An interface for event listeners.
| abstract void |
onEvent(T value, FirebaseFirestoreException error)
onEvent will be called with the new value or the error if an error occurred.
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onEvent will be called with the new value or the error if an error occurred. It's guaranteed that exactly one of value or error will be non-null.
| value | The value of the event. null if there was an error. |
|---|---|
| error | The error if there was error. null otherwise. |