Perspectiveswitcher不会创建用于切换透视图的命令对象

Question

问题是我的代码中的命令对象为null，我不知道为什么。

我将Lars Vogel的e4-perspective-switcher与这里的问题How to add Perspective Bar Switcher to pure eclipse 4 rcp application结合使用。

public class PerspectiveSwitcher {

    @Inject
    private ECommandService commandService;

    @Inject
    private EHandlerService handlerService;


    @PostConstruct
    public void createControls(Composite parent, EModelService modelService) {
        Composite body = new Composite(parent, SWT.NONE);
        body.setLayout(new GridLayout());
        body.setBackground(parent.getBackground());

        Button button = new Button(body, SWT.PUSH);
        button.setText("switch");
        GridData data = new GridData(SWT.FILL, SWT.FILL, true, false);
        data.minimumHeight = 20;
        button.setLayoutData(data);
        button.addSelectionListener(new SelectionAdapter() {
            @Override
            public void widgetSelected(SelectionEvent e) {
                List<MPerspective> perspectives = modelService.findElements(app,
                        PTApplicationConstants.PERSPECTIVE_ID_MANAGER, MPerspective.class, null);
                MPerspective perspective = perspectives.get(0);

                HashMap<String, Object> parameters = new HashMap<>(2);
                parameters.put(E4WorkbenchParameterConstants.COMMAND_PERSPECTIVE_ID, perspective.getElementId());
                parameters.put(E4WorkbenchParameterConstants.COMMAND_PERSPECTIVE_NEW_WINDOW, "false");

                ParameterizedCommand command = commandService
                        .createCommand(E4WorkbenchCommandConstants.PERSPECTIVES_SHOW_PERSPECTIVE, parameters);
                handlerService.executeHandler(command);

                partService.switchPerspective(perspective);

                super.widgetSelected(e);
            }
        });
    }
}