返回按钮实现

import UIKit  
  
class NextViewController: UIViewController {  
  
    var label = UILabel()  
    var labelContent = " "  
    var button = UIButton()  
    override func viewDidLoad() {  
        super.viewDidLoad()
        //创建一个按钮，尺寸，标题，背景色，目标方法
        button.frame = CGRectMake(20, 80, 50, 50)  
        button.setTitle("Back", forState: UIControlState.Normal)  
        button.backgroundColor = UIColor.blackColor()  
        button.addTarget(self, action: "backPressed:", forControlEvents: UIControlEvents.TouchUpInside)  //TouchUpInside指离开按钮触发动作；TouchDown指按下触发，不管是否离开。
        self.view.addSubview(button)  
        // Do any additional setup after loading the view.  
    }  
  
    override func didReceiveMemoryWarning() {  
        super.didReceiveMemoryWarning()  
        // Dispose of any resources that can be recreated.  
    }  
      
    func backPressed(sender: AnyObject){  
        //返回上一个视图  
        dismissViewControllerAnimated(true, completion: nil)  //撤回之前的视图的方法
    }