Move all fragment work to UI thread

[newyankeecodeshop]

Summary

Our app crashed with the following call stack:

java.util.ConcurrentModificationException
  at java.util.HashMap$HashIterator.nextEntry(HashMap.java:851)
  at java.util.HashMap$ValueIterator.next(HashMap.java:879)
  at androidx.fragment.app.FragmentStore.findFragmentByTag(FragmentStore.java:233)
  at androidx.fragment.app.FragmentManager.findFragmentByTag(FragmentManager.java:1677)
  at com.reactcommunity.rndatetimepicker.RNTimePickerDialogModule.open(RNTimePickerDialogModule.java:99)
  at java.lang.reflect.Method.invoke(Method.java:-2)
  at com.facebook.react.bridge.JavaMethodWrapper.invoke(JavaMethodWrapper.java:372)
  at com.facebook.react.bridge.JavaModuleWrapper.invoke(JavaModuleWrapper.java:151)
  at com.facebook.react.bridge.queue.NativeRunnable.run(NativeRunnable.java:-2)
  at android.os.Handler.handleCallback(Handler.java:751)
  at android.os.Handler.dispatchMessage(Handler.java:95)
  at com.facebook.react.bridge.queue.MessageQueueThreadHandler.dispatchMessage(MessageQueueThreadHandler.java:27)
  at android.os.Looper.loop(Looper.java:154)
  at com.facebook.react.bridge.queue.MessageQueueThreadImpl$4.run(MessageQueueThreadImpl.java:226)
  at java.lang.Thread.run(Thread.java:761)

It would appear to be caused by this code running at the same time the UI thread is manipulating the map of fragments. Given that the code that adds/updates fragments must run on the UI thread, it would seem that code that queries for fragments also needs to use the UI thread.

Test Plan

Used the updated code in our app and made sure the time picker dialog functions properly.

What's required for testing (prerequisites)?

An Android app that shows the date and time pickers.

What are the steps to reproduce (after prerequisites)?

I was not able to reproduce it given that it involves two threads manipulating fragments at the same time.

Compatibility

OS	Implemented
iOS	N/A
Android	✅

Checklist

• I have tested this on a device and a simulator
• I added the documentation in README.md
• I updated the typed files (TS and Flow)
• I added a sample use of the API in the example project (example/App.js)
• I have added automated tests, either in JS or e2e tests, as applicable

[vonovak]

thank you for the PR!

[vonovak]

🎉 This PR is included in version 3.0.8 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

Your semantic-release bot 📦🚀

[msschwartz]

To help other devs down the road if they run across this error. This is the error message I get using any version before 3.0.8: Method addObserver must be called on the main thread