I have three classes that conforms to same object type (protocol).
class Bicycle: Vehicle {}
class Car : Vehicle {}
class Truck: Vehicle {}
class Bus : Vehicle {}
I have an array that holds objects of the above classes like
let vehicle1 = Car()
let vehicle2 = Bicycle()
let vehicle3 = Truck()
let vehicle4 = Car()
let vehicle5 = Bus()
let listOfVehicles = [vehicle1, vehicle2, vehicle3, vehicle4, vehicle5]
Now I need an array which will tell me the index of the parameter that passed.
func getFirstIndex<T: Vehicle>(for targetObject: T) -> Int {
guard let index = listOfVehicles.firstIndex(where: { $0 is targetObject.Type })
else {
return -1
}
return index
}
If I call getFirstIndex(for: vehicle3), I need to get 2 and
If I call getFirstIndex(for: vehicle4), I need to get 0,
because vehicle4's type and vehicle1's type is same which is Car.
But I am getting compile-error "Type of expression is ambiguous without more context".
Does anyone have any clue.
Just replace targetObject.Type with T
Related
Hi I do have array of custom objects in swift, like below
Objects of below class
Class Person {
let name: String
let pointsEarned: CGFloat
}
Array is like below
let person1 = Person(“name1”, “5.6”)
let person2 = Person(“name2”, “6.6”)
let person3 = Person(“name3”, “1.6”)
let persons = [person1, person2, person3 ]
I would like find person who’s earned points are close to 7.0
Is there extension on array I can write for this?
Appreciate any help! Thanks.
Sort your objects by their distance from the goal (7), computed asabs(goal - score)`:
people.sort { abs(7 - $0.score) < abs(7 - $1.score) }
Alexander's answer is good, but you only need the min.
public extension Sequence {
func min<Comparable: Swift.Comparable>(
by getComparable: (Element) throws -> Comparable
) rethrows -> Element? {
try self.min {
try getComparable($0) < getComparable($1)
}
}
}
I also think abs as a global function looks archaic. magnitude is the same value.
persons.min { ($0.pointsEarned - 7).magnitude }
You can use the argument label with a trailing closure if you want:
persons.min(by:) { ($0.pointsEarned - 7).magnitude }
I am quite new to swift. I am attempting to define a global array of type [String] and then access the array for navigation through subscripts via UISwipeGestureRecognizer, which are then fed into loadedContentForAsset(name: String) to display a .scn model. I have included the code for the global definition; I am getting a Thread 1: EXC_BREAKPOINT (code=1, subcode=0x1049d69c8) signal when executing the code.. on the last line of the included.
Here is my global definition:
import Foundation
class Main {
let faceOverlayArray: [String]
init(faceOverlayArray:[String]) {
self.faceOverlayArray = ["overlayModelBlack", "overlayModelBlue", "overlayModelRed", "overlayModelGreen", "overlayModelWhite"]
}
}
let faceOverlayArray1 = (faceOverlayArray: ["overlayModelBlack", "overlayModelBlue", "overlayModelRed", "overlayModelGreen", "overlayModelWhite"]) as! [String]
Any suggestions or pointers are greatly appreciated!
Here modified code that works:
`class Main {
let faceOverlayArray: [String]
var faceOverlayContent: SCNNode
init(faceOverlayArray:[String],faceOverlayContent:SCNNode) {
self.faceOverlayArray = ["overlayModelBlack", "overlayModelBlue", "overlayModelRed", "overlayModelGreen", "overlayModelWhite"]
self.faceOverlayContent = loadedContentForAsset(named: faceOverlayArray1[0])
}
}
let faceOverlayArray1 = ["overlayModelBlack", "overlayModelBlue", "overlayModelRed", "overlayModelGreen", "overlayModelWhite"]`
This is the didSwipe() method that I am attempting to use to cycle through the array (it continues to return the same index)
public func didSwipeRight() -> String {
let arrayLength = faceOverlayArray1.count
var index = 0
index = (index < arrayLength) ? index+1 : 0
print(index)
var faceOverlayContent = faceOverlayArray1[index]
return faceOverlayContent
}
I've been stuck trying to fix an issue in my application that prevents me from getting my desired result.
When pushing segue to the next view controller, I passed two objects of the same class to var original:[Person] = [] and var edited:[Person] = []
if (segue.identifier == "showSummary") {
let vc = segue.destination as! SummaryViewController
vc.original = myObject
vc.edited = Bill.calculateBill(myObject, switchServiceCharge.isOn, switchGST.isOn)
vc.gst = (switchServiceCharge.isOn, switchGST.isOn)
}
Before calculateBill, the original value of a property inside is 11.
