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Fast mutation method sent to an immutable object

I just cannot fool this error, I am trying to add a string to an array as I always do in objective-c, but a quick one gives me a strange error.

var fileArray:NSMutableArray = []

alert.addAction(UIAlertAction(title: "Done", style: UIAlertActionStyle.Default, handler:{ (UIAlertAction)in
            self.fileArray.addObject(self.urlTextField.text)
            self.processURL()
        }))

ERROR:
Application terminated due to uncaught "NSInternalInconsistencyException", reason: '- [__ NSCFArray insertObject: atIndex:]: mutation method posted to immutable object

How fileArray

unchanged? I declare this as MutableArray !!!!!!

EDIT: so the problem is how i populate the array

fileArray = myDict?.valueForKey("fileList") as! NSMutableArray

this solved the problem

fileArray = myDict?.valueForKey("fileList")!.mutableCopy() as! NSMutableArray
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2 answers


An array does not become mutable just because you declare it as such or because you change it with as! NSMutableArray

. An array is only mutable if it is created as a mutable array with [[NSMutableArray alloc] ....]

or by creating a mutableCopy array.



(the same applies to dictionaries, strings, NSSet and NSData)

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Since your array only contains one type, I would recommend using Swift types, this is much easier, var

modified, let

is immutable



var fileArray : Array<String> = []

alert.addAction(UIAlertAction(title: "Done", style: UIAlertActionStyle.Default, handler:{ (UIAlertAction)in
            self.fileArray.append(self.urlTextField.text)
            self.processURL()
        }))
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