解析JSON时，Nil Coalescing返回nil而不是默认值

Question

Im parsing JSON and I'm having an issue when i use nil coalescing to try and return a default value for a key / value set that sometimes doesn't exist. The website I'm parsing json from is http://heroesjson.com . The creator has even given me a map of how to parse it. Where I run into problems is when I try to parse the talents key. Not every talent has a "cooldown" or "prerequisite" key. SO I tried to use nil coalescing to assign a default value if the key/value set doesn't exist BUT when I try to assign the value to iCooldown or sPrerequisite, i get the error unexpectedly found nil when trying to unwrap optional. How can that be since I gave it a default value?

//Parse Talent Class
                        if let talentsArray = dict[x]["talents"] as? Dictionary<String, AnyObject> {

                            for y in 0 ..< dict.count {
                                if let allHeroTalents = talentsArray["\(y)"]{
                                    for z in 0 ..< allHeroTalents.count {


                                            let id = allHeroTalents[z]["id"]
                                            let name = allHeroTalents[z]["name"]
                                            let description = allHeroTalents[z]["description"]
                                            let cooldown = allHeroTalents[z]["cooldown"] ?? 0.0
                                            let prerequisite = allHeroTalents[z]["prerequisite"] ?? ""
                                            let icon = allHeroTalents[z]["icon"]


                                            let sId = id as? String
                                            let sName = name as? String
                                            let sDescription = description as? String
                                            //let iCooldown = cooldown as! Double
                                            //let sPrerequisite = prerequisite as! String
                                            let sIcon = icon as? String
                                            //let talent = Talent(id: sId!, name: sName!, description: sDescription!, cooldown: iCooldown, prerequisite: sPrerequisite, icon: sIcon!)
                                        print("\(hero.name) has talent \(cooldown)")


                                    }
                                }
                            }

                        }

I have included the whole file below for reference. My main file just calls func parseData().

