swift -NavigationController,代理传值

//
//  ViewController.swift
//  NavigationController
//

import UIKit
import Foundation

class ViewController: UIViewController,FontSizeChangDelegate {

    var  myLabel :UILabel?

;//声明一个UILabel对象 全局的
    override func viewDidLoad() {
        super.viewDidLoad()
        //self.title = "百度";
        self.navigationItem.title = "百度";

        let nextItem = UIBarButtonItem(title: "下一页", style: .Plain, target: self, action: "nextPage");
        self.navigationItem.rightBarButtonItem = nextItem;

        //放一个Label能够显示文字
        let rect = CGRect(x: 0, y: 100, width: 320, height: 44);
        myLabel = UILabel(frame: rect);
        myLabel!.text = "欢迎来到百度";
        self.view.addSubview(myLabel!);

        // Do any additional setup after loading the view, typically from a nib.
    }

    func nextPage(){
        NSLog("按钮被点击了");
        let svc = SubViewController();

        //设置这个协议

        svc.delegate = self;
        self.navigationController?.pushViewController(svc, animated: true);

    }
//  代理方法
    func fontSizeDidChange(controller: SubViewController, fontSize: Int) {
        println("controller is\(controller) fontsize:\(fontSize)");
        let font = UIFont.systemFontOfSize(Float(fontSize));//这里有错误
        myLabel!.font = font;
    }
    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }

}

//
//  SubViewController.swift
//  NavigationController
//

import UIKit
import Foundation
//定义一个协议

protocol FontSizeChangDelegate:NSObjectProtocol{
    //定义的一个协议函数/代理的一个函数
    //參数1 当前controller本身
    //參数2 字体大小
    func fontSizeDidChange(controller:SubViewController,fontSize:Int);
}

class SubViewController: UIViewController {
    var fontSize:Int = 20;
    //定义一个delegate对象
    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("增大字体大小", 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)
        {
            //调用里面的协议方法
            delegate?.fontSizeDidChange(self,fontSize:fontSize);
        }
    }
    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }

    /*
    // MARK: - Navigation

    // In a storyboard-based application, you will often want to do a little preparation 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.
    }
    */

}