使用 didSelectRowAtIndexPath 进行转场

Question

我有一个核心数据项目的主从 VC 设置。如果searchBar 处于活动状态，则显示一组结果，如果未处于活动状态，则 fetchedResultsController 中的对象将显示在 MasterVC 中。

我一直在尝试使用 prepareForSegue 进行转场，但我的导师建议我使用 didSelectRowAtIndexPath 进行转场。

override func tableView(tableView: UITableView, didSelectRowAtIndexPath indexPath: NSIndexPath) {
    var selectedNote: Note

    // Check to see which table view cell was selected.
    if tableView == self.tableView {
        selectedNote = self.fetchedResultsController.objectAtIndexPath(indexPath) as! Note // <--this is "everything"
    } else {
        // need this to unwrap the optional
        if let filteredObjects = filteredObjects {
            selectedNote = filteredObjects[indexPath.row]
        }
    }

    // Set up the detail view controller to show.
    let detailViewController = DetailViewController()
    detailViewController.detailDescriptionLabel = selectedNote.valueForKey("noteBody") as! UILabel

    // Note: Should not be necessary but current iOS 8.0 bug requires it.
    tableView.deselectRowAtIndexPath(tableView.indexPathForSelectedRow()!, animated: false)

    // original code
    navigationController?.pushViewController(detailViewController, animated: true)

}

我收到此编译器错误：

Variable 'selectedNote' used before being initialized--在方法顶部声明！

如果我像这样在selectedNote 之前添加"self"：

    detailViewController.detailDescriptionLabel = self.selectedNote.valueForKey("noteBody") as! UILabel

'MasterViewController' does not have a member named 'selectedNote' 尽管在那里。所以我显然在搞砸一些事情。

我在let detailViewController = DetailViewController() 和lldb 之前放置了一个断点，它打印出正确的对象。我在这里四处寻找解决方案，但我做不到。我在 GitHub 上找不到适用的代码。

class Note: NSManagedObject {

    @NSManaged var dateCreated: NSDate
    @NSManaged var dateEdited: NSDate
    @NSManaged var noteTitle: String
    @NSManaged var noteBody: String

}

任何想法如何将selectedNote 的属性转发给detailViewController？

更新：

根据我得到的回复，我已经用这段代码关闭了编译器警告：

override func tableView(tableView: UITableView, didSelectRowAtIndexPath indexPath: NSIndexPath) {
    var selectedNote: Note?

    // Check to see which table view cell was selected.
    if tableView == self.tableView {
        selectedNote = self.fetchedResultsController.objectAtIndexPath(indexPath) as? Note // <--this is "everything"
    } else {
        // need this to unwrap the optional
        if let filteredObjects = filteredObjects {
            selectedNote = filteredObjects[indexPath.row]
        }
    }

    // Set up the detail view controller to show.
    let detailViewController = DetailViewController()

    detailViewController.detailDescriptionLabel.text = (selectedNote!.valueForKey("noteBody") as! String)

    // Note: Should not be necessary but current iOS 8.0 bug requires it.
    tableView.deselectRowAtIndexPath(tableView.indexPathForSelectedRow()!, animated: false)

    // original code
    navigationController?.pushViewController(detailViewController, animated: true)

}

但是当它崩溃时，我在控制台中得到了这个： There are already notes in the app fatal error: unexpectedly found nil while unwrapping an Optional value

但是，当我键入 po selectedObject 时，我单击的对象会显示在控制台中。

Answer 1

您需要像这样将 selectedNote 声明为可选：

  var selectedNote: Note?

然后在使用之前检查值是否存在。

  if let note = selectedNote {
    // Set up the detail view controller to show.
    let detailViewController = DetailViewController()
    detailViewController.detailDescriptionLabel = note.valueForKey("noteBody") as! UILabel

    // Note: Should not be necessary but current iOS 8.0 bug requires it.
    tableView.deselectRowAtIndexPath(tableView.indexPathForSelectedRow()!, animated: false)            
    // original code
    navigationController?.pushViewController(detailViewController, animated: true)
  }

更新：

问题是您正在尝试创建 DetailViewController

let detailViewController = DetailViewController()

但是您需要的是引用 DetailViewController 以便将信息传递给它。

因此，您可以在 Interface builder 中创建从 Master 到 Detail 控制器的 segue。然后从 didSelectRowAtIndexPath

中删除逻辑

 override func tableView(tableView: UITableView, didSelectRowAtIndexPath indexPath: NSIndexPath) {

    // Note: Should not be necessary but current iOS 8.0 bug requires it.
    tableView.deselectRowAtIndexPath(tableView.indexPathForSelectedRow()!, animated: false)
}

并在prepareForSegue方法中实现：

override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {

    if segue.identifier == "showDetail" {

        if let cell = sender as? UITableViewCell {

            let indexPath = tableView.indexPathForCell(cell)!

            var selectedNote: Note?

            if filteredObjects?.count > 0 {
                selectedNote = filteredObjects![indexPath.row]
            }else {
                selectedNote = self.fetchedResultsController.objectAtIndexPath(indexPath) as? Note // <--this is "everything"
            }

            if let note = selectedNote {

                let controller = (segue.destinationViewController as! UINavigationController).topViewController as! DetailViewController
                controller.detailItem = note
            }
        }
    }
}

showDetail - 您需要在 IB 中设置的 segue 标识符。 var detailItem: AnyObject? - 你需要在 DetailViewController 中声明它。