发生致命错误：展开可选的iOS Swift时找到nil

Question

This is a little strange to me that I'm getting this error when trying to show an NSDate converted to a string in a UICollectionViewCell. In viewDidLoad I am grabbing objects from parse and storing them in an NSMutableArray called vaccineData (which after debugging, is successful). Then in cellForItemAtIndexPath I have the following:

let myCell: VaccineCollectionViewCell = collectionView.dequeueReusableCellWithReuseIdentifier("vaccineIdentifier", forIndexPath: indexPath) as! VaccineCollectionViewCell

  //Document Images
    let vaccinePost = self.vaccineData.objectAtIndex(indexPath.row) as! PFObject
    if let imagesPosting: PFFile = (vaccinePost["documentImage"] as! PFFile) {
        imagesPosting.getDataInBackgroundWithBlock({ (imageData, error) -> Void in
            if (error == nil) {
                let image:UIImage = UIImage(data: imageData!)!

                myCell.dogumentImage.image = image as UIImage
            }
        })
    }

  //Uploaded Date
    let datePost = self.vaccineData.objectAtIndex(indexPath.row) as! PFObject
    if let date:NSDate = (datePost["updatedAt"] as! NSDate) {

        let dateformatter = NSDateFormatter()
        dateformatter.dateStyle = NSDateFormatterStyle.LongStyle
        dateformatter.timeStyle = NSDateFormatterStyle.NoStyle

        let updateString = dateformatter.stringFromDate(date)

        myCell.uploadedTime.text = updateString
        print("Uploaded Time: \(updateString)")
    } else {
        print("There was an error")
    }

    return myCell

My app crashes on the line:

if let date:NSDate = (datePost["updatedAt"] as! NSDate)

It won't even give me the else print error statement. I know the image code is working correctly bc I've commented out the NSDate code and it showed the image. I've double checked keyword spellings, delegates, datasources but can't find where or why this is nil. Can someone spot if I'm missing anything? Thanks in advance!

Answer 1

As to why the else-block is not reached - because you force downcast, not optionally (do not know the exact terminology). The correct code reading syntax would be:

if let date = datePost["updatedAt"] as? NSDate {

} else {
    print("There was an error")
}

As to why the updatedAt is not actually set - no idea, maybe because you did not update the entry yet. But you should probably simply use the property updatedAt instead anyway:

if let date = datePost.updatedAt {

} else {
    print("There was an error")
}