The calculateBill is a class function in another class Bill:
class func calculateBill(_ bill: [Person],_ svcCharge: Bool,_ GST: Bool) -> [Person] {
var mutableBill = bill
for i in 0 ..< mutableBill.count {
for j in 0 ..< mutableBill[i].items.count {
let tax = Bill.getGSTForIndividual(mutableBill[i].items[j].itemPrice, svcCharge, GST)
mutableBill[i].items[j].itemPrice += tax
}
}
return mutableBill
}
class func getGSTForIndividual(_ individualAmt: Decimal,_ svcCharge: Bool,_ GST: Bool) -> Decimal {
var taxCost : Decimal = 0.00
let SERVICE_CHARGE = Bill.getServiceCharge() //0.10
let GOODS_SERVICE_TAX = Bill.getGST() //0.07
if (svcCharge && GST) {
taxCost = individualAmt * SERVICE_CHARGE
taxCost = taxCost + ((individualAmt + taxCost) * GOODS_SERVICE_TAX)
}
else if (!svcCharge && GST) {
taxCost = individualAmt * GOODS_SERVICE_TAX
}
else if (svcCharge && !GST) {
taxCost = individualAmt * SERVICE_CHARGE
}
else {
taxCost = 0.00
}
return taxCost
}
When I did a print() to test whether the properties inside are different, they both yield the same results somehow...
print(original[0].items[0].itemPrice) //12.947000000000000123904, originally 11
print(edited[0].items[0].itemPrice) //12.947000000000000123904
What exactly is going on and why do both the objects have the same properties even though I have declared them differently?
I'm guessing that Person is probably declared as a class, not a struct. This means that it's a reference type, and when you:
var mutableBill = bill
you're not actually making a copy of bill, but rather another reference to the same object. So, when you change the properties on mutableBill, you also change the properties on bill, since they both point to the same object.
The solution is to make an actual copy of bill. The two options are either to declare Person as a struct, in which case you will always get a copy, or else to make an initializer on Person that takes another Person and initializes itself using the passed-in Person's properties:
init(person: Person) { ... }
I have this class
class InboxInterests {
var title = ""
var eventID = 0
var count = ""
var added = 0
init(title : String, eventID : NSInteger, count: String, added : NSInteger) {
self.title = title
self.eventID = eventID
self.count = count
self.added = added
}
}
And i use it like this
var array: [InboxInterests] = [InboxInterests]()
Add item
let post = InboxInterests(title: "test",eventID : 1, count: "test", added: 0)
self.array.append(post)
I want to find the index by eventID key and change the value of added key in the same index
How is that possible?
For me, the above answer did not work. So, what I did was first find the index of the object that I want to replace then using the index replace it with the new value
if let row = self.upcoming.index(where: {$0.eventID == id}) {
array[row] = newValue
}
In Swift 5.0:
if let row = self.upcoming.firstIndex(where: {$0.eventID == id}) {
array[row] = newValue
}
Since you are using a class, use filter and first to find the value:
array.filter({$0.eventID == id}).first?.added = value
In this you:
filter the array down to elements that match the event ID
pick the first result, if any
then set the value
This works since classes are pass by reference. When you edit the return value from array.filter({$0.eventID == id}).first?, you edit the underlying value. You'll need to see the answers below if you are using a struct
EDIT: In Swift 3 you can save yourself a couple of characters
array.first({$0.eventID == id})?.added = value
EDIT: Swift 4.2:
array.first(where: { $0.eventID == id })?.added = value
array.filter {$0.eventID == id}.first?.added = value
The filter operator is not the best in this case, it works for some of you because classes are passed by reference.
Explanation: (You can copy the following code in a playground if you want to verify it).
class Book {
let id: Int
var title = "default"
init (id: Int) {
self.id = id
}
}
var arrayBook = [Book]()
arrayBook.append(Book(id: 0))
arrayBook.append(Book(id:1))
arrayBook.forEach { book in
print(book.title)
}
arrayBook.filter{ $0.id == 1 }.first?.title = "modified"
arrayBook.forEach { book in
print(book.title)
}
Arrays are copied by value not reference, so when you are using filter you are creating a new array (different than the initial), but when you modify the new one, the initial one gets modified too because both are pointing to the same class (classed are passed by reference), so after the filter your array will have changed and the new one gets deallocated. So in this case it will print "default", "default" and then "default, "modified".
What happens if you change class for struct, the value will be passed by value not reference so you will have 2 arrays in memory with different values, so if you go through arrayBooks again it will print before the filter "default","default", and then "default", "default" again. Because when you are using the filter you are creating and modifying a new array that will get deallocated if you do not store it).
