添加navbar以及上面的左右按钮代码

UINavigationBar *navBar = [[UINavigationBaralloc] initWithFrame:CGRectMake(0, 0, 824, 44)];

navBar.barStyle = UIBarStyleDefault;

UINavigationItem *navItem = [[UINavigationItemalloc] init];

navItem.leftItemsSupplementBackButton = YES;

navItem.title = @"Add CRA";

UIBarButtonItem *leftButton = [[UIBarButtonItemalloc] initWithTitle:@"Back"

style:UIBarButtonItemStylePlain

target:self

action:@selector(back)];

navItem.leftBarButtonItem = leftButton;

UIBarButtonItem *rightButton = [[UIBarButtonItemalloc] initWithTitle:@"Done"

style:UIBarButtonItemStylePlain

target:self

action:@selector(done)];

navItem.rightBarButtonItem = rightButton;

navBar.items = @[navItem];

[self.view addSubview:navBar];