I have the following generic class where I want to manage a string hash:
class NamedProfile<T> {
private var set = [String:T]()
private var profiles = [String]()
private let userDefaults = NSUserDefaults.standardUserDefaults()
private let profileName:String
var currentSet = ""
init(name:String, set:[String:T]) {
profileName = name
self.set = set
if let existingProfiles = userDefaults.objectForKey(name) as? [String] {
profiles = existingProfiles
}
for key in profiles {
if let existingProfile = userDefaults.objectForKey(profileNamed(name)) as? T {
set[key] = existingProfile // <-- error
}
}
}
private func profileNamed(name:String) -> String { return "\(profileName) \(name)" }
}
Why does the compiler croak in the above assignment?
In
init(name:String, set:[String:T]) {
// ...
set[key] = existingProfile // <-- error
// ...
}
set refers to the (immutable) method parameter.
Use self.set instead to refer to the property.
Related
After downcasting an array of structs, my Variables View window shows that all of the values in my struct have shifted "down" (will explain in a second). But when I print(structName), the values are fine. However, when I run an equality check on the struct, it once again behaves as though my values have shifted.
For example, I am trying to downcast Model A to ModelProtocol. var m = Model A and has the values {id: "1234", name: "Cal"}. When I downcast, m now has the values { id:"\0\0", name:"1234" }.
Actual Example Below:
Models that I want to downcast:
struct PrivateSchoolModel: Decodable, SchoolProtocol {
var id: String
var name: String
var city: String
var state: String
}
struct PublicSchoolModel: Decodable, SchoolProtocol {
var id: String
var name: String
var city: String
var state: String
var latitude: String
var longitude: String
}
Protocol I want to downcast to:
protocol SchoolProtocol {
var id: String { get set }
var name: String { get set }
var city: String { get set }
var state: String { get set }
var longitude: Float { get set }
var latitude: Float { get set }
}
extension SchoolProtocol {
var longitude: Float {
get { return -1.0 }
set {}
}
var latitude: Float {
get { return -1.0 }
set {}
}
}
Downcasting:
guard let downcastedArr = privateSchoolArray as? [SchoolProtocol] else { return [] }
Result (item at index 0) or originalArr:
id = "1234"
name = "Leo High School"
city = "Bellview"
state = "WA"
Result (item at index 0) of downcastedArr:
id = "\0\0"
name = "1234"
city = "Leo High School"
state = "Bellview"
But if I print(downcastArr[0]), it will show:
id = "1234"
name = "Leo High School"
city = "Bellview"
state = "WA"
But if I try originalArray[0].id == downcastArr[0].id, it returns false
My Code with the problem:
class SchoolJSONHandler {
private enum JSONFile: String {
case publicSchool = "publicSchool"
case privateSchool = "privateSchool"
}
private lazy var privateSchoolArray = getPrivateSchools()
private lazy var publicSchoolArray = getPublicSchools()
func getSchoolArray(sorted: Bool, filtered: Bool, by stateAbbreviation: String?) -> [SchoolProtocol] {
var schools = combineArrays()
if sorted {
schools.sort(by: { $0.name < $1.name })
}
if filtered {
guard let abbr = stateAbbreviation else { return [] }
schools = schools.filter {
return $0.state == abbr
}
}
return schools
}
private func combineArrays() -> [SchoolProtocol] {
// EVERYTHING IS FINE IN NEXT LINE
let a = privateSchoolArray
// PROBLEM OCCURS IN NEXT 2 LINES WHEN DOWNCASTING
let b = privateSchoolArray as [SchoolProtocol]
let c = publicSchoolArray as [SchoolProtocol]
return b + c
}
private func getPublicSchools() -> [PublicSchoolModel] {
guard let jsonData = getJSONData(from: .publicSchool) else { return [] }
guard let schools = decode(jsonData: jsonData, using: [PublicSchoolModel].self) else { return [] }
return schools
}
private func getPrivateSchools() -> [PrivateSchoolModel] {
guard let jsonData = getJSONData(from: .privateSchool) else { return [] }
guard let schools = decode(jsonData: jsonData, using: [PrivateSchoolModel].self) else { return [] }
return schools
}
private func getJSONData(from resource: JSONFile) -> Data? {
let url = Bundle.main.url(forResource: resource.rawValue, withExtension: "json")!
