In my Swift class I have the following:
var detailItem: Task?
var cellData:[String:String] = [:]
/* prepareForSegue not called before */
if (detailItem == nil) {
self.cellData = ["id":"", "titolo":"", "oggetto":"", "check_mail":"", "progetto_nome":"", "assegnato_a":"", "richiesto_da":"", "priorita":"", "termine_consegna":"", "stato":"Aperto"]
}
/* prepare for segue has been called */
else {
self.cellData["id"] = String(stringInterpolationSegment: self.detailItem!.id)
self.cellData["titolo"] = self.detailItem!.titolo
self.cellData["oggetto"] = self.detailItem!.oggetto
if (self.detailItem!.check_mail) {
self.cellData["check_mail"] = "true"
}
else {
self.cellData["check_mail"] = "false"
}
self.cellData["progetto_nome"] = self.detailItem!.progetto_nome
self.cellData["assegnato_a"] = self.detailItem!.assegnato_a
self.cellData["richiesto_da"] = self.detailItem!.richiesto_da
self.cellData["priorita"] = self.detailItem!.priorita
self.dateFormatter.dateFormat = "yyyy-MM-dd"
self.cellData["termine_consegna"] = self.dateFormatter.stringFromDate(self.detailItem!.termine_consegna)
self.cellData["stato"] = self.detailItem!.stato
var editButton:UIBarButtonItem = UIBarButtonItem(title: "Modifica", style: UIBarButtonItemStyle.Plain, target: self, action: "switchMode:")
self.navigationItem.rightBarButtonItem = editButton
}
where some properties of the Task class are optionals (like the id) and so they may be nil.
When I need to perform a task update operation I need to retrieve the data from cellData, create a task object and use it to update the database which requires an id. So this is what I do:
var taskToUpdate = Task(id: self.cellData["id"]!.toInt(),
...)
The problem is that id is always set to nil. I have tried:
println(self.cellData["id"]!.toInt())
and what I get is this:
Optional("Optional(102)").
Which is the correct way to cast that into Int?
The function toInt() returns always an optional because there are only a few cases where strings can be converted to integers. If you can ensure that the value is never nil, unwrap it
println(self.cellData["id"]!.toInt()!)
otherwise use optional bindings
If let idInt = self.cellData["id"]!.toInt() { println(idInt) }
You have two problems there:
.toInt() returns an optional.
The id in self.detailItem!.id is probably an optional, too.
The result is that an optional id with value 102 is converted to "Optional(102)" and not "102" as you would expect.
I would advise you a simple solution - don't use dictionaries to hold your data, use objects where properties have the correct types. Don't go around converting your numbers to strings and back. Otherwise you will have to put force unwraps everywhere, e.g.:
String(stringInterpolationSegment: self.detailItem!.id!)
Related
In the code I'm not able to remove optional from the value inside the lbltotalamount.
The value in lblTotalAmount is not removing its optional value from it.
Why? The value in grandtotal gets optional removed but when I assign it to a label it returns an optional value again.
The lblTottalAmount is getting an optional value. I want to remove it.
if success == false {
var grandtotal: Any? = value["total"]
if grandtotal != nil {
print("O!O!O!O/\(grandtotal!)")
grandtotal = String(describing: grandtotal)
self.lblTotalAmount.text = ([grandtotal]) as! String // (here I am not able to remove optional)
}
The problem is in the line
grandtotal = String(describing: grandtotal)
You check for nil but you don't unwrap the value so it's still an optional.
And you are misusing String(describing. Never use it for types which can be converted to String with an init method.
Use always conditional downcast
if success == false {
if let grandtotal = value["total"] as? Double {
self.lblTotalAmount.text = String(grandtotal)
}
}
I'm working with Swift 3.
I would like to have this C syntax :
int myVar;
int *pointer = &myVar;
So modifying pointer or myVar does the same exact same thing.
