| Note: This tutorial assumes that you have completed the previous tutorials: Understanding Service Types, Service Discovery via Polling. |
 Please ask about problems and questions regarding this tutorial on answers.ros.org. Don't forget to include in your question the link to this page, the versions of your OS & ROS, and also add appropriate tags. |
Service Discovery via Callbacks
Description: Shows how to do service discovery with jmdns using callbacks.Keywords: zeroconf jmdns
Tutorial Level: INTERMEDIATE
Contents
Notes
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This is mostly working now - particularly for android systems however this part of the jmmdns code is still fairly experimental and will be likely to change. If you run into issues, please contact <d DOT stonier AT gmail DOT com>, we're working the jmdns developer to improve certain parts of the discovery mechanisms.
Code Sample
1 import java.util.ArrayList;
2 import com.github.ros_java.zeroconf_jmdns_suite.jmdns.Zeroconf;
3 import com.github.ros_java.zeroconf_jmdns_suite.jmdns.DiscoveredService;
4 import com.github.ros_java.zeroconf_jmdns_suite.jmdns.ZeroconfDiscoveryHandler;
5 import com.github.ros_java.zeroconf_jmdns_suite.jmdns.DiscoveredService;
6
7 class DiscoveryHandler implements ZeroconfDiscoveryHandler {
8 public DiscoveryHandler() {
9 this.discovered_services = new ArrayList<DiscoveredService>();
10 }
11 public void serviceAdded(DiscoveredService service) {
12 // custom handling code
13 }
14
15 public void serviceRemoved(DiscoveredService service) {
16 // custom handling code
17 }
18
19 public void serviceResolved(DiscoveredService service) {
20 // custom handling code
21 }
22 private ArrayList<DiscoveredService> discovered_services;
23 }
24
25 Zeroconf discovery = new Zeroconf();
26 DiscoveryHandler discovery_handler = new DiscoveryHandler();
27 zeroconf.setDefaultDiscoveryCallback(discovery_handler);
28 discovery.addListener("_ros-master._tcp","local");
Breaking it Down
Initialise the module:
Add a default discovery handler (written by yourself) (see further down for an example). This will be used to handle callbacks for every listener you add.
Alternatively, you can add specific handlers for specific listeners:
1 TCPDiscoveryHandler tcp_discovery_handler = new TCPMasterDiscoveryHandler();
2 discovery.addListener("_ros-master._tcp","local",tcp_discovery_handler);
3 UDPDiscoveryHandler udp_discovery_handler = new UDPMasterDiscoveryHandler();
4 discovery.addListener("_ros-master._udp","local",udp_discovery_handler);
Example
Example code can be found in the jmdns tutorials and also in indigo implementation of the android ros master browser.
