I have a loop like so that creates a string representing a url:
for(var i = 1; i < 6; i++)
{
let urlString: String = "http://{...}/data/\(i).txt"
var downloader = FileDownloader(url: urlString, array: peopleArray, table: theTable)
downloaderQueue.addOperation(downloader)
}
FileDownloader constructor is as follows:
let urlString: String
var personArray: Array<Person> = []
var person: Person
let table: UITableView
init(url: String, array: Array<Person>, table: UITableView)
{
self.urlString = url
self.person = Person()
self.personArray = array
self.table = table
}
When this code runs, lldb gives me the error:
fatal error: unexpectedly found nil while unwrapping an Optional value
(lldb)
And I know the problem is the string because of the debugger output:
downloader Lecture_14.FileDownloader 0x000000016fd89f60 0x000000016fd89f60
Foundation.NSOperation NSOperation
urlString String "unexpectedly found nil while unwrapping an Optional value"
_core _StringCore
Any ideas why this would be happening?
In Xcode, option-click on each of the variables in use: urlString, peopleArray and theTable.
The popup that appears will show you whether the variable is an optional variable by appending a ? to the class name.
From your code above, urlString should not be an optional and therefore should not be the problem. But check the other variables in use and see if any of them are optionals.
If so, use something like this:
if let checkedPeopleArray = peopleArray {
// now you can use checkedPeopleArray and be sure it is not nil
}
A couple of other points to make your code more Swift-like:
Your loop can be written like this, using Swift's range instead of the traditional C-style loop:
for i in 1..<6 {
let urlString: String = "http://{...}/data/\(i).txt"
}
When declaring an array, Apple changed this from the first version of Swift. Instead of:
var personArray: Array<Person> = []
try:
var personArray: [Person]() // empty array for Person objects
And in your init:
init(url: String, array: [Person], table: UITableView)
Functionally the same, but I feel it is better to use the changes to the language as they appear because there is no telling when/if Apple might remove the old syntax.
Related
I'm having issues with appending an optional value to an array in Swift. The view I'm writing is for the creation of a routine for the gym. However my Routine object is not being instantiated as it should be.
I have experience with other programming languages but I am fairly new to Swift, and optionals.
My ViewController contains an optional variable:
var routine: Routine?
Where the Routine class contains:
name: String
exerciseList: [String]()
numOfSets: [Int]()
When I am preparing it to send the newly created routine to my other ViewController, I take the values from user input to edit the fields of the object.
let name = routineName.text ?? ""
let numberOne = Int(numOfSetsOne.text ?? "0") //numOfSetsOne is a text label
routine?.exerciseList.append(selectedExerciseOne!) //Haven't tested to see if this works yet
routine?.numOfSets[0] = numberOne! //This line is not working
routine = Routine(name: name)
To try a little debugging I put print statements on either side of the line like so:
print ("numberOne Value: \(numberOne!)")
routine?.numOfSets[0] = numberOne!
print ("numOfSets[0] Value: \(routine?.numOfSets[0])")
I expected the output from the second print statement to be identical to the first. However the terminal output:
numberOne Value: 3
numOfSets[0] Value: nil
Does anyone know what has gone wrong here?
Thanks
You have declared a property that may contain a Routine, but you have not assigned an instance of Routine to that property before trying to use it.
This means that, for example,
routine?.numSets[0] = numberOne!
doesn't do anything - routine is nil and so the statement is skipped.
You should create an appropriate init function for your Routine class and use that to create a new Routine and assign it to routine
For example:
class Routine {
var name: String
var exerciseList = [String]()
var numberOfSets = [Int]()
init(named: String) {
self.name = named
}
}
Then you can say
let name = routineName.text ?? ""
let numberOne = Int(numOfSetsOne.text ?? "0")
self.routine = Routine(named: name)
self.routine?.numberOfSets.append(numberOne!)
Coordinating related arrays can get a bit messy, so I would use a single array:
struct ExerciseSet {
let exerciseName: String
let sets: Int
}
class Routine {
var name: String
var exerciseList = [ExerciseSet]()
init(named: String) {
self.name = named
}
}
Your Routine is not initialised before its being assigned value
try
let name = routineName.text ?? ""
let numberOne = Int(numOfSetsOne.text ?? "0")
routine = Routine(name: name)
routine?.exerciseList.append(selectedExerciseOne!)
routine?.numOfSets[0] = numberOne!
just a bit of hindsight for you to understand my problem. I am currently coding an iOS app for events where I have a GuestList CoreData saved on device.
On viewDidLoad, it will fetch the coredata object and place it into an array of [GuestDetails]
Now the Guestdetail object struct is as follows:
private(set) public var guestFirstName: String
private(set) public var guestLastName: String?
private(set) public var guestEmail: String?
private(set) public var guestPhone: String?
private(set) public var guestUUID: UUID
private(set) public var guestBarcode: String?
private(set) public var guestCheckedIn: Bool
Such that only first name, UUID and checkinStatus are compulsory. I have already set up adding by JSON but now my issue is on my GuestListViewController, I have a searchbar
I am using the following code and array to make sure I can filter.
