Wave Gadgets with GWT – Build improvements

June 10th, 2009 Alex Moffat Posted in GWT, Google Wave | 11 Comments »

I’ve found a couple of things to make the process of building a Google Wave Gadget with GWT easier. In my previous post on Building a Google Wave Gadget with GWT I used a script element in the GWT module.xml file to include the wave.js file and I created a NeedsRpc interface to generate the <Require feature=”rpc”/> element in the ModulePrefs. There are easier ways to accomplish both of these tasks using the Google API Libraries for Google Web Toolkit but they are not very well, if at all, documented.

To include the wave.js script it’s better to use the @Gadget.InjectContent annotation. This will add the content of one or more files to the top to of the Content element in the gadget xml file. I added @Gadget.InjectContent(files={”ModuleContent.txt”}) as an annotation to the HelloWorld class. ModuleContent.txt contains <script type=”text/javascript” src=”http://wave-api.appspot.com/public/wave.js”></script>. Adding the wave.js script in this way also solves the problem I was having with wave.isInWaveContainer() always returning false. It must have been the result of an initialization order issue.

A similar technique can be used for the ModulePrefs. Adding @Gadget.InjectModulePrefs(files = {”ModulePrefs.txt”}) as an annotation, also to the HelloWorld class will add the contents of ModulePrefs.txt into the ModulePrefs element. ModulePrefs.txt contains <Require feature=”rpc”/>. The final result is

@Gadget.ModulePrefs(title = "Hello Wave World")
@Gadget.InjectModulePrefs(files = {"ModulePrefs.txt"})
@Gadget.InjectContent(files = {"ModuleContent.txt"})
public class HelloWorld extends Gadget {

with no need for extra interfaces or dummy methods and the correct initialization behavior.