6aa9140f67
- Add platform capability reference (Android & iOS OS-level facts) - Add plugin behavior exploration template (executable test matrices) - Add plugin requirements & implementation directive - Add Android-specific implementation directive with detailed test procedures - Add exploration findings from code inspection - Add improvement directive for refining documentation structure - Add Android alarm persistence directive (OS capabilities) All documents include: - File locations, function references, and line numbers - Detailed test procedures with ADB commands - Cross-platform comparisons - Implementation checklists and code examples
245 lines
6.7 KiB
Markdown
245 lines
6.7 KiB
Markdown
# Android Alarm Persistence, Recovery, and Limitations
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**Author**: Matthew Raymer
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**Date**: November 2025
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**Status**: Engineering Directive - Active Reference
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## Purpose
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This document provides a **clean, consolidated, engineering-grade directive** summarizing Android's abilities and limitations for remembering, firing, and restoring alarms across:
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- App kills
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- Swipes from recents
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- Device reboot
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- **Force stop**
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- User-triggered reactivation
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This is the actionable version you can plug directly into your architecture docs.
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---
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## 1. Core Principle
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Android does **not** guarantee persistence of alarms across process death, swipes, or reboot.
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It is the app's responsibility to **persist alarm definitions** and **re-schedule them** under allowed system conditions.
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The following directives outline **exactly what is possible** and **what is impossible**.
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---
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## 2. Allowed Behaviors (What *Can* Work)
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### 2.1 Alarms survive UI kills (swipe from recents)
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`AlarmManager.setExactAndAllowWhileIdle(...)` alarms **will fire** even after:
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- App is swiped away
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- App process is killed by the OS
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The OS recreates your app's process to deliver the `PendingIntent`.
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**Directive:**
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Use `setExactAndAllowWhileIdle` for alarm execution.
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---
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### 2.2 Alarms can be preserved across device reboot
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Android wipes all alarms on reboot, but **you may recreate them**.
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**Directive:**
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1. Persist all alarms in storage (Room DB or SharedPreferences).
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2. Add a `BOOT_COMPLETED` / `LOCKED_BOOT_COMPLETED` broadcast receiver.
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3. On boot, load all enabled alarms and reschedule them using AlarmManager.
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**Permissions required:**
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- `RECEIVE_BOOT_COMPLETED`
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**Conditions:**
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- User must have launched your app at least once before reboot to grant boot receiver execution.
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---
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### 2.3 Alarms can fire full-screen notifications and wake the device
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**Directive:**
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Implement `setFullScreenIntent(...)`, use an IMPORTANCE_HIGH channel with `CATEGORY_ALARM`.
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This allows Clock-app–style alarms even when the app is not foregrounded.
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---
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### 2.4 Alarms can be restored after app restart
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If the user re-opens the app (direct user action), you may:
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- Scan the persistent DB
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- Detect "missed" alarms
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- Reschedule future alarms
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- Fire "missed alarm" notifications
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- Reconstruct WorkManager/JobScheduler tasks wiped by OS
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**Directive:**
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Create a `ReactivationManager` that runs on every app launch and recomputes the correct alarm state.
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---
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## 3. Forbidden Behaviors (What *Cannot* Work)
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### 3.1 You cannot survive "Force Stop"
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**Settings → Apps → YourApp → Force Stop** triggers:
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- Removal of all alarms
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- Removal of WorkManager tasks
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- Blocking of all broadcast receivers (including BOOT_COMPLETED)
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- Blocking of all JobScheduler jobs
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- Blocking of AlarmManager callbacks
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- Your app will NOT run until the user manually launches it again
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**Directive:**
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Accept that FORCE STOP is a hard kill.
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No scheduling, alarms, jobs, or receivers may execute afterward.
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---
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### 3.2 You cannot auto-resume after "Force Stop"
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You may only resume tasks when:
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- The user opens your app
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- The user taps a notification belonging to your app
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- The user interacts with a widget/deep link
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- Another app explicitly targets your component
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**Directive:**
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Provide user-facing reactivation pathways (icon, widget, notification).
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---
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### 3.3 Alarms cannot be preserved solely in RAM
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Android can kill your app's RAM state at any time.
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**Directive:**
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All alarm data must be persisted in durable storage.
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---
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### 3.4 You cannot bypass Doze or battery optimization restrictions without permission
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Doze may defer inexact alarms; exact alarms with `setExactAndAllowWhileIdle` are allowed.
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**Directive:**
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Request `SCHEDULE_EXACT_ALARM` on Android 12+.
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---
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## 4. Required Implementation Components
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### 4.1 Persistent Storage
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Create a table or serialized structure for alarms:
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```
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id: Int
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timeMillis: Long
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repeat: NONE | DAILY | WEEKLY | CUSTOM
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label: String
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enabled: Boolean
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```
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---
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### 4.2 Alarm Scheduling
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Use:
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```kotlin
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alarmManager.setExactAndAllowWhileIdle(
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AlarmManager.RTC_WAKEUP,
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triggerAtMillis,
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pendingIntent
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)
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```
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---
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### 4.3 Boot Receiver
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Reschedules alarms from storage.
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---
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### 4.4 Reactivation Manager
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Runs on **every app launch** and performs:
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- Load pending alarms
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- Detect overdue alarms
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- Reschedule future alarms
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- Trigger notifications for missed alarms
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---
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### 4.5 Full-Screen Alarm UI
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Use a `BroadcastReceiver` → Notification with full-screen intent → Activity.
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---
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## 5. Summary of Android Alarm Capability Matrix
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| Scenario | Will Alarm Fire? | Reason |
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| --------------------------------------- | --------------------------------------- | --------------------------------------------------------------- |
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| **Swipe from Recents** | ✅ Yes | AlarmManager resurrects the app process |
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| **App silently killed by OS** | ✅ Yes | AlarmManager still holds scheduled alarms |
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| **Device Reboot** | ❌ No (auto) / ✅ Yes (if you reschedule) | Alarms wiped on reboot |
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| **Doze Mode** | ⚠️ Only "exact" alarms | Must use `setExactAndAllowWhileIdle` |
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| **Force Stop** | ❌ Never | Android blocks all callbacks + receivers until next user launch |
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| **User reopens app** | ✅ You may reschedule & recover | All logic must be implemented by app |
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| **PendingIntent from user interaction** | ✅ If triggered by user | User action unlocks the app |
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---
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## 6. Final Directive
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> **Design alarm behavior with the assumption that Android will destroy all scheduled work on reboot or force-stop.
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>
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> Persist all alarm definitions. On every boot or app reactivation, reconstruct and reschedule alarms.
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>
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> Never rely on the OS to preserve alarms except across UI process kills.
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>
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> Accept that "force stop" is a hard stop that cannot be bypassed.**
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---
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## Related Documentation
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- [Boot Receiver Testing Guide](./boot-receiver-testing-guide.md)
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- [App Startup Recovery Solution](./app-startup-recovery-solution.md)
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- [Reboot Testing Procedure](./reboot-testing-procedure.md)
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---
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## Future Directives
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Potential follow-up directives:
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- **How to implement the minimal alarm system**
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- **How to implement a Clock-style robust alarm system**
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- **How to map this to your own app's architecture**
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