Objective-C Protocols Not Sending Message - objective-c

Question

I have read around, and it seems as though delegates would be really useful in my app. Unfortunately, every tutorial about protocols I have tried has failed - the delegate is not receiving the message! It would be great if someone could tell me what I'm doing wrong.
I created a really simple test app with two ViewControllers, a FirstViewController and a SecondViewController. I have set them up in container views to see the effect properly.
My Main.storyboard looks like this:
The purpose of the test app is to change the background colour of the SecondViewController when one of the buttons is pressed in the FirstViewController.
Here is FirstViewController.h:
#import <UIKit/UIKit.h>
#protocol FirstViewControllerDelegate
-(void)colourDidChange:(UIColor *)theColour;
#end
#interface FirstViewController : UIViewController{
UIButton *redButton;
UIButton *blueButton;
}
#property (nonatomic, retain) id <FirstViewControllerDelegate> delegate;
#property (nonatomic, retain) IBOutlet UIButton *redButton;
#property (nonatomic, retain) IBOutlet UIButton *blueButton;
-(IBAction)redPressed;
-(IBAction)bluePressed;
My FirstViewController.m:
#import "FirstViewController.h"
#interface FirstViewController ()
#end
#implementation FirstViewController
#synthesize redButton, blueButton;
#synthesize delegate;
-(IBAction)redPressed{
[self.delegate colourDidChange:[UIColor redColor]];
}
-(IBAction)bluePressed{
[self.delegate colourDidChange:[UIColor blueColor]];
}
-(void)viewDidLoad
{
[super viewDidLoad];
}
I think I have implemented the protocol and the calling of the delegate correctly.
Here is my SecondViewController.h:
#import <UIKit/UIKit.h>
#import "FirstViewController.h"
#interface SecondViewController : UIViewController <FirstViewControllerDelegate>
-(void)colourDidChange:(UIColor *)theColour;
And my SecondViewController.m:
-(void)colourDidChange:(UIColor *)theColour{
self.view.backgroundColor = theColour;
}
-(void)viewDidLoad
{
[super viewDidLoad];
FirstViewController *firstView = [[FirstViewController alloc]init];
firstView.delegate = self;
}
I have breakpointed the project and realised that colourDidChange: in the SecondViewController is never executed.
It would be much appreciated if someone could point out what I have done wrong, whether declaring (or conforming to) the delegate poorly or not setting the delegate the right way.
Many thanks.

Answer 1

I suspect that there are 2 instances of FirstViewController, one created by your storyboard and another one created in SecondViewController's viewDidLoad method.
When theFirstViewController creates SecondViewController it could set the delegate property or use an Outlet to connect them.
Note: delegate properties should not be retain, they should be assign (or weak with ARC).

Answer 2

You are honestly very close. Container views will call the prepareForSegue: method, so you should be initializing the second view controller's delegate in this method:
- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender {
if ([segue.identifier isEqualToString:#"TypeContainerViewSegueNameHere"]) {
SecondViewController *viewController = (SecondViewController *)segue.destinationViewController;
viewController.delegate = self;
}
}
This way you know that you are getting the instance of SecondViewController that will be in use. Also, you do not need to redeclare the delegate method in your SecondViewController.h file:
-(void)colourDidChange:(UIColor *)theColour;
Finally, in storyboard set the title of the container view segue to SecondViewController to whatever title you like and then copy paste that title to where 'TypeContainerViewSegueNameHere' is written above.
EDIT 1:
A typical situation would be similar to this:
#protocol ViewControllerDelegate;
#interface ViewController : UIViewController
#property (nonatomic, strong) id<ViewControllerDelegate>delegate;
#end
#protocol ViewControllerDelegate <NSObject>
- (void) delegateMethod;
#end
...
#implementation ViewController
- (void) buttonAction:(id)sender {
[self.delegate delegateMethod];
}
- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender {
if ([segue.identifier isEqualToString:#"TypeContainerViewSegueNameHere"]) {
SecondViewController *viewController = (SecondViewController *)segue.destinationViewController;
viewController.delegate = self;
}
}
#end
...
#interface SecondViewController : UIViewController <ViewControllerDelegate>
#end
...
#implementation SecondViewController
- (void)delegateMethod {
}
#end
That said, you could make your main view controller the delegate of your FirstViewController, which has the two view containers as seen in your screenschot. And then call a delegate method from the main view controller to the second view controller. Although I am curious as to why you have these two view controllers as child view controllers rather than placing a view and two buttons in one view controller.
EDIT 2:
Here is an example (written quickly and not tested). Think of it as a triangle of delegates:
#protocol FirstViewControllerDelegate;
#interface FirstViewController : UIViewController
#property (nonatomic, strong) id<FirstViewControllerDelegate>delegate;
#end
#protocol FirstViewControllerDelegate <NSObject>
- (void) firstViewControllerDelegateMethod;
#end
...
#implementation FirstViewController
- (void) buttonAction:(id)sender {
[self.delegate firstViewControllerDelegateMethod];
}
#end
...
#protocol MainViewControllerDelegate;
#interface MainViewController : UIViewController <FirstViewControllerDelegate>
#end
#protocol MainViewControllerDelegate <NSObject>
- (void) mainViewControllerDelegateMethod;
#end
...
#implementation MainViewController
- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender {
if ([segue.identifier isEqualToString:#"TypeContainerViewSegueNameHere"]) {
SecondViewController *viewController = (SecondViewController *)segue.destinationViewController;
viewController.delegate = self.delegate;
}
if ([segue.identifier isEqualToString:#"TypeContainerViewSegueNameHere"]) {
FirstViewController *viewController = (FirstViewController *)segue.destinationViewController;
viewController.delegate = self;
}
}
- (void)firstViewControllerDelegateMethod {
[self.delegate mainViewControllerDelegateMethod];
}
#end
...
#interface SecondViewController : UIViewController <MainViewControllerDelegate>
#end
...
#implementation SecondViewController
- (void)mainViewControllerDelegateMethod {
}
#end
Like I said, you should think about reducing the complexity of this section of your app and consider putting all of your views in one view controller.