[cloud_firestore] Fix possible NullPointerException

[juliocbcotta]

Description

Removed Activity Reference from plugin to avoid possible NullPointerException.
AsyncTasks are not needed to run Transactions, however transactions are not guaranteed run in UI Thread so the Handler is still needed to send data to Dart.

Related Issues

flutter/flutter#38692

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[collinjackson]

It looks like you removed all the AsyncTask calls here and I think that those are necessary so I would be surprised if this works.

I'm seeing integration test failures on Android (note: the Flutterfire CI only runs integration tests on iOS right now but I'm working on fixing that)

Can we keep the AsyncTask part but call result.success() on the original thread?

jackson-macbookpro4:example jackson$ flutter drive test_driver/cloud_firestore.dart 
Found multiple connected devices:
Android SDK built for x86 • emulator-5554                        • android-x86 • Android 9 (API 28) (emulator)
iPhone X                  • 10EBB3FA-C04F-44EA-804B-52DD0C08AC50 • ios         • iOS 12.1 (simulator)
Using device Android SDK built for x86.
Starting application: test_driver/cloud_firestore.dart
Initializing gradle...                                              0.8s
Resolving dependencies...                                           1.6s
"build/app/outputs/apk/app.apk" does not exist.
ERROR: [TAG] Failed to resolve variable '${junit.version}'              
ERROR: [TAG] Failed to resolve variable '${animal.sniffer.version}'     
warning: unknown enum constant Scope.LIBRARY_GROUP                      
  reason: class file for android.support.annotation.RestrictTo$Scope not found
warning: unknown enum constant Scope.LIBRARY_GROUP                      
warning: unknown enum constant Scope.LIBRARY_GROUP                      
Note: /Users/jackson/git/plugins_flutterfire/packages/cloud_firestore/android/src/main/java/io/flutter/plugins/firebase/cloudfirestore/CloudFirestorePlugin.java uses or overrides a deprecated API.
Note: Recompile with -Xlint:deprecation for details.                    
Note: /Users/jackson/git/plugins_flutterfire/packages/cloud_firestore/android/src/main/java/io/flutter/plugins/firebase/cloudfirestore/CloudFirestorePlugin.java uses unchecked or unsafe operations.
Note: Recompile with -Xlint:unchecked for details.                      
3 warnings                                                              
Running Gradle task 'assembleDebug'...                                  
Running Gradle task 'assembleDebug'... Done                        35.8s
Built build/app/outputs/apk/debug/app-debug.apk.
Installing build/app/outputs/apk/app.apk...                         2.4s
I/flutter ( 6004): Observatory listening on http://127.0.0.1:39831/sWZuJW6jnNw=/
[info ] FlutterDriver: Connecting to Flutter application at http://127.0.0.1:59154/sWZuJW6jnNw=/
[trace] FlutterDriver: Isolate found with number: 1242708047141067
[trace] FlutterDriver: Isolate is paused at start.
[trace] FlutterDriver: Attempting to resume isolate
[trace] FlutterDriver: Waiting for service extension
I/flutter ( 6004): 00:00 +0: Firestore getDocumentsWithFirestoreSettings
[info ] FlutterDriver: Connected to Flutter application.
I/flutter ( 6004): 00:00 +1: Firestore getDocumentsFromCollection
I/flutter ( 6004): 00:01 +2: Firestore getDocumentsFromCollectionGroup
I/flutter ( 6004): 00:01 +3: Firestore increment
I/flutter ( 6004): 00:03 +4: Firestore includeMetadataChanges
I/flutter ( 6004): 00:03 +5: Firestore runTransaction
[warning] FlutterDriver: Instance of '_WebSocketImpl' is closed with an unexpected code 1005
[warning] FlutterDriver: Instance of '_WebSocketImpl' is closed with an unexpected code 1005
[warning] FlutterDriver: request_data message is taking a long time to complete...
Stopping application instance.

[collinjackson]

I found this surprising, I would expect that you'd need to call longValue here if an int was passed from Dart. Are you sure?

[juliocbcotta]

Well, it should work.
If you look here you can see that a dart int can fit a java Long.

[juliocbcotta]

Ohh, I tested. It broke. Moving to Integer solves.

[juliocbcotta]

@collinjackson there is no documentation in cloud firestore saying that we need to offload the actions to another thread. With my experience using firebase in android, that is never the case, as any work that need to be in a separated thread is executed with Task api.
If you want I can try to improve the sample so it touches more places in plugin, but I would not recommend bringing the AsyncTasks back.

[juliocbcotta]

@collinjackson I partly understood the problem.
When you run a transaction with just one operation it seems to work alright.
When the transaction has multiple operations the AsyncTask makes it work, but it is really odd that need. I included some actions in the example so it will easier to spot.

[juliocbcotta]

I am closing this PR as I am not able to keep it updated.