How to i pass Data in a 2 tabbed-Application? - ios

Question

I have an application i am making but here is the problem which i been spedning hours figuring out.
I have a Tab-Based app, The first tab has a UILabel Object which should display an NSString from the SecondViewController.m which has a Method:
-(IBAction) save: (id) sender{
// This String holds data from the secondViewController's textfield to be passed to the
// UILabel whch is on the firsViewController.m
NSString *data = self.addDataTextfield.text;
}
I have used many methods including Singletons but they dont work as i have read somewhere that singletons are meant to pass data from Parent to child and child cant send data to the parent controller in this case BUT the Only way would be to use Protocols which i am but i am kind of lost using this method. Here is what i have on my secondViewController.h
#import <UIKit/UIKit.h>
#import "singletonObj.h"
#import "AppDelegate.h"
// Using a Protocol to pass data Back to the parent view
#protocol passStringDelegate <NSObject>
-(void) enteredString: (NSString *)string;
#end
#interface SecondViewController : UIViewController <UITextFieldDelegate>
{
singletonObj *object; // This singleton isnt being used, Just there incase
}
#property (strong, nonatomic)IBOutlet UITextField*addDataTextField;
- (IBAction)Save:(id)sender;
#property (retain) id <passStringDelegate> delegate;
#end
SO my Question is, is there any way i cando this and pass data from this secondViewController using #protocol or at least can anyone show me how to Use NSNotificationCenter within this code to pass data ? i dont feel comftarble using the AppDelegate class to pass data as it seems to go against apple's way or prepareforSegue which doesnt work for me.
I been searching around but most i find do the data being sent from the parent to the child but i dont see Tabbed based examples where the ChildViewController can send an NSString to the ParentViewController to display that data on an UILAbel.

Answer 1

There are several ways to do this. From any of the tab bar controller's content controllers, you can access another of the controllers with something like self.tabBarController.viewControllers[0]. This will reference the controller in the first tab. So, if you want to pass a string back to the first controller from the second, create a string property in the first controller (say, passedInString), and in the second controller, have something like this:
FirstViewController *first = self.tabBarController.viewControllers[0];
first.passedInString = self.stringToPass;

Answer 2

Ok #user2994008, in a UITabBarController app setup, I would not use a delegation pattern at forces coupling between the child view controllers in some manner. Posting a notification will get the job done, the only problem is what should trigger the notification to be posted. In this case, a quick and dirty way is to just post the notification in viewWillDisapper: as that will get called when the user switches tabs.
SecondViewController.m
//SecondViewController.m
//this is the view with the UITextField in it
#import "SecondViewController.h
#implementation SecondViewController
- (void)viewWillDisappear:(BOOL)animated {
[super viewWillDisappear:animated];
NSLog(#"%s", __FUNCTION__);
//since this gets called when the user switches tabs, i'll post the
//notification from this method
//retrieve our text field's text and store it in a dictionary
NSDictionary *dict = #{"text":self.addDataTextField.text};
//add the dictionary as userInfo: and post notification
[[NSNotificationCenter defaultCenter] postNotificationName:#"myAwesomeNotification" object:nil userInfo:dict];
}
//all other second view controller methods here
#end
FirstViewController.m
//FirstViewController.m
#import "FirstViewController.h"
#implementation FirstViewController
-(void)viewDidLoad {
[super viewDidLoad];
//add an observer for the notification and tell it what method to call when it gets the notification
[[NSNotificationCenter defaultCenter] addObserver:self
selector:#selector(actionTriggeredByNotification:) name:#"myAwesomeNotification" object:nil];
}
- (void)actionTriggeredByNotification:(NSNotification*)notification {
NSLog(#"%s", __FUNCTION__);
NSDictionary *userInfo = [notification userInfo];
NSString *data = userInfo[#"text"];
NSLog(#"Text data is: %#", data);
}
- (void)dealloc {
//be sure to remove observer
[[NSNotificationCenter defaultCenter] removeObserver:self];
//if using ARC, don't call super dealloc
}
//all other first view controller methods
#end
Also, drop the singleton stuff trying to pass data that way. That gets into trying to create what are in essence global variables and you don't really want that for passing simple strings around.
And while using notifications work ok here, some other solutions could be implemented using key-value observing (KVO) or adhering to the UITextFieldDelegate protocol and sending a message from one of those delegate methods. Even so, all these techniques still open up questions about when you actually want to retrieve the textfield's text.
Once you get your bearings, I'd HIGHLY recommend looking into ReactiveCocoa. It's a library designed specifically for solving problems like yours.