Unable to figure out how to prevent crash with Date type and wrapping in Swift 3

Question

I'm working with MPMediaQuery and specifically Podcasts. I'm having a very difficult time with Optionals and wrapping/unwrapping in this particular case.

    titleFilter = MPMediaPropertyPredicate(value: selectedPodcastTitle, forProperty: MPMediaItemPropertyPodcastTitle, comparisonType: .equalTo)
    qryPodcasts.addFilterPredicate(titleFilter)

    for junk in qryPodcasts.items!{

        //works fine
        if let sTitle  = junk.title {
            print("episode title: \(sTitle)")
        }else{
            print("episode title is nil")
        }

        //works fine
        if let dRelease = junk.releaseDate {
            print("episode release date: \(dRelease)")
        }else{
            print("episode release date is nil")
        }
        if #available(iOS 10.0, *) {
            // can't figure out how to make this work
            // crashes on some podcasts and I suspect it's when 'addedDate' is nil
            if let dAdded: Date = junk.dateAdded {
                print("episode added date: \(junk.dateAdded)")
            }else{
                print("episode added date is nil")
            }
        } else {
            print("episode added date is not available")
        }
    }

Have you tried setting a breakpoint and following the flow of the program? Maybe there's a side effect of something going on. Also try, instead of using the property accessor, `junk.value(forProperty: the date added key)` and see what that gives you. If it is null or something funky, you may have stumbled into a swift bug. — hola, Mar 12 '17 at 06:26

score 1 · Accepted Answer · answered Mar 12 '17 at 07:48

Seems the nullability of dateAdded is wrongly annotated in the current iOS SDK, and you may need some workaround.

Try this extension:

extension MPMediaItem {
    func getAddedDate() -> Date? {
        return self.perform(#selector(getter: MPMediaItem.dateAdded))?.takeUnretainedValue() as! NSDate? as Date?
    }
}

And use it like:

        if let dAdded = junk.getAddedDate() {
            print("episode added date: \(dAdded)")
        }else{
            print("episode added date is nil")
        }

You'd better send a bug report to Apple about this issue. (It may be classified as duplicate, but the number may affect.)

Thanks, that worked. One thing to note is that "dateAdded" is only available since iOS 10 so I had to wrap both the extension clause and my usage like so: `extension MPMediaItem { @available(iOS 10.0, *) func getAddedDate() -> Date? { return self.perform(#selector(getter: MPMediaItem.dateAdded))?.takeUnretainedValue() as! NSDate? as Date? } }` — wayneh, Mar 12 '17 at 15:24

Luan Tran · Answer 2 · 2017-03-12T06:47:03.683

0

After the last discussion, the dateAdded has un-nullable type Date and crash happen when it = nil.

So I recommend it type should Date? and you should unwrapping it.

 if let dAdded = junk.dateAdded {
 }

or check it will nil at this situation.

 if junk.dateAdded != nil {
 }

edited Mar 12 '17 at 06:47

answered Mar 12 '17 at 06:21

Luan Tran

1,142
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15

dateAdded is typed as `var dateAdded: Date { get }`. The compiler knows the type. Also it's not a nullable type, but that only gives a warning. – hola Mar 12 '17 at 06:25
Did it crash when `dateAdded = nil` right at `let dAdded: Date = junk.dateAdded` ? – Luan Tran Mar 12 '17 at 06:26
Regardless of the methods I use it is crashing at the "let" or "if" line. I changed to if junk.dateAdded != nil and the compiler is stating "Comparing non-optional value of type 'Date' to nil always returns true" – wayneh Mar 12 '17 at 06:44
Also, if I use `if let dAdded = junk.dateAdded` the compiler complains: "Initializer for conditional binding must have Optional type, not 'Date' " – wayneh Mar 12 '17 at 06:47
Yes. Because it's type is un-nullable `Date`. You should change `dateAdded` type to `Date` to `Date?` because it can be nil. Or you have to find out why it nil in init? – Luan Tran Mar 12 '17 at 06:49
Can't change to `Date` or `Date?` - compiler complains "Non-optional expression of type 'Date' used in a check for optionals" – wayneh Mar 12 '17 at 06:53
Where compiler show that error? Can you update more code where you init the `junk`. – Luan Tran Mar 12 '17 at 07:07

Unable to figure out how to prevent crash with Date type and wrapping in Swift 3

2 Answers2