ViewController 之间的切换

 1 -(IBAction)btnRegisterClicked:(id)sender
 2 {
 3     if(secondViewController==nil)
 4     {
 5         secondViewController = [[SecondViewController alloc] initWithNibName:nil bundle:nil];
 6     }
 7 
 8     [self.view.superview addSubview:secondViewController.view];
 9     [self.view removeFromSuperview];
10 }