无法在某些iPhone模拟器中保存UserDefault数组（Swift 3）

Question

I'm saving an array using UserDefault and for the most part it's working incredibly great. However in some simulators such as iPhone 7, iPhone 5 (iOS 9.3), and iPhone 6 (iOS 9.3) the simulator crashes in the line where I try loading one of my arrays from UserDefaults.

@IBAction func AddGraphComponent(_ sender: UIButton) {
    var weighText:UITextField!
    let alert = UIAlertController(title: "Enter new Weight!", message: "Please enter your Weight, followed by the date in which your weight was recorded", preferredStyle: UIAlertControllerStyle.alert)
    alert.addTextField { (weighText) in
        weighText.placeholder = "Weight"
        weighText.keyboardType = UIKeyboardType.numberPad
    }
    alert.addTextField { (dateText) in
        dateText.placeholder = "Date (MM/YY)"
    }
    let confirmAction = UIAlertAction(title: "Save", style: UIAlertActionStyle.default) { (_) in
        let field = alert.textFields![0] as? UITextField
        let weigh = alert.textFields![1] as? UITextField
        if (field?.text)! == "" || (weigh?.text)! == "" {
            let alert1 = UIAlertController(title: "Error!", message: "Please fill in BOTH fields", preferredStyle: UIAlertControllerStyle.alert)
            alert1.addAction(UIAlertAction(title: "OK", style: UIAlertActionStyle.default, handler: nil))
            self.present(alert1, animated: true, completion: nil)
        }else {
            print((field?.text)!,(weigh?.text)!)
            let dataInt:Int = Int((field?.text!)!)!
            self.chartData.append(dataInt)
            self.chartLegend.append((weigh?.text)!)

            var weighting = UserDefaults.standard.array(forKey: "chartData") as! [Int]
            var dating = UserDefaults.standard.array(forKey: "chartLegend") as! [String]// this is where the error is EXC_BAD_INSTRUCTION (code=EXC_1386_INVOP,subcode=0x0)

            weighting.append((dataInt))
            dating.append((weigh?.text)!)


            self.kUserDefault.set(weighting, forKey: "chartData")
            self.kUserDefault.set(dating, forKey: "chartLegend")
            self.kUserDefault.synchronize()

            self.lineChart.reloadData()

            print("\((dating))")
            print("\((weighting))")
        }
    }
    alert.addAction(UIAlertAction(title: "Cancel", style: UIAlertActionStyle.cancel, handler: nil))
    alert.addAction(confirmAction)
    self.present(alert, animated: true, completion: nil)
}

at the line where I write var dating = UserDefaults.standard.array(forKey: "chartLegend") as! [String] var dating = UserDefaults.standard.array(forKey: "chartLegend") as! [String] my code crashes on said device simulators. I wonder as to why this is. Is there an error in my code, or is this a bug? I'm using swift 3 on Xcode 8.0

Answer 1

You are retrieving the array before you set it, which means there's a good chance it's nil , and you are force casting it with as! , which is something else you should avoid because in situations like this, it crashes.

I suggest you do var dating = UserDefaults.standard.array(forKey: "chartLegend") as? [String] ?? [String]() var dating = UserDefaults.standard.array(forKey: "chartLegend") as? [String] ?? [String]() var dating = UserDefaults.standard.array(forKey: "chartLegend") as? [String] ?? [String]() instead to prevent the crash, and to get more familiar with optionals in general.

My rule is to NEVER use ! to unwrap an optional outside of IBOutlets . I use if , guard and ?? instead.

Answer 2

This is happening most likely because UserDefaults doesn't find anything named 'chartData' or 'chartLegend' and then reading it as nil. What you want to do is use a if let to safely check if there is a value you can receive.

Take a look here:

if let weighting = UserDefaults.standard.array(forKey: "chartData") as? [Int] {
    //Do your stuff
    weighting.append((dataInt))
    self.kUserDefault.set(weighting, forKey: "chartData")
    print("\((weighting))")
}
if let dating = UserDefaults.standard.array(forKey: "chartLegend") as? [String] {
    //do your stuff here
    dating.append((weigh?.text)!)
    self.kUserDefault.set(dating, forKey: "chartLegend")
     print("\((dating))")
}
self.kUserDefault.synchronize()

As rmaddy commented, it is important that you do a clean install on simulator and real device before testing modified code, especially when you are dealing with read/write from storage.

Edit:

Another approach is to use the guard statements.

guard let dating = UserDefaults.standard.array(forKey: "chartLegend") as? [String] 
else{ 
//dating is nil
}