Swift：在运行时以非可选的方式检测到意外的nil值：强制转换为可选失败

Question

I have a UITableViewController loading its entries from Core Data via a NSFetchedResultsController . Like this:

let historyItem = fetchedResults.objectAtIndexPath(indexPath) as HistoryItem

historyItem has a title property defined like this:

@NSManaged var title: String

but somehow the core data has a nil value for title in some entries which causes EXC_BAD_ACCESS because title is not String? . This problem has been addressed at Check if property is set in Core Data? and the high-voted answer there suggests something like this:

    if let possibleTitle = historyItem.title as String? {
        NSLog("possibleTitle was set OK")
    } else {
        NSLog("possibleTitle was nil")
    }

but I just tried that and it still gave me EXC_BAD_ACCESS:

That same problem and solution is also mentioned at Swift - casting a nil core data string as an optional value and my earlier duplicate question Swift: handling an unexpected nil value, when variable is not optional but it doesn't work for me. I'm using Xcode 6.2 and iOS8.

Am I misunderstanding something, please? Should this approach work?

Answer 1

I think you should make your title an optional if core data can return nil value for title

@NSManaged var title: String?

And test it without the cast

if let possibleTitle = historyItem.title{
    NSLog("possibleTitle was set OK")
} else {
    NSLog("possibleTitle was nil")
}