Swift UI学习之基础：UIButton,UILabel and UISlider

//  http://blog.csdn.net/woaifen3344/article/details/29840275    
//  RootViewController.swift  
//  UIDemos  
//  
//  Created by sixiaobo on 14-6-10.  
//  Copyright (c) 2014年 com.huangyibiao. All rights reserved.  
//  
  
import Foundation  
import UIKit  
  
class RootViewController : UIViewController, UIAlertViewDelegate {  
    var _label: UILabel? // optional type, must type var  
      
    func originX() -> CGFloat {  
        let version: String = UIDevice.currentDevice().systemVersion  
        return version >= "7.0" ? 64.0 : 0.0  
    }  
          
    //  
    // 重载需要使用关键字override  
    override func viewDidLoad() {  
        super.viewDidLoad() // 先调用父类的  
       
        //  
        // @name create button  
        println(self.originX())  
        let button = UIButton(frame: CGRectMake(30, self.originX() + 30, 100, 30))  
        button.setTitle("button", forState:UIControlState.Normal)  
        button.backgroundColor = UIColor.blackColor()  
        button.setTitleColor(UIColor.whiteColor(), forState:.Normal)  
        // add an action  
        button.addTarget(self, action: "onButtonClick:", forControlEvents: UIControlEvents.TouchUpInside)  
        self.view.addSubview(button)  
        // @} end create button  
          
        //  
        // @name create label  
        _label = UILabel(frame: CGRectMake(30, self.originX() + 70, 100, 60))  
        _label!.text = "label"  
        _label!.backgroundColor = UIColor.clearColor()  
        _label!.textColor = UIColor.redColor()  
        // use NSTextAlignment  
        _label!.textAlignment = NSTextAlignment.Center  
        self.view.addSubview(_label!)  
        // @} end create label  
          
        //  
        // @name create UISlider  
        let slider = UISlider(frame: CGRectMake(30, self.originX() + 130, 60, 30))  
        slider.addTarget(self, action: "clickSlider:", forControlEvents: .ValueChanged)  
        slider.minimumValue = 17.0  
        slider.maximumValue = 36.0  
        self.view.addSubview(slider)  
        // @} end create UISlider  
    }  
      
    func onButtonClick(sender: UIButton!) {  
       // UIAlertController.showAlert(self, title: "title", message: "message")  
       // UIAlertController.showAlert(self, title: "title", message: "message", cancelButtonTitle: "cancel", okButtonTitle: "ok")  
        UIAlertController.showAlert(self, title: "title", message: "message", cancelButtonTitle: "cancel", okButtonTitle: "ok", okHandler: {  
            (UIAlertAction) in  
            println("no nothing")  
        })  
    }  
      
    func alertView(alertView: UIAlertView!, clickedButtonAtIndex buttonIndex: Int) {  
        println("clicked button at index: \(buttonIndex)")  
    }  
      
    func clickSlider(sender: UISlider!) {  
        _label!.font = UIFont.systemFontOfSize(sender.value)  
    }  
}