I decide some JSON and try to typecast it to a dictionary of String: classy and it fails. I have found that often the reason I have trouble doing something is because of a misunderstanding of how Swift works, so here is what I want to happen. Feel free to tell me that I am doing it wrong and if I do it this way all will be wonderful.
I want my data to live between runs of the app so I have to save the data to storage between runs. I have an object, data and associated code, and I have places where changes I make to a copy should reflect back to the original so it is a class. I have a bunch of these objects and most of the time I pick the one I want based on an id that is an integer. An array is not good since it would be a sparse array cause come ids are not used. I came up with a dictionary with a key of the id and data of the structure. I turned the key from an Int to a String, by changing the Int id to a String, cause converting a dictionary to JSON is MUCH easier for a key that is a string. I save the JSON string. When the app starts again I read the string in and convert the JSON string to Any. Then I typecast the result to the desired dictionary. This is where it fails. The cast does not work. In my Googling the samples I found said this should work.
Here is my code:
class Y: Codable, Hashable {
var a: String = "c"
static func ==(lhs: Y, rhs: Y) -> Bool {
return lhs.a == rhs.a
}
func hash(into hasher: inout Hasher) {
hasher.combine(a)
}
}
struct ContentView: View {
var body: some View {
VStack {
Button ("Error") {
var y = Y()
var yDict = [String: Y]()
yDict["0"] = y
do {
let encodedData = try JSONEncoder().encode(yDict)
let jsonString = String(data: encodedData, encoding: .utf8)
let decoded = try JSONSerialization.jsonObject(with: encodedData, options: [])
if let yyDictDec = decoded as? [String:Y] {
print("yDict after decide")
print (yyDictDec)
}
} catch {
print(error.localizedDescription)
}
print("x")
}
}
}
}
In this code the if yyDictDec = is failing, I think, cause the prints after it never happen. I can cast it as [String, Any] but I really need it to be my class.
My problem is in the convert JSON back to the dictionary. I feel I am missing something fairly simple.
Don´t use JSONSerialization use JsonDecoder and decode it to the the type it was before encoding. e.g.:
let decoded = try JSONDecoder().decode([String: Y].self, from: encodedData)
Related
I'm looking to run a Cloud-Code function from a Swift application and receive an object as a response. The response object from Parse is a standard JSON object as defined below and is not an object stored is Parse. Essentially, I'm looking to end up with an custom object defining the results of a cloud function's execution, not an object stored in the database.
I'm struggling with decoding the CloudCode response on the Swift side of things to a custom object following the Decodable protocol.
Sample Cloud Code
Parse.Cloud.define("MyCloudFunc", function(request, response) {
var results = {
"someBooleanProperty": true,
"someIntProperty": 1,
};
response.success(results);
}
Sample Swift Code
PFCloud.callFunction(inBackground: "MyCloudFunc", withParameters: []) { (result, error) in
// Printing `result` at this point shows what appears to be a JSON object.
guard let data = result as? Data else { return }
// Whatever type `result` actually is cannot be cast as Data, so we never make it past here.
guard let response = try? JSONDecoder().decode(MyDecodableStruct, from: data) else { return }
// DO SOMETHING WITH THE RESULT
}
Decodable Struct
struct MyDecodableStruct: Decodable {
var someBooleanProperty:Bool
var someIntProperty: Int
}
Question
How can I take that response from the Parse Cloud Code and end up with a decoded object of type MyDecodableStruct?
UPDATE
As suggested in the comments/answers, Parse is returning a Dictionary. I have been able to get everything working with the below; however, I feel there is a better way than double-conversion.
PFCloud.callFunction(inBackground: "MyCloudFunc", withParameters: []) { (result, error) in
guard let jsonString = result as? String else { return }
guard let data = jsonString.data(using: String.Encoding.utf8) else { return }
guard let response = try? JSONDecoder().decode(MyDecodableStruct.self, from: data) else { return }
// DO SOMETHING WITH RESULT.
}
Am I overlooking a way to convert from the Dictionary directly Data without doing the JSON conversion in-between?
Part of PFCloud's job is to create generic collection types from the cloud function response. Since the cloud function is answering a JS object, PFCloud should -- without the app noticing -- transmit JSON and parse it before invoking the callFunction callback.
