NSArray element failed to match the Swift Array

Please show your code. Generally that happens when you cast `Any` (which is `id` in Objective-C) to Swift collection types,

such as `as? [[String: Any]]` or something like that. Without your code, we cannot answer to What should I do?.

Consider this code:

let d = NSDictionary()
let n = NSNull()
let a = NSArray(array: [d, n])
let s = a as! [NSDictionary]
print(s)

It fails on line 4 with the exact the error you’re seeing. The various Objective-C collection types (

NSArray

,

NSDictionary

, and so on) accept any type of elements. In contrast, the equivalent Swift types require that all elements be of one specific type. If you cast the former to the latter, Swift checks the types of the elements to prevent bogus data entering the Swift realm.

In my example, the

NSArray

contains elements of two different types,

NSDictionary

and

NSNull

, and the latter causes Swift to trap.

The best way to avoid this is not work with heterogeneous collections in the first place. If you can’t fix that, you’ll have to unpack the heterogeneous collection very carefully. For example, this code will convert the

NSArray

to a Swift array of optional dictionaries, mapping

NSNull

to

nil

:

let s = a.map { e -> NSDictionary? in
    switch e {
    case is NSNull: return nil
    case let d as NSDictionary: return d
    default: fatalError()
    }
}

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