Best practice for pushing a viewController in UINavigationController stack - ios

Question

Sorry if this question was asked prior.
I wanted to know how do we handle navigationController stack like am looking for best practices
for now what i am doing is I check if a viewcontroller is already present and then in the navigation stack and then i pop it back by doing something like this
bool flag = NO;
for(LoginViewController *vc in self.navigationController.viewControllers)
{
if ([vc isKindOfClass:[LoginViewController class]]) {
flag = YES;
}
}
if (flag!=YES ){
LoginViewController *objVC = [[LoginViewController alloc]init];
[self.navigationController pushViewController:objVC animated:YES];
objVC = nil;
}else
{
[self.navigationController popViewControllerAnimated:YES];
}
Do i really need to check if any viewcontroller is already present in the navigation stack prior pushing it or does the navigation controller takes care of it and at sometime removes the viewcontroller which are not in use. Is there a better way to do this or am i already doing the right thing
In short how we can stop a viewcontroller from being pushed into the navigation stack twice.

Answer 1

popViewControllerAnimated will always pop the top most VC on the stack. It operates in LIFO fashion.
LoginViewController may not necessarily be the top most element on the stack hence in order to remove it you have to modify code this way.
LoginViewController *loginVC = nil;
NSUInteger index = [self.navigationController.viewControllers indexOfObjectPassingTest:^BOOL (id obj, NSUInteger idx, BOOL *stop) {
return [obj isKindOfClass:[LoginViewController class]];
}];
if (index != NSNotFound) {
//Found VC on stack
//Get LoginViewController instance
loginVC = [myArray objectAtIndex:index];
NSMutableArray *viewControllers = [NSMutableArray arrayWithArray:self.navigationController.viewControllers];
//Remove LoginViewController obj from stack
[viewControllers removeObjectIdenticalTo:loginVC];
//Reassign new array which does not contain LoginViewController
navigationController.viewControllers = viewControllers;
}
else {
//VC not found on stack
LoginViewController *objVC = [[LoginViewController alloc]init];
[self.navigationController pushViewController:objVC animated:YES];
}
Hope that helps!