var str_componets = "I Like Swift "

str_componets.componentsSeparatedByString(" ")

这样，str_componets分成了四部分：

["I", "Like", "Swift", ""]

也可以用NSCharacterSet进行分割：

var str_componets = "I would prefer a face-to-face talk with my friends"

str_componets.componentsSeparatedByCharactersInSet(NSCharacterSet(charactersInString: " -"))

这样，str_componets分成了：

["I", "would", "prefer", "a", "face", "to", "face", "talk", "with", "my", "friends"]