NCal

A native Android app that talks directly to Nextcloud's CalDAV endpoint — no DAVx⁵, no separate tasks app, no Android Calendar/Tasks Provider in the middle. One app, full CRUD, for both events and tasks, plus subtasks, reminders, and home screen widgets — built to run on phones with no Google Play Services at all.

The Android project lives in ncal/; open that folder in Android Studio.

Why this exists

No mainstream Android app natively renders both VEVENT (events) and VTODO (tasks) from CalDAV in one UI. DAVx⁵ + Etar + Tasks.org gets you three apps for one job. This is the fourth option: one app, one account, one sync engine.

Privacy & security

• No Google Play Services, anywhere. Sync, reminders, and the home screen widgets all use plain AOSP/AndroidX APIs (AlarmManager, NotificationManager, androidx.glance, androidx.work) — every one of these is a core platform capability, not a Google service, so the app runs unmodified on GrapheneOS, LineageOS, or any other de-googled ROM.
• No analytics, crash reporting, or ad SDKs. Check ncal/app/build.gradle.kts — every dependency is either AndroidX/Jetpack, OkHttp, or biweekly (iCalendar parsing). Nothing phones home to a vendor.
• No third-party server. The only network calls in the app go to whatever Nextcloud server URL you enter at login (data/network/CalDavClient.kt). There is no hardcoded third-party endpoint anywhere in the source.
• Everything is encrypted at rest. Server URL, username, and app password live in EncryptedSharedPreferences (data/prefs/SecurePrefs.kt, AES-256-GCM/SIV via an Android Keystore-backed MasterKey). The local Room cache itself is an SQLCipher-encrypted database (ncal_encrypted.db), not plain SQLite — nothing the app writes to disk, including the widgets' own tiny bit of navigation state, is ever unencrypted. android:allowBackup="false" also keeps Android's cloud backup from ever exporting any of it off-device.
• HTTPS only. usesCleartextTraffic="false" blocks plain HTTP at the OS network layer, and the login screen always normalizes whatever you type to https://.
• Local-first. The calendar/task cache is a local, encrypted database. It exists purely so the UI renders instantly and works offline; the server is always the source of truth on next sync.

Features

• Agenda — unified, day-grouped list of events and tasks. Syncs automatically every time the app is opened, plus pull to refresh any time.
• Month view — a full calendar grid with events rendered as spanning colored pills and tasks as dot + text, exactly mirroring what's on the home screen widget (they share the same layout algorithm). Tap a day to see its agenda below the grid.
• Tasks — dedicated checklist view. Tasks render as an indented tree under their parent, not a flat list.
• Subtasks — assign any task a parent task (stored as the standard iCalendar RELATED-TO property, so it round-trips with Nextcloud's own Tasks app and other CalDAV clients). The parent picker excludes the task itself and its own descendants to prevent cycles. The Tasks screen and the Tasks widget both render the real parent/child tree (util/TaskTree.kt is shared by both).
• Recurrence — a Repeats picker (Daily/Weekly/Monthly/Yearly, interval, and an end condition of never/after N times/on a date) for both events and tasks, backed by a real iCal RRULE.
• Conflict handling — a stale save (someone else changed or deleted the item since you opened it) surfaces every field that actually differs and lets you pick, per field, whether your edit or the server's current value wins ("All mine"/"All theirs" shortcuts too), instead of just failing with an error.
• Reminders — add one or more reminders to any event or task (at the scheduled time, or a preset offset before it: 5 min up to 1 week). Reminders fire as real system notifications via AlarmManager exact alarms — not a best-effort background job — and survive reboots and app updates. Tapping a reminder notification opens the app directly to that item.
• Task status, priority, % complete, location, and URL — full VTODO fields, not just a completed checkbox: a proper status (Not started / In progress / Completed / Cancelled), an iCal PRIORITY 1-9 picker color-coded 1-4 red/5 yellow/6-9 blue (surfaced as the task's leading dot everywhere it's shown — Tasks list, Month view, both widgets), a 0-100% completion slider, and location/URL fields shared with events.
• Home screen widgets (see below).
• Calendars — pick which calendars/task-lists sync, mirroring what you'd see in Nextcloud's own sidebar.
• Recurring events and tasks — RRULE (FREQ=DAILY/WEEKLY/MONTHLY/YEARLY with INTERVAL/COUNT/UNTIL) is evaluated client-side to re-date each item to its next upcoming occurrence. See "Editing recurring items" below for what this doesn't cover.

Home screen widgets

Two widgets, built with Jetpack Glance (androidx.glance:glance-appwidget), which compiles down to plain RemoteViews/AppWidgetProvider — no Google dependency:

• Month grid widget ("Calendar Month" in the widget picker) — the exact same month view as the in-app Month screen (shared layout code in util/MonthGridLayout.kt), with ‹ › month navigation and tap-to-open on any event or task. Resizable, and fonts/day-circle size/event-lane count all scale up when you make the widget bigger instead of leaving blank space.
• Next Tasks widget ("Tasks" in the widget picker) — a scrollable list of incomplete tasks grouped and ordered by due date, with a tap-to-complete circle on each row (color-coded by priority) and tap-to-open on the row itself.