I have another array that is called
searchResultArray = [GuestDetails]()
So essentially I would copy all my guest details to searchResultArray and that is the one that the tableView is getting its sources from.
Now as part of the search, I used this code which I found on appcoda
searchResultArray = guestData.filter({guestData -> Bool in
(guestData.guestFirstName.lowercased().contains(searchText.lowercased())) ||
(guestData.guestLastName?.lowercased().contains(searchText.lowercased()))! ||
(guestData.guestBarcode?.contains(searchText))!
})
The issue is that my app is crashing, if I only search by first name it will not crash since those are force unwrapped nicely, but if I add the code to search lastName or Barcode, it will crash. I understand that it is probably because of explicitly unwrapped but xcode would not let me NOT unwrap it.
I have tried using map (which does not help, unless i am not familiar enough with it),
I have tried .compact (but I could not get it to work as i am not sure how it can access the inside of an GuestDetail object to remove nils)
The issue is the array of [GuestDetails] itself will not contain null some details inside a GuestDetails object might, hence causing it to crash.
My question is, how do I get it to search by firstname(already possible), lastname and barcode?
Thanks and I hope the question was elaborate enough.
I would avoid using forced unwrapping like so:
searchResultArray = guestData.filter({guestData -> Bool in
let searchLowercased = searchText.lowercased()
if guestData.guestFirstName.lowercased().contains(searchLowercased) {
return true
}
if let guestLastName = guestData.guestLastName, guestLastName.lowercased().contains(searchLowercased) {
return true
}
if let guestBarcode = guestData.guestBarcode, guestBarcode.lowercased().contains(searchLowercased) {
return true
}
return false
})
Answering your question from comments: You don't have to use ? operator on optionals because we use Optional Binding if let syntax. So for example:
if let guestLastName = guestData.guestLastName if guestData.guestLastName is nil than we will just jump out of this if statement. then you see , in the if statement, we will go pass this comma only if guestData.guestLastName is not nil, that is why we can use the guestLastName variable that is unwrapped String and is no longer optional String?, we than proceed to check if search term matches the guestLastName and return true.
Please read: if let , if var, guard let,guard var and defer statements in swift
It would be even better if you happen to add another property to your Data and avoid doing all this if else you can do something like:
searchResultArray = guestData.filter({guestData -> Bool in
let searchLowercased = searchText.lowercased()
let matches:[String?] = [guestData.guestFirstName, guestData.guestLastName, guestData.guestBarcode]
let nonNilElements = matches.compactMap { $0 }
for element in nonNilElements {
if element.lowercased().contains(searchLowercased) {
return true
}
}
return false
})
It's an interesting little problem, so let's generalize it. Here's our test data, comparable to your array of GuestDetails:
struct S {
var s1 : String
var s2 : String?
var s3 : String?
}
var array = [S]()
array.append(S(s1: "test", s2: "yo", s3: "ha"))
array.append(S(s1: "test", s2: nil, s3: nil))
array.append(S(s1: "Howdy", s2: "Bonjour", s3: "Hello"))
let target = "hello"
Some S properties are Optional, others are not.
So the problem is: Filter array down to only those elements where any S property contains our target string, using case insensitive comparison.
We can do that in one statement:
let filteredArray = array.filter {
[$0.s1,$0.s2,$0.s3].compactMap {$0}
.map {$0.localizedCaseInsensitiveContains(target)}
.contains(true)
}
It's not quite as efficient as what #Ladislav wrote, because we keep looping inside map even after we've found our string. But the inefficiency is probably not significant.
I am using Vapor for Swift backend. Following is the code i am working with.
drop.post("postTodo") { request in
var jsonContent: JSON?
if let contentType = request.headers["Content-Type"], contentType.contains("application/json"), let jsonData = request.json {
jsonContent = jsonData
print("Got JSON: \(jsonContent)")
}
guard let id = jsonContent?.node.object?["id"]?.string
else {
return JSON(["message": "Please include mandatory parameters"])
}
let tempId = Int(id)!
I am getting "id" as optional string for eg: Optional("123") for jsonContent?.node.object?["id"]?.string
When I try to convert it to int using Int(id)! i get back nil
If i try to do let tempId = Int(id!) it gives error.
But when i do the same thing in playground i get proper int value.
let id: String?
id = "1234"
let myInt = Int(id!)
Why Optional string to Int is not working properly in my Vapor app ?
Any idea.
If "id" is an optional string, then you probably don't want to be force unwrapping it with the "!".
The safest approach would be something like:
if let id = id
{
let myIdAsInt = Int(id)
}
The reason it "works" in the playground, is you are definitely assigning a non-nil value to the string (therefore you get away with the force unwrap).
String!might contain a string, or it might contain nil. It’s like a regular optional, but Swift lets you access the value directly without the unwrapping safety. If you try to do it, it means you know there’s a value there – but if you’re wrong your app will crash.
var optionalString: String? = "123"
// first check if it doesn't contain nil
if let str = optionalString {
// string to -> Int
if let id = Int(str) {
print(id) // work with id
}
} else {
// optionalString contains nil
}
what i found is in my iOS code i had a struct with optional properties coz of which when mapped to Dict gave object with optional values to keys.
