When using the objectContribution-element (which is part of the org.eclipse.ui.popupMenus-extension point), I often (practically always) want to delegate to some command instead of implementing some action myself (since usually, I have the command and a handler already implemented). I'm doing this by using ICommandService and IHandlerService, but it feels there should be a way to achieve this programmatically. I could use viewerContribution instead of objectContribution, but then I would lose the easy way of showing the menu entry only when certain object types are selected. Ideally, I would like to use the enablement-checks that already exist for my handlers to apply to the menu entry defined by the objectContribution.
Ok, here's what I was missing: instead of using the org.eclipse.ui.popupMenus-extension point, I had to use the org.eclipse.ui.menus-extension point with a menuContribution that has its locationURI-attribute pointing to popup:org.eclipse.ui.popup.any?after=additions. This menuContribution can include a command-element (achieving the goal of binding directly to an existing command), and this command-element´s visibleWhen-element can be bound to the activation status of the bound command's handler via the checkEnabled-attribute (achieving the goal of having the popup-menu entry visible only when the enablement for the command handler is satisfied).
What's bad is that the documentation of the org.eclipse.ui.menus-extension point states that the org.eclipse.ui.popupMenus-extension point is to be considered deprecated, but the documentation of org.eclipse.ui.popupMenus does not mention this fact.
来源：https://stackoverflow.com/questions/5915550/missing-link-between-objectcontribution-and-command