Try this:
var myString: String = "hello hi";
var myStringArr = myString.componentsSeparatedByString(" ")
Where myString is the name of your string, and myStringArr contains the components separated by the space.
Then you can get the components as:
var hello: String = myStringArr [0]
var hi: String = myStringArr [1]
Doc: componentsSeparatedByString
EDIT: For Swift 3, the above will be:
var myStringArr = myString.components(separatedBy: " ")
Doc: components(separatedBy:)