So the posted cloud code result will the be a dictionary. Check to see that with...
if result is Dictionary<AnyHashable,Any> {
print("result is a Dictionary")
}
To convert that to the OP struct, add a from-dictionary initializer to it...
struct MyDecodableStruct: Decodable {
var someBooleanProperty:Bool
var someIntProperty: Int
init(dictionary: [AnyHashable,Any]) {
self.someBooleanProperty = dictionary["someBooleanProperty"] as? Bool ?? false
self.someIntProperty = dictionary["someIntProperty"] as? Int ?? 0
}
}
I'm trying to parse JSON with currency rates contains dynamic keys and a dynamic number of values. Output depends on input parameters, such as Base currency and several currencies to compare.
Example of JSON:
{
"USD_AFN": 70.129997,
"USD_AUD": 1.284793,
"USD_BDT": 82.889999,
"USD_BRL": 3.418294,
"USD_KHR": 4004.99952
}
, or:
{
"EUR_CAD": 0.799997
}
Also, I should be able to change Base currency and currencies to compare, and change number of currencies to compare.
I already tried this answer.
What is the optimal way to handle it?
Thanks
Additional info
So, I made the struct without the initializer
struct CurrencyRate: Codable {
var results : [String:Double]
}
and trying to decode it
do { let results = try decoder.decode(CurrencyRate.self, from: dataToDecode) print(results) } catch { print("Error") }
I'm still getting the error.
Eventually, I just need an array of currency rates (values) to populate it in a Table View.
After some experimentation my Playground looks as follows:
import Cocoa
import Foundation
let jsonData = """
{
"USD_AFN": 70.129997,
"USD_AUD": 1.284793,
"USD_BDT": 82.889999,
"USD_BRL": 3.418294,
"USD_KHR": 4004.99952
}
""".data(using: .utf8)!
do {
let obj = try JSONSerialization.jsonObject(with:jsonData, options:[])
print(obj) // this is an NSDictionary
if let dict = obj as? [String:Double] {
print(dict) // This is not "just" a cast ... more than I thought
}
}
struct CurrencyRate: Codable {
var results : [String:Double]
}
// If you use a "results"-key it _must_ be present in your JSON, but it would allow to add methods
let resultsJson = """
{
"results" : {
"USD_AFN": 70.129997,
"USD_AUD": 1.284793,
"USD_BDT": 82.889999,
"USD_BRL": 3.418294,
"USD_KHR": 4004.99952
}
}
""".data(using: .utf8)!
do {
let currencyRate = try JSONDecoder().decode(CurrencyRate.self, from: resultsJson)
print(currencyRate)
}
// this is probably the easiest solution for just reading it
do {
let rates = try JSONDecoder().decode([String:Double].self, from:jsonData)
print(rates)
}
// While you could do the following it does not feel "proper"
typealias CurrencyRatesDict = [String:Double]
extension Dictionary where Key == String, Value == Double {
func conversionRate(from:String, to:String) -> Double {
let key = "\(from)_\(to)"
if let rate = self[key] {
return rate
} else {
return -1.0
}
}
}
do {
let currRates = try JSONDecoder().decode(CurrencyRatesDict.self, from:jsonData)
print(currRates)
print(currRates.conversionRate(from:"USD", to:"AUD"))
}
This taught me a few things. I would not have thought that a NSDictionary (which is produced by JSONSerialization.jsonObject automatically and has no types) converts this easily into a [String:Double], but of course it might fail and you should write some error handling to catch it.
Your CurrencyRate struct would have the advantage to allow easy extensions. Since Dictionaries are structs it is not possible to derive from them. As the last version illustrates it is possible to add a conditional extension to a Dictionary. However this would add your new function to any Dictionary matching the signature which might be acceptable in many cases even though it 'feels' wrong from the design perspective.
As you can see there is a whole bunch of ways to deal with this in Swift. I would suggest you use the Codable protocol and an additional key. Most probably there are "other things" you will want to do with your object.
I'm Having trouble with JSON and Swift 2.
I'm getting this Array from the server
[{"KidName":"Jacob","KidId":1,"GardenID":0},
{"KidName":"Sarah","KidId":2,"GardenID":0},
{"KidName":"Odel","KidId":3,"GardenID":0}]
I'm familiar with JSON and I know it's not the recommended way to get a JSON, since it's supposed to be something like
{"someArray":[{"KidName":"Jacob","KidId":1,"gardenID":0}, .....