do {
let jsonData = try Data(contentsOf: url)
return jsonData
}
catch {
print(error)
}
return nil
}
private func decode<M: Decodable>(jsonData: Data, using modelType: M.Type) -> M? {
do {
//here dataResponse received from a network request
let decoder = JSONDecoder()
let model = try decoder.decode(modelType, from:
jsonData) //Decode JSON Response Data
return model
} catch let parsingError {
print("Error", parsingError)
}
return nil
}
}
And then it is just called in another class by schoolJSONHandler.getSchoolArray(sorted: true, filtered: true, by: "WA")
I am new to Swift and I am following a tutorial on how to create a social media app with Xcode and Firebase. However, I got this error:
Instance member 'database' cannot be used on type 'DatabaseReference'
Here is my code:
import Foundation
import Firebase
class Post {
private var _username: String!
private var _userImg: String!
private var _postImg: String!
private var _likes: Int!
private var _postKey: String!
private var _postRef: DatabaseReference
var username: String {
return _userImg
}
var postImg: String {
get {
return _postImg
}set {
_postImg = newValue
}
}
var likes: Int {
return _likes
}
var postKey: String {
return _postKey
}
init(imgUrl: String, likes: Int, username: String, userImg: String) {
_likes = likes
_postImg = postImg
_username = username
_userImg = userImg
}
init(postKey: String, postData: Dictionary<String, AnyObject>) {
_postKey = postKey
if let username = postData["username"] as? String {
_username = username
}
if let userImg = postData["userImg"] as? String{
_userImg = userImg
}
if let postImage = postData["imageUrl"] as? String {
_postImg = postImage
}
if let likes = postData["likes"] as? Int {
_likes = likes
}
_postRef = DatabaseReference.database().reference().child("posts")
}
}
I get my error on the third to last line that says:
_postRef = DatabaseReference.database().reference().child("posts")
The database property is an instance type, meaning it must be referenced by an instance of DatabaseReference. Your call to DatabaseReference.database is accessing for a class, or static, type. You need to change your call to an instance of DatabaseReference.
Presumably, you need to initialize an instance of DatabaseReference. I don't know Firebase to know what is required for that, but that will take care of your issue.
Essentially:
let databaseReference = DatabaseReference() // Likely won't work, but some init method here will
_postRef = databaseReference.database()... // Whatever you need here
It sounds like you're looking for either:
_postRef = Database.database().reference("posts")
Or
_postRef = DatabaseReference.root.child("posts")
Let say I have following code
class Foo {
}
var fooArray : Array<Foo> = Array<Foo>()
// This is important because in my code I will get Any (vs Array<Foo)
var fooArrayAny : Any = foo
I want to be able to get a Type Foo out of variable fooArrayAny.
If I had fooArray, I would do something like that:
let type = fooArray.dynamicType.Element().dynamicType
However, this doesn't work with fooArrayAny. It says that it has no member Element()
If you set NSObject as the base class of Foo, then you could use the following code:
class EVReflectionTests: XCTestCase {
func testArrayInstance() {
let fooArray : Array<Foo> = Array<Foo>()
let fooArrayAny : Any = fooArray
if let arr = fooArray as? Array {
let i = arr.getArrayTypeInstance(arr)
print("i = \(i)")
}
}
}
class Foo: NSObject {
}
extension Array {
public func getArrayTypeInstance<T>(arr:Array<T>) -> T {
return arr.getTypeInstance()
}
public func getTypeInstance<T>() -> T {
let nsobjectype : NSObject.Type = T.self as! NSObject.Type
let nsobject: NSObject = nsobjectype.init()
return nsobject as! T
}
}
This code is a snippet of my library EVReflection
Update:
I noticed a mistake in the code above. I used fooArray instead of fooArrayAny. When changing that to fooArrayAny I get the same error as you that the compiler does not have the Element. After playing around with this, I found out a solution that does work. Again it has parts of code of my EVReflection library.