 import Foundation class Hero { var id: String? var attributeid: String? var name: String? var title: String? var description: String? var role: String? var type: String? var gender: String? var franchise: String? var difficulty: String? var icon: String? var ratings: Ratings? var stats: Stats? var talents: [Talent]? init(id: String, attributeid: String, name: String, title: String, description: String, role: String, type: String, gender: String, franchise: String, difficulty: String, icon: String){ self.id = id self.attributeid = attributeid self.name = name self.title = title self.description = description self.role = role self.type = type self.gender = gender self.franchise = franchise self.difficulty = difficulty self.icon = icon } } class Ratings { var damage: Int? var utility: Int? var survivability: Int? var complexity: Int? init(damage: Int, utility: Int, survivability: Int, complexity: Int) { self.damage = damage self.utility = utility self.survivability = survivability self.complexity = complexity } } class Stats { var hp: Int? var hpPerLevel: Int? var hpRegen: Double? var hpRegenPerLevel: Double? var mana: Int? var manaPerLevel: Int? var manaRegen: Double? var manaRegenPerLevel: Double? init(hp: Int, hpPerLevel: Int, hpRegen: Double, hpRegenPerLevel: Double, mana: Int, manaPerLevel: Int, manaRegen: Double, manaRegenPerLevel: Double) { self.hp = hp self.hpPerLevel = hpPerLevel self.hpRegen = hpRegen self.hpRegenPerLevel = hpRegenPerLevel self.mana = mana self.manaPerLevel = manaPerLevel self.manaRegen = manaRegen self.manaRegenPerLevel = manaRegenPerLevel } } class Talent { var id: String? var name: String? var description: String? var cooldown: Double? var prerequisite: String? var icon: String? init(id: String, name: String, description: String, cooldown: Double, prerequisite: String, icon: String) { self.id = id self.name = name self.description = description self.cooldown = cooldown self.prerequisite = prerequisite self.icon = icon } } class Ability { var id: String? var name: String? var description: String? var shortcut: String? var cooldown: Double? var manaCost: Double? var manaCostPerSecond: Double? var aimType: String? var heroic: Bool? var trait: Bool? var mount: Bool? var icon: String? init(id: String, name: String, description: String, shortcut: String, cooldown: Double, manaCost: Double, manaCostPerSecond: Double, aimType: String, heroic: Bool, trait: Bool, mount: Bool, icon: String){ self.id = id self.name = name self.description = description self.shortcut = shortcut self.cooldown = cooldown self.manaCost = manaCost self.manaCostPerSecond = manaCostPerSecond self.aimType = aimType self.heroic = heroic self.trait = trait self.mount = mount self.icon = icon } } func parseData(){ let urlString = "http://heroesjson.com/heroes.json" let session = NSURLSession.sharedSession() let url = NSURL(string: urlString)! session.dataTaskWithURL(url) { (data: NSData?, response:NSURLResponse?, error: NSError?) -> Void in if let responseData = data { do { let json = try NSJSONSerialization.JSONObjectWithData(responseData, options: NSJSONReadingOptions.AllowFragments) if let dict = json as? [Dictionary<String, AnyObject>] { for x in 0 ..< dict.count { if let id = dict[x]["id"], let attributeid = dict[x]["attributeid"], let name = dict[x]["name"], let title = dict[x]["title"], let description = dict[x]["description"], let role = dict[x]["role"], let type = dict[x]["type"], let gender = dict[x]["gender"], let franchise = dict[x]["franchise"], let difficulty = dict[x]["difficulty"], let icon = dict[x]["icon"] { let hero = Hero(id: id as! String, attributeid: attributeid as! String, name: name as! String, title: title as! String, description: description as! String, role: role as! String, type: type as! String, gender: gender as! String, franchise: franchise as! String, difficulty: difficulty as! String, icon: icon as! String) // Parse Ratings Class if let dataArray = dict[x]["ratings"] as? Dictionary<String, Int> { if let damage = dataArray["damage"], let utility = dataArray["utility"], let survivability = dataArray["damage"], let complexity = dataArray["complexity"] { let rating = Ratings(damage: damage , utility: utility , survivability: survivability , complexity: complexity ) hero.ratings = rating //print("\\(hero.name) has a damage rating of \\(hero.ratings!.damage)") } } //Parse Stats Class if let statsArray = dict[x]["stats"] as? Dictionary<String, AnyObject> { if let dummy = statsArray[hero.id!]{//error handleing for vikings if let hp = statsArray[hero.id!]!["hp"], let hpPerLevel = statsArray[hero.id!]!["hpPerLevel"], let hpRegen = statsArray[hero.id!]!["hpRegen"], let hpRegenPerLevel = statsArray[hero.id!]!["hpRegenPerLevel"], let mana = statsArray[hero.id!]!["mana"], let manaPerLevel = statsArray[hero.id!]!["manaPerLevel"], let manaRegen = statsArray[hero.id!]!["manaRegen"], let manaRegenPerLevel = statsArray[hero.id!]!["manaRegenPerLevel"] { let stats = Stats(hp: hp as! Int, hpPerLevel: hpPerLevel as! Int, hpRegen: hpRegen as! Double, hpRegenPerLevel: hpRegenPerLevel as! Double, mana: mana as! Int, manaPerLevel: manaPerLevel as! Int, manaRegen: manaRegen as! Double, manaRegenPerLevel: manaRegenPerLevel as! Double) hero.stats = stats } }//closes let dummy } //Parse Talent Class if let talentsArray = dict[x]["talents"] as? Dictionary<String, AnyObject> { for y in 0 ..< dict.count { if let allHeroTalents = talentsArray["\\(y)"]{ for z in 0 ..< allHeroTalents.count { let id = allHeroTalents[z]["id"] let name = allHeroTalents[z]["name"] let description = allHeroTalents[z]["description"] let cooldown = allHeroTalents[z]["cooldown"] ?? 0.0 let prerequisite = allHeroTalents[z]["prerequisite"] ?? "" let icon = allHeroTalents[z]["icon"] let sId = id as? String let sName = name as? String let sDescription = description as? String //let iCooldown = cooldown as! Double //let sPrerequisite = prerequisite as! String let sIcon = icon as? String //let talent = Talent(id: sId!, name: sName!, description: sDescription!, cooldown: iCooldown, prerequisite: sPrerequisite, icon: sIcon!) print("\\(hero.name) has talent \\(cooldown)") } } } } // Parse Ability Class if let abilitiesArray = dict[x]["abilities"] as? Dictionary<String, AnyObject> { for c in 0 ..< abilitiesArray.count { for d in 0 ..< abilitiesArray.count { if let dummy = abilitiesArray[hero.id!]{ let id = abilitiesArray[hero.id!]!["id"] let name = abilitiesArray[hero.id!]!["name"] let description = abilitiesArray[hero.id!]!["description"] let shortcut = abilitiesArray[hero.id!]!["shortcut"] let cooldown = abilitiesArray[hero.id!]!["cooldown"] let manaCost = abilitiesArray[hero.id!]!["manaCost"] let manaCostPerSecond = abilitiesArray[hero.id!]!["manaCostPerSecond"] let aimType = abilitiesArray[hero.id!]!["aimType"] let heroic = abilitiesArray[hero.id!]!["heroic"] let trait = abilitiesArray[hero.id!]!["trait"] let mount = abilitiesArray[hero.id!]!["mount"] let icon = abilitiesArray[hero.id!]!["icon"] let sId = id as? String let sName = name as? String let sDescription = description as? String let sShortcut = shortcut as? String let sCooldown = cooldown as? Double let sManaCost = manaCost as? Double let sManaCostPerSecond = manaCostPerSecond as? Double let sAimType = aimType as? String let sHeroic = heroic as? Bool let sTrait = trait as? Bool let sMount = mount as? Bool let sIcon = icon as? String // let abilities = Ability(id: sId!, name: sName!, description: sDescription!, shortcut: sShortcut!, cooldown: sCooldown!, manaCost: sManaCost!, manaCostPerSecond: sManaCostPerSecond!, aimType: sAimType!, heroic: sHeroic!, trait: sTrait!, mount: sMount!, icon: sIcon!) } } } } heroes.append(hero) } } } } catch { print("Could not serialize") } } }.resume() } 

