GAMBAS BOOK 3.19.1

The component gb.web.feed - WebFeed for short - corresponds to the RSS 2.0 specification, which you can also read about at https://cyber.harvard.edu/rss/rss.html.

Areas of application for RSS are, for example, news sites, blogs or podcasts whose contents are updated regularly - often several times a day. In addition to the RSS document structure and the terminology of RSS, you should also know XML as the basis of structured data in order to be able to use the WebFeed component successfully.

An RSS file is an XML file consisting of several 'channels', which in turn consist of 'entries'. Each entry is a unit that summarises a `news item` or whatever the content of the feed is. The gb.web.feed component can both read and write RSS files and supports images, media attachments, text input elements and cloud tags.

• The way to read an RSS feed is to create an RSS object, fill it with content and then parse it for the content you want to read. The next step is to then display the RSS feed data stored in a suitable format.
• You write RSS files via an object-oriented interface by creating an RSS object, assigning it channel objects (Channels) and in turn creating entry objects (Items) in them and filling them with data. The result is an XML document.

Example of an excerpt from an RSS feed:

<?xml version="1.0" encoding="UTF-8" ?>
<?xml-stylesheet href="/resources/xsl/rss2.jsp" type="text/xsl"?>
<rss version="2.0" xmlns:content="http://purl.org/rss/1.0/modules/content/">
<channel>
...
  <item>
    <title>Corona-Pandemie ...</title>
    <link>https://www.....html</link>
    <pubDate>Sun, 11 Oct 2020 10:14:50 +0200</pubDate>
    ...
    <description>Die gemeldeten Infektionszahlen bleiben hoch. ...</description>
  </item>
...
</channel>
</rss>

This class represents an RSS document. Its properties are those of its individual elements. It behaves like a read-write array of RssItem objects.

• You can use the class Rss to either read the content of an RSS document or to create an RSS document.
• You can create an object of the class Rss - as with all other classes of the WebFeed component.

In the following example, the RSS feed data in XML format (→ Chapter 18.12.5 RSS reader) of a website is read out. Here is the abbreviated RSS XML source text excerpt for an entry:

<item>
  <title>DFB-Elf ...</title>
  <link>http://www.unsersport.de/fussball/nationalmannschaft/...html</link>
  <description>Die Nationalmannschaft gewinnt in Krusemark mit 12:0 gegen den SV Heidesand.</description>
</item>

You can go through the individual RSS entries in the order in which they appear in the RSS document:

Dim hRss As Rss
Dim hRssItem As RssItem

For Each hRssItem In hRss
  ...
Next

The following source code returns an RssItem at the `index` RSS document position:

Dim hRss As Rss
Dim hRssItem As RssItem

hRssItem = hRss [ Index As Integer ]

So you replace an existing item in the RSS document at the position `Index`:

Dim hRss As Rss
Dim hRssItem As RssItem

hRss [ Index As Integer ] = hRssItem

• When asked what the many classes of the gb.web.feed component do, the following applies across the board:
• Each class represents a specific part of an RSS document as an object. What this means in concrete terms can be found in the RSS specification mentioned above.
• The WebFeed component implements a so-called document-object model.. On the one hand, this means that the document is parsed and the individual components can be manipulated as Gambas objects.
• Or you create a tree of Gambas objects with the help of the RSS classes and write a valid RSS XML document from it. To do this, add your elements in order. The use of the three properties title, link and description of the class Rss is mandatory to create an RSS document. All other properties are optional. Then call the method ToString() to get the XML document string.

The Rss class has these properties:

Table 24.12.0.1 : Properties of the class Rss

The class Rss has these methods:

Table 24.12.0.2 : Methods of the class Rss

Properties of the class:

Table 24.12.0.3 : Properties of the RssCategory class.

The class has the following three integer constants:

RssCloud.XmlRpc (0)RssCloud.Soap (1)RssCloud.HttpPost (2).

These are the properties of the class:

Table 24.12.0.4 : Properties of the RssCloud class.

You can create the class:

Dim hRssDate As RssDate
hRssDate = New RssDate ( [ Date As Date, Zone As String ] )

This class has only two properties:

Table 24.12.0.5 : Properties of the RssDate class

The class has these three properties:

Table 24.12.0.6 : Properties of the class RssEnclosure

GUID stands for 'Globally Unique IDentifier' - as a globally unique identifier for a particular feed item/article. The class has these properties:

Table 24.12.0.7 : Properties of the class RssGuid

The class RssImage has these properties:

Table 24.12.0.8 : Properties of the RssImage class.

These are the properties of the class RssItem:

Table 24.12.0.9 : Properties of the class RssItem

These are the two properties of the class RssSource:

The class describes a text input field that can optionally be displayed with the feed to implement a comment function. The specification provides that RSS generators allow the creator of an RSS document to create text input fields and a corresponding CGI script on the domain. A reader of the RSS feed can thus - if his RSS feed client supports it - send a text directly from the display of the feed to the generator.

The class has these properties:

Table 24.12.0.11 : Properties of the class RssTextInput