Question

当我调用将ViewController推送到详细的聊天控制器（一对一聊天）时，我有以下代码。但是，如果我单击得太快，则将视图控制器推两次。我看了两次动画。谁能指出我的错误所在？该代码来自LBTA的YouTube课程（Firebase聊天）。

override func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {
    let message = messages[indexPath.row]
    guard let chatPartnerId = message.chatPartnerId() else {return}

    let ref = Database.database().reference().child("users").child(chatPartnerId)
    ref.observeSingleEvent(of: .value, with: { (snapshot) in
        guard let dictionary = snapshot.value as? [String: AnyObject] else {
            return
        }
        let user = ChatUser(dictionary: dictionary)
        user.id = chatPartnerId
        self.showChatControllerForUser(user)

    }, withCancel: nil)

}

func showChatControllerForUser(_ user: ChatUser) {
    let chatLogController = ChatLogController(collectionViewLayout: UICollectionViewFlowLayout())
    chatLogController.chatUser = user
    navigationController?.pushViewController(chatLogController, animated: true)
}

Answer 1

问题是您允许用户多次点击，这导致视图控制器被多次按下。您必须防止这种情况。

因此，一种选择是创建一个全局变量isObserving，该全局变量不允许多次观察。

var isObserving: Bool = false

override func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {

    if !isObserving {
        isObserving = true
        ...
        ref.observeSingleEvent(of: .value, with: { snapshot in
            ...
            self.isObserving = false
            self.showChatControllerForUser(user)
        })
    }
}

建议更好的用户体验。如果观察需要一些时间，则应让用户知道有些东西需要时间。因此，您可以例如开始和停止加载UIActivityIndicatorView。您也可以通过使用表格视图的isUserInteractionEnabled来禁止用户多次选择单元格。

Answer 2

为避免此问题，您可以采取的措施是禁用表视图用户交互，并在推送到第二个视图控制器后重新启用它。

override func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {
    // add this:
    tableView.isUserInteractionEnabled = false
    let message = messages[indexPath.row]
    guard let chatPartnerId = message.chatPartnerId() else {return}

    let ref = Database.database().reference().child("users").child(chatPartnerId)
    ref.observeSingleEvent(of: .value, with: { (snapshot) in
        guard let dictionary = snapshot.value as? [String: AnyObject] else {
            return
        }
        let user = ChatUser(dictionary: dictionary)
        user.id = chatPartnerId
        self.showChatControllerForUser(user)

    }, withCancel: nil)

}

func showChatControllerForUser(_ user: ChatUser) {
    let chatLogController = ChatLogController(collectionViewLayout: UICollectionViewFlowLayout())
    chatLogController.chatUser = user
    // edit this:
    navigationController?.pushViewController(chatLogController, animated: true)

    navigationController?.pushViewController(chatLogController, animated: true, completion: {
        self.tableView.isUserInteractionEnabled = true
    })
}

默认情况下，pushViewController(_:animated:)没有完成处理程序，因此，作为一种解决方法，我们可以添加以下扩展来实现：

extension UINavigationController {
    public func pushViewController(
        _ viewController: UIViewController,
        animated: Bool,
        completion: @escaping () -> Void)
    {
        pushViewController(viewController, animated: animated)

        guard animated, let coordinator = transitionCoordinator else {
            DispatchQueue.main.async { completion() }
            return
        }

        coordinator.animate(alongsideTransition: nil) { _ in completion() }
    }
}

_{引自：https://stackoverflow.com/a/33767837/5501940}

Answer 3

您的代码没有错误，双击一个单元格，这只是Swift不会检查的内容。

您可以尝试执行以下操作来避免这种情况：


override func viewWillAppear(){
    super.viewWillAppear()

    self.view.isUserInteractionEnabled = true // you need to enable user interaction if user comes back
}

override func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {

    self.view.isUserInteractionEnabled = false // this will prevent further taps

    let message = messages[indexPath.row]
    guard let chatPartnerId = message.chatPartnerId() else {return}

    let ref = Database.database().reference().child("users").child(chatPartnerId)
    ref.observeSingleEvent(of: .value, with: { (snapshot) in
        guard let dictionary = snapshot.value as? [String: AnyObject] else {
            return
        }
        let user = ChatUser(dictionary: dictionary)
        user.id = chatPartnerId
        self.showChatControllerForUser(user)

    }, withCancel: nil)

}

func showChatControllerForUser(_ user: ChatUser) {
    let chatLogController = ChatLogController(collectionViewLayout: UICollectionViewFlowLayout())
    chatLogController.chatUser = user
    navigationController?.pushViewController(chatLogController, animated: true)
}

希望对您有帮助！

Answer 4

问题是您仅在获得服务器响应后才按下ViewController，并且可以在响应之前再次轻按按钮。

因此，您可以立即推送视图控制器，然后在推送的视图控制器上请求数据，或者使用@Robert Dresler这样的变量来防止“请求”。

PushViewController两次当我双击得太快时

4 个答案: