選択されたリソースの所属するプロジェクトを取得するには

org.eclipse.core.resourcesを依存関係に追加して以下のコードでとれる。

package org.okazuki.helloworld.actions;

import org.eclipse.core.resources.IProject;
import org.eclipse.core.resources.IResource;
import org.eclipse.jface.action.IAction;
import org.eclipse.jface.dialogs.MessageDialog;
import org.eclipse.jface.viewers.ISelection;
import org.eclipse.jface.viewers.IStructuredSelection;
import org.eclipse.ui.IWorkbenchWindow;
import org.eclipse.ui.IWorkbenchWindowActionDelegate;

public class ProjectAction implements IWorkbenchWindowActionDelegate {

	private IWorkbenchWindow window;
	private IStructuredSelection selection;
	
	public void dispose() {

	}

	public void init(IWorkbenchWindow window) {
		this.window = window;
	}

	public void run(IAction action) {
		if (selection == null) {
			return;
		}
		print(selection.getFirstElement().getClass());
		if (selection.getFirstElement() instanceof IResource) {
			IResource resource = (IResource) selection.getFirstElement();
			IProject project = resource.getProject();
			MessageDialog.openConfirm(window.getShell(), "Project", project.getName());
		}
	}
	
	private void print(Class clazz) {
		for (Class c : clazz.getInterfaces()) {
			System.out.println(c);
			print(c);
		}
	}

	public void selectionChanged(IAction action, ISelection selection) {
		if (selection instanceof IStructuredSelection) {
			this.selection = (IStructuredSelection) selection;
		} else {
			this.selection = null;
		}
	}

}

ただ、これだとNavigator上でじゃないとうまく動かない。
Package Explorer上だと駄目だから、もう一工夫かな。