If I make properties non optional and send it to vapor backend after it works fine.
So basically it was the case of using Optionals properly.
I have created a class as such:
class Task {
var name:String
var description:String
var date:NSDate
var taskCompleted:Bool
init(name:String, description:String,date:NSDate, taskCompleted:Bool){
self.name = name
self.description = description
self.date = date
self.taskCompleted = taskCompleted
}
}
I then create a new object like so:
let newTask:AnyObject = Task(name: taskName.text!, description: descriptionInput.text, date: datePicker.date, taskCompleted: false)
Later on I add the object to an array:
var tasks = [AnyObject]()
tasks.append(newTask)
However, when I try to access the object again like so I get an error:
print(tasks[0].name)
ERROR: unexpectedly found nil while unwrapping an Optional value
Your array is of type [AnyObject]. If you want to avoid using as keyword, you should make it of type [Task] because AnyObject doesn't necesseraly have a name property. This is why it yells found nil while unwrapping an Optional value.
Try this :
let newTask:Task = Task(name: taskName.text!, description: descriptionInput.text, date: datePicker.date, taskCompleted: false)
var tasks = [Task]()
tasks.append(newTask)
print(tasks[0].name)
Like Lindsey said, you can use the as keyword if you want to have different types of objects in it but I don't think that is what you want.
In your current code tasks[0] is of type AnyObject which does not have a "name" property. Try changing:
print(tasks[0].name)
to
print((tasks[0] as! Task).name)
in order to change tasks[0] from AnyObject to Task.
Currently when you access a task from your array you get back an AnyObject which knows nothing about your name attribute.
You can do one of two things depending on what you are trying to accomplish
You can set your array to be of type [Task] not AnyObject.
Cast the AnyObject to Task when retrieving it from array. (task[0] as! Task).name
I am doing what I believe to be a very simple task. I'm trying to get a value out of a dictionary if the key exists. I am doing this for a couple keys in the dictionary and then creating an object if they all exist (basically decoding a JSON object). I am new to the language but this seems to me like it should work, yet doesn't:
class func fromDict(d: [String : AnyObject]!) -> Todo? {
let title = d["title"]? as? String
// etc...
}
It gives me the error: Operand of postfix ? should have optional type; type is (String, AnyObject)
HOWEVER, if I do this, it works:
class func fromDict(d: [String : AnyObject]!) -> Todo? {
let maybeTitle = d["title"]?
let title = maybeTitle as? String
// etc...
}
It appears to be basic substitution but I may be missing some nuance of the language. Could anyone shed some light on this?
The recommended pattern is
if let maybeTitle = d["title"] as? String {
// do something with maybeTitle
}
else {
// abort object creation
}
It is possibly really a question of nuance. The form array[subscript]? is ambiguous because it could mean that the whole dictionary (<String:AnyObject>) is optional while you probably mean the result (String). In the above pattern, you leverage the fact that Dictionary is designed to assume that accessing some key results in an optional type.
After experimenting, and noticing that the ? after as is just as ambiguous, more, here is my solution:
var dictionary = ["one":"1", "two":"2"]
// or var dictionary = ["one":1, "two":2]
var message = ""
if let three = dictionary["three"] as Any? {
message = "\(three)"
}
else {
message = "No three available."
}
message // "No three available."
This would work with all non-object Swift objects, including Swift Strings, numbers etc. Thanks to Viktor for reminding me that String is not an object in Swift. +
If you know the type of the values you can substitute Any? with the appropriate optional type, like String?
There are a few of things going on here.
1) The ? in d["title"]? is not correct usage. If you're trying to unwrap d["title"] then use a ! but be careful because this will crash if title is not a valid key in your dictionary. (The ? is used for optional chaining like if you were trying to call a method on an optional variable or access a property. In that case, the access would just do nothing if the optional were nil). It doesn't appear that you're trying to unwrap d["title"] so leave off the ?. A dictionary access always returns an optional value because the key might not exist.
2) If you were to fix that:
let maybeTitle = d["title"] as? String
The error message changes to: error: '(String, AnyObject)' is not convertible to 'String'
The problem here is that a String is not an object. You need to cast to NSString.
let maybeTitle = d["title"] as? NSString
This will result in maybeTitle being an NSString?. If d["title"] doesn't exist or if the type is really NSNumber instead of NSString, then the optional will have a value of nil but the app won't crash.
3) Your statement:
let title = maybeTitle as? String
does not unwrap the optional variable as you would like. The correct form is:
if let title = maybeTitle as? String {
// title is unwrapped and now has type String
}
So putting that all together:
if let title = d["title"] as? NSString {
// If we get here we know "title" is a valid key in the dictionary, and
// we got the type right. title has now been unwrapped and is ready to use
}
title will have the type NSString which is what is stored in the dictionary since it holds objects. You can do most everything with NSString that you can do with String, but if you need title to be a String you can do this:
if var title:String = d["title"] as? NSString {
title += " by Poe"
}
and if your dictionary has NSNumbers as well:
if var age:Int = d["age"] as? NSNumber {
age += 1
}