Also I don't know if it makes any difference, but in my case myVar is an array containing elements of a class and pointer is a pointer to one element of this array.
The & also exists in Swift but can only be used as part of a parameter list (e.g. init, func, closure).
var i = 5
let ptr = UnsafeMutablePointer(&i)
print(ptr.pointee) // 5
// or
let ptr = UnsafeMutablePointer<Int>.allocate(capacity: 1)
ptr.initialize(to: 5)
// or with a closure
let ptr: UnsafePointer = { $0 }(&i)
(Assuming I understand what you're asking for....)
Try the following code in a playground. It should print "99" three times.
class Row {
var rowNumber = 0
}
var rows = [Row]()
let testRow = Row()
testRow.rowNumber = 1
rows.append(testRow)
let selectedRow = rows[0]
selectedRow.rowNumber = 99
print(testRow.rowNumber)
print(selectedRow.rowNumber)
print(rows[0].rowNumber)
By default, there's no copying of objects as part of an assignment statement. If it were a struct, that would be different.
Adding a bit for completeness:
If you want a similar effect with scalar values instead of objects, Swift supplies various types of wrappers.
let intPointer = UnsafeMutablePointer<Int>.allocate(capacity: 8) // Should be 1, not 8 according to comment re: docs
let other = intPointer
other.pointee = 34
print(intPointer.pointee)
(Warning: I haven't used these wrappers for anything except experimenting in a playground. Don't trust it without doing some research.)
Same example as #Phillip. But I used struct. In this example rows[0] won't change:
struct Row {
var rowNumber = 0
}
var rows = [Row]()
var testRow = Row()
testRow.rowNumber = 1
rows.append(testRow)
var selectedRow = rows[0]
selectedRow.rowNumber = 99
print(testRow.rowNumber) // prints 1
print(selectedRow.rowNumber) // prints 99
print(rows[0].rowNumber) // prints 1
There are no C style pointers (Unsafe Pointer) as the question asks however objects are shared by reference and structures are by value:
Swift assign, pass and return a value by reference for reference type and by copy for Value Type
structures are always copied when they are passed around in your code, but classes are passed by reference.
For example
How to have pointers/ references to objects
class Song {
init(title: String, image: String, file: String, volume: Float, queuePlayer: AVQueuePlayer, playerLooper: AVPlayerLooper?) {
self.title = title
self.image = image
...
}
var title: String
var image: String
...
}
var aSong = Song(title: "", image: "", ...)
var arrOfSongReferences: [Song] = [Song]()
arrOfSongReferences.append(aSong)
var ptrToASong: Song = aSong
aSong = nil
// Due to Swift garbage collection ARC (Automatic Reference Counting), we still have references to the original aSong object so it won't be deleted
If data is struct you cannot do this
struct Song {
var title: String
var image: String
...
}
var aSong: Song = Song(title: "", image: "", ...)
var copyOfASong: Song = aSong
Method
You can also pass by reference into a function
// this would be inside a class, perhaps Player. It doesn't have to be a static btw
static func playSound(_ sound: inout Song, volume: Float = 0.0) {
if (sound.playerLooper == nil) {
...
}
}
// usage
Player.playSound(sound: &aSong)
So here I have a basic setup
var preferenceSpecification = [String : String?]()
preferenceSpecification["Key"] = "Some Key"
preferenceSpecification["Some Key"] = nil
preferenceSpecification["DefaultValue"] = "Some DefaultValue"
print(preferenceSpecification)
var defaultsToRegister = [String : String]()
if let key = preferenceSpecification["Key"], let defaultValueKey = preferenceSpecification["DefaultValue"] {
defaultsToRegister[key] = preferenceSpecification[defaultValueKey]!
}
But the error points out where it demands that I force unwrap this, to be like this:
defaultsToRegister[key!] = preferenceSpecification[defaultValueKey!]!
Which doesn't make sense, because keyValue and defaultValue already are unwrapped
When you extract a value from a dictionary like this using subscript
[String: String?]
you need to manage 2 levels of optional. The first one because the subscript returns an optional. The second one because the value of you dictionary is an optional String.
