It is possible to use an existing ViewController with PerformSegueWithIdentifier? - objective-c

Question

I use the method performSegueWithIdentifier:sender: to open a new ViewController from a storyboard-file programmatically. This works like a charm.
But on every time when this method is being called, a new ViewController would be created. Is it possible to use the existing ViewController, if it exista? I don't find anything about this issue (apple-doc, Stack Overflow, ...).
The Problem is:
On the created ViewController the user set some form-Elements and if the ViewController would be called again, the form-elements has the initial settings :(
Any help would be appreciated.
Edit:
I appreciate the many responses. Meanwhile, I'm not familiar with the project and can not check your answers.

Answer 1

Use shouldPerforSegueWithIdentifier to either allow the segue to perform or to cancel the segue and manually add your ViewController. Retain a pointer in the prepareForSegue.
... header
#property (strong, nonatomic) MyViewController *myVC;
... implementation
-(BOOL) shouldPerformSegueWithIdentifier:(NSString *)identifier sender:(id)sender{
if([identifier isEqualToString:#"MySegueIdentifier"]){
if(self.myVC){
// push on the viewController
[self.navigationController pushViewController:self.myVC animated:YES];
// cancel segue
return NO;
}
}
// allow the segue to perform
return YES;
}
-(void) prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender
{
if([segue.identifier isEqualToString:#"MySegueIdentifier"]){
// this will only be called the first time the segue fires for this identifier
// retian a pointer to the view controller
self.myVC = segue.destinationViewController;
}
}

Answer 2

To reuse an existing UIViewController instance with a segue create the segue from scratch and provide your own (existing) destination (UIViewController). Do not forget to call prepareForSegue: if needed.
For example:
UIStoryboardSegue* aSegue = [[UIStoryboardSegue alloc] initWithIdentifier:#"yourSegueIdentifier" source:self destination:self.existingViewController]
[self prepareForSegue:aSegue sender:self];
[aSegue perform];

Answer 3

Following code makes singleton view controller.
Add them to your destination view controller implementation, then segue will reuse the same vc.
static id s_singleton = nil;
+ (id) alloc {
if(s_singleton != nil)
return s_singleton;
return [super alloc];
}
- (id) initWithCoder:(NSCoder *)aDecoder {
if(s_singleton != nil)
return s_singleton;
self = [super initWithCoder:aDecoder];
if(self) {
s_singleton = self;
}
return self;
}

Answer 4

I faced this problem today and what I have done is to create the view controller manually and store it's reference.
Then every time I need the controller, check first if exists.
Something like this:
MyController *controller = [storedControllers valueForKey:#"controllerName"];
if (!controller)
{
controller = [[UIStoryboard storyboardWithName:#"MainStoryboard_iPhone" bundle:NULL] instantiateViewControllerWithIdentifier:#"MyControllerIdentifierOnTheStoryboard"];
[storedControllers setValue:controller forKey:#"controllerName"];
}
[self.navigationController pushViewController:controller animated:YES];
Hope it helps.

Answer 5

Create a property for the controller.
#property (nonatomic, weak) MyController controller;
And use some kind of lazy initialization in performSegueWithIdentifier:sender
if (self.controller == nil)
{
self.controller = [MyController alloc] init]
...
}
In this case, if controller was already created, it will be reused.

Answer 6

Firstly you would be going against Apple's design in Using Segues: "A segue always presents a new view controller".
To understand why it might help to know that what a segue does is create a new view controller and then the perform calls either showViewController or showDetailViewController depending on what kind of segue it is. So if you have an existing view controller just call those methods! e.g.
- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath{
Event *object = [self.fetchedResultsController objectAtIndexPath:indexPath];
self.detailViewController.detailItem = object;
[self showDetailViewController:self.detailViewController.navigationController sender:self];
}

Answer 7

You would need to make the Viewcontroller into a singleton class.