How do I stop this enumeration? I have the following code and Xcode complaining that I cannot assign a value to let constant. Stopping is probably a simple thing but I'm quite the noobie with Swift, so please bear with me.
self.enumerateChildNodesWithName("//*") {
spaceshipNode, stop in
if (( spaceshipNode.name?.hasSuffix("ship") ) != nil) {
for enemyNode in self.children {
if (enemyNode.name == "enemy"){
if(enemyNode.containsPoint(spaceshipNode.position)){
self.gotoGameOverScene(spaceshipNode)
stop = true // Error: Cannot assign to value: 'stop' is a 'let' constant
}
}
}
}
}
Generally you'd better show your code as text. With which we can easily copy & paste, and test it, or edit it.
In your code, the type of stop should be shown as UnsafeMutablePointer<ObjCBool> in the Quick Help pane of Xcode.
You need to modify the content of the pointer, in Swift2:
stop.memory = true
In Swift 3, the property memory is renamed to pointee:
stop.pointee = true
Apple's documentation suggests that we stop enumeration via stop.initialize(to: true).
Related
I am trying to write code that waits until a variable equals a certain value. Here is the code I have written:
var i = 0
for i in 1...10 {
playtrial()
repeat {
} while (WasItCorrect=="")
WasItCorrect = ""
}
The idea is that the function will call playtrial, wait until the variable WasItCorrect has a value (other than ""), reset WasItCorrect, and then repeat (for a total of 10 times).
The code produces no errors. However, after plastral is done, the program seems to stop responding and does not allow any new input / button pressing.
I assume the problem is that my repeat/while loop goes forever and never gives a chance for anything else to happen and therefore other functions which change the value of WasItCorrect cannot run. As a VisualBasic 6 programmer who is just starting to learn Swift, I would guess I would need the Swift version of DoEvents. Is that true?
Any advice on how to fix this code would be greatly appreciated.
You can use didSet property of the variable. It will be called whenever the value changed.
var i = 0 {
didSet {
print("Hello World.")
if i == certainValue {
// do something
}
}
}
Still a beginner with just playing around with some basic functions in swift.
Can someone tell me what is wrong with this code?
import UIKit
var guessInt: Int
var randomNum = arc4random_uniform(10)
if Int(randomNum) == guessInt {
println ("correct")
} else {
println; "no, the number is not. guess again"
}
So far the only error I'm getting is that
guessInt
is being used before being initialized!
I've tried to type everything again but still have the same error.
Thanks in advance.
In Swift you cannot read a value before it's set, which you're doing here:
if Int(randomNum) == guessInt
If you change your declaration from this:
var guessInt:Int
to this:
var guessInt = 6
then your code will work as expected (assuming you want the user's guess to be 6).
You've declared guessInt but now you need to initialize, or set it to some initial value.
For example:
let guessInt = 3
Another option is to declare guessInt as an "Optional", meaning that it can be nil, in fact it will be initialized to nil. This will print "no, ...." until you assign guessInit to a non nil value in the range of values produced by arc4random_uniform(10), but it will compile and run cleanly.
var guessInt:Int? // note the ? after Int this marks it as an Optional
var randomNum = arc4random_uniform(10)
if Int(randomNum) == guessInt {
println ("correct")
} else {
println; "no, the number is not. guess again"
}
I'm very new to swift, but proficient in other languages like Java, JavaScript, C, ... I'm lost with Swift syntax when it comes to create expressions. Look at this basic example where I just try to find out if one string is contained into another by calling String.rangeOfString that returns an Optional Range (Range?)
This works as expected:
let LEXEMA:String="http://"
let longUrl:String="http://badgirls.many/picture.png"
let range=longUrl.rangeOfString(LEXEMA);
if (range? != nil) {
// blah
}
Now I'm trying to combine the expression inside the if, something like:
if (longUrl.rangeOfString(LEXEMA)? !=nil) {
// blah
}
But I always get syntax errors, the above yields a "Expected Separator" and can't understand why. Done some more tests:
if (absolutePath.rangeOfString(URL_LEXEMA) !=nil) { }
Expected Separator before "!"
if absolutePath.rangeOfString(URL_LEXEMA) !=nil { }
Braced block of statements is an unused closure
What am I doing wrong?
If you’re coming from other like Java, you might be thinking of optionals like pointers/references, and so used to equating them to nil and if non-nil, using them. But this is probably going to lead to more confusion. Instead, think of them like a container for a possible result, that you need to unwrap to use. if let combines the test and unwrapping operation.
