How to lock text in Facebook share button in swift?

I am trying to implement share button in my spritekit swift game. It works well but I don't know how to lock the text, so user can't change it before posting to facebook. Thanks for any help.

my code looks like this:

    func shareToFacebook() {

    var sharetoface : SLComposeViewController = SLComposeViewController(forServiceType: SLServiceTypeFacebook)
    sharetoface.setInitialText("My score was \(score)")

    let vc: UIViewController = self.view!.window!.rootViewController!
    vc.presentViewController(sharetoface, animated: true, completion: nil)

    }