So when you write
if let value = preferenceSpecification["someKey"] {
}
you get value defined as an optional String.
Here's the code to fix that
if let
optionalKey = preferenceSpecification["Key"],
key = optionalKey,
optionalDefaultValueKey = preferenceSpecification["DefaultValue"],
defaultValueKey = optionalDefaultValueKey,
value = preferenceSpecification[defaultValueKey] {
defaultsToRegister[key] = value
}
Suggestions
You should avoid force unwrapping as much as possible. Instead you managed to put 3 ! on a single line!
You should also try to use better name for your constants and variables.
You could also define an extension which helps get rid of the double optional situation.
extension Dictionary where Value == Optional<String> {
func flattened(_ key: Key) -> Value {
if let value = self[key] {
return value
}
return nil
}
}
Usage: preferenceSpecification.flattened("someKey")
I am attempting to use Parse to call up some variables and put them into a struct that is already initialized. The calling of the variables is happening smoothly and the data is available, but the inputing of the class into the function is not happening.
'unit' is a struct that has the name, hp, attack, etc. variables contained within it.
Is it not possible to pass along an instance of a struct and modify it's values like this? It would save me a lot of copy-pasting code to do it this way.
Thanks for your help!
func fetchStats(name: String, inout nameOfClass: unit) {
var unitStatArray = []
let query = PFQuery(className: "UnitStats")
query.whereKey("name", equalTo: name)
query.findObjectsInBackgroundWithBlock{(objects:[PFObject]?, error: NSError?)->Void in
if (error == nil && objects != nil){ unitStatArray = objects! }
nameOfClass.name = "\(unitStatArray[0].objectForKey("name")!)"
print("class name is \(nameOfClass.name)")
print("cannon name is \(cannon.name)")
nameOfClass.hitPoints = unitStatArray[0].objectForKey("hitPoints") as! Double
nameOfClass.hitPointsMax = unitStatArray[0].objectForKey("hitPointsMax") as! Double
nameOfClass.attack = unitStatArray[0].objectForKey("attack") as! Double
nameOfClass.defense = unitStatArray[0].objectForKey("defense") as! Double
nameOfClass.rangedAttack = unitStatArray[0].objectForKey("rangedAttack") as! Double
nameOfClass.rangedDefense = unitStatArray[0].objectForKey("rangedDefense") as! Double
nameOfClass.cost = unitStatArray[0].objectForKey("cost") as! Int
}
}
fetchStats("3-inch Ordnance Rifle", nameOfClass: &cannon)
This is an attempt to explain what I had in mind when writing my comment above.
Because there's an asynchronous call to findObjectsInBackgroundWithBlock, the inout won't help you here. The idea is to add a callback fetched like this:
func fetchStats(name: String, var nameOfClass: unit, fetched: unit -> ()) {
// your code as above
query.findObjectsInBackgroundWithBlock {
// your code as above plus the following statement:
fetched(nameOfClass)
}
}
This can be called with
fetchStats("3-inch Ordnance Rifle", nameOfClass: cannon) { newNameOfClass in
nameOfClass = newNameOfClass
}
(all of this code has not been tested)
The point is that you understand that your code is asynchronous (I know, I'm repeating myself). After you have called fetchStats you don't know when the callback (here: the assignment nameOfClass = newNameOfClass) will be executed. You cannot assume the assignment has been done after fetchStats has returned.
So whatever you need to do with the changed nameOfClass: the corresponding statements must go into the callback:
fetchStats("3-inch Ordnance Rifle", nameOfClass: cannon) { newNameOfClass in
// do whatever you want with the received newNameOfClass
}
Hope this helps.
So I am trying to get the Actual Variable Name as String in Swift, but have not found a way to do so... or maybe I am looking at this problem and solution in a bad angle.
