UITableView允许使用滑动手势删除某些类型的请求

Question

我有一个表视图，它显示了一个名为请求的对象列表。它有三个部分。即接受、接收和发送。每个段的对象为3个数组。

我希望只为已接受和发送的段启用删除行(依次为对象)。

这是我目前的实现。

func tableView(_ tableView: UITableView, trailingSwipeActionsConfigurationForRowAt indexPath: IndexPath) -> UISwipeActionsConfiguration? {

    var deleteAction: UIContextualAction?

    switch currentShowingStatus {
    case .accepted:
        deleteAction = UIContextualAction(style: .destructive, title: "Delete") { action, view, completionHandler in
            let request = self.acceptedRequests[indexPath.row]
            completionHandler(true)
        }
    case .sent:
        deleteAction = UIContextualAction(style: .destructive, title: "Delete") { action, view, completionHandler in
            let request = self.sentRequests[indexPath.row]
            completionHandler(true)
        }
    default:
        break
    }


    if let deleteAction = deleteAction {
        let configuration = UISwipeActionsConfiguration(actions: [deleteAction])
        configuration.performsFirstActionWithFullSwipe = false
        return configuration
    } else {
        return UISwipeActionsConfiguration(actions: [])
    }
}

正如您所看到的，有相当多的重复代码。而且我无法提取出UIContextualAction声明部分，因为它是完成处理程序。选择要删除的对象就发生在那里。

我也不能将UISwipeActionsConfiguration定义为局部变量，并且由于必须使用UIContextualAction实例初始化类，所以减少了它的重复。

注意:为了不显示单元格中的滑动操作，您必须将一个空操作数组传递给UISwipeActionsConfiguration。返回nil并不能做到这一点。

所以所有这些都产生了一段丑陋的代码。我想知道是否有更好的方法来重构这个。

替代方法

我没有先检查段，然后再添加多个删除操作，而是将段部件检查放在一个完成处理程序中，如下所示。

func tableView(_ tableView: UITableView, trailingSwipeActionsConfigurationForRowAt indexPath: IndexPath) -> UISwipeActionsConfiguration? {
    var actions = [UIContextualAction]()

    let deleteAction = UIContextualAction(style: .destructive, title: "Delete") { action, view, completionHandler in
        switch self.currentShowingStatus {
        case .accepted:
            let request = self.acceptedRequests[indexPath.row]
            self.deleteClientRequest(request)
        case .sent:
            let request = self.sentRequests[indexPath.row]
            self.deleteClientRequest(request)
        default:
            break
        }
        completionHandler(true)
    }

    switch currentShowingStatus {
    case .accepted, .sent:
        actions.append(deleteAction)
    case .received:
        actions.removeAll()
    }

    let configuration = UISwipeActionsConfiguration(actions: actions)
    configuration.performsFirstActionWithFullSwipe = false
    return configuration
}

缺点是，我仍然必须再次检查段，以显示只接受和发送段的滑动动作。

Answer 1

在第一个实现中，如果在开关语句的所有情况下对deleteAction进行初始化，则可以使它成为常量：

    let deleteAction: UIContextualAction?
    switch currentShowingStatus {
    case .accepted:
        deleteAction = UIContextualAction(...)
    case .sent:
        deleteAction = UIContextualAction(...)
    case .received:
        deleteAction = nil
    }

这就清楚地表明，变量在使用之前精确地初始化了一次。我还会用显式的default:代替case received:。这对读者来说是显而易见的，在这种情况下，不配置swipe操作(不查找枚举定义)，如果添加了更多的情况，则强制您更新代码。

可以通过初始化操作数组来避免UISwipeActionsConfiguration的双重定义：

    let actions: [UIContextualAction]
    switch currentShowingStatus {
    case .accepted:
        actions = [UIContextualAction(...)]
    case .sent:
        actions = [UIContextualAction(...)]
    default:
        actions = []
    }

    let configuration = UISwipeActionsConfiguration(actions: actions)
    configuration.performsFirstActionWithFullSwipe = false
    return configuration

不过，它仍然是UIContextualAction的代码复制。

在您的替代方法中，您可以从actions数组中追加或删除元素。但是这个数组最初是空的。与上面类似，您可以将其简化为

    let deleteAction = ...

    let actions: [UIContextualAction]
    switch currentShowingStatus {
    case .accepted, .sent:
        actions = [deleteAction]
    case .received:
        actions = []
    }

但是- as，您注意到，- you不得不再次评估闭包中的self.currentShowingStatus。由于另一个原因，我会避免这样做:您所依赖的事实是，在执行闭包时，状态并没有改变。

如果首先初始化请求，则可以避免UIContextualAction的代码重复：

   let request: Request?
   switch currentShowingStatus {
   case .accepted:
       request = self.acceptedRequests[indexPath.row]
   case .sent:
       request = self.sentRequests[indexPath.row]
   case .received:
       request = nil
   }

   if let request = request {
       let deleteAction = UIContextualAction(style: .destructive, title: "Delete") {
           _, _, completionHandler in
           self.deleteClientRequest(request)
           completionHandler(true)
       }
       let configuration = UISwipeActionsConfiguration(actions: [deleteAction])
       configuration.performsFirstActionWithFullSwipe = false
       return configuration
   } else {
       return UISwipeActionsConfiguration(actions: [])
   }

还请注意，未使用的闭包参数可以被通配符参数_替换。

我可能会这样做，但你当然可以把这些技巧结合起来：

    let request: Request?
    switch currentShowingStatus {
    case .accepted:
        request = self.acceptedRequests[indexPath.row]
    case .sent:
        request = self.sentRequests[indexPath.row]
    case .received:
        request = nil
    }

    let actions: [UIContextualAction]
    if let request = request {
        actions = [UIContextualAction(style: .destructive, title: "Delete") {
            _, _, completionHandler in
            self.deleteClientRequest(request)
            completionHandler(true)
            }]
    } else {
        actions = []
    }

    let configuration = UISwipeActionsConfiguration(actions: actions)
    configuration.performsFirstActionWithFullSwipe = false
    return configuration