Today I come across a very strange situation while getting value from dictionary.I have made two cases here.
Case 1
if I write code below
let str = "{\"num\":2}"
var dict = convertToDictionary(text: str)!
if let num = dict["num"] as? Float {
print("Value is \(num)")
} else {
print("parse error")
}
func convertToDictionary(text: String) -> [String: Any]? {
if let data = text.data(using: .utf8) {
do {
return try JSONSerialization.jsonObject(with: data, options: []) as? [String: Any]
} catch {
print(error.localizedDescription)
}
}
return nil
}
As you can see value for key num is Integer but while fetching value from dictionary I expect value as Float. so it should go to else block but it prints the value.
Case 2
var test = 2
var dict:[String:Any] = [String:Any]()
dict["num"] = test
if let num = dict["num"] as? Float {
print("Value is \(num)")
} else {
print("parse error")
}
As I have not defined data type so by default it should be integer here & I expect value to be Float. This does work as I expect
Now here is does not print value it show the parse error
Please explain to me why this is happening ?
The answer is - dictionaries in those two cases are actually not identical.
In second case, the value of dict["num"] in of Int type, because you explicitly assigned an Int to it.
In first case however, you get a dictionary via JSONSerialization which turns numbers to NSNumber instances. So, the value of dict["num"] is of NSNumber type. And NSNumber initialized with an Int can be succesfuly cast to both Int and Float
In the first case you're creating json and inserting into dict which is getting the value in [String: Any] format. Here dict["num"] is in NSNumber format.
In the second case you created the dict with [String: Any] format but put the value as Int. var test = 2 this line makes variable test as Int and when you're inserting that value into dict with format [String: Any], it's taking the value of format Any as Int.
So basically in second case, dict["num"] is Int.
From Apple Doc, variable will take the datatype of the value it was assigned at the beginning.
That's why you can convert Any to Float at the first case but cannot convert Int to Float at the second.
If you try with var test: Float = 2, you'll get the value at the second case also.
try
if let num = dict["num"] as? NSNumber {
let floatValue = num.floatValue
print("Value is \(floatValue)")
} else {
print("parse error")
}
Related
I have an app where users can rate films they have watched, and I want to be able to put these in a tableView. The rating is stored in Firestore, and I want to put both the KEY and value into a Struct so I can access it for the tableView.
However any site/tutorial/stack question I have seen only gets the Maps value, but not the key (in this case, the title name). I can access the value, but only by using the field key, but that is what I am trying to get (see attempt 1)
Struct:
struct Rating: Codable {
var ratedTitle: String
var ratedRating: Int
}
Variable:
var ratedList = [Rating]()
Load data function (attempt 1):
let dbRef = db.collection("Users").document(userID)
dbRef.getDocument { document, error in
if let error = error {
print("There was an error \(error.localizedDescription)")
} else {
if let docData = document!.data() {
let titleRating = docData["Title Ratings"] as? [String: Int]
let midnightMass = titleRating!["Midnight Mass"]
print("Rating given to Midnight Mass: \(midnightMass!) stars")
}
}
}
//Prints: Rating given to Midnight Mass: 2 stars
Also tried (but I don't know how to get this array onto a tableView and have the first index as the Title label, and the second index a Rating label for each movie in the array) attempt 2:
if let docData = document!.data() {
let titleRating = docData["Title Ratings"] as? [String: Int]
self.userRatedList = titleRating!
print("userRatedList: \(self.userRatedList)")
}
//Prints: userRatedList: ["Midnight Mass": 2, "Bly Manor": 5]
Attempt 3:
if let docData = document!.data() {
let titleRating = docData["Title Ratings"] as? [String: Int]
self.ratedList = [Rating(ratedTitle: <#T##String#>, ratedRating: <#T##Int#>)]
//Don't know what I would put as the ratedTitle String or ratedRating Int.
self.ratedList = [Rating(ratedTitle: titleRating!.keys, ratedRating: titleRating!.values)]
//Cannot convert value of type 'Dictionary<String, Int>.Keys' to expected argument type 'String'
//Cannot convert value of type 'Dictionary<String, Int>.Values' to expected argument type 'Int'
}
Firstly, I am not sure why you need the struct to conform to Codable?
