fix: improve event scheduling logic on reboot (#743)

* fix: call `goAsync()` before doing background work in boot completed receiver

It's the recommended mechanism. Otherwise, there's a good chance that the system may kill the process as soon as `onReceive()` returns.

* fix: remove `canScheduleExactAlarms()` check for Android 13 and above

`AlarmManager.canScheduleExactAlarms()` should return `true` for `USE_EXACT_ALARM` as per the source code, but skipping the check shouldn't hurt. It might also help in case OEMs have customized this behavior.

See: https://android.googlesource.com/platform/frameworks/base/+/refs/heads/main/apex/jobscheduler/service/java/com/android/server/alarm/AlarmManagerService.java#2850

* fix: reschedule events when time is set or when timezone changes

* refactor: delegate startup work to work manager

 - This receiver was doing too much work and likely timed out when there are many events. Using a dedicated job should prevent such issues.
 - The `android.permission.FOREGROUND_SERVICE` permission is required prior to Android 12 for expedited work.

* fix: reschedule events on app startup when alarms are missing

This should help with recovery in case the app was force-stopped or if the alarms were cleared somehow, e.g., by battery optimization or if the OS ate the BOOT_COMPLETED broadcast for some reason.

* docs: update changelog


Refs: https://github.com/FossifyOrg/Calendar/issues/217

CHANGELOG.md

@@ -5,12 +5,12 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
 ## [Unreleased]
-
 ### Changed
 - Declined events will no longer trigger notifications ([#732])
 
 ### Fixed
 - Fixed incorrect widget font size on foldable devices ([#337])
+- Fixed missing or delayed reminders in some cases ([#217])
 
 ## [1.6.0] - 2025-08-21
 ### Added
@@ -117,6 +117,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 [#148]: https://github.com/FossifyOrg/Calendar/issues/148
 [#196]: https://github.com/FossifyOrg/Calendar/issues/196
+[#217]: https://github.com/FossifyOrg/Calendar/issues/217
 [#262]: https://github.com/FossifyOrg/Calendar/issues/262
 [#337]: https://github.com/FossifyOrg/Calendar/issues/337
 [#394]: https://github.com/FossifyOrg/Calendar/issues/394

app/build.gradle.kts

@@ -145,6 +145,7 @@ dependencies {
     implementation(libs.androidx.swiperefreshlayout)
     implementation(libs.androidx.print)
     implementation(libs.bundles.room)
+    implementation(libs.androidx.work.runtime.ktx)
     ksp(libs.androidx.room.compiler)
     detektPlugins(libs.compose.detekt)
 }

app/src/main/AndroidManifest.xml

@@ -24,6 +24,10 @@
         android:name="android.permission.USE_FINGERPRINT"
         tools:node="remove" />
 
+    <uses-permission
+        android:name="android.permission.FOREGROUND_SERVICE"
+        android:maxSdkVersion="32" />
+
     <queries>
         <package android:name="org.fossify.contacts.debug" />
         <package android:name="org.fossify.contacts" />
@@ -39,7 +43,7 @@
         android:required="false" />
 
     <application
-        android:name="org.fossify.commons.FossifyApp"
+        android:name=".App"
         android:allowBackup="true"
         android:appCategory="productivity"
         android:icon="@mipmap/ic_launcher"
@@ -281,14 +285,16 @@
             android:exported="false" />
 
         <receiver
-            android:name=".receivers.BootCompletedReceiver"
+            android:name=".receivers.RescheduleEventsReceiver"
             android:exported="true">
 
             <intent-filter>
                 <action android:name="android.intent.action.BOOT_COMPLETED" />
-                <action android:name="android.intent.action.QUICKBOOT_POWERON" />
-                <action android:name="com.htc.intent.action.QUICKBOOT_POWERON" />
                 <action android:name="android.intent.action.MY_PACKAGE_REPLACED" />
+                <action android:name="android.intent.action.QUICKBOOT_POWERON" />
+                <action android:name="android.intent.action.TIMEZONE_CHANGED" />
+                <action android:name="android.intent.action.TIME_SET" />
+                <action android:name="com.htc.intent.action.QUICKBOOT_POWERON" />
             </intent-filter>
         </receiver>
 
@@ -296,6 +302,9 @@
             android:name=".receivers.AutomaticBackupReceiver"
             android:exported="false" />
 