Both widgets refresh automatically whenever you sync, save, or delete something in the app, and independently of the app being open at all: a WorkManager periodic job (sync/SyncScheduler.kt, sync/SyncWorker.kt) calls repository.fullSync() roughly every 30 minutes whenever the device has network - matching the widgets' own OS-level redraw floor, since syncing more often than a widget can even show an update buys nothing.

Architecture

• Kotlin + Jetpack Compose (Material 3), MVVM, single-activity, no DI framework (ui/ViewModelFactory.kt is a small hand-rolled factory instead).
• CalDavClient (data/network/) — hand-rolled CalDAV client over OkHttp. Speaks PROPFIND (discover calendars/task-lists), REPORT (calendar-query to fetch VEVENT/VTODO), and PUT/DELETE with If-Match/If-None-Match for safe, conflict-aware writes. Every successful PUT captures the server's returned ETag so the next edit doesn't race against a stale local copy.
• biweekly — parses/generates the actual iCalendar (RFC 5545) payloads, including VALARM (reminders) and RELATED-TO (subtasks).
• Room, on an SQLCipher-encrypted database (data/db/) — local cache so every screen (and both widgets) render instantly and survive being offline, without ever touching disk unencrypted.
• NextcloudRepository — single source of truth gluing the network client, the DB, reminder scheduling, and widget refresh together. Every screen reads from Room Flows; every write goes through save()/delete(), which do the network call first, then update the cache, reminders, and widgets.
• ReminderScheduler (notifications/) — schedules one exact AlarmManager alarm per item, always for its next upcoming reminder offset; the receiver re-arms the following offset each time it fires, so there's never more than one pending alarm per item to track.
• MonthGridWidget / NextTasksWidget (widget/) — Glance widgets that read straight from the same repository the app uses.

Setup

1. Create a Nextcloud app password — not your real login password. Settings → Security → Devices & sessions → Create new app password.
2. Open ncal/ in Android Studio (Koala/2024.1 or newer). Let it sync Gradle.
3. Run on a device or emulator (min SDK 26 / Android 8+).
4. On first launch, enter your server URL, username, and the app password.
5. Go to the Calendars screen (gear icon) and confirm which calendars/task-lists are enabled.
6. Optional: long-press your home screen → Widgets → NCal, then add "Calendar Month" and/or "Tasks".

Run the (small, growing) JVM unit test suite with ./gradlew test — no emulator needed.

Editing recurring items

Recurring items get two guarantees, both regression-tested in IcsMapperTest:

• Editing the series' actual start/end/due time is safe. [CalendarItem.start]/end/ due hold the resolved next occurrence for a recurring item (what every list/grid displays), not the master date - so the edit screen shows/edits a separate recurrenceMasterStart/End/Due for a recurring item instead, with a note that the change applies to the whole series. Editing them writes the true master DTSTART/DTEND/DUE; leaving them untouched round-trips the original value exactly, so an unrelated edit (e.g. just the title) can never silently shift a series forward the way it used to.
• A rule the Repeats picker can't represent is left completely alone. BYDAY/ BYMONTH/etc-based rules (or anything outside Daily/Weekly/Monthly/Yearly) show as "Does not repeat" in the picker but are never flattened or overwritten by it.

Where to look first if you want to extend it

• data/network/CalDavClient.kt — all server communication.
• util/IcsMapper.kt — the iCalendar ⇄ app-model translation layer (events, tasks, subtasks, reminders).
• util/MonthGridLayout.kt — the month-grid layout algorithm shared by the in-app Month screen and the month widget.
• data/repository/NextcloudRepository.kt — the sync/cache/reminder/widget orchestration.
• notifications/ReminderScheduler.kt — reminder alarm scheduling.
• sync/SyncWorker.kt / sync/SyncScheduler.kt — the periodic background sync job.
• util/TaskTree.kt — the parent/child ordering shared by the Tasks screen and widget.
• util/RecurrenceUtils.kt — re-dates a recurring item to its next occurrence for display.
• data/repository/SaveConflictException.kt — the 412-conflict data carried to the edit screen's dialog.
• util/ConflictDiff.kt — computes which fields actually differ for the merge dialog.
• widget/ — the two Glance home screen widgets.

Building a signed release

ncal/app/build.gradle.kts reads signing credentials from a git-ignored ncal/keystore.properties (storePassword, keyPassword, keyAlias, storeFile) — generate your own keystore and fill that file in; nothing under ncal/keystore/ or ncal/keystore.properties is tracked by git, and no signing key ships in this repo. Without that file present, :app:assembleRelease still produces an unsigned APK.

License

GPL-3.0 — see LICENSE.