NSMutableArray and NSArray in swift

Question

Initially I declared my array as:

var wrongAnswersArray: NSArray? = []
wrongAnswerLabel.isHidden = (wrongAnswersArray?.count)! <= 0 ? true:false

and my app worked fine. Later, I needed to modify the array so I declared it as mutable but I couldn't use the same statement for getting the count. XCode suggested to modified the statement in the following manner:

var wrongAnswersArray: NSMutableArray? = []
wrongAnswerLabel.isHidden = (wrongAnswersArray!).count <= 0 ? true:false

This compiles but fails at run time

1) Why couldn't we use the same statement? Why do NSArray and NSMutableArray behave differently?

2) Any way to solve this run time error?

Any documentation related to this would be helpful.

Jack · Accepted Answer · 2017-06-22 08:46:13Z

1

Use [String] like swift-array & make it let for constants & var for mutable(variable)

var wrongAnswersArray: [String] = []
wrongAnswerLabel.isHidden = (wrongAnswersArray.count) <= 0 ? true:false

Further you can get help with https://developer.apple.com/library/content/documentation/Swift/Conceptual/Swift_Programming_Language/CollectionTypes.html

edited Jun 22, 2017 at 8:46

answered Jun 22, 2017 at 8:34

Jack

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3 Comments

A_G Over a year ago

Thanks!! It made the entire code simpler. Earlier I was using '?' everywhere. I am new to swift. I will follow the documentation you sent.

Sajjon Over a year ago

This answer is not so "Swifty", and is unnecessarily verbose. You should use my "Swiftier" and more reactive answer: stackoverflow.com/a/44694853/1311272

Aehmlo Over a year ago

A couple of notes: ternaries containing ? true : false do not need to exist (just use the condition instead), and why would the array have fewer than zero elements (use wrongAnswersArray.isEmpty or similar instead)?

Sajjon · Accepted Answer · 2017-06-22 09:57:51Z

Why hassel with array.count <= 0 ? true : false? And why <= even? Can an array have a negative length? You should just do this instead:

// start empty
var wrongAnswers = [String]()
... // app might append wrong answers to the array

// Later check:
wrongAnswersLabel.isHidden = wrongAnswers.isEmpty // done!

Even better:
Or you could "react" to changes to the array, by using Swift "property observer", e.g. "willSet":

// start empty
var wrongAnswers: [String] = [] {
    willSet {
        // Using `willSet` instead of `didSet` allows for use of implicitly declared variable `newValue`
        // which is good since it makes refactoring simpler, not having to refer to the name
        // of this variable (`wrongAnswers`) which we might want to change in the future
        wrongAnswersLabel.isHidden = newValue.isEmpty
    }
}

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