AnyObject to Array?

To cast your data to an array:

var twDataArray = (twData as! NSArray) as Array

The code above first casts twData to an NSArray, and then to an Array via a bridging cast. A bridging cast is a special type of cast which converts an Objective-C type to it's _ObjectiveCBridgeable conformant, Swift counterpart.

(Note that I didn't need to write Array<AnyObject> because the element AnyObject is inferred in the bridging cast from NSArray → Array)

Note that the cast above is a forced downcast. Only use this if you're absolutely sure that twData is going to be an instance of NSArray. Otherwise, use an optional cast.

var twDataArray = (twData as? NSArray) as Array?

Try the following, you can iterate through the array as given below.

for element in twData as! Array<AnyObject> {    print(element)}

This works in a playground:

var data: Array<Dictionary<String,String>>? = twData as? Array<Dictionary<String, String>>

the difference from your code is that twData does not require the ? at the end - it is an optional so the as? operator will take care of verifying that it can be case to an array of dictionaries - needless to say, if it's nil, as? will evaluate to nil