Answer 1

I might be wrong, but it seems that you are using your Dictionary as an Array. which causes you to unwrap optional values that are not there.

From your code:

//- talentsArray is a dictionary! 
if let talentsArray = dict[x]["talents"] as? Dictionary<String, AnyObject> {
    for y in 0 ..< dict.count {
        //- talentsArray["\(y)"] y is a value from 0 to the count, not necesarilly a key.
        if let allHeroTalents = talentsArray["\(y)"]{
            for z in 0 ..< allHeroTalents.count {
              // ...
            }
        }
    }
}

Dictionaries do not maintain order, if you need to iterate through them you can Enumerate your dictionary, you have to use the for (key, value) in dictionary syntax. Something along the lines of:

if let talents = dict[x]["talents"] as? Dictionary<String, AnyObject> {
    for (index, talent) in talents {
        for attribute in talent {
           // Do your thing.
        }
    }
}

Your problem as I understand it, is not the coalescing, but the incorrect use of the dictionary DS. I replicated the API call and can see that even if you where to iterate through it while treating the index as the key of the dictionary, you'll run into some trouble as the keys are in no way sequential:

UPDATE

As I mentioned in the comments, while your solution works let cooldown = item[cooldown]! will force unwrap your optional, which is not the best approach when dealing with optional values fetched from an API (Specially if they are not always included in the data as you mention in the original question). Assuming that your 'cooldown' is a double and 'prerequisite' is a string, I would implement it like this:

let cooldown = item["cooldown"] as? Double ?? 0.00
let prerequisite = item["prerequisite"] as? String ?? ""

This approach will unwrap your optional while casting to the correct expected type, and then coalesce the value of the key value pair. This approach is much safer as it does not assume that the API Call will contain these keys.

Hope this helps!