Now, based off what I see, "Title Ratings" is a dictionary with a String key and an Int value. You are overcomplicating this. If you want to access the key and value of each element individually, use a for-in loop.
//Declare your global variable
var ratedList = [Rating]()
//If you are using an if let, there is not need to force unwrap
if let docData = document.data() {
if let userRatingList = docData["Title Ratings"] as? [String: Int] {
for (key, value) in userRatingList {
let rating = Rating(ratedTitle: key, ratedRating: value)
ratedList.append(rating)
}
//reload your tableView on the main thread
DispatchQueue.main.async {
tableView.reloadData()
}
}
}
I'm new to Swift and ObjC and can't get this simple bit of code to work. I get the error 'String?' is not convertible to 'String'; did you mean to use 'as!' to force downcast?
guard let data = context as? Dictionary<String,String> else {return}
var str : String
str = data["Score"] as String //<<<I get the error here
When I change it to as! I know get this warning: Forced cast from 'String?' to 'String' only unwraps optionals; did you mean to use '!'?
Any ideas how to extract the string from the dictionary so I can use it?
It might be possible, that the key "Score" is not set in your dictionary and may return nil. Use this code to unwrap the optional:
if let score = data["Score"] {
str = score
}
Since you already unwrapped context to Dictionary<String, String>, Swift will automatically infer the type of score as String.
You don't need to cast because data dictionary would always return optional String type and you can use guard statement
guard let str = data[Score] else { return }
// Your code here
The type returned by subscripting a Dictionary is an optional, since it is valid to subscript it with non-existinent keys. So, as per the error message, in a dictionary with String values, the return type is String?.
If you know for sure that the key always exist in the dictionary, you can force-unwrap it as data["Score"]! to make the type String (without casting, but crashing if it doesn't exist). Otherwise handle the nil in some way, e.g., if let str = data["Score"] or str = data["Score"] ?? "0".
Use like this:
if let dataDictionary = context as? [String: Any] {
if let someString = dataDictionary["score"] as? String {
print(someString)
}
}
We don't know what kind of data you're working with but you're likely either getting back a dictionary actually of type [String: String], in which case you would:
func getData(context: [String: String]) {
guard let str = context["Score"] else {
return
}
print(str)
}
...or you're really getting back a dictionary of type [String: Any] (more common with database dictionaries), in which case you would:
func getData(context: [String: Any]) {
guard let str = context["Score"] as? String else {
return
}
print(str)
}
I have received this response from the server and I am sure there must be a more efficient way to convert it into an object.
I have the following response:
[
id=2997,rapidViewId=62,state=ACTIVE,name=Sprint7,startDate=2018-11-20T10:28:37.256Z,endDate=2018-11-30T10:28:00.000Z,completeDate=<null>,sequence=2992,goal=none
]
How do I convert it nicely into a well formed swift object in the simplest way?
Here is my attempt which gives me just the Sprint Value
if sprintJiraCustomField.count > 0 {
let stringOutput = sprintJiraCustomField.first?.stringValue // convert output to String
let name = stringOutput?.components(separatedBy: "name=") // get name section from string
let nameFieldRaw = name![1].components(separatedBy: ",") // split out to the comma
let nameValue = nameFieldRaw.first!
sprintDetail = nameValue// show name field
}
Not sure what format you want but the below code will produce an array of tuples (key, value) but all values are strings so I guess another conversion is needed afterwards
let items = stringOutput.components(separatedBy: ",").compactMap( {pair -> (String, String) in
let keyValue = pair.components(separatedBy: "=")
return (keyValue[0], keyValue[1])
})
This is a work for reduce:
let keyValueStrings = yourString.components(separatedBy: ",")
let dictionary = keyValueStrings.reduce([String: String]()) {
(var aggregate: [String: String], element: String) -> [String: String] in
let elements = element.componentsSeparatedByString("=")
let key = elements[0]
// replace nil with the value you want to use if there is no value
let value = (elements.count > 1) ? elements[1] : nil
aggregate[key] = value
return aggregate
}
This is a functional approach, but you can achieve the same using a for iteration.
