Triggering delegate method in ViewController from Appdelegate

Question

I'm trying to use the AppDelegate to trigger a delegate method in the viewcontroller via and NSTimer. So in the AppDelegate, I basically have:

AppDelegate.h

@protocol TestDelegate <NSObject>

-(void)testFunction:(NSString *)testString;

@end

@interface AppDelegate : UIResponder <UIApplicationDelegate>
@property (strong, nonatomic) id<TestDelegate> testDelegate;
...
@end

AppDelegate.m

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{

    [self.window makeKeyAndVisible];


    self.timer = [NSTimer scheduledTimerWithTimeInterval:10.0
                                                  target:self
                                                selector:@selector(trigger:)
                                                userInfo:nil
                                                 repeats:YES];
    return YES;
}

-(void)trigger:(id)sender {
   [self.testDelegate testFunction:self];
}

In my view controller I have:

ViewController.h

@interface ViewController : UIViewController <TestDelegate>
    @property (nonatomic, strong) AppDelegate *appDelegate;
@end

ViewController.m

@implementation ViewController
   ...
   -(void)viewDidLoad {
       self.appDelegate = [[UIApplication sharedApplication] delegate];
       self.appDelegate.testDelegate = self;
   }

   -(void)testfunction:(NSString *)testString {
       NSLog(@"%@", testString);
   }
@end

when I load the ViewController in my app, nothing happens? I know the NSTimer is successfully firing, but the delegate method isn't being triggered.

in my appdelegate.h, I have @property (strong, nonatomic) id<TestDelegate> testDelegate; — Allen
– Allen, Commented Jan 17, 2014 at 13:25
Whenever you can - you create ViewController and assign it as delegate — Grzegorz Krukowski
– Grzegorz Krukowski, Commented Jan 17, 2014 at 13:33

Abizern · Accepted Answer · 2014-01-17 13:59:07Z

1

your function declaration is:

-(void)testFunction:(NSString *)testString;

But you call it as:

[self.testDelegate testFunction:self];

so you are sending self to a parameter that is expecting a pointer to an NSString, which is obviously incorrect.

Also, rather than using a timer, I'd use GCD like so:

double delayInSeconds = 10.0;
dispatch_time_t popTime = dispatch_time(DISPATCH_TIME_NOW, (int64_t)(delayInSeconds * NSEC_PER_SEC));

dispatch_after(popTime, dispatch_get_main_queue(), ^(void){
    if [self.testDelegate respondsToSelector:@selector(testFunction:)] {
        [self.testDelegate testFunction:@"Test String"];
    }
});

edited Jan 17, 2014 at 13:59

answered Jan 17, 2014 at 13:53

Abizern

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5 Comments

Allen Over a year ago

thanks for the answer, just curious because i haven't gotten a concise answer, but why GCD over NSTimer? What are the drawbacks of using NSTimer?

ahwulf Over a year ago

THe other question is why did the original code compile since there is a protocol defined?

Abizern Over a year ago

I prefer using a GCD in this case because I'm only firing it once. This way I don't have another property to hold the timer, And I don't have to set up all the code to create the timer either. Also, consider the case where you want the timer to do one thing. You don't need to write a method as the callback, you can write the code in the block, so you can see straight away what the timer will run.

ahwulf Over a year ago

I saw that, but if there is a defined protocol id<TestDelegate> the compiler should have noticed you sending self to testFunction expecting an NSString

Abizern Over a year ago

Maybe it did. Not everyone pays attention to warnings, though. Although I highly recommend building with 0 warnings - what are we, Windows programmers?

Grzegorz Krukowski · Accepted Answer · 2014-01-17 13:36:42Z

1

Use:

[[UIApplication sharedApplication].testDelegate = self;

instead of all that:

self.appDelegate = [[UIApplication sharedApplication] delegate];
self.appDelegate.testDelegate = self;

answered Jan 17, 2014 at 13:36

Grzegorz Krukowski

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Comments

tanz · Accepted Answer · 2014-01-17 13:39:43Z

1

Where do you assign your VC as delegate? Is it your VC assigning itself during initialisation/view did load? If you're not doing that I would assign it in ViewDidLoad.

- (void)viewDidLoad
{
     [super viewDidLoad];
     [[UIApplication sharedApplication]delegate].testDelegate = self;
}

Also you would probably want to set the property in AppDelegate weak instead of strong to avoid retaining the VC when/if it is dismissed.

edited Jan 17, 2014 at 13:39

answered Jan 17, 2014 at 13:32

tanz

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2 Comments

Allen Over a year ago

I just added this to viewcontroller viewdidload, but it still doesn't work for some reason?

Grzegorz Krukowski Over a year ago

that should be a question acctually

Retro · Accepted Answer · 2014-01-17 13:28:40Z

0

check like

if(!testDelegate) {
   [self.testDelegate testFunction:self];
}

and if your controller is in your navigation controller then loop through and find your controller alive object and assign delegate.

But I would recommended this kinda functionality using LocalNotification

answered Jan 17, 2014 at 13:28

Retro

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