componentRef installMode Attribute

The installMode attribute of the <componentRef> element specifies the way in which the referenced component should be installed and targeted thereafter. If the referenced component is installed as TOPLEVEL, then it can be used by any other component just as if it had been directly installed by a plan. However, if the referenced component is installed as NESTED, then its installation is implicitly scoped to that of the referencing component, and its services are only available to the referencing component.

Logically, a nested referenced component defines a finer-grained unit of functionality required by the referencing component, but not otherwise useful to other components. Whereas a toplevel referenced component defines services that will be used by the referencing component, but may also be used by other components.

The lifetime of a nested referenced component is implicitly scoped to that of the referencing component. The nested referenced component can only be installed during the installation of the referencing component, and is implicitly uninstalled when the referencing component is uninstalled. In contrast, the lifetime of a toplevel referenced component is not tied to that of the referencing component in any way. The referencing component may install a toplevel referenced component when it is installed, or the referenced component have been installed previously or later by other means. When the referencing component is uninstalled, a toplevel referenced component will remain installed unless it is explicitly uninstalled by the referencing component. Other components are also free to uninstall it.