NavigationBar alpha value changed automatically after dismissing view controller - objective-c

Question

Weird thing
navigationbar'alpha value changes after dismissing view controller
Step
Click button that presents a new viewcontroller
Set navigation bar alpha to 0.0 when the button is clicked
Dismiss viewcontroller which I presented right before.
Result [NG]
navigationbar'alpha value is set to 1.0
Expected result
navigationbar's alpha should be 0.0 as expected
Below sample is pretty much easy
ViewController class
- (void)viewWillAppear:(BOOL)animated {
NSLog(#"%s : %f", __func__, self.navigationController.navigationBar.alpha);
}
- (void)viewDidAppear:(BOOL)animated {
NSLog(#"%s : %f", __func__, self.navigationController.navigationBar.alpha);
}
- (void)viewWillDisappear:(BOOL)animated {
NSLog(#"%s : %f", __func__, self.navigationController.navigationBar.alpha);
}
- (void)viewDidLoad {
[super viewDidLoad];
self.navigationController.navigationBar.backgroundColor = [UIColor orangeColor];
self.view.backgroundColor = [UIColor whiteColor];
UIButton *clickMe = [[UIButton alloc] initWithFrame:CGRectMake(100, 100, 100, 30)];
[clickMe setTitle:#"clickme" forState:UIControlStateNormal];
[clickMe setTitleColor:[UIColor blackColor] forState:UIControlStateNormal];
[clickMe addTarget:self action:#selector(btnClicked) forControlEvents:UIControlEventTouchUpInside];
[self.view addSubview:clickMe];
}
- (void)btnClicked {
self.navigationController.navigationBar.alpha = 0.0f;
second *sec = [[second alloc] init];
[self presentViewController:sec animated:YES completion:nil];
}
second class
- (void)viewDidLoad {
[super viewDidLoad];
// Do any additional setup after loading the view, typically from a nib.
self.navigationController.navigationBar.backgroundColor = [UIColor orangeColor];
self.view.backgroundColor = [UIColor yellowColor];
UIButton *getBack = [[UIButton alloc] initWithFrame:CGRectMake(100, 100, 100, 40)];
[getBack setTitle:#"getBack" forState:UIControlStateNormal];
[getBack setTitleColor:[UIColor blackColor] forState:UIControlStateNormal];
[getBack addTarget:self action:#selector(btnClicked) forControlEvents:UIControlEventTouchUpInside];
[self.view addSubview:getBack];
}
- (void)btnClicked {
[self dismissViewControllerAnimated:YES completion:nil];
}
I really would like to know what happened in this..
If someone knows this, let me know.. Thank you in advance.