Notifications
Notifications are for information that should reach the user outside the currently visible Fission view. A completed export, a missed message, or a scheduled reminder belongs here. A validation message inside the current screen usually does not; use Toast, Modal, or another Fission overlay for in-app feedback.
By the end of this guide, you will know how to build a sync-complete notification that can later grow into scheduled reminders and push delivery. The same pattern applies to larger apps: declare the capability when native configuration is needed, store the result in typed app state, request the host operation from a reducer, and test both success and failure with a memory host.
Do not use the notification capability as a replacement for normal UI. If the user is already looking at the relevant screen, show a Fission widget. Use a notification when the host owns delivery through the operating system, browser, launcher, notification center, or push service.
1. Start with the state the screen needs
Add the smallest state fields the screen needs to render honestly. For this flow, useful state is:
#[derive(Default)]
struct NotificationState {
// Add these fields to your existing app state.
last_notification_id: Option<NotificationId>,
notification_error: Option<String>,
}
impl GlobalState for NotificationState {}
State is the source of truth for the UI. Do not store whether the host "probably" succeeded; wait for the typed success action and store the returned value.
2. Configure the target and host
There is no single safe add-capability value for this feature because the product owns the route/provider details, or because the default host can expose the feature without generated permission files. You still configure the shell explicitly and review target packaging before release.
Notifications are declared through shell setup because the product owns notification categories, push identifiers, service-worker files, action ids, and deep-link routes. Fission cannot invent those values safely. Mobile targets need permission prompts. Web push usually needs a service worker and secure origin. Desktop targets need the host provider and, for packaged apps, platform-specific notification metadata where the operating system or store requires it.
This is the difference between the Fission API, a provider, and packaging configuration:
•
The Fission API is the typed Rust contract your reducer calls, such as ctx.effects.camera().capture_photo(...).
•
The provider is the shell-side Rust implementation that turns that typed request into the correct OS, browser, or hardware call.
•
Packaging configuration is the manifest, plist, entitlement, service-worker, protocol, domain, or store metadata that lets the platform permit that call in a real installed app.
If the API exists but the provider is missing, the request returns a typed unsupported error. If the provider exists but packaging is missing, the operating system or browser may deny the request before the provider can complete it.
3. Define reducers for success and failure
Capability work finishes later, after the reducer that started it has returned. You therefore need one reducer for the successful result and one reducer for the error path.
#[fission_reducer(NotificationShown)]
fn on_notification_shown(state: &mut NotificationState, receipt: NotificationReceipt) {
state.last_notification_id = Some(receipt.id);
state.notification_error = None;
}
#[fission_reducer(NotificationFailed)]
fn on_notification_failed(state: &mut NotificationState, error: NotificationError) {
state.notification_error = Some(error.message);
}
Keep both paths explicit. A denied permission, unavailable device, unsupported host, or cancelled prompt is not an exceptional mystery; it is normal product behavior the UI should explain.
4. Request the capability from a reducer
Call the capability from the reducer that handles the user's intent. The reducer queues a host effect and returns. The runtime later dispatches either the success reducer or the failure reducer.
ctx.effects
.notifications()
.show(NotificationRequest {
id: NotificationId::new("sync-complete"),
title: "Sync complete".into(),
body: "Your workspace is up to date.".into(),
deep_link: Some("fission://sync/history".into()),
..Default::default()
})
.on_ok(ctx.effects.bind(
NotificationShown(NotificationReceipt::default()),
reduce_with!(on_notification_shown),
))
.on_err(ctx.effects.bind(
NotificationFailed(NotificationError::default()),
reduce_with!(on_notification_failed),
));
The call does not run the OS API directly. It records a typed host request. That keeps shared app logic portable across Fission targets where the capability applies, plus static-site previews and tests.
5. Trigger the reducer from the UI
Wire the user-facing control with the normal Fission action pattern. This example uses a small widget so the binding has one clear home.
struct ShowSyncNotificationButton;
impl From<ShowSyncNotificationButton> for Widget {
fn from(component: ShowSyncNotificationButton) -> Self {
let (ctx, view) = fission::build::current::<NotificationState>();
let run = with_reducer!(ctx, ShowSyncNotification, on_show_sync_notification);
Button::new("Show sync notification")
.disabled(false)
.on_press(run)
.into()
}
}
Rename the widget and action for your product, but keep the shape: the widget dispatches one typed action, the reducer starts the capability request, and the success or failure reducer updates state.
6. Provide and test the host behavior
Register a NotificationHost with .with_notification_host(...) in shells that provide real notifications, or use MemoryNotificationHost in tests. If the host cannot show, schedule, badge, or register push, it must return NotificationError instead of pretending delivery happened.
Test the reducer with MemoryNotificationHost, a success receipt, and a denied/unsupported error. Add an integration test for notification responses if the notification opens a deep link or action button.
A useful first test creates the app with the memory host, dispatches the start action, feeds the queued effect through the host, and asserts that the reducer updates state from the returned payload. Add a second test for the error path before you ship the screen.
Platform expectations
Android and iOS have direct notification systems but require permission prompts and, for push, provider registration. Windows and macOS have native notification systems. Linux depends on the desktop notification service. Web notifications require browser permission; push generally requires a service worker and provider setup.
For a cross-platform summary, read the capability matrix. For exact request fields, provider traits, and generated configuration, see the Notifications reference.
Finished capability flow
A complete Notifications integration has all of these pieces in place:
Piece | What should exist |
|---|---|
Configuration | fission.toml declares the capability and generated platform files contain the permission text, manifest entry, entitlement, domain, or protocol metadata the target needs. |
State | App state records the in-flight flag, the successful value, and the user-facing error separately. |
Reducers | One reducer starts the host request, one handles success, and one handles denial, unsupported hosts, cancellation, or provider errors. |
Provider | The shell registers a real provider for production and a memory provider for tests. |
Tests | At least one test covers success and one covers permission denial or unsupported host behavior. |
Diagnose capability failures
Capability failures should be safe to retry and easy to explain. Start by checking fission.toml, then run fission doctor, then inspect the generated target files. If the provider is missing, the request should return an unsupported error. If the provider exists but the platform configuration is wrong, the OS or browser will usually deny the request before the provider can complete it. Keep those cases distinct in the UI so users know whether they can retry, change settings, connect hardware, or choose another path.
Fission
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Copyright (c) 2026 Fission
Ready to use today. Widget APIs are expected to remain stable; some runtime and shell APIs may change before 1.0.0.
Fission 0.7.0