So then you can use Swift’s basic way of mapping. for example you will have your custom object struct. First, you will add an init method to it. Then map your object like this:
init(with dictionary: [String: Any]?) {
guard let dictionary = dictionary else { return }
attribute = dictionary["attrName"] as? String
}
let customObjec = CustomStruct(dictionary: dictionary)
We already have some suggestion to first split the string at each comma and then split each part at the equals sign. This is rather easy to code and works well, but it is not very efficient as every character has to be checked multiple times. Writing a proper parser using Scanner is just as easy, but will run faster.
Basically the scanner can check if a given string is at the current position or give you the substring up to the next occurrence of a separator.
With that the algorithm would have the following steps:
Create scanner with the input string
Check for the opening bracket, otherwise fail
Scan up to the first =. This is the key
Consume the =
Scan up to the first , or ]. This is the value
Store the key/value pair
If there is a , consume it and continue with step 3
Consume the final ].
Sadly the Scanner API is not very Swift-friendly. With a small extension it is much easier to use:
extension Scanner {
func scanString(_ string: String) -> Bool {
return scanString(string, into: nil)
}
func scanUpTo(_ delimiter: String) -> String? {
var result: NSString? = nil
guard scanUpTo(delimiter, into: &result) else { return nil }
return result as String?
}
func scanUpTo(_ characters: CharacterSet) -> String? {
var result: NSString? = nil
guard scanUpToCharacters(from: characters, into: &result) else { return nil }
return result as String?
}
}
With this we can write the parse function like this:
func parse(_ list: String) -> [String: String]? {
let scanner = Scanner(string: list)
guard scanner.scanString("[") else { return nil }
var result: [String: String] = [:]
let endOfPair: CharacterSet = [",", "]"]
repeat {
guard
let key = scanner.scanUpTo("="),
scanner.scanString("="),
let value = scanner.scanUpTo(endOfPair)
else {
return nil
}
result[key] = value
} while scanner.scanString(",")
guard scanner.scanString("]") else { return nil }
return result
}
I have a class in my app, where the user inputs values and i set them to an instance of the class, then i upload this data to Database, but i have to convert the class to something the database accepts and i'm converting to dictionary using Mirror Reflection. Some properties in my class can be nil, because by design not all properties are required. But i can't pass nil values to the database.
I have recreated my example is very simplified playground. i didn't set a value for the name property of the class
I tried to check for nil before adding the key, value pair to the dictionary
Below is my code
import UIKit
class Color: NSObject {
var name: String?
var code: Int?
var shade: String?
}
let cl = Color()
cl.code = 3456
cl.shade = "DARK"
var colorDict = [String: Any]()
for x in Mirror(reflecting: cl).children.makeIterator() {
if let val = x.value as Any? {
print(type(of: val))
colorDict[x.label!] = val
}
}
print (colorDict)
the output in console is as below
Optional<String>
Optional<Int>
Optional<String>
["name": nil, "code": Optional(3456), "shade": Optional("DARK")]
how can i check for nil values and skip adding that property to the Dictionary
i have tried to loop through the dictionary after i add all values including nils and check for values too but i get the below warning
Comparing non-optional value of type 'Any' to nil always returns false
declaring the dictionary as below
var colorDict = [String: Any?]()
for x in colorDict {
if x.value == nil {
colorDict.removeValue(forKey: x.key)
}
}
removes the warning but it doesn't remove anything.
I would really appreciate your help.
