How to use delegate between two ViewController without StoryBoard? - ios

Question

I'd like to trigger a message from viewController to another viewController.
And I coded like below, but viewController didn't call delegate.
I want to call delegate without stroyboard. I just want to send a message to another viewController.
viewController2.h
#protocol ViewController2Delegate;
#interface ViewController2 : UIViewController
#property (nonatomic, weak) id<ViewController2Delegate> delegate;
#end
#protocol ViewController2Delegate <NSObject>
- (void)showSomethingByDelegate;
#end
viewController2.m
#import "ViewController2.h"
#interface ViewController2 ()
#end
#implementation ViewController2
- (void)viewDidLoad {
[super viewDidLoad];
// Do any additional setup after loading the view.
}
- (IBAction)buttonPressed:(id)sender {
[self.delegate showSomethingByDelegate];
}
#end
viewController.m
#import "ViewController.h"
#import "ViewController2.h"
#interface ViewController ()
<ViewController2Delegate>
#end
#implementation ViewController
- (void)viewDidLoad {
[super viewDidLoad];
ViewController2 *vc2 = [[ViewController2 alloc] init];
vc2.delegate = self;
}
// Below method was not called by delegate.
- (void)showSomethingByDelegate {
NSLog(#"Button Was Pressed!!!");
}
#end

Answer 1

well let me show an example more simple.
File: firstVC.h
/* This define the protocol object,
you can write methods required or optional the diference is when
the protocol is used in a class, xcode show you a yellow warning with required methods
like UITableViewDelegate, UITextFieldDelegate... */
#protocol firstVCDelegate <NSObject>
#required
- (void)didMessageFromOtherViewController: (NSString *)messageStr;
#optional
- (void)didOtherMessageNotRequired: (NSString *)messageStr;
#end
/* This is the definition of first UIViewController */
#interface firstViewController : UIViewController
#end
/* This is the definition of second UIViewController object with
a property that is our protocol 'firstVCDelegate' */
#interface secondViewController : UIViewController
#property (nonatomic, weak) id <firstVCDelegate> firstVCDelegate;
- (void)executeDelegateProcess;
#end
File: firstVC.m
#import "firstVC.h"
#pragma mark - First UIViewController with delegate
#interface firstViewController() <firstVCDelegate>
#end
#implementation firstViewController
- (void)viewDidLoad
{
[super viewDidLoad];
// Creating the 'secondViewController' object with delegate on this class
secondViewController *svc = [secondViewController new];
// Assign the delegate class
[svc setFirstVCDelegate: self];
// Run the delegate logic
[svc executeDelegateProcess];
}
- (void)didMessageFromOtherViewController:(NSString *)messageStr
{
// Receiving the message from the instance of our protocol in the 'secondViewController' class
NSLog(#"MESSAGE #1: %#", messageStr);
}
- (void)didOtherMessageNotRequired:(NSString *)messageStr
{
// Receiving the message in optional method
NSLog(#"MESSAGE #2: %#", messageStr);
}
#end
#pragma mark - Second UIViewController
#implementation secondViewController
- (void)viewDidLoad
{
[super viewDidLoad];
}
- (void)setFirstVCDelegate:(id<firstVCDelegate>)firstVCDelegate
{
if (firstVCDelegate)
_firstVCDelegate = firstVCDelegate;
}
- (void)executeDelegateProcess
{
// This method is only for demo
// You can execute your delegate in the way you need to use
if (_firstVCDelegate) {
[_firstVCDelegate didMessageFromOtherViewController: #"Hello world, using the required method from secondViewController class"];
[_firstVCDelegate didOtherMessageNotRequired: #"Hello code using the optional method"];
}
}
#end
In your appDelegate.m in the method didFinishLaunchingWithOptions you can put this, and you need to #import "firstVC.h"
self.window = [[UIWindow alloc] initWithFrame: [[UIScreen mainScreen] bounds]];
self.window.autoresizesSubviews = YES;
[self.window makeKeyAndVisible];
[_window setRootViewController: [firstViewController new]];
Execute and see two logs messages, I hope I've helped :)

Answer 2

ViewController2 *vc2 = [[ViewController2 alloc] init];
This line of code is not doing what you think it is, this is creating a NEW instance of ViewController2 and storing it inside the variable vc2. At no point (based on your code) is this variable added to the navigation stack and displayed on screen.
Edit
Also as noticed by Holex, your vc2 variable will be removed from memory after the viewDidLoad is finished as you are not holding onto a reference of it. You would either need to create a property to hold onto it, or push it onto the navigation stack for the navigationController to hold onto it.
There are multiple ways to solve this issue:
Instead of creating a new viewController2, find a reference to the one already displayed on the screen (if it is on the screen).
If its not on the navigation stack, add vc2 to the navigation stack [self.navigationController pushViewController:vc2 animated:YES]; (assuming you have a navigation controller).
If not on the stack, and not intending to use a navigationController, present vc2 modally, such as [self presentViewController:vc2 animated:YES completion:nil];