+        <receiver android:name=".receivers.DummyAlarmReceiver"
+            android:exported="false" />
+
         <provider
             android:name="androidx.core.content.FileProvider"
             android:authorities="${applicationId}.provider"

app/src/main/kotlin/org/fossify/calendar/App.kt

@@ -0,0 +1,14 @@
+package org.fossify.calendar
+
+import org.fossify.calendar.extensions.hasDummyAlarm
+import org.fossify.calendar.jobs.AppStartupWorker
+import org.fossify.commons.FossifyApp
+
+class App : FossifyApp() {
+    override fun onCreate() {
+        super.onCreate()
+        if (!hasDummyAlarm()) {
+            AppStartupWorker.start(this)
+        }
+    }
+}

app/src/main/kotlin/org/fossify/calendar/extensions/Context.kt

@@ -45,6 +45,7 @@ import org.fossify.calendar.helpers.DEFAULT_START_TIME_NEXT_FULL_HOUR
 import org.fossify.calendar.helpers.DELETE_ALL_OCCURRENCES
 import org.fossify.calendar.helpers.DELETE_FUTURE_OCCURRENCES
 import org.fossify.calendar.helpers.DELETE_SELECTED_OCCURRENCE
+import org.fossify.calendar.helpers.DUMMY_ALARM_REQUEST_CODE
 import org.fossify.calendar.helpers.EVENT_ID
 import org.fossify.calendar.helpers.EVENT_OCCURRENCE_TS
 import org.fossify.calendar.helpers.EventsHelper
@@ -81,6 +82,7 @@ import org.fossify.calendar.models.ListSectionMonth
 import org.fossify.calendar.models.Task
 import org.fossify.calendar.receivers.AutomaticBackupReceiver
 import org.fossify.calendar.receivers.CalDAVSyncReceiver
+import org.fossify.calendar.receivers.DummyAlarmReceiver
 import org.fossify.calendar.receivers.NotificationReceiver
 import org.fossify.calendar.services.MarkCompletedService
 import org.fossify.calendar.services.SnoozeService
@@ -116,6 +118,7 @@ import org.fossify.commons.helpers.ensureBackgroundThread
 import org.fossify.commons.helpers.isOreoPlus
 import org.fossify.commons.helpers.isRPlus
 import org.fossify.commons.helpers.isSPlus
+import org.fossify.commons.helpers.isTiramisuPlus
 import org.joda.time.DateTime
 import org.joda.time.DateTimeConstants
 import org.joda.time.Days
@@ -123,6 +126,7 @@ import org.joda.time.LocalDate
 import java.io.File
 import java.io.FileOutputStream
 import java.util.Calendar
+import java.util.concurrent.TimeUnit
 import kotlin.math.absoluteValue
 import kotlin.math.roundToInt
 
@@ -847,7 +851,7 @@ fun Context.getFirstDayOfWeek(date: DateTime): String {
 }
 
 fun Context.getFirstDayOfWeekDt(date: DateTime): DateTime {
-    var today = date.withTimeAtStartOfDay()
+    val today = date.withTimeAtStartOfDay()
     var currentDate = today
     if (!config.startWeekWithCurrentDay) {
         val firstDayOfWeek = config.firstDayOfWeek
@@ -997,13 +1001,26 @@ fun Context.addImportIdsToTasks(callback: () -> Unit) {
 
 fun Context.getAlarmManager() = getSystemService(Context.ALARM_SERVICE) as AlarmManager
 
