Schedules a block asynchronously for execution and optionally associates it with a dispatch group.
- iOS 8.0+
- macOS 10.10+
- UIKit for Mac 13.0+Beta
- tvOS 9.0+
- watchOS 2.0+
- Xcode 8.0+
The dispatch group to associate with the work item. If you specify
NULL, the block is not associated with a group.
The quality-of-service class to use when executing the block. This parameter determines the priority with which the block is scheduled and executed. For a list of possible values, see
Additional attributes to apply when executing the block. For a list of possible values, see
Work Item Flags
The block containing the work to perform. This block has no return value and no parameters.