fix: resolve issue #622 - periodic tasks running at incorrect frequencies

[ened]

Summary

This PR fixes issue #622 where periodic tasks on Android were running at incorrect frequencies when re-registered with different intervals.

Fixes #622

Problem

When developers register a periodic task multiple times with the same unique name but different frequencies (common during development), the original task frequency persists due to the default ExistingPeriodicWorkPolicy.KEEP behavior.

Example scenario:

1. Register task with 15-minute frequency during testing
2. Later register same task with 2-hour frequency
3. Task continues running every 15 minutes instead of 2 hours

Solution

1. Changed default policy from KEEP to UPDATE for periodic tasks

   • UPDATE policy ensures new configurations replace existing ones
   • Less disruptive than REPLACE - doesn't cancel running workers
   • Preserves original timing calculations

2. BREAKING: Separated ExistingWorkPolicy and ExistingPeriodicWorkPolicy enums

   • Mirrors Android's native WorkManager API design
   • Provides better type safety - impossible to use wrong policy type
   • registerPeriodicTask now requires ExistingPeriodicWorkPolicy

Changes

• ✅ Updated default periodic work policy to UPDATE in WorkManagerUtils.kt
• ✅ Created separate ExistingPeriodicWorkPolicy enum in Pigeon API
• ✅ Updated all platform implementations to use correct policy types
• ✅ Added comprehensive documentation with upstream Android links
• ✅ Created example app demo with frequency dropdown and UPDATE policy
• ✅ Updated CHANGELOG.md files for all affected packages

Testing

• All Flutter tests pass (50 tests across all packages)
• All native Android tests pass
• Example app builds and demonstrates the fix
• Code formatting checks pass

Breaking Change

Before:

Workmanager().registerPeriodicTask(
  "task", "task",
  existingWorkPolicy: ExistingWorkPolicy.replace, // Wrong type
);

After:

Workmanager().registerPeriodicTask(
  "task", "task",
  existingWorkPolicy: ExistingPeriodicWorkPolicy.update, // Correct type
);

This is a well-justified breaking change that improves API clarity and prevents developer confusion.

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[Copilot]

Pull Request Overview

This PR fixes issue #622 where periodic tasks on Android were running at incorrect frequencies when re-registered with different intervals. The solution introduces a separate ExistingPeriodicWorkPolicy enum and changes the default policy from KEEP to UPDATE to ensure new task configurations replace existing ones.

• Separate ExistingWorkPolicy and ExistingPeriodicWorkPolicy enums for better type safety
• Change default periodic work policy from KEEP to UPDATE to fix frequency persistence issue
• Update all platform implementations to use the new enum type consistently

Reviewed Changes

Copilot reviewed 22 out of 22 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
workmanager_platform_interface/pigeons/workmanager_api.dart	Added new ExistingPeriodicWorkPolicy enum with comprehensive documentation
workmanager_platform_interface/lib/src/workmanager_platform_interface.dart	Updated method signature to use ExistingPeriodicWorkPolicy
workmanager_android/android/src/main/kotlin/dev/fluttercommunity/workmanager/WorkManagerUtils.kt	Changed default policy to UPDATE and updated mapping function
workmanager/lib/src/workmanager_impl.dart	Updated method signature to match platform interface
example/lib/main.dart	Added demonstration of UPDATE policy with frequency selection

Comments suppressed due to low confidence (2)

workmanager_platform_interface/pubspec.yaml:19

• Removing flutter_test dependency from dev_dependencies may break existing development workflows or CI/CD pipelines that depend on it for testing. Consider if this removal is intentional and necessary.

dev_dependencies:

example/pubspec.yaml:21

• Removing flutter_test dependency from the example app's dev_dependencies may prevent running tests for the example. This could impact the ability to validate example functionality through automated testing.

  flutter_lints: ^6.0.0