如何分离在另一个范围中定义的侦听器？

Question

我在viewWillAppear() 函数中定义了一个侦听器，并试图在viewWillDisappear 函数中删除/分离它。但是，我无法访问viewWillDisappear() 函数中的侦听器，因此无法使用.remove() 将其分离。

我的代码：

override func viewWillAppear(_ animated: Bool) {
    super.viewWillAppear(true)

     let db = Firestore.firestore()
     let docRef = db.collection("collection").document("document")

    let listener = docRef.addSnapshotListener { (querySnapshot, errur) in
     ....
     }
}




 override func viewWillDisappear(_ animated: Bool) {
    listener.remove() //ERROR: Use of unresolved identifier 'listener'
}

我意识到错误是因为“侦听器”是在另一个范围内定义的，但我如何仍然可以访问它以在 viewWillDisappear() 中删除它？

Answer 1

private var listener: ListenerRegistration?

override func viewWillAppear(_ animated: Bool) {
    super.viewWillAppear(true)

    let db = Firestore.firestore()
    let docRef = db.collection("collection").document("document")

    listener = docRef.addSnapshotListener { (querySnapshot, errur) in
         // ....
     }
}

override func viewWillDisappear(_ animated: Bool) {
    // always call super.viewWillDisappear also.
    super.viewWillDisappear(animated)
    listener.remove() //ERROR: Use of unresolved identifier 'listener'
    listener = nil
}