Xcode中TextView控件如何自动滚动到最后一条swift

• swift

    @IBOutletweakvar showInfo: UITextView! 
     //将字符串的值赋予到textview里面
    ShowInfo!.text = ShowInfo!.text+"\n"+str
     //读取textview的range
    let nsra:NSRange = NSMakeRange((ShowInfo!.text.lengthOfBytes(using: String.Encoding.utf8))-1, 1)   
     //将textview滚动到最后一栏。
    ShowInfo!.scrollRangeToVisible(nsra)