Swift实现IOS界面的跳转

iOS开发中界面跳转有两种方式，上下跳转和左右跳转。

下跳转_TO：

let secondViewController = SecondViewController()
self.presentViewController(secondViewController, animated: true, completion: nil)

上跳转_BACK：

dismissViewControllerAnimated(true, completion: nil)

右跳转_TO:

（将新的视图控制器PUSH到navigationController中，相当于入栈操作）

let secondViewController = SecondViewController()
self.navigationController!.pushViewController(secondViewController, animated: true)

左跳转_BACK：

（将当前视图控制器从导航视图控制器堆栈中移除，从而返回到了上一级界面）

( - ) BACK_到上一级:

let firstViewController = FirstViewController()
self.navigationController?.popViewControllerAnimated(true)

( - ) BACK_指定界面：

// 获得视图控制器中的某一视图控制器
let viewController = self.navigationController?.viewControllers[0]
self.navigationController?.popToViewController(viewController as! UIViewController, animated: true)

( - ) BACK_根视图：

self.navigationController?.popToRootViewControllerAnimated(true)

根视图的设置需要在AppDelegate中设置：

var window: UIWindow?
func application(application: UIApplication, didFinishLaunchingWithOptions launchOptions: [NSObject: AnyObject]?) -> Bool
{
    var firstViewController = FirstViewController()
    var rootNavigationViewController = UINavigationController(rootViewController: firstViewController)  

    self.window!.rootViewController = rootNavigationViewController  

    return true
}