Answer 2

I stumbled across the answer by messing with my code. Apparently all I needed to do was unwrap (use !) the variable going into the nil coalescing operator.

let cooldown = item["cooldown"]! ?? 0.00
let prerequisite = item["prerequisite"]! ?? ""

Entire Working Code

 import Foundation class Hero { var id: String? var attributeid: String? var name: String? var title: String? var description: String? var role: String? var type: String? var gender: String? var franchise: String? var difficulty: String? var icon: String? var ratings: Ratings? var stats: Stats? var talents: [String: [Talent]]? var abilities: [String: [Ability]]? init(id: String, attributeid: String, name: String, title: String, description: String, role: String, type: String, gender: String, franchise: String, difficulty: String, icon: String){ self.id = id self.attributeid = attributeid self.name = name self.title = title self.description = description self.role = role self.type = type self.gender = gender self.franchise = franchise self.difficulty = difficulty self.icon = icon } } class Ratings { var damage: Int? var utility: Int? var survivability: Int? var complexity: Int? init(damage: Int, utility: Int, survivability: Int, complexity: Int) { self.damage = damage self.utility = utility self.survivability = survivability self.complexity = complexity } } class Stats { var hp: Int? var hpPerLevel: Int? var hpRegen: Double? var hpRegenPerLevel: Double? var mana: Int? var manaPerLevel: Int? var manaRegen: Double? var manaRegenPerLevel: Double? init(hp: Int, hpPerLevel: Int, hpRegen: Double, hpRegenPerLevel: Double, mana: Int, manaPerLevel: Int, manaRegen: Double, manaRegenPerLevel: Double) { self.hp = hp self.hpPerLevel = hpPerLevel self.hpRegen = hpRegen self.hpRegenPerLevel = hpRegenPerLevel self.mana = mana self.manaPerLevel = manaPerLevel self.manaRegen = manaRegen self.manaRegenPerLevel = manaRegenPerLevel } } class Talent { var id: String? var name: String? var description: String? var cooldown: Double? var prerequisite: String? var icon: String? init(id: String, name: String, description: String, cooldown: Double, prerequisite: String, icon: String) { self.id = id self.name = name self.description = description self.cooldown = cooldown self.prerequisite = prerequisite self.icon = icon } } class Ability { var id: String? var name: String? var description: String? var shortcut: String? var cooldown: Double? var manaCost: Double? var manaCostPerSecond: Double? var aimType: String? var heroic: Bool? var trait: Bool? var mount: Bool? var icon: String? init(id: String, name: String, description: String, shortcut: String, cooldown: Double, manaCost: Double, manaCostPerSecond: Double, aimType: String, heroic: Bool, trait: Bool, mount: Bool, icon: String){ self.id = id self.name = name self.description = description self.shortcut = shortcut self.cooldown = cooldown self.manaCost = manaCost self.manaCostPerSecond = manaCostPerSecond self.aimType = aimType self.heroic = heroic self.trait = trait self.mount = mount self.icon = icon } } func parseData() { let urlString = "http://heroesjson.com/heroes.json" let session = NSURLSession.sharedSession() let url = NSURL(string: urlString)! session.dataTaskWithURL(url) { (data: NSData?, response:NSURLResponse?, error: NSError?) -> Void in if let responseData = data { do { let json = try NSJSONSerialization.JSONObjectWithData(responseData, options: NSJSONReadingOptions.AllowFragments) if let dict = json as? [Dictionary<String, AnyObject>] { for x in 0 ..