Swift-navigationcontroller, Proxy pass value

viewcontroller.swift//navigationcontroller//import uikitimport foundationclass ViewController: Uiviewcontroller,fontsizechangdelegate {var mylabel:uilabel?
;//declares an Uilabel object global override Func Viewdidload () {super.viewdidload ()//self.title = "Baidu";                Self.navigationItem.title = "Baidu"; Let Nextitem = Uibarbuttonitem (title: "Next Page", Style:.)        Plain, target:self, Action: "NextPage");                Self.navigationItem.rightBarButtonItem = Nextitem;        Put a label to be able to display text let rect = CGRect (x:0, y:100, width:320, height:44);        MyLabel = UILabel (Frame:rect); mylabel!.        Text = "Welcome to Baidu";               Self.view.addSubview (mylabel!);    Additional setup after loading the view, typically from a nib.        } func NextPage () {NSLog ("button was clicked");                Let svc = Subviewcontroller ();        Set this protocol svc.delegate = self; Self.navigationcontroller?.            Pushviewcontroller (SVC, animated:true); }//Proxy method Func Fontsizedidchange (Controller:subviewcontroller, Fontsize:int) {println ("Controller is\ (Control ler) fontsize:\ (fontsize) ");       Let font = Uifont.systemfontofsize (Float (fontSize));//There is an error mylabel! here.    Font = font; } override func Didreceivememorywarning () {super.didreceivememorywarning ()//Dispose of any resources t    Hat can be recreated. }}

subviewcontroller.swift//Navigationcontroller//import Uikitimport foundation//define a protocol protocol fontsizechangdelegate:nsobjectprotocol{//Define a protocol function/agent for a function//parameter 1 current controller itself//Parameters 2 font size func fontsizedidch Ange (Controller:subviewcontroller,fontsize:int);}    Class Subviewcontroller:uiviewcontroller {var fontsize:int = 20;    Define a Delegate object Var delegate:fontsizechangdelegate?;                Override Func Viewdidload () {super.viewdidload () Self.view.backgroundColor = Uicolor. Whitecolor ();        Self.title = "Page2";        Self.backgroundcolor = Uicolor. Whitecolor ();        Do any additional setup after loading the view. var btn = Uibutton.buttonwithtype (.        System) as UIButton;        var frame = CGRect (x:100, y:100, width:100, height:100);        Btn.frame = frame; Btn.settitle ("Increase font size", forstate:.)        Normal); Btn.addtarget (Self, Action: "ClickMe:", forControlEvents:.        Touchupinside);    Self.view.addSubview (BTN);    }Func ClickMe (Sender:uibutton) {//self.navigationcontroller? 
. poptorootviewcontrolleranimated (True);                fontsize++ println ("FontSize is\ (FontSize)"); if ((delegate)! = nil) {//Call inside the Protocol method delegate?.        Fontsizedidchange (self,fontsize:fontsize); }} override Func Didreceivememorywarning () {super.didreceivememorywarning ()//Dispose of any Resour    Ces that can be recreated. }/*//MARK:-Navigation//In a storyboard-based application, you'll often want to do a little Preparati On before navigation override Func Prepareforsegue (Segue:uistoryboardsegue, sender:anyobject?)
{//Get the new view controller using Segue.destinationviewcontroller.    Pass the selected object to the new view controller. }    */}

Swift-navigationcontroller, Proxy pass value