FBOpenGraphAction runtime error in Swift

问题

I am trying to create a Facebook custom story in my iOS App. I am developing the app in Swift.

var graphObject: NSMutableDictionary = FBGraphObject.openGraphObjectForPostWithType(
    "app: type",
    title: "new", 
    image: nil,
    url: nil, 
    description: "description"
)

        (I am getting a runtime error on the following line)
        **var graphAction: FBOpenGraphAction = FBGraphObject.graphObject() as FBOpenGraphAction**


graphAction.setObject(UIImage(named: "default"), forKey: "image")
graphAction.setObject(graphObject, forKey: "break")

Am i doing something wrong while declaring the FBOpenGraphAction? Any help would be appreciated.

Thanks

来源：https://stackoverflow.com/questions/25055801/fbopengraphaction-runtime-error-in-swift