I tried to run the WWDC 2019 session 707 example project ColorFeed in iPad Pro 11" with iPadOS 13 beta (17A5492t). Was running on device, not launched via Xcode.
https://developer.apple.com/videos/play/wwdc2019/707
I added logging functions and also run Console App on Mac to monitor the app running on iPad. The background app refresh task does not seem to ever get launched.
In the log file it's visible that dasd (DuetActivitySchedulerDaemon) processes the registered background task request every 5 to 50 seconds, but the task's CurrentScore never exceeds the ThresholdScore, which results in DecisionToRun:0.
Console output:
bgRefresh-com.example.apple-samplecode.ColorFeed.refresh:B60719:[
{name: ApplicationPolicy, policyWeight: 50.000, response: {Decision: Can Proceed, Score: 0.35}}
{name: DeviceActivityPolicy, policyWeight: 5.000, response: {Decision: Can Proceed, Score: 0.33}}
] sumScores:60.576667, denominator:96.410000, FinalDecision: Can Proceed FinalScore: 0.628323}
'bgRefresh-com.example.apple-samplecode.ColorFeed.refresh:B60719' CurrentScore: 0.628323, ThresholdScore: 0.808861 DecisionToRun:0
'bgRefresh-com.example.apple-samplecode.ColorFeed.refresh:B60719' has compatibility score of -0.040691 with com.apple.rtcreportingd:ART:19BFBA. Bailing out.
What added to the confusion was the example code not canceling the scheduled task request upon application exit. In Console the task requests from previous app sessions were being processed by the dasd even though the app had already been quit.
This seems to be in line with the earlier experience of other people with the background app refresh not really working in earlier iOS versions, either. Could somebody explain what's going on, and what kind of performance can be expected from this BackgroundTasks framework? I'm looking for a way to monitor external sensors that are constantly broadcasting parameters over the network interface or Bluetooth LE. Is there a way to achieve this when the app is in the background?