# Notifications

**URL:** https://heroiclabs.com/docs/nakama/tutorials/unity/pirate-panic/notifications/
**Summary:** Learn how to add notification to the Pirate Panic tutorial game.
**Keywords:** notifications, nakama
**Categories:** nakama, unity, pirate-panic

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# Notifications

Notifications are a great way to let players know about interesting events while in game. In this section we'll learn how to use the Nakama [notification](../../../../concepts/notifications/) engine to send alerts and messages to players whenever a particular action triggers them.

In-app notifications can be sent from the server, then received by clients and displayed in-game. If they are marked as persistent, then the server can accept notifications even if their recipient is offline.

Remember that in-app notifications are different from push notifications you might get on your phone. They only appear when players are in-game.

## Sending notifications

First, let's set up the server-side code to trigger notification sends.

Notifications can be bound to [register hooks](../../../../server-framework/introduction/#hooks) that fire before or after a certain event. Nakama handles the logic of detecting when events occur.

For example, if we want to reward players when they add their first friend , there is a `RegisterAfterAddFriends` hook that runs after a friend is added:

**quests.ts**

```typescript
let afterAddFriendsFn: nkruntime.AfterHookFunction<void, nkruntime.AddFriendsRequest> = function(ctx: nkruntime.Context, logger: nkruntime.Logger, nk: nkruntime.Nakama, data: void, request: nkruntime.AddFriendsRequest) {
    let subject = JSON.stringify("A new friend!");
    let content = { reward: 1000 };
    let code = 1;
    let senderId = null; // Server sent
    let persistent = true;

    nk.notificationSend(ctx.userId, subject, content, code, senderId, persistent);
}

...
initializer.registerAfterAddFriends(afterAddFriendsFn); // Don't forget to register the hook!
```

Here, the function `notificationSend` will deliver a notification to the user `ctx.userId` when they add a new friend. In this function:

- `Content` is a JSON object with custom key-value pairs for whatever data you'd like to send in the notification
- The `code` is used to specify custom notification types and can be anything desired greater than `0`. Codes `0` and below are reserved by the [system](../../../../concepts/notifications/#notification-codes)
- If a notification was sent by another player, then `senderId` will be the user ID of whoever sent it. In this case, the message was generated by the server so it should be `null`
- If a notification has `persistent = true`, then it will be sent even if the player is offline. When the player re-joins, they can then read the list of pending notifications using [ListNotificationsAsync](../../../../concepts/notifications/#list-notifications)

## Receiving notifications

Now that we have a system to send notifications, let's set up the client side.

For this we also bind a function to a hook, this time the `ReceivedNotification` hook for when a notification arrives. We then use this function to process the data we sent from the server:

**NotificationPopup.cs**

```csharp
public void Init(GameConnection connection) {
    connection.Socket.ReceivedNotification += NotificationReceived;
}

private class Reward {
    public int reward = 0;
}

private void NotificationReceived(IApiNotification notification) {
    if (notification.Code == 1) {
        Reward reward = JsonUtility.FromJson<Reward>(notification.Content);
        _titleText.text = notification.Subject;
        _descriptionText.text = "Received reward: " + reward.reward;
        ...
    }
}
```

Here we receive the notification in the form of an `IApiNotification`, which then contains all of the data we inputted to `notificationSend` on the server.

Since `content` is a JSON object, we need to unpack it into a C# object. We know that the expected format is an object with a single key `reward` containing a number, so we can create a class `Reward` with this structure and convert `Content` into it using `JsonUtility.FromJson`.

We then set Text objects `_titleText` and `_descriptionText` to assign with the desired subject and description.