class EVReflectionTests: XCTestCase {
func testArrayInstance() {
let fooArray : Array<Foo> = Array<Foo>()
let fooArrayAny : Any = fooArray
if let _ = fooArrayAny as? NSArray {
var subtype: String = "\(Mirror(reflecting: fooArrayAny))"
subtype = subtype.substringFromIndex((subtype.componentsSeparatedByString("<") [0] + "<").endIndex)
subtype = subtype.substringToIndex(subtype.endIndex.predecessor())
print("The type of the array elements = \(subtype)")
if let instance = swiftClassFromString(subtype) {
print("An instance of the array element = \(instance)")
let type = instance.dynamicType
print("An instance of the array element = \(type)")
}
}
}
// All code below is a copy from the EVReflection library.
func swiftClassFromString(className: String) -> NSObject? {
var result: NSObject? = nil
if className == "NSObject" {
return NSObject()
}
if let anyobjectype : AnyObject.Type = swiftClassTypeFromString(className) {
if let nsobjectype : NSObject.Type = anyobjectype as? NSObject.Type {
let nsobject: NSObject = nsobjectype.init()
result = nsobject
}
}
return result
}
func swiftClassTypeFromString(className: String) -> AnyClass! {
if className.hasPrefix("_Tt") {
return NSClassFromString(className)
}
var classStringName = className
if className.rangeOfString(".", options: NSStringCompareOptions.CaseInsensitiveSearch) == nil {
let appName = getCleanAppName()
classStringName = "\(appName).\(className)"
}
return NSClassFromString(classStringName)
}
func getCleanAppName(forObject: NSObject? = nil)-> String {
var bundle = NSBundle.mainBundle()
if forObject != nil {
bundle = NSBundle(forClass: forObject!.dynamicType)
}
var appName = bundle.infoDictionary?["CFBundleName"] as? String ?? ""
if appName == "" {
if bundle.bundleIdentifier == nil {
bundle = NSBundle(forClass: EVReflection().dynamicType)
}
appName = (bundle.bundleIdentifier!).characters.split(isSeparator: {$0 == "."}).map({ String($0) }).last ?? ""
}
let cleanAppName = appName
.stringByReplacingOccurrencesOfString(" ", withString: "_", options: NSStringCompareOptions.CaseInsensitiveSearch, range: nil)
.stringByReplacingOccurrencesOfString("-", withString: "_", options: NSStringCompareOptions.CaseInsensitiveSearch, range: nil)
return cleanAppName
}
}
class Foo: NSObject {
}
The output of this code will be:
The type of the array elements = Foo
An instance of the array element = <EVReflection_iOS_Tests.Foo: 0x7fd6c20173d0>
An instance of the array element = Foo
Swift 5
Its old but I want to share my version if someone needs it.
I use ModelProtocol and I suggests you use protocol so we can do operation to model via protocol (ex: static instantiating).
protocol ModelProtocol {}
class Foo: ModelProtocol {
}
Since I can't check type is Array, I use CollectionProtocol and create Array extension to get Element via protocol.
protocol CollectionProtocol {
static func getElement() -> Any.Type
}
extension Array: CollectionProtocol {
static func getElement() -> Any.Type {
return Element.self
}
}
Testing.
var fooArray: Array<Foo> = Array<Foo>()
var fooArrayAny: Any = fooArray
let arrayMirrorType = type(of: fooArrayAny)
String(describing: "arrayMirrorType: \(arrayMirrorType)")
if arrayMirrorType is CollectionProtocol.Type {
let collectionType = arrayMirrorType as! CollectionProtocol.Type
String(describing: "collectionType: \(collectionType)")
let elementType = collectionType.getElement()
String(describing: "elementType: \(elementType)")
let modelType = elementType as! ModelProtocol.Type
String(describing: "modelType: \(modelType)")
// ... now you can do operation to modelType via ModelProtocol
}
Printing.
