Providing updated application data for previewing applications on a display

Embodiments provide methods and systems for updating application data in snapshots of applications for previewing. Some embodiments update application data by determining when current application data may expire and retrieving updated application data. The application data for various applications in a preview mode may be updated based on an allotted budget. Permission can be selectively granted to applications to obtain updated data so as to control the budget. Application data in the snapshots may appear updated to a user as the user browses the dock without requiring the applications to request updated application data when the user enters the dock, regardless of whether each application is active. Further, some embodiments may generate a snapshot using a layer hierarchy and image layer data generated while the application was last running if the time associated with when the application was last active is later than the time associated with an existing snapshot.