# Notification Events

Listen for push notification events, handle user responses, and manage active notifications.

The Airship SDK provides events for when a push is received or a notification is interacted with. Apps can use these events for custom push processing. Registering for an event is optional; the SDK will automatically launch the application without the need to set one.

## Notification Events

### Push Received

Listen for when a push notification is received. This event fires whether the app is in the foreground or background.

```csharp
Airship.Shared.OnPushReceived += (PushMessage message) => {
    // Handle push received event
};
```


### Push Opened

Listen for when a user taps a notification.

```csharp
Airship.Shared.OnPushOpened += (PushMessage message) => {
    // Handle notification open
};
```


### Registration Token Updates

Listen for when the push registration token is generated or updated.

```csharp
Airship.Shared.OnPushTokenReceived += (string pushToken) => {
    // Send the token to your backend if needed
};
```


You can also retrieve the current token at any time.

```csharp
string token = Airship.Shared.push.GetPushToken();
```


### Notification Status Changes

Monitor changes to the notification permission status.

```csharp
Airship.Shared.OnNotificationStatusChanged += (PushNotificationStatus status) => {
    Debug.Log("Is opted in: " + status.isOptedIn);
};
```


## Managing Active Notifications

You can retrieve and clear notifications that are currently displayed in the notification center.

### Get Active Notifications

Retrieve the list of currently displayed notifications. `GetActiveNotifications` is asynchronous, so run it as a coroutine.

```csharp
StartCoroutine(Airship.Shared.push.GetActiveNotifications((IEnumerable<PushMessage> notifications) => {
    // Handle active notifications
}));
```


> **Note:** On Android, this list only includes notifications sent through Airship.


### Clear Notifications

Clear all notifications for the app:

```csharp
Airship.Shared.push.ClearNotifications();
```


Clear a specific notification by identifier:

```csharp
Airship.Shared.push.ClearNotification(identifier);
```


> **Note:** On Android, you can use this method to clear notifications outside of Airship. The identifier is in the format `<id>:<tag>`.


## Silent Notifications

Silent notifications are push messages that do not present a notification to the user. These are typically used to briefly wake the app from a background state to perform processing tasks or fetch remote content.

> **Important:** We recommend that you thoroughly test your implementation to confirm that silent notifications do not generate any device notifications.


### Platform Configuration

For iOS, set the `content_available` property to `true` in the [iOS override object](https://www.airship.com/docs/developer/rest-api/ua/schemas/platform-overrides/#iosoverrideobject).

For Android, all push messages are delivered in the background, and by default Airship will treat messages without an `alert` as silent.

> **Note:** Pushes sent with the `content_available` property (iOS) or without an `alert` (Android) do not have guaranteed delivery. Factors affecting delivery include battery life, whether the device is connected to WiFi, and the number of silent pushes sent within a recent time period. These metrics are determined solely by iOS/Android and APNs/FCM. Therefore, this feature is best used for supplementing the regular behavior of the app rather than providing critical functionality. For instance, an app could use a silent push to pre-fetch new data ahead of time in order to reduce load times when the app is later launched by the user.


### Handling Silent Notifications

Silent notifications trigger the `OnPushReceived` event but do not display a notification to the user.

```csharp
Airship.Shared.OnPushReceived += (PushMessage message) => {
    if (string.IsNullOrEmpty(message.Alert))
    {
        // Perform background work
    }
};
```