@interface RootViewController (){    UIView *view1;    UIView *view2;    int    flag;}@end@implementation RootViewController- (void)viewDidLoad{    [super viewDidLoad];    flag = 1;        UIButton *button = [[UIButton alloc]initWithFrame:CGRectMake(130, 65, 50, 35)];    [button setTitle:@"点击" forState:UIControlStateNormal];    [button setTitleColor:[UIColor greenColor] forState:UIControlStateNormal];    [button addTarget:self action:@selector(click) forControlEvents:UIControlEventTouchUpInside];    [self.view addSubview:button];        view1 = [[UIView alloc]initWithFrame:CGRectMake(0, 100, 320, 480)];    view1.backgroundColor = [UIColor grayColor];        view2 = [[UIView alloc]initWithFrame:CGRectMake(0, 100, 320, 480)];    view2.backgroundColor = [UIColor orangeColor];}- (void)click{        [UIView beginAnimations:nil context:nil];    [UIView setAnimationDuration:0.6f];    [UIView setAnimationTransition:UIViewAnimationTransitionFlipFromLeft forView:self.view cache:NO];        if (flag == 1) {                [self.view addSubview:view1];        flag = 2;            }else if(flag == 2){                [self.view addSubview:view2];        flag = 1;    }    [UIView commitAnimations];}