arrayMirrorType: Array<Foo>
collectionType: Array<Foo>
elementType: Foo
modelType: Foo
class Foo {
var foo: Int = 1
}
struct Boo {
var boo: String = "alfa"
}
func f(array: Any) {
let mirror = Mirror(reflecting: array)
let arraytype = mirror.subjectType
switch arraytype {
case is Array<Foo>.Type:
let fooArray = array as! Array<Foo>
print(fooArray)
case is Array<Boo>.Type:
let booArray = array as! Array<Boo>
print(booArray)
default:
print("array is not Array<Foo> nor Array<Boo>")
break
}
}
var fooArray : Array<Foo> = []
fooArray.append(Foo())
var anyArray : Any = fooArray // cast as Any
f(anyArray) // [Foo]
var booArray : Array<Boo> = []
booArray.append(Boo())
anyArray = booArray // cast as Any
f(anyArray) // [Boo(boo: "alfa")]
var intArray : Array<Int> = []
anyArray = intArray // cast as Any
f(anyArray) // array is not Array<Foo> nor Array<Boo>
I have a swift struct named Product which takes a Dictionary in its init method. I want to compute a price value in a local Price struct within my Product. I want this value to be a let constant since it won't ever change, but swift won't allow me to do that without using var, saying that the let constant is not properly initialized.
How can I make my value property inside my Price struct a let constant in this case?
struct Product {
let price: Price
init(dictionary: Dictionary<String, AnyObject>) {
if let tmp = dictionary["price"] as? Dictionary<String, AnyObject> { price = Price(dictionary: tmp) } else { price = Price() }
}
struct Price {
var value = ""
init() {
}
init(dictionary: Dictionary<String, AnyObject>) {
if let xForY = dictionary["xForY"] as? Array<Int> {
if xForY.count == 2 {
value = "\(xForY[0]) for \(xForY[1])"
}
}
if let xForPrice = dictionary["xForPrice"] as? Array<Int> {
if value == "" && xForPrice.count == 2 {
value = "\(xForPrice[0]) / \(xForPrice[1]):-"
}
}
if let reduced = dictionary["reduced"] as? String {
if value == "" {
value = "\(reduced):-"
}
}
}
}
}
You have to rewrite the code so that the compiler gets what you intend to do actually. It is not clever enough to deduce it from the way you coded it.
I would also suggest that you make the initializer for the Price struct failable instead of using an empty string for the value property. As a consequence of that change the price property of the Product struct becomes an optional.
struct Product {
let price: Price?
init(dictionary: Dictionary<String, AnyObject>) {
if let tmp = dictionary["price"] as? Dictionary<String, AnyObject> {
price = Price(dictionary: tmp)
}
else {
price = nil
}
}
struct Price {
let value : String
init?(dictionary: Dictionary<String, AnyObject>) {
if let xForY = dictionary["xForY"] as? Array<Int> where xForY.count == 2 {
value = "\(xForY[0]) for \(xForY[1])"
}
else if let xForPrice = dictionary["xForPrice"] as? Array<Int> where xForPrice.count == 2 {
value = "\(xForPrice[0]) / \(xForPrice[1]):-"
}
else if let reduced = dictionary["reduced"] as? String {
value = "\(reduced):-"
}
else {
return nil
}
}
}
}
The trouble is that (1) you're assigning to value in the declaration, (2) you're not assigning a value in init(), and (3) you're referencing and reassigning value in init([String: AnyObject]). You can only assign a value to a constant once and can only reference its value after its been assigned to.
To fix the issue, you can either make your property publicly readonly:
private(set) var value: String = ""
Or you can use a second variable inside your init:
struct Price {
let value: String
init() {
self.value = ""
}
init(dictionary: Dictionary<String, AnyObject>) {
var v: String = ""
if let xForY = dictionary["xForY"] as? Array<Int> {
if xForY.count == 2 {
v = "\(xForY[0]) for \(xForY[1])"
}
}
if let xForPrice = dictionary["xForPrice"] as? Array<Int> {
if v == "" && xForPrice.count == 2 {
v = "\(xForPrice[0]) / \(xForPrice[1]):-"
}
}
if let reduced = dictionary["reduced"] as? String {
if v == "" {
v = "\(reduced):-"
}
}
self.value = v
}
}
Is there a way to list all Variables of a class in Swift?
