使用didSelectRowAtIndexPath

Question

我有一个核心数据项目的主细节VC设置.如果searchBar是活动的，则显示一组结果，如果它不是活动的，则fetchedResultsController中的对象将显示在MasterVC中。

我一直在尝试使用prepareForSegue来完成任务，但是我的导师建议我使用didSelectRowAtIndexPath来完成这个任务。

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)

}

我得到了这个编译器错误：

Variable 'selectedNote' used before being initialized--它是在方法的顶部声明的！

如果我在"self"之前添加selectedNote，如下所示：

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

'MasterViewController' does not have a member named 'selectedNote'尽管在那里。所以很明显我搞砸了什么。

我在let detailViewController = DetailViewController()之前放置了一个断点，在lldb中，它打印出了正确的对象。我已经在这里找了个解决方案，但我现在还不够。我找不到适用于GitHub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的属性向前传递给detailViewController

更新：

根据我得到的响应，我用以下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，我会把它放在控制台上：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，我单击的对象将显示在控制台中。

Answer 1

您需要声明selectedNote为可选的，如下所示：

  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，您需要的是对DetailViewController的引用，以便将信息传递给它。

因此，您可以在接口构建器中创建从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
            }
        }
    }
}

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