XML-RPC support for Uiml.net

I meant to blog about this a long time ago, but I never actually got to it. In August, I implemented an extension to the call mechanism in Uiml.net that allows a UIML interface to call external application logic via the XML-RPC protocol.

I made an example UIML interface, which connects to the UserLand Betty server at betty.userland.com. It then resolves the state name from a state code entered by the user. Here are some screenshots of the rendered interface:

We use the standard UIML call tag. Here’s how we specify the behavior of the user interface:

<behavior>
  <rule>
    <condition>
      <event part-name="go" class="ButtonPressed"/>
    </condition>
    <action>
      <property part-name="stateName" name="text">
        <call name="Betty.GetStateName">
          <param>
            <property part-name="stateCode" name="text"/>
          </param>
        </call>
      </property>
    </action>
  </rule>
</behavior>

The XML-RPC web service is described in the logic part like this:

<logic>
  <d-component id="Betty" location="xmlrpc://betty.userland.com/RPC2">
    <d-method id="GetStateName" returns-value="System.String" maps-to="examples.getStateName">
      <d-param id="code" type="System.Int32"/>
    </d-method>
  </d-component>
</logic>

What has changed is that Uiml.net now checks for a protocol handler in the location attribute. If it’s xmlrpc://, we try to resolve the call using XML-RPC. Remember that local calls just specify the maps-to attribute.

We didn’t implement XML-RPC communication from scratch, but used a simple XML-RPC library for .NET: XmlRpcCS. The project seems to be dead since 2003, but it still works fine.

Takis has provided packages for XmlRpcCS (xmlrpccs) itself and for the dynamic Uiml.net XML-RPC glue library (uimlnet-xml-rpc).