< dict.count { if let id = dict[x]["id"], let attributeid = dict[x]["attributeid"], let name = dict[x]["name"], let title = dict[x]["title"], let description = dict[x]["description"], let role = dict[x]["role"], let type = dict[x]["type"], let gender = dict[x]["gender"], let franchise = dict[x]["franchise"], let difficulty = dict[x]["difficulty"], let icon = dict[x]["icon"] { let hero = Hero(id: id as! String, attributeid: attributeid as! String, name: name as! String, title: title as! String, description: description as! String, role: role as! String, type: type as! String, gender: gender as! String, franchise: franchise as! String, difficulty: difficulty as! String, icon: icon as! String) // Parse Ratings Class if let dataArray = dict[x]["ratings"] as? Dictionary<String, Int> { if let damage = dataArray["damage"], let utility = dataArray["utility"], let survivability = dataArray["damage"], let complexity = dataArray["complexity"] { let rating = Ratings(damage: damage , utility: utility , survivability: survivability , complexity: complexity ) hero.ratings = rating //print("\\(hero.name) has a damage rating of \\(hero.ratings!.damage)") } } //Parse Stats Class if let statsArray = dict[x]["stats"] as? Dictionary<String, AnyObject> { if let dummy = statsArray[hero.id!]{//error handleing for vikings - parsing without this causes errors if let hp = statsArray[hero.id!]!["hp"], let hpPerLevel = statsArray[hero.id!]!["hpPerLevel"], let hpRegen = statsArray[hero.id!]!["hpRegen"], let hpRegenPerLevel = statsArray[hero.id!]!["hpRegenPerLevel"], let mana = statsArray[hero.id!]!["mana"], let manaPerLevel = statsArray[hero.id!]!["manaPerLevel"], let manaRegen = statsArray[hero.id!]!["manaRegen"], let manaRegenPerLevel = statsArray[hero.id!]!["manaRegenPerLevel"] { let stats = Stats(hp: hp as! Int, hpPerLevel: hpPerLevel as! Int, hpRegen: hpRegen as! Double, hpRegenPerLevel: hpRegenPerLevel as! Double, mana: mana as! Int, manaPerLevel: manaPerLevel as! Int, manaRegen: manaRegen as! Double, manaRegenPerLevel: manaRegenPerLevel as! Double) hero.stats = stats } }//closes let dummy } //Parse Talent Class if let talentsDict = dict[x]["talents"] as? Dictionary<String, AnyObject> { for (index, talentsAtLevel) in talentsDict { var talents = [Talent]() for item in talentsAtLevel as! [AnyObject] { let id = item["id"] let name = item["name"] let description = item["description"] let cooldown = item["cooldown"]! ?? 0.00 let prerequisite = item["prerequisite"]! ?? "" let icon = item["icon"] let sId = id as? String let sName = name as? String let sDescription = description as? String let iCooldown = cooldown as! Double let sPrerequisite = prerequisite as! String let sIcon = icon as? String let talent = Talent(id: sId!, name: sName!, description: sDescription!, cooldown: iCooldown, prerequisite: sPrerequisite, icon: sIcon!) talents.append(talent) } hero.talents = ["\\(index)": talents] } } //Parse Ability Class if let abilitiesDict = dict[x]["abilities"] as? Dictionary<String, AnyObject> { for (index, abilitiesAtLevel) in abilitiesDict { //index = heroid var abilities = [Ability]() for item in abilitiesAtLevel as! [AnyObject] { //item = ability let id = item["id"]! ?? "" let name = item["name"]! ?? "" let description = item["description"]! ?? "" let shortcut = item["shortcut"]! ?? "" let cooldown = item["cooldown"]! ?? 0.0 let manaCost = item["manaCost"]! ?? 0.0 let manaCostPerSecond = item["manaCostPerSecond"]! ?? 0.0 let aimType = item["aimType"]! ?? "" let heroic = item["heroic"]! ?? false let trait = item["trait"]! ?? false let mount = item["mount"]! ?? false let icon = item["icon"]! ?? "" let sId = id as? String let sName = name as? String let sDescription = description as? String let sShortcut = shortcut as? String let sCooldown = cooldown as? Double let sManaCost = manaCost as? Double let sManaCostPerSecond = manaCostPerSecond as? Double let sAimType = aimType as? String let sHeroic = heroic as? Bool let sTrait = trait as? Bool let sMount = mount as? Bool let sIcon = icon as? String let ability = Ability(id: sId!, name: sName!, description: sDescription!, shortcut: sShortcut!, cooldown: sCooldown!, manaCost: sManaCost!, manaCostPerSecond: sManaCostPerSecond!, aimType: sAimType!, heroic: sHeroic!, trait: sTrait!, mount: sMount!, icon: sIcon!) abilities.append(ability) } hero.abilities = ["\\(index)": abilities] } } heroes.append(hero) } } } } catch { print("Could not serialize") } } }.resume() }