For example:
class foo {
var a:Int? = 1
var b:String? = "John"
}
I want to list it like this: [a:1, b:"John"]
How you can do it in Swift 3.0 recursively:
import Foundation
class FirstClass {
var name = ""
var last_name = ""
var age = 0
var other = "abc"
func listPropertiesWithValues(reflect: Mirror? = nil) {
let mirror = reflect ?? Mirror(reflecting: self)
if mirror.superclassMirror != nil {
self.listPropertiesWithValues(reflect: mirror.superclassMirror)
}
for (index, attr) in mirror.children.enumerated() {
if let property_name = attr.label {
//You can represent the results however you want here!!!
print("\(mirror.description) \(index): \(property_name) = \(attr.value)")
}
}
}
}
class SecondClass: FirstClass {
var yetAnother = "YetAnother"
}
var second = SecondClass()
second.name = "Name"
second.last_name = "Last Name"
second.age = 20
second.listPropertiesWithValues()
results:
Mirror for FirstClass 0: name = Name
Mirror for FirstClass 1: last_name = Last Name
Mirror for FirstClass 2: age = 20
Mirror for FirstClass 3: other = abc
Mirror for SecondClass 0: yetAnother = YetAnother
The following should use reflection to generate the list of members and values. See fiddle at http://swiftstub.com/836291913/
class foo {
var a:Int? = 1
var b:String? = "John"
}
let obj = foo()
let reflected = reflect(obj)
var members = [String: String]()
for index in 0..<reflected.count {
members[reflected[index].0] = reflected[index].1.summary
}
println(members)
Output:
[b: John, a: 1]
Maybe a bit late for the party, but this solution using reflection and Mirror is 100% working:
class YourClass : NSObject {
var title:String
var url:String
...something other...
func properties() -> [[String: Any]] {
let mirror = Mirror(reflecting: self)
var retValue = [[String:Any]]()
for (_, attr) in mirror.children.enumerated() {
if let property_name = attr.label as String! {
retValue.append([property_name:attr.value])
}
}
return retValue
}
}
and somewhere in your code...
var example = MoreRow(json: ["title":"aTitle","url":"anURL"])
print(example.listPropertiesWithValues())
I got clue from here. https://medium.com/#YogevSitton/use-auto-describing-objects-with-customstringconvertible-49528b55f446
This is a demo above Swift 4.0.
import Foundation
extension CustomStringConvertible {
var description : String {
var description: String = ""
if self is AnyObject { // unsafeAddressOf((self as! AnyObject))
description = "***** \(type(of: self)) - <\(Unmanaged.passUnretained(self as AnyObject).toOpaque())>***** \n"
} else {
description = "***** \(type(of: self)) *****\n"
}
let selfMirror = Mirror(reflecting: self)
for child in selfMirror.children {
if let propertyName = child.label {
description += "\(propertyName): \(child.value)\n"
}
}
return description
}
}
extension NSObject {
var description: String {
var description: String = ""
if self is AnyObject { // unsafeAddressOf((self as! AnyObject))
description = "***** \(type(of: self)) - <\(Unmanaged.passUnretained(self as AnyObject).toOpaque())>***** \n"
} else {
description = "***** \(type(of: self)) *****\n"
}
let selfMirror = Mirror(reflecting: self)
for child in selfMirror.children {
if let propertyName = child.label {
description += "\(propertyName): \(child.value)\n"
}
}
return description
}
}
class AA: CustomStringConvertible {
var a: String = "aaa"
}
class BB: NSObject {
var b: String = "bbb"
}
let aa = AA()
print(aa)
let bb = BB()
print(bb.description)
Output --
***** AA - <0x00000001001038e0>*****
a: aaa
***** BB - <0x0000000100103310>*****
b: bbb