从'（）'转换为不相关的类型'String'总是失败

Question

I'm trying to step through an [AnyObject] array from a completion block and cast the items as Strings so that I can then put them in a tableView. However, when I try to append the individual values of the array I get this error: Cast from '()' to unrelated type 'String' always fails . Here is the code:

client.historyForChannel(ids, start: nil, end: nil, withCompletion: { (result, status) -> Void in

    if status == nil {
        if result!.data.messages.count > 0 {
            let historyMessages = result!.data.messages as? [String]
            for value in historyMessages!{
                self.messagesArray.append(value) as? String //error
            }
        }
    }
})

If it helps, I'm using PubNub to create/store messages in my Swift app.

Thanks!

Answer 1

When you wrote

self.messagesArray.append(value) as? String

you probably meant

self.messagesArray.append(value as? String)

although

self.messagesArray.append(value)

should suffice because historyMessages is already of type [String]! .

The error is saying that you are casting the result of self.messagesArray.append(value) (which is Void because append does not return anything) to String , which does always fail.

As an aside, your code uses way more exclamation points than it should. You should be using guard-let to make sure your variables are non-nil.