Pass index back to parent view controller - objective-c

Question

The NSMutableArray detailsDataSource and int detailIndex is passed on to next View Controller from
MainDetailViewController.m:
#import "UsersDetailViewController.h"
...
- (void)swipeDetectedUp:(UISwipeGestureRecognizer *)sender
{
UsersDetailViewController *usersController = [[self storyboard] instantiateViewControllerWithIdentifier:#"UsersController"];
[self.navigationController pushViewController:usersController animated:NO];
usersController.usersDataSource = [[NSMutableArray alloc] initWithArray:detailsDataSource];
usersController.userDetailIndex = detailIndex;
}
Swipe through the index in UserDetailViewController.m:
- (void)swipeDetectedRight:(UISwipeGestureRecognizer *)sender
{
if (userDetailIndex != 0)
userDetailIndex--;
}
When swipeDetectedDown to pop back, MainDataViewController needs to know which object at index to display:
- (void)swipeDetectedDown:(UISwipeGestureRecognizer *)sender
{
//jump to correct object at index, same as current object at index in this view
[self.navigationController popViewControllerAnimated:NO];
}
Code suggestions?

Answer 1

Use NSNotificationCenter to send an object back to the MainDataViewController...
Example:
In UsersDetailViewController populate an NSDictionary with a key=>value pair then send it over to where you want it to go.
NSArray *key = [NSArray arrayWithObject:#"myIndex"];
NSArray *object = [NSArray arrayWithObject:detailIndex];
NSDictionary *dictionary = [NSDictionary dictionaryWithObjects:object forKeys:key];
[[NSNotificationCenter defaultCenter] postNotificationName:#"MainDataViewController" object:self userInfo:dictionary];
Note: You need to setup an identifier on MainDataViewController called MainDataViewController or whatever you want to call it. Using the VC name keeps it simpler.
Then on MainDataViewController do this in the viewDidLoad() method.
[[NSNotificationCenter defaultCenter] addObserver:self selector:#selector(receiveNotification:) name:#"MainDataViewController" object:nil];
And then receive the notification by using the following method:
- (void)receiveNotification:(NSNotification *) notification
{
if([[notification name] isEqualToString:#"MainDataViewController"])
{
NSDictionary *dictionary = [NSDictionary dictionaryWithDictionary:[notification userInfo]];
if([dictionary valueForKey:#"myIndex"])
{
// do whatever you need to do with the passed object here. In your case grab the detailIndex and use it for something...
}
}
}

Answer 2

The easy part is to put the UsersDetailViewController pointer into a property of MainDetailViewController so it can access self.usersController.usersDataSource & self.usersController.userDetailIndex later. Then the only trick is to have it know when the UsersDetailViewController was popped.
In code I used to write, I often tried something like making MainDetailViewController be a delegate of UsersDetailViewController, and having a delegate method in MainDetailViewController be called when the UsersDetailViewController want to close programmatically, and in that do both the popViewControllerAnimated: and update the MainDetailViewController's state. In other words, always have the parent's code pop the child off. This works, but not in the case where you have the child view controller pop automatically via the navigation controller's back button say, so overall I'd argue against that technique.
I think there's better solutions for having the parent's code get called when its child is popped. Perhaps implement a viewWillAppear method and if self.usersController is set there, then you know you're coming back from the UsersDetailViewController, at that point access the other controller's properties and finally clear self.usersController.