从Appdelegate触发ViewController中的委托方法

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.

Answer 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.

Answer 2

Use:

[[UIApplication sharedApplication].testDelegate = self;

instead of all that:

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

Answer 3

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"];
    }
});

Answer 4

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