The solution is using map, creating a new array with all the values but with the modified items or fields that we want and then replace our array with the new one. This will print "default", "default" before the map, and then "default", "modified"
This will work with structs, classes and everything that you want :).
struct Book {
let id: Int
var title = "default"
init (id: Int) {
self.id = id
}
}
var arrayBook = [Book]()
arrayBook.append(Book(id: 0))
arrayBook.append(Book(id:1))
arrayBook.forEach { book in
print(book.title)
}
arrayBook = arrayBook.map{
var mutableBook = $0
if $0.id == 1 {
mutableBook.title = "modified"
}
return mutableBook
}
arrayBook.forEach { book in
print(book.title)
}
array = array.map { $0.eventID == id ? newValue : $0 }
If you conform your class to Equatable then this would work:
extension Array where Element: Equatable {
#discardableResult
public mutating func replace(_ element: Element, with new: Element) -> Bool {
if let f = self.firstIndex(where: { $0 == element}) {
self[f] = new
return true
}
return false
}
}
Use like this:
array.replace(prev, with: new)
is there a possibility to get an object from an array with an specific property? Or do i need to loop trough all objects in my array and check if an property is the specific i was looking for?
edit: Thanks for given me into the correct direction, but i have a problem to convert this.
// edit again: A ok, and if there is only one specific result? Is this also a possible method do to that?
let imageUUID = sender.imageUUID
let questionImageObjects = self.formImages[currentSelectedQuestion.qIndex] as [Images]!
// this is working
//var imageObject:Images!
/*
for (index, image) in enumerate(questionImageObjects) {
if(image.imageUUID == imageUUID) {
imageObject = image
}
}
*/
// this is not working - NSArray is not a subtype of Images- so what if there is only 1 possible result?
var imageObject = questionImageObjects.filter( { return $0.imageUUID == imageUUID } )
// this is not working - NSArray is not a subtype of Images- so what if there is only 1 possible result?
You have no way to prove at compile-time that there is only one possible result on an array. What you're actually asking for is the first matching result. The easiest (though not the fastest) is to just take the first element of the result of filter:
let imageObject = questionImageObjects.filter{ $0.imageUUID == imageUUID }.first
imageObject will now be an optional of course, since it's possible that nothing matches.
If searching the whole array is time consuming, of course you can easily create a firstMatching function that will return the (optional) first element matching the closure, but for short arrays this is fine and simple.
As charles notes, in Swift 3 this is built in:
questionImageObjects.first(where: { $0.imageUUID == imageUUID })
Edit 2016-05-05: Swift 3 will include first(where:).
In Swift 2, you can use indexOf to find the index of the first array element that matches a predicate.
let index = questionImageObjects.indexOf({$0.imageUUID == imageUUID})
This is bit faster compared to filter since it will stop after the first match. (Alternatively, you could use a lazy sequence.)
However, it's a bit annoying that you can only get the index and not the object itself. I use the following extension for convenience:
extension CollectionType {
func find(#noescape predicate: (Self.Generator.Element) throws -> Bool) rethrows -> Self.Generator.Element? {
return try indexOf(predicate).map({self[$0]})
}
}
Then the following works:
questionImageObjects.find({$0.imageUUID == imageUUID})
Yes, you can use the filter method which takes a closure where you can set your logical expression.
Example:
struct User {
var firstName: String?
var lastName: String?
}
let users = [User(firstName: "John", lastName: "Doe"), User(firstName: "Bill", lastName: "Clinton"), User(firstName: "John", lastName: "Travolta")];
let johns = users.filter( { return $0.firstName == "John" } )
Note that filter returns an array containing all items satisfying the logical expression.
More info in the Library Reference
Here is a working example in Swift 5
class Point{
var x:Int
var y:Int
init(x:Int, y:Int){
self.x = x
self.y = y
}
}
var p1 = Point(x:1, y:2)
var p2 = Point(x:2, y:3)
var p3 = Point(x:1, y:4)
var points = [p1, p2, p3]
// Find the first object with given property
// In this case, firstMatchingPoint becomes p1
let firstMatchingPoint = points.first{$0.x == 1}
// Find all objects with given property
// In this case, allMatchingPoints becomes [p1, p3]
let allMatchingPoints = points.filter{$0.x == 1}
Reference:
Trailing Closure
Here is other way to fetch particular object by using object property to search an object in array.
if arrayTicketsListing.contains({ $0.status_id == "2" }) {
let ticketStatusObj: TicketsStatusList = arrayTicketsListing[arrayTicketsListing.indexOf({ $0.status_id == "2" })!]
print(ticketStatusObj.status_name)
}
Whereas, my arrayTicketsListing is [TicketsStatusList] contains objects of TicketsStatusList class.
// TicketsStatusList class
class TicketsStatusList {
internal var status_id: String
internal var status_name: String
init(){
status_id = ""
status_name = ""
}
}