Extracting values from anyobject dictionary into array - ios

Question

My other question was marked as being identical to another but it didn't answer the problem I was having.
Here is the code:
if status == "OK" {
self.selectedRoute = (dictionary["routes"] as! Array<Dictionary<NSObject, AnyObject>>)[0]
self.overviewPolyline = self.selectedRoute["overview_polyline"] as! Dictionary<NSObject, AnyObject>
let legs = self.selectedRoute["legs"] as! Array<Dictionary<NSObject, AnyObject>>
let steps = legs[0]["steps"]!
for i in 0...steps.count - 1 {
let step_coordinate = steps[i]["start_location"]!
print(step_coordinate!["lat"]!!)
}
}
The print statement gives this result
40.7609205
40.7640121
40.7595325
40.7501637
40.7481923
40.7393448
40.7252038
40.7225337
40.718295
but if I swap the print statement out to grab the values and put them in an array I get the fatal error: found nil.
Can someone explain why this is the case? How can I grab these values if not through a for loop?

Answer 1

Here's a cleaner version of your code.
Rules:
Don't force unwrap anything!
Optionally cast values coming from [NSObject: AnyObject] lookups.
Use guard statements and if let to safely unwrap optionals.
Don't index arrays that might be empty without checking first.
if status == "OK" {
guard let routes = dictionary["routes"] as? [[NSObject: AnyObject]] else { return }
self.selectedRoute = routes.first ?? [:]
self.overviewPolyline = self.selectedRoute["overview_polyline"] as? [NSObject: AnyObject] ?? [:]
guard let legs = self.selectedRoute["legs"] as? [[NSObject: AnyObject]] else { return }
let firstleg = legs.first ?? [:]
guard let steps = firstleg["steps"] as? [[NSObject: AnyObject]] else { return }
for step in steps {
if let step_coordinate = step["start_location"] as? [NSObject: AnyObject] {
if let lat = step_coordinate["lat"] as? Double {
print(lat)
// append lat to array of lats
lats.append(lat)
}
}
}
}