All apps have asynchronous workflows. Apple's NSOperation and NSOperationQueue provide a foundation for building arbitrarily complex workflows. This demo code coincides with my STL CocoaHeads talk on techniques for building "async workflows".
Slides and Demo Code
The demo code shows how to:
- use dependent operations
- pass data between operations using a thread-safe key/value store (i.e
Session) - track progress using
NSProgress - support an easy to understand cancellation policy
- allow app background execution (with just a few lines of code)
Be sure to review the CocoaHeads presentation slides for additional notes and details.
Workflows
You can use the techniques described in this talk and the demo code to design and implement some really neat workflows.
Workflows include, but are definitely not limited to:
- signing in users with dynamic on-boarding steps
- managing external resources (e.g. large files such as images, SQLite files, etc.)
- downloading (using background
URLSession) - decompressing
- validating
- file system management
- downloading (using background
- any type of web service request
- building and validating requests
- transforming the result
- importing the result into a local data store (i.e. Core Data or SQLite)
- accessing a local SQLite database
- extracting
- transforming
- publishing results
- discovering and opening connections to external IP-enabled hardware
- signing out users
Additional Resources
Here's a short list of related WWDC videos
- WWDC 2015 Advanced NSOperations
- WWDC 2015 Best Practices In Progress Reporting
- WWDC 2017 Modernizing Grand Central Dispatch Usage