- (void)presentViewController:(UIViewController *)viewControllerToPresent animated:(BOOL)flag completion:(void (^)(void))completion

MainVC *mainVC = [[MainVC alloc] init];[self presentViewController:mainVC animated:YES completion:nil];

这种方式一般出现在需要使用者完成某件事情，如输入密码、增加资料等操作后，才能(回到跳转前的控制器)继续。例如系统的WIFI连接输入密码提示。默认动画是从下至上。

 

- (void)pushViewController:(UIViewController *)viewController animated:(BOOL)animated

这种方式一般是使用者浏览资料，继而可以前进到下一个页面或回到上一个页面。默认动画是从右至左。

 

- (void)addChildViewController:(UIViewController *)childController

这个方法出现在iOS5以后，通过它即使不使用NavigationController也能够实现view hierarchy。有以下优点：

1.页面逻辑很清晰，相应的View对应相应的ViewController。

2.当某个子View没有显示时，将不会被Load，减少了内存的使用。

3.当内存紧张时，没有Load的View将被首先释放，优化了程序的内存释放机制。

#import "ViewController.h"#import "FirstVC.h"#import "SecondVC.h"#import "ThirdVC.h"@interface ViewController (){    FirstVC *firstVC;    SecondVC *secondVC;    ThirdVC *thirdVC;}@property (weak, nonatomic) IBOutlet UIView *contentView;@property (strong, nonatomic) UIViewController *currentVC;@end@implementation ViewController- (void)viewDidLoad {    [super viewDidLoad];    // Do any additional setup after loading the view, typically from a nib.        firstVC = [[FirstVC alloc] init];    secondVC = [[SecondVC alloc] init];    thirdVC = [[ThirdVC alloc] init];        [self addChildViewController:firstVC];    [self addChildViewController:secondVC];    [self addChildViewController:thirdVC];        [self.contentView addSubview:thirdVC.view];        self.currentVC = thirdVC;}- (IBAction)onClick:(id)sender {    if(self.currentVC==firstVC && [sender tag]==1) {        return;    }        if(self.currentVC==secondVC && [sender tag]==2) {        return;    }        if(self.currentVC==thirdVC && [sender tag]==3) {        return;    }        UIViewController *oldVC = self.currentVC;        switch ([sender tag]) {        case 1: {            [self transitionFromViewController:self.currentVC toViewController:firstVC duration:1 options:UIViewAnimationOptionTransitionCurlUp animations:^{                            } completion:^(BOOL finished) {                if(finished) {                    self.currentVC = firstVC;                }                else {                    self.currentVC = oldVC;                }            }];        }        break;        case 2: {            [self transitionFromViewController:self.currentVC toViewController:secondVC duration:1 options:UIViewAnimationOptionTransitionCurlUp animations:^{                            } completion:^(BOOL finished) {                if(finished) {                    self.currentVC = secondVC;                }                else {                    self.currentVC = oldVC;                }            }];        }        break;        case 3: {            [self transitionFromViewController:self.currentVC toViewController:thirdVC duration:1 options:UIViewAnimationOptionTransitionCurlUp animations:^{                            } completion:^(BOOL finished) {                if(finished) {                    self.currentVC = thirdVC;                }                else {                    self.currentVC = oldVC;                }            }];        }        break;        default:            break;    }}- (void)didReceiveMemoryWarning {    [super didReceiveMemoryWarning];    // Dispose of any resources that can be recreated.}@end