-fun Context.setExactAlarm(triggerAtMillis: Long, operation: PendingIntent, type: Int = AlarmManager.RTC_WAKEUP) {
-    val alarmManager = getAlarmManager()
+fun Context.setExactAlarm(
+    triggerAtMillis: Long,
+    operation: PendingIntent,
+    type: Int = AlarmManager.RTC_WAKEUP
+) = with(getAlarmManager()) {
     try {
-        if (isSPlus() && alarmManager.canScheduleExactAlarms() || !isSPlus()) {
-            alarmManager.setExactAndAllowWhileIdle(type, triggerAtMillis, operation)
-        } else {
-            alarmManager.setAndAllowWhileIdle(type, triggerAtMillis, operation)
+        when {
+            // USE_EXACT_ALARM *cannot* be revoked by users on Android 13+
+            isTiramisuPlus() -> setExactAndAllowWhileIdle(type, triggerAtMillis, operation)
+
+            // SCHEDULE_EXACT_ALARM *may* be revoked by users/system on Android 12
+            isSPlus() && canScheduleExactAlarms() -> {
+                setExactAndAllowWhileIdle(type, triggerAtMillis, operation)
+            }
+
+            // No special permissions are needed *before* Android 12
+            !isSPlus() -> setExactAndAllowWhileIdle(type, triggerAtMillis, operation)
+
+            // Fallback to *inexact* alarms for Android 12. This will cause delayed reminders.
+            else -> setAndAllowWhileIdle(type, triggerAtMillis, operation)
         }
     } catch (e: Exception) {
         showErrorToast(e)
@@ -1023,3 +1040,25 @@ fun Context.getWeekNumberWidth(): Int {
         0
     }
 }
+
+/**
+ * Returns true if the dummy alarm is already scheduled.
+ */
+fun Context.hasDummyAlarm(): Boolean {
+    return PendingIntent.getBroadcast(
+        this, DUMMY_ALARM_REQUEST_CODE,
+        Intent(this, DummyAlarmReceiver::class.java),
+        PendingIntent.FLAG_NO_CREATE or PendingIntent.FLAG_IMMUTABLE
+    ) != null
+}
+
+fun Context.scheduleDummyAlarm() {
+    setExactAlarm(
+        triggerAtMillis = System.currentTimeMillis() + TimeUnit.DAYS.toMillis(1),
+        operation = PendingIntent.getBroadcast(
+            this, DUMMY_ALARM_REQUEST_CODE,
+            Intent(this, DummyAlarmReceiver::class.java),
+            PendingIntent.FLAG_UPDATE_CURRENT or PendingIntent.FLAG_IMMUTABLE
+        )
+    )
+}

app/src/main/kotlin/org/fossify/calendar/helpers/Constants.kt

@@ -13,6 +13,7 @@ const val ROW_COUNT = 6
 const val COLUMN_COUNT = 7
 const val SCHEDULE_CALDAV_REQUEST_CODE = 10000
 const val AUTOMATIC_BACKUP_REQUEST_CODE = 10001
+const val DUMMY_ALARM_REQUEST_CODE = 10002
 const val FETCH_INTERVAL = 3 * MONTH_SECONDS
 const val MAX_SEARCH_YEAR =
     2051218800L  // 2035, limit search results for events repeating indefinitely

app/src/main/kotlin/org/fossify/calendar/jobs/AppStartupWorker.kt

@@ -0,0 +1,76 @@
+package org.fossify.calendar.jobs
+
+import android.app.NotificationChannel
+import android.app.NotificationManager
+import android.content.Context
+import androidx.core.app.NotificationCompat
+import androidx.work.CoroutineWorker
+import androidx.work.ExistingWorkPolicy
+import androidx.work.ForegroundInfo
+import androidx.work.OneTimeWorkRequestBuilder
+import androidx.work.OutOfQuotaPolicy
+import androidx.work.WorkManager
+import androidx.work.WorkerParameters
+import org.fossify.calendar.R
+import org.fossify.calendar.extensions.checkAndBackupEventsOnBoot
+import org.fossify.calendar.extensions.recheckCalDAVCalendars
+import org.fossify.calendar.extensions.scheduleAllEvents
+import org.fossify.calendar.extensions.scheduleDummyAlarm
+import org.fossify.calendar.extensions.scheduleNextAutomaticBackup
+import org.fossify.commons.extensions.notificationManager
+
+/**
+ * Does everything that needs to be done on device boot, app updates, etc.
+ */
+class AppStartupWorker(
+    context: Context,
+    params: WorkerParameters,
+) : CoroutineWorker(context, params) {
+
+    override suspend fun doWork(): Result = with(applicationContext) {
+        try {
+            scheduleAllEvents()
+            scheduleDummyAlarm()
+            scheduleNextAutomaticBackup()
+            checkAndBackupEventsOnBoot()
+        } catch (_: Throwable) {
+            return Result.retry()
+        }
+
+        recheckCalDAVCalendars(true) {}
+        Result.success()
+    }
+
+    // expedited work on before Android 12 requires a foreground service
+    override suspend fun getForegroundInfo(): ForegroundInfo {
+        val channelId = "app_startup_worker"
+        val channelName = applicationContext.getString(R.string.app_name)
+        NotificationChannel(channelId, channelName, NotificationManager.IMPORTANCE_MIN).apply {
+            setSound(null, null)
+            applicationContext.notificationManager.createNotificationChannel(this)
+        }
+
+        val notification = NotificationCompat.Builder(applicationContext, channelId)
+            .setSmallIcon(R.drawable.ic_calendar_vector)
+            .setContentTitle(applicationContext.getString(R.string.app_name))
+            .setOngoing(true)
+            .build()
+        return ForegroundInfo(42, notification)
+    }
+
+    companion object {
+        fun start(
+            context: Context,
+            replaceExistingWork: Boolean = false
+        ) {
+            WorkManager.getInstance(context)
+                .enqueueUniqueWork(
+                    "initialize_fossify_calendar",
+                    if (replaceExistingWork) ExistingWorkPolicy.REPLACE else ExistingWorkPolicy.KEEP,
+                    OneTimeWorkRequestBuilder<AppStartupWorker>()
+                        .setExpedited(OutOfQuotaPolicy.RUN_AS_NON_EXPEDITED_WORK_REQUEST)
+                        .build()
+                )
+        }
+    }
+}

