrives, and one chunk of
-    received data may start an element that isn't completed until a later chunk
-    arrives. This enables the parser to operate asynchronously as the data
-    arrives, instead of having to wait until all the data has arrived.
-
-    \sa QNetworkReply, QXmlStreamReader
-*/