The way of unwrapping objects of type Any that contain optionals is kind of weird but you can check that the values aren't nil in your mirror like this:
for x in Mirror(reflecting: cl).children {
if case Optional<Any>.some(let val) = x.value {
print(type(of: val))
colorDict[x.label!] = val
}
}
You can do this really easily in a one-liner, using filter:
let dict: [String : Any?] = ["Foo" : 3, "Bar" : nil, "Baz" : "Qux"]
let noNils = dict.filter { $0.value != nil }
print(noNils) // prints ["Foo": Optional(3), "Baz": Optional("Qux")]
As i have suggested, initialise all values.
If you decide not to store the nil values you will end up with children that some of them will have 1, some 2 and some 3 nodes, nothing wrong with that, BUT what happens when you go to read them?
You havent shared any info as to how these values will be used by the app, but assuming you have one function to read the properties/nodes of stored colors, it will go to read all 3 :
ref.child("colors").child("someSpecificColor").observeSingleEvent(of: .value, with: { (snapshot) in
// Get color values
let value = snapshot.value as? NSDictionary
let name = value?["name"] as? String ?? ""
let code = value?["code"] as? String ?? ""
let shade = value?["shade"] as? String ?? ""
// ...
}) { (error) in
print(error.localizedDescription)
}
See the issue?
Here is a simple solution :
var colorDict = [String: Any?]()
for x in Mirror(reflecting: cl).children.makeIterator() {
if let val = x.value, val != nil {
print(type(of: val))
colorDict[x.label!] = val
}
}
Here before to print and add you val, you check if the val is different than nil. As your output suggests in your console log you print :
Optional<String>
Optional<Int>
Optional<String>
val is an optional. So, if it's nil it won't be added. If not, you enter into the if statement and that's it.
I'm trying to look for items equal or less than zero in my query like so.....
for zeroItems in snapshot.value as! NSDictionary where zeroItems.value["Value"] as! Int <= 0
I'm getting an Expected type error. Please explain and show me how to correct.
You may want to consider applying a filter to simplify the logic to only include elements less than zero. I've created a working example in the IBM Swift Sandbox.
import Foundation
// Construct the data structure with demo data
struct Snapshot {
let value: NSDictionary
}
let dict: NSDictionary = [ "a" : -1, "b" : 0, "c" : 1]
let snapshot = Snapshot(value: dict)
//Apply a filter
let zeroItems = snapshot.value.filter{Int($0.1 as! NSNumber) <= 0}
//View the result
print(zeroItems)
Almost certainly you've overused Any if you have to use this many as! casts in a single line. Create a custom struct for this type and convert the data to that. If you're passing around NSDictionary and using as! very much, you're fighting the system.
That said, to make this work you probably just need more parentheses. Something like:
for zeroItems in (snapshot.value as! NSDictionary) where (zeroItems.value["Value"] as! Int) <= 0
But this is horrible Swift, so avoid this if possible.
You interpreting snapshot.value as Dictionary, so zeroItems is a tuple of key and value.
As I understand you having array of dictionaries, and you want to filter them by "Value" key, right?
If so then you may use following code:
// dictionary with Value key, and Int value
let dict: [String: Any] = ["Value":-1]
// array of dictionaries
let value: [[String: Any]] = [dict, <**add here as many as you want**>]
// get only array of integeres
let onlyIntegers = value.flatMap { $0["Value"] as? Int }.filter {$0 <= 0 }
print(onlyIntegers)
// get array of dictionaries which passes <=0 check
let onlyLessOrEqualTo0 = value.filter { dict in
if let value = dict["Value"] as? Int {
return value <= 0
}
return false
}
print(onlyLessOrEqualTo0)
First of all, adding some parentheses will help in seeing where the problem is:
for zeroItems in myDict as! NSDictionary where (zeroItems.value["Value"] as! Int) <= 0
Now, we get "Type 'Any' has no subscript members". So the problem is that you haven't told Swift what the type is of zeroItems's value, which I think is a dictionary of , judging from your code:
This compiles for me:
for zeroItems in myDict as! Dictionary<String, Dictionary<String, Int>> where zeroItems.value["Value"]! <= 0
However, this is not pretty. You could probably get more readable code using filter as was suggested in another answer.