29

I keep getting an error of "ambiguous use of subscript," in my Swift code. I don't know what's causing this error. It just randomly popped up. Here's my code:

if let path = NSBundle.mainBundle().pathForResource("MusicQuestions", ofType: "plist") {
    myQuestionsArray = NSArray(contentsOfFile: path)
}

var count:Int = 1
let currentQuestionDict = myQuestionsArray!.objectAtIndex(count)

if let button1Title = currentQuestionDict["choice1"] as? String {
    button1.setTitle("\(button1Title)", forState: UIControlState.Normal)
}

if let button2Title = currentQuestionDict["choice2"] as? String {
    button2.setTitle("\(button2Title)", forState: UIControlState.Normal)
}

if let button3Title = currentQuestionDict["choice3"] as? String {
    button3.setTitle("\(button3Title)", forState: UIControlState.Normal)
}
if let button4Title = currentQuestionDict["choice4"] as? String {
    button4.setTitle("\(button4Title)", forState: UIControlState.Normal)
}

if let question = currentQuestionDict["question"] as? String!{
    questionLabel.text = "\(question)"
}
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5
  • Do you know what is Subscripts? If not, subscripts is a shortcut to access to a element of a collection. Take a look at this By the way, could you post the type of your currentQuestionDict to understand the context. Commented Nov 11, 2015 at 0:21
  • The type? It's basically just an NSDictionary filled with strings. Commented Nov 11, 2015 at 0:40
  • Do not say what it is "basically". Every Swift variable has a declaration which gives it a specific type. Show the declaration of currentQuestionDict. The entire answer to your question depends upon that declaration. To hide it is silly: it is the answer. Show it. Commented Nov 11, 2015 at 1:00
  • Isn't let currentQuestionDict = myQuestionsArray!.objectAtIndex(count) the declaration? Commented Nov 11, 2015 at 1:02
  • Good, I think that explains it. Commented Nov 11, 2015 at 1:14

3 Answers 3

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36

The problem is that you are using NSArray:

myQuestionsArray = NSArray(contentsOfFile: path)

This means that myQuestionArray is an NSArray. But an NSArray has no type information about its elements. Thus, when you get to this line:

let currentQuestionDict = myQuestionsArray!.objectAtIndex(count)

...Swift has no type information, and has to make currentQuestionDict an AnyObject. But you can't subscript an AnyObject, so expressions like currentQuestionDict["choice1"] cannot compile.

The solution is to use Swift types. If you know what currentQuestionDict really is, type it as that type. At the very least, since you seem to believe it is a dictionary, make it one; type it as [NSObject:AnyObject] (and more specific if possible). You can do this in several ways; one way is by casting when you create the variable:

let currentQuestionDict = 
    myQuestionsArray!.objectAtIndex(count) as! [NSObject:AnyObject]

In short, never use NSArray and NSDictionary if you can avoid it (and you can usually avoid it). If you receive one from Objective-C, type it as what it really is, so that Swift can work with it.

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9 Comments

Excellent. Even more important, though, is to understand what I've said.
There is something I'm a bit confused about in your answer. You said that you can't subscript an AnyObject, but after you wrote ` myQuestionsArray!.objectAtIndex(count) as! [NSObject:AnyObject]`, the app ran successfully.
Because after that there is no AnyObject in this story. We cast it to an [NSObject:AnyObject], aka a dictionary - and that is something you can subscript.
Oh. I think I understand what you did now.
You might want to read my book about Swift: apeth.com/swiftBook/ch04.html#_casting
|
7

["Key"] has causing this error. New Swift update, you should use objectForKey to get your value. In you case just change the your code to ;

if let button1Title = currentQuestionDict.objectForKey("choice1") as? String {
    button1.setTitle("\(button1Title)", forState: UIControlState.Normal)
}
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3

This is the code I used to solve the error:

    let cell:AddFriendTableViewCell = tableView.dequeueReusableCellWithIdentifier("Cell", forIndexPath: indexPath) as! AddFriendTableViewCell

    let itemSelection = items[indexPath.section] as! [AnyObject] //'items' is an array of NSMutableArrays, one array for each section

    cell.label.text = itemSelection[indexPath.row] as? String

Hope this helps!

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