Question

override func shouldPerformSegue(withIdentifier identifier: String, sender: Any?) -> Bool {

    if identifier == "ChosenCell" {

        if let indexPath = tableView.indexPath(for: sender as! UITableViewCell) {
            reference.child("List").child(storyArray[indexPath.row].name).observeSingleEvent(of: .childAdded) { snapshot in
                let snapshotValue = snapshot.value as! Dictionary<String,String>

                if snapshotValue["Creator"]! != self.currentUser!.email! {
                    //return false
                    //continue
                } else {
                    let alert = UIAlertController(title: "Warning", message: "Enter password:", preferredStyle: .alert)
                    let action = UIAlertAction(title: "OK", style: .default) { alertAction in
                        let textField = alert.textFields![0] as UITextField
                        if textField.text! != snapshotValue["Password"]! {
                            //return false
                        }
                    }
                    alert.addTextField { textField in
                        textField.placeholder = "password"
                    }
                    alert.addAction(action)
                    self.present(alert, animated: true, completion: nil)
                }
            }
        }
    }
    return true
}

当用户选择单元格时，如果用户是currentUser，或者没有密码＆＃34; ChosenCell＆＃34; segue应该表演。否则警告：＆＃34;请输入密码＆＃34;。如果密码是正确的＆＃34; ChosenCell＆＃34; segue应该表演。我怎么能这样做？

Answer 1

在这种情况下，func shouldPerformSegue始终返回true，因为observeSingleEvent在后台线程中执行，而shouldPerformSegue不等待observeSingleEvent的完成。您应该以这种方式实现逻辑：

func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {
    let name = storyArray[indexPath.row].name
    reference.child("List").child(name).observeSingleEvent(of: .childAdded) { snapshot in

        let snapshotValue = snapshot.value as! [String : String]
        if snapshotValue["Creator"]! == self.currentUser!.email! { // user is the creator of this cell, so perform segue
            performSegue(withIdentifier: "ChosenCell", sender: nil)
        } else { // user is not the creator of this cell
            let alert = UIAlertController(title: "Warning", message: "Enter password:", preferredStyle: .alert)
            let action = UIAlertAction(title: "OK", style: .default) { alertAction in
                let textField = alert.textFields!.first
                if textField.text! != snapshotValue["Password"]! { // wrong password
                    // show error message
                } else { // right password
                    performSegue(withIdentifier: "ChosenCell", sender: nil)
                }
            }
            alert.addTextField { textField in
                textField.placeholder = "password"
            }
            alert.addAction(action)
            present(alert, animated: true)
        }
    }
}

Swift 4.如何从Firebase完成处理程序返回方法返回bool

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