# How to track the first play(ing) event on iOS

Sometimes you want to know when a new stream starts playing for the first time, for example to forward a `firstplay` event to an analytics back-end. THEOplayer does not expose such an event, but you can implement it yourself, which gives you more control over its logic.

The implementation below listens for the first `playing` event after every source change. If the viewer pauses and resumes the stream, the event is not dispatched again. If the viewer switches to another stream, it is dispatched once more.

You can swap out the `playing` event for a `play` event, or for any other event for that matter.

## Usage

```swift
var firstPlayingListener: EventListener?

func addFirstPlayingListener() {
    firstPlayingListener = player.addEventListener(type: PlayerEventTypes.PLAYING) { [weak self] _ in
        self?.removeFirstPlayingListener()
        print("First playing event!")
    }
}

func removeFirstPlayingListener() {
    if let firstPlayingListener {
        player.removeEventListener(type: PlayerEventTypes.PLAYING, listener: firstPlayingListener)
        self.firstPlayingListener = nil
    }
}

player.addEventListener(type: PlayerEventTypes.SOURCE_CHANGE) { [weak self] _ in
    self?.removeFirstPlayingListener()
    self?.addFirstPlayingListener()
}
```

Instead of `SOURCE_CHANGE`, you can also listen for `LOADED_META_DATA`, which is dispatched once the player has loaded the metadata of the new stream.

## Related articles

* [How do you know when a stream or an advertisement is playing?](https://docs-preview.optiview.dolby.com/pr-863/theoplayer/how-to-guides/ios/player/detect-stream-or-ad-playing.md)