app/src/main/kotlin/org/fossify/calendar/receivers/BootCompletedReceiver.kt

@@ -1,22 +0,0 @@
-package org.fossify.calendar.receivers
-
-import android.content.BroadcastReceiver
-import android.content.Context
-import android.content.Intent
-import org.fossify.calendar.extensions.*
-import org.fossify.commons.helpers.ensureBackgroundThread
-
-class BootCompletedReceiver : BroadcastReceiver() {
-
-    override fun onReceive(context: Context, intent: Intent) {
-        ensureBackgroundThread {
-            context.apply {
-                scheduleAllEvents()
-                notifyRunningEvents()
-                recheckCalDAVCalendars(true) {}
-                scheduleNextAutomaticBackup()
-                checkAndBackupEventsOnBoot()
-            }
-        }
-    }
-}

app/src/main/kotlin/org/fossify/calendar/receivers/DummyAlarmReceiver.kt

@@ -0,0 +1,12 @@
+package org.fossify.calendar.receivers
+
+import android.content.BroadcastReceiver
+import android.content.Context
+import android.content.Intent
+import org.fossify.calendar.extensions.scheduleDummyAlarm
+
+class DummyAlarmReceiver : BroadcastReceiver() {
+    override fun onReceive(context: Context, intent: Intent?) {
+        context.scheduleDummyAlarm()
+    }
+}

app/src/main/kotlin/org/fossify/calendar/receivers/RescheduleEventsReceiver.kt

@@ -0,0 +1,35 @@
+package org.fossify.calendar.receivers
+
+import android.annotation.SuppressLint
+import android.content.BroadcastReceiver
+import android.content.Context
+import android.content.Intent
+import org.fossify.calendar.extensions.notifyRunningEvents
+import org.fossify.calendar.jobs.AppStartupWorker
+import org.fossify.commons.helpers.ensureBackgroundThread
+
+class RescheduleEventsReceiver : BroadcastReceiver() {
+
+    @SuppressLint("UnsafeProtectedBroadcastReceiver")
+    override fun onReceive(context: Context, intent: Intent) {
+        val action = intent.action ?: return
+        AppStartupWorker.start(
+            context = context,
+            replaceExistingWork = action == Intent.ACTION_TIME_CHANGED
+                    || action == Intent.ACTION_TIMEZONE_CHANGED
+        )
+
+        val shouldNotifyRunningEvents = action != Intent.ACTION_TIME_CHANGED
+                && action != Intent.ACTION_TIMEZONE_CHANGED
+                && action != Intent.ACTION_MY_PACKAGE_REPLACED
+
+        if (shouldNotifyRunningEvents) {
+            val result = goAsync()
+            ensureBackgroundThread {
+                context.notifyRunningEvents()
+                result.finish()
+            }
+        }
+    }
+}
+

gradle/libs.versions.toml

@@ -11,6 +11,7 @@ multidex = "2.0.1"
 print = "1.1.0"
 constraintlayout = "2.2.1"
 swiperefreshlayout = "1.1.0"
+work = "2.9.1"
 #Room
 room = "2.7.2"
 #Fossify
@@ -29,6 +30,7 @@ androidx-constraintlayout = { module = "androidx.constraintlayout:constraintlayo
 androidx-multidex = { module = "androidx.multidex:multidex", version.ref = "multidex" }
 androidx-print = { module = "androidx.print:print", version.ref = "print" }
 androidx-swiperefreshlayout = { module = "androidx.swiperefreshlayout:swiperefreshlayout", version.ref = "swiperefreshlayout" }
+androidx-work-runtime-ktx = { module = "androidx.work:work-runtime-ktx", version.ref = "work" }
 #Room
 androidx-room-runtime = { module = "androidx.room:room-runtime", version.ref = "room" }
 androidx-room-ktx = { module = "androidx.room:room-ktx", version.ref = "room" }