Passing data back from child view controller

Question

I am a beginner, and I have a project in which I need to pass data back from a childviewcontroller. Specifically, I have a picker view in my container and I want to be able to use it to select an option (say to simplify just a color to chose from an array of ten colours). Then I would like to be able to access the chosen color in my parent view controller and do something with it. I have researched this for a couple of days now and the closest answer to what I am looking for I found in a related question on S.O. Here it is:

"Regarding passing value to the containerView controller, you can make a property in the ChildViewController of the value you want it to be passed. Then in your ParentViewController do something like the following:

self.ChildViewController.yourProperty = yourValue

The opposite can be done in 4 ways:

You can make a delegate protocol to communicate the data between your controllers.

You can post a notification in your ChildViewController and add the parent controller as an observer.

You can use KVO.

And the easiest way out, you can make a property in your parentviewController and access it like the following:"

((YourParentViewControllerClassType *)self.parentViewController).yourParentProperty = TheValueYouWant;

Now, I would like to try the fourth option first as delegation, kvo and so on are options I have read about but not ready to tackle yet. What I would need help with is the last option.

Say I had a property in my child view controller where I store the chosen color. Something like:

@interface ViewController ()

@property NSString *ChosenColorInChildVC;

@end

And then, later on:

self.ChosenColorInChildVC = [self pickerView:myPickerView titleForRow:[myPickerView selectedRowInComponent:1] forComponent:1]];

how would I pass that value using the proposed:

((YourParentViewControllerClassType *)self.parentViewController).yourParentProperty = TheValueYouWant;

Can someone dumb it down a little further for me? Thanks

Answer 1

I'm going to explain you with an example how delegation works.

Edit your ChildViewController.h like this:

@protocol ChildViewControllerDelegate; 

@interface ChildViewController : UIViewController

@property (weak)id <ChildViewControllerDelegate> delegate;

@end

@protocol ChildViewControllerDelegate <NSObject > 

- (void) passValue:(UIColor *) theValue;

@end

On your ChildViewController.m when you want to pass something back to the ParentViewController , do like this:

 - (void) myMethod
 {
   [delegate passValue:[UIColor redColor]]; // you pass the value here
 }

On your ParentViewController.h

#import "ChildViewController.h"

@interface ParentViewController : UIViewController <ChildViewControllerDelegate >  // you adopt the protocol
{
}

On your ParentViewController.m:

- (void) passValue:(UIColor *) theValue
   {
      //here you receive the color passed from ChildViewController
   }

Now be careful. Everything will work only if you set the delegate. So when you declare ChildViewController inside your ParentViewController class, do like this:

ChildViewController * controller = [[ChildViewController alloc]initWithiNibName:@"ChildViewController"];
controller.delegate = self; //without this line the code won't work!

Answer 2

@metronic is right; use delegation.

Also typically you will include the sender in your delegate methods:

-(void) childViewController:(ChildViewController*)viewController passValue:(UIColor*) theValue 

Answer 3

Noted: this is very important.

Write protocol declaration code above the #import lines e.g.

@protocol -----

@end

import ----

@interface classname ---