With this in mind, here’s how you could adapt your code:
let LEXEMA: String="http://"
let longUrl: String="http://badgirls.many/picture.png"
if let range = longUrl.rangeOfString(LEXEMA) {
// use range, which will be the unwrapped non-optional range
}
else {
// no such range, perhaps log an error if this shouldn’t happen
}
Note, that ? suffixing behaviour you were using changes in Swift 1.2 so even the code in your question that compiles in 1.1 won’t in 1.2.
It’s possible that sometimes you are whether there was a value returned, but you don’t actually need that value, just to know it wasn’t nil. In that case, you can compare the value to nil without the let:
if longUrl.rangeOfString(LEXEMA) != nil {
// there was a value, but you don't care what that value was
}
That said, the above is probably better expressed as:
if longUrl.hasPrefix(LEXEMA) { }
For starters:
You don't need parenthesis with if statements unless you have nested parenthetical subexpressions that require it.
You don't need to specify the type on the left side of the = of a let or var declaration if Swift can figure it out from the right side of the =. Very often Swift can figure it out, and you can tell that Swift can figure it out, so you can avoid that redundant clutter.
You do need to specify the type if Swift cannot figure out the type from
the right side. Example:
For example, consider the following lines:
let LEXEMA = "http://"
let longUrl = "http://badgirls.many/picture.png"
Swift can figure out that they're strings.
Similarly for this function or class that returns a UIView:
var myView = ViewReturningClassOrFunc()
Consider this:
#IBOutlet var myView : UIView!
In the above line, Swift cannot figure out ahead of time it will be assigned a UIView, so you have to provide the type. By providing a ! at the end you've made it an implicitly unwrapped optional. That means, like ?, you're indicating that it can be nil, but that you are confident it will never be nil at the time you access it, so Swift won't require you to put a ! after it when you reference it. That trick is a time saver and big convenience.
You should NOT add the ? to the line:
if (longUrl.rangeOfString(URL_LEXEMA) !=nil) {
As another answer pointed out, you're missing the let.
if let longUrl.rangeOfString(URL_LEXEMA) {
println("What do I win? :-)")
}
swift is case sensitive language. you need to check about whitespaces as well
if longUrl.rangeOfString(LEXEMA) != nil {
//your condition
}
there should be space between statement != nil
Just add a space between != and nil like:
if longUrl.rangeOfString(LEXEMA) != nil {
// blah
}
I tested your code in playground, an error of Expected ',' separator reported.
And do not forget the rules that 1s and 0s and Airspeed Velocity said.
I have this variable
var taxableTotalText = String(28)
it is populated from a second view controller, it works well except when you use the app for the first time, if the string is blank it crashes the app. I have tried
if taxableTotalText.isEmpty {
NSUserDefaults().setObject("0.00", forKey: String(28))
}
but it didn't work.
I would like to use some code like this
if TaxableAllowancesBtn "Has never been pushed" {
NSUserDefaults().setObject("0.00", forKey: String(28))
}
else {
//do nothing
}
TaxableTotal.text = NSUserDefaults().stringForKey(taxableTotalText)
but "Has never been pushed" needs to be some real swift coding.
At the moment i am just using
NSUserDefaults().setObject("0.00", forKey: String(28))
it stops my app from crashing but also forces my label to be "0.00" every time I reopen the app. A simple segue and back fixes the issue but its bugging me.
Can someone please swap my english for swift, or suggest a better way to solve this issue.
Thank you
You can use the "??" nil coalescing operator to return a default value instead of nil.
TaxableTotal.text = NSUserDefaults().stringForKey("yourKey") ?? "0.00"
With the code below, the local songs variable is never able to be iterated despite all the checks to the contrary ( println shows the value stored ). The other thing is that the Xcode debugger seems to jump all over the place in the init method.
let gLibraryManager = LibraryManager()
class LibraryManager {
var Songs = Dictionary<String, String>()
init() {
println("struct being initialized from NSDefaults")
let userDefaults = NSUserDefaults.standardUserDefaults();
var result:AnyObject = userDefaults.objectForKey(LIKED_LIST)
println(result)
var local = result as? Dictionary<String,String>
if local != nil {
println("local not nil: \(local!)")
for (id,title) in local! {
Songs[id] = title
}
if Songs.count > 0 {
println("NSDefaults detected: \(Songs)")
} else {
println("no NSDefaults detected. Initializing empty")
}
}
}
ok. i figured out what is was.
I had set the Swift Compiler - Code Generation. Optimization level to -Fastest. This was to prevent the extremely slow creation of Dictionaries.
However, it appears this breaks the ability to iterate structures.
It also seems to resolve the weird bouncing around of breakpoints.
This was a needle in a haystack that tooks many hours. I guess the moral of the story is not to mess with compiler flags yet.