@Override
	public DomainFile[] getData() {
		// Program Manager will take care of programs.
		// We need to take care of Project Data Type Archives.
		List<DomainFile> domainFileList = new ArrayList<>();
		List<Archive> allArchives = dataTypeManagerHandler.getAllArchives();
		for (Archive archive : allArchives) {
			if (archive instanceof ProjectArchive && archive.isModifiable()) {
				domainFileList.add(((ProjectArchive) archive).getDomainFile());
			}
		}
		return domainFileList.toArray(new DomainFile[domainFileList.size()]);
	}
Create the actions for the menu on the tool.
Ghidra/Features/Base/src/main/java/ghidra/app/plugin/core/datamgr/DataTypeManagerPlugin.java