So this is basically what I want to do:
var appId: String? = nil
//This is true, since appId is actually the name of the var appId
if( appId.getVarName = "appId"){
appId = "CommandoFurball"
}
Unfortunately I have not been able to find in apple docs anything that is close to this but this:
varobj.self or reflect(var).summary
however, this gives information of what is inside the variable itself or the type of the variable in this case being String and I want the Actual name of the Variable.
This is officially supported in Swift 3 using #keyPath()
https://github.com/apple/swift-evolution/blob/master/proposals/0062-objc-keypaths.md
Example usage would look like:
NSPredicate(format: "%K == %#", #keyPath(Person.firstName), "Wendy")
In Swift 4 we have something even better: \KeyPath notation
https://github.com/apple/swift-evolution/blob/master/proposals/0161-key-paths.md
NSPredicate(format: "%K == %#", \Person.mother.firstName, "Wendy")
// or
let keyPath = \Person.mother.firstName
NSPredicate(format: "%K == %#", keyPath, "Andrew")
The shorthand is a welcome addition, and being able to reference keypaths from a variable is extremely powerful
As per the updated from this answer, it is supported in Swift 3 via #keyPath
NSPredicate(format: "%K == %#", #keyPath(Person.firstName), "Andrew")
This is my solution
class Test {
var name: String = "Ido"
var lastName: String = "Cohen"
}
let t = Test()
let mirror = Mirror(reflecting: t)
for child in mirror.children {
print(child.label ?? "")
}
print will be
name
lastName
This works:
struct s {
var x:Int = 1
var y:Int = 2
var z:Int = 3
}
var xyz = s()
let m = Mirror(reflecting: xyz)
print(m.description)
print(m.children.count)
for p in m.children {
print(p.label as Any)
}
I've come up with a swift solution, however unfortunately it doesn't work with Ints, Floats, and Doubles I believe.
func propertyNameFor(inout item : AnyObject) -> String{
let listMemAdd = unsafeAddressOf(item)
let propertyName = Mirror(reflecting: self).children.filter { (child: (label: String?, value: Any)) -> Bool in
if let value = child.value as? AnyObject {
return listMemAdd == unsafeAddressOf(value)
}
return false
}.flatMap {
return $0.label!
}.first ?? ""
return propertyName
}
var mutableObject : AnyObject = object
let propertyName = MyClass().propertyNameFor(&mutableObject)
It compares memory addresses for an object's properties and sees if any match.
The reason it doesn't work for Ints, Floats, and Doubles because they're not of type anyobject, although you can pass them as anyobject, when you do so they get converted to NSNumbers. therefore the memory address changes. they talk about it here.
For my app, it didn't hinder me at all because I only needed it for custom classes. So maybe someone will find this useful. If anyone can make this work with the other datatypes then that would be pretty cool.
Completing the accepted answer for extensions:
The property needs to be #objc.
var appId: String? {
....
}
You need to use #keyPath syntax, \ notation is not supported yet for extensions.
#keyPath(YourClass.appId)
The best solution is Here
From given link
import Foundation
extension NSObject {
//
// Retrieves an array of property names found on the current object
// using Objective-C runtime functions for introspection:
// https://developer.apple.com/library/mac/documentation/Cocoa/Conceptual/ObjCRuntimeGuide/Articles/ocrtPropertyIntrospection.html
//
func propertyNames() -> Array<String> {
var results: Array<String> = [];
// retrieve the properties via the class_copyPropertyList function
var count: UInt32 = 0;
var myClass: AnyClass = self.classForCoder;
var properties = class_copyPropertyList(myClass, &count);
// iterate each objc_property_t struct
for var i: UInt32 = 0; i < count; i++ {
var property = properties[Int(i)];
// retrieve the property name by calling property_getName function
var cname = property_getName(property);
// covert the c string into a Swift string
var name = String.fromCString(cname);
results.append(name!);
}
// release objc_property_t structs
free(properties);
return results;
}
}