So my first question is it possible to run over the first JSON I've post and get the KidName number without editing the JSON and Add to it a JSON OBJECT to hold the array ?
my second question is really with Swift 2, how can I get the KidName (after I've edited the JSON to have an holder for the array)?
this is my code... (please read the Notes I've added)
BTW, I'm familiar with SwiftyJSON as well...
// Method I've build to get the JSON from Server, the Data is the JSON
sendGetRequest { (response, data ) -> Void in
// need to convert data to String So I can add it an holder
if let str = NSString(data: data, encoding: NSUTF8StringEncoding) as? String {
/**
after editing the str, i'm Having a valid JSON, let's call it fixedJSON
*/
let fixedJSON = "{\"kidsArray\":\(dropLast)}"
// Now I'm converting it to data back again
let jsonTodata = fixedJSON.dataUsingEncoding(NSUTF8StringEncoding, allowLossyConversion: false)!
// After Having the data, I need to convert it to JSON Format
do{
let dataToJson = try NSJSONSerialization.JSONObjectWithData(jsonTodata, options: []) as! [String:AnyObject]
//Here I'm getting the KidID
if let kidID = jsonSe["kidsArray"]![0]["KidId"]!!.integerValue {
print("kidID in first index is: \(kidID)\n")
}
//NOW trying to get the KidName which not working
if let kidname = jsonSe["kidsArray"]![0]["KidName"]!!.stringValue {
print("KidName is \(kidname)\n")
}
}
So as you can see, I'm not able to get the KidName.
Any Help Would be Appreciate.
You can use the following function to get the 'someArray' array and then use this getStringFromJSON function to get the 'KidName' value.
func getArrayFromJSON(data: NSDictionary, key: String) -> NSArray {
if let info = data[key] as? NSArray {
return info
}
else {
return []
}
}
let someArray = self.getArrayFromJSON(YourJSONArray as! NSDictionary, key: "someArray")
func getStringFromJSON(data: NSDictionary, key: String) -> String {
if let info = data[key] as? String {
return info
}
return ""
}
let KidName = self.getStringFromJSON(someArray as! NSDictionary, key: "KidName")
Hope this might be useful to you.
I googled a lot, pretty much copied code i found online from tutorials to simply parse a json String in Swift to useable objects.
Code:
func parseJson(json: String) -> [AnyObject] {
let data = json.dataUsingEncoding(NSUTF8StringEncoding)
do {
if let array = try NSJSONSerialization.JSONObjectWithData(data!, options: NSJSONReadingOptions.MutableContainers) as? [AnyObject] {
return array
}
}
catch {
// Error hanndling here
}
return [AnyObject]()
}
Json String im trying to parse:
"response":{"loggedIn":false,"message":"Some errormessage here"}}
What happens:
The program won't jump into the if let array = ... It stops there since it can't parse the string to json (or AnyObject) and will simply go to return AnyObject.
Why does this happen and how do i fix it?
Adjust your code a little to allow for better debugging:
func parseJson(json: String) -> [AnyObject] {
let data = json.dataUsingEncoding(NSUTF8StringEncoding)
do {
let parsed = try NSJSONSerialization.JSONObjectWithData(data!, options: NSJSONReadingOptions.MutableContainers)
if let array = parsed as? [AnyObject] {
return array
}
}
catch {
print(error)
}
return [AnyObject]()
}
Two changes there:
Printing any error caught.
Doing JSONObjectWithData and the as? conversion in two separate steps.
Pasting this in a playground quickly reveals an error being caught: "JSON text did not start with array or object and option to allow fragments not set." Your JSON fragment is missing the opening {.
Once that problem is fixed, you’ll see that parsed gets set, but the subsequent if let array = parsed as? [AnyObject] falls through. That’s because your top-level element is a dictionary, not an array, so casting to [AnyObject] fails.
I'm new to Swift - trying to read a JSON file from a URL. My attempt below.
The JSON looks valid - I tested it with JSONLint but it keeps crashing.
