GCMNavStackMachine is a state machine that's backed by a UINavigationController. The API is inspired by
YBStatechart, but we've tailored it specifically to suit
UINavigationControllers.
A UINavigationController will present a sequence of UIViewControllers but those UIViewControllers shouldn't know too much about their context. That is, they shouldn't know which UIViewControllers are presented before or after. Having that knowledge limits reusability.
A nice pattern is to pull the flow logic into a state machine which is responsible for handling events and transitioning the UINavigationController between sub-UIViewControllers. The sub-UIViewControllers know nothing about the state machine and they can easily be reused in other state machines.
_stackMachine = [[GCMNavStackMachine alloc] initWithNavigationController:navigationController];
MYViewController *vc1 = [[MYViewController alloc] init];
MYViewController *vc2 = [[MYViewController alloc] init];
vc1.delegate = self;
vc2.delegate = self;
[navigationController pushViewController:vc1 animated:YES];
[_stackMachine.onEvent:@"advance" forController:vc1 doBlock:^{
[navigationController pushViewController:vc2 animated:YES];
}];
[_stackMachine.onEvent:@"advance" forController:vc2 doBlock:^(id payload){
[weakSelf save];
[weakSelf.presentingViewController dismissViewControllerAnimated:YES completion:nil];
}];
[_stackMachine.onEvent:@"cancel" doBlock:^(id payload){
[weakSelf cancel];
[weakSelf.presentingViewController dismissViewControllerAnimated:YES completion:nil];
}];
...
#pragma mark - MYViewControllerDelegate
- (void)myViewControllerDidAdvance:(MYViewController *)myVC {
// if we receive this message for vc1, then we should advance to vc2
// if we receive this message for vc2, we should save and commit
// the stack machine will handle those details
[_stackMachine dispatchEvent:@"advance"];
}
- (void)myViewControllerDidCancel:(MYViewController *)myVC {
[_stackMachine dispatchEvent:@"cancel"];
}