XML application examples

How to define DDS applications in XML.

How to define DDS applications in XML.

Sections:

• Example XML definition
• Creating and looking up the DDS entities
• Using IDL-based types

Example XML definition

The following is the configuration (ddsApplication.xml) that we will be using in the examples in this section:

<?xml version="1.0" encoding="UTF-8"?>
<dds xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
     xsi:noNamespaceSchemaLocation="https://community.rti.com/schema/current/rti_dds_profiles.xsd">
 
  <types>
      <struct name="Shape">
        <member name="color" stringMaxLength="128" type="string" key="true"/>
        <member name="x" type="int32"/>
        <member name="y" type="int32"/>
        <member name="shapesize" type="int32"/>
      </struct>
  </types>
 
  <domain_library name="ExampleDomainLibrary">
    <domain name="ExampleDomain" domain_id="0">
 
      <!-- Register the type Shape and use its definition above -->
      <register_type name="Shape" type_ref="Shape"/>
 
      <!-- Register the type MyType but do not provide an XML definition. -->
      <!-- The application will use a C# type -->
      <register_type name="MyType"/>
 
      <topic name="Square" register_type_ref="Shape"/>
      <topic name="MyTypeTopic" register_type_ref="MyType"/>
 
    </domain>
  </domain_library>
 
  <domain_participant_library name="ExampleParticipantLibrary">
    <domain_participant name="ExamplePublicationParticipant"
                        domain_ref="ExampleDomainLibrary::ExampleDomain">
      <publisher name="ExamplePublisher">
        <data_writer name="ShapeWriter" topic_ref="Square"/>
      </publisher>
    </domain_participant>
 
    <domain_participant name="ExampleSubscriptionParticipant"
                        domain_ref="ExampleDomainLibrary::ExampleDomain">
      <data_reader name="ShapeReader" topic_ref="Square">
        <content_filter name="ExampleTopic" kind="builtin.sql">
          <expression>color='BLUE'</expression>
        </content_filter>
      </data_reader>
    </domain_participant>
 
    <domain_participant name="ExampleIdlParticipant"
                        domain_ref="ExampleDomainLibrary::ExampleDomain">
      <publisher name="ExamplePublisher">
        <data_writer name="MyTypeWriter" topic_ref="MyTypeTopic"/>
      </publisher>
    </domain_participant>
  </domain_participant_library>
</dds>

Creating and looking up the DDS entities

Example: Create the participants defined in the XML file

 
    var provider = new Rti.Dds.Core.QosProvider("ddsApplication.xml");
 
    // Create the participants identified by the name we used in their
    // XML definition. This operation also creates all the contained
    // entities (topics, publishers, subscribers, readers, writers)
    using var pubParticipant = provider.CreateParticipantFromConfig(
        "ExampleParticipantLibrary::ExamplePublicationParticipant");
 
    using var subParticipant = provider.CreateParticipantFromConfig(
        "ExampleParticipantLibrary::ExampleSubscriptionParticipant");
 

Example: lookup the DataWriter and publish data

 
    // Look up the writer using the name we used in its XML definition
    //
    // The type of ShapeWriter is DynamicData, because ShapeType is
    // defined in the XML <types> tag and therefore created at runtime.
    var writer = pubParticipant.LookupDataWriter<DynamicData>(
        "ExamplePublisher::ShapeWriter");
 
    DynamicData data = writer.CreateData();
    data.SetValue("color", "RED");
    data.SetValue("shapesize", 70);
    data.SetValue("x", 10);
    data.SetValue("y", -10);
    writer.Write(data);
 

Example: lookup the DataReader and receive data

 
    var reader = subParticipant.LookupDataReader<DynamicData>("ShapeReader");
 
    reader.DataAvailable += _ =>
    {
        using var samples = reader.Take();
        foreach (var sample in samples.ValidData())
        {
            Console.WriteLine(sample);
        }
    };
 
    // ...
 

Using IDL-based types

The previous examples used DynamicData, but it is also possible to use strongly typed C# classes generated from IDL even if the readers and writers are defined in XML.

Example: Register an IDL type used by a writer or reader defined in XML

 
    // Register specific types (a)
    // The 'name' argument must correspond to the name used in
    // <register_type name="MyType"/>
    DomainParticipantFactory.Instance.RegisterTypeSupport<Example.MyType>(
        name: "MyType");
 
    // Or register a namespace within an assembly (b)
    DomainParticipantFactory.Instance.RegisterNamespace(
        typeof(Example.MyType).Assembly,
        "Example");
 
    // Whenever a type is referenced in the XML file, the QosProvider will
    // now look for its definition among those that have been explicitly
    // registered (a) or belong in a registered namespace (b)
    var provider = new QosProvider("ddsApplication.xml");
    using var participant = provider.CreateParticipantFromConfig(
        "ExampleParticipantLibrary::ExampleIdlParticipant");
 
    // Now we can look up a reader or a writer that uses Example.MyType
    // instead of DynamicData
    DataWriter<Example.MyType> writer =
        participant.LookupDataWriter<Example.MyType>(
            "ExamplePublisher::MyTypeWriter");
 
    var sample = new Example.MyType { /* ... */ };
    writer.Write(sample);
 
    Console.WriteLine(writer.Topic.TypeName);