Thoughts?
func getRemoteJsonFile() -> NSDictionary {
//Create a new url
let remoteUrl:NSURL? = NSURL(string: "http://nfl-api.azurewebsites.net/myplayers.json")
//check if its nil
if let actualRemoteUrl = remoteUrl {
//try to get the data
let filedata:NSData? = NSData(contentsOfURL: actualRemoteUrl)
//check if its nil
if let actualFileData = filedata {
//parse out the dictionaries
let jsonDict = NSJSONSerialization.JSONObjectWithData(actualFileData, options: NSJSONReadingOptions.AllowFragments, error: nil) as NSDictionary
return jsonDict
}
}
return NSDictionary()
}
This took me a second to figure out, so I don't blame you for missing it.
The JSON you linked to is minified, so it's difficult to see the structure. Let's take a look at (a fragment of) it after piping it through a prettifier:
[
{
"PlayerId":2501863,
"PlayerName":"Peyton Manning",
"PlayerTeam":"DEN",
"PlayerPosition":"QB",
"PlayerPassingYards":4727,
"PlayerPassingTDs":39,
"PlayerInterceptions":15,
"PlayerRushingYards":-24,
"PlayerRushingTDs":0,
"PlayerReceivingYards":0,
"PlayerReceivingTDs":0,
"PlayerReturnYards":0,
"PlayerReturnTDs":0,
"PlayerFumbleTDs":0,
"PlayerTwoPointConversions":2,
"PlayerFumblesLost":2,
"PlayerTeamLogo":"http://i.nflcdn.com/static/site/7.0/img/logos/teams-gloss-81x54/den.png"
}
]
Huh. It's encased in brackets, which means that it's an array.
It's an array, so you can't cast it as an NSDictionary. Instead, you could cast it as an NSArray, but why not use native Swift types?
Well, if you don't like types, you're about to find out, but I still think that this is a better way, because it forces you to think about the data you're parsing.
So we have the first part of our type definition for this function; it's an array ([]). What components is our array made up of? We could go with a simple NSDictionary, but we're doing full native types here, so let's use a native Swift dictionary.
To do that, we have to know the types of the dictionary (the syntax for a native dictionary type is [KeyType: ValueType]). Examining the JSON shows that all of the keys are Strings, but the values are of varying types, so we can use AnyObject.
That gives us a dictionary type of [String: AnyObject], and our entire JSON is an array of that, so the final type is [[String: AnyObject]] (wow).
Now that we have the proper type, we can modify the function you're using to parse the JSON a bit.
First of all, let's use our new type for the return and cast values. Then, let's make the return type optional in case something goes wrong and add an error variable to document that.
A cleaned up function would look something like this:
func getData() -> [[String: AnyObject]]? {
let data: NSData? = NSData(contentsOfURL: NSURL(string: "http://nfl-api.azurewebsites.net/myplayers.json")!)
if let req: NSData = data {
var error: NSError?
if let JSON: [[String: AnyObject]] = NSJSONSerialization.JSONObjectWithData(req, options: NSJSONReadingOptions.AllowFragments, error: &error) as? [[String: AnyObject]] {
return JSON
}
}
return nil
}
That's it!
We can now call the function and extract values from our [[String: AnyObject]] (again, wow) like this:
if let data: [[String: AnyObject]] = getData() {
println(data[0]["PlayerName"]!) // Peyton Manning
}
Update your code with this:
func getRemoteJsonFile() -> [NSDictionary] {
// Create a new URL
let remoteUrl:NSURL? = NSURL(string: "http://nfl-api.azurewebsites.net/myplayers.json")
let urlString:String = "\(remoteUrl)"
// Check if it's nil
if let actualRemoteUrl = remoteUrl {
// Try to get the data
let fileData:NSData? = NSData(contentsOfURL: actualRemoteUrl)
// Check if it's nil
if let actualFileData = fileData {
// Parse out the dictionaries
let arrayOfDictionaries:[NSDictionary]? = NSJSONSerialization.JSONObjectWithData(actualFileData, options: NSJSONReadingOptions.MutableContainers, error: nil) as [NSDictionary]?
if let actualArrayOfDictionaries = arrayOfDictionaries {
// Successfully parsed out array of dictionaries
return actualArrayOfDictionaries
}
}
}
return [NSDictionary]()
}
This is working fine for me.