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POObjective-C Protocols Not Sending Message
 

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    <p>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.</p> <p>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:</p> <p><img src="https://i.stack.imgur.com/Vf5nf.png" alt="Main.storybord"></p> <p>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.</p> <p>Here is FirstViewController.h:</p> <pre><code>#import &lt;UIKit/UIKit.h&gt; @protocol FirstViewControllerDelegate -(void)colourDidChange:(UIColor *)theColour; @end @interface FirstViewController : UIViewController{ UIButton *redButton; UIButton *blueButton; } @property (nonatomic, retain) id &lt;FirstViewControllerDelegate&gt; delegate; @property (nonatomic, retain) IBOutlet UIButton *redButton; @property (nonatomic, retain) IBOutlet UIButton *blueButton; -(IBAction)redPressed; -(IBAction)bluePressed; </code></pre> <p>My FirstViewController.m:</p> <pre><code>#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]; } </code></pre> <p>I think I have implemented the protocol and the calling of the delegate correctly.</p> <p>Here is my SecondViewController.h:</p> <pre><code>#import &lt;UIKit/UIKit.h&gt; #import "FirstViewController.h" @interface SecondViewController : UIViewController &lt;FirstViewControllerDelegate&gt; -(void)colourDidChange:(UIColor *)theColour; </code></pre> <p>And my SecondViewController.m:</p> <pre><code>-(void)colourDidChange:(UIColor *)theColour{ self.view.backgroundColor = theColour; } -(void)viewDidLoad { [super viewDidLoad]; FirstViewController *firstView = [[FirstViewController alloc]init]; firstView.delegate = self; } </code></pre> <p>I have breakpointed the project and realised that <code>colourDidChange:</code> 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.</p> <p>Many thanks.</p>
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    1. COWhere did you breakpoint? In -colourDidChange:? or in -redPressed/-bluePressed? That may help to determine where things broke down, e.g. if in the actions, perhaps delegate was nil thus why things didn't progress along. I can see a couple errors: 1. delegate properties are a weak property ('weak' or 'assign'), not a retain/strong. Also, IBAction's should have a signature of -(IBAction):foo:(id)sender; your actions lack the 'id' argument.
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    2. COI breakpointed both - when blue/redPressed was called, the self.delegate was 0x0. Setting variables from another class has never worked for me.
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    3. COOK. My guess is you may have 2 FirstViewController instances, especially since the 'firstView' created in your SectionViewController isn't necessarily created in a typical way. Since you're using Storyboards, you could try exposing the delegate as an IBOutlet and hooking it up in the storyboard instead of in -viewDidLoad.
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