CODEWITHSUNDEEP
objective-c
Blake Loizides
Blake Loizides

Reputation: 985

`Unrecognized selector sent to instance`

In my app I have an animation that scrolls across the screen. My problem is that when I use an @selector to call my animation the thread crashes.

If I use the same @selector to call another function in my page it works perfect but when call this function it doesn't seem to work. If I put my code in the viewDidLoad section it works fine.

I tried quite a few of these links for unrecognized selector sent to instance in Stackoverflow but nothing helped. I also tried - (void)imageSpawn instead of - (void) imageSpawn:(id)sender withEvent:(UIEvent *) event and change the selector to (imageSpawn) instead of `(ImageSpawn:) still no luck....

- (void)viewDidLoad {

    [self performSelector:@selector(imageSpawn:) withObject:nil afterDelay:3];
}

- (void) imageSpawn:(id) sender withEvent:(UIEvent *) event
{

    UIImage* image = [UIImage imageNamed:@"ae"];
    UIImageView *rocket = [[UIImageView alloc] initWithImage:image];
    rocket.frame = CGRectMake(-25, 200, 25, 40);
    [UIView animateWithDuration:5 animations:^(){rocket.frame=CGRectMake(345, 200, 25, 40);} completion:^(BOOL finished){if (finished){

           //trigger an event.
           UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Tapped row!"
                                                           message:[NSString stringWithFormat:@"Shot"]
                                                          delegate:nil
                                                 cancelButtonTitle:@"Yes, I did!"
                                                 otherButtonTitles:nil];
           [alert show];
        }
    }];
    [myScrollView addSubview:rocket];
} 



2013-03-28 10:14:31.661 shotplacementgiude001[16897:c07] -[SelectedCellViewController imageSpawn:]: unrecognized selector sent to instance 0xa159480
2013-03-28 10:14:31.663 shotplacementgiude001[16897:c07] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[SelectedCellViewController imageSpawn:]: unrecognized selector sent to instance 0xa159480'
*** First throw call stack:
(0x16b4012 0x13c1e7e 0x173f4bd 0x16a3bbc 0x16a394e 0xdbf5b3 0x1673376 0x1672e06 0x165aa82 0x1659f44 0x1659e1b 0x27157e3 0x2715668 0x305ffc 0x2c3d 0x2b65 0x1) libc++abi.dylib: terminate called throwing an exception
(lldb)

Upvotes: 0

Views: 952

Answers (2)

βhargavḯ
βhargavḯ

Reputation: 9836

- (void)viewDidLoad 
{
     [self performSelector:@selector(imageSpawn:withEvent:) withObject:nil withObject:nil];
}

Your method defination contains two parameter - (void) imageSpawn:(id) sender withEvent:(UIEvent *) event, so you need to call method with two parameters in selector.

NOTE

If you want to pass two object to selector then another method is available that is performSelector:withObject:withObject:

Which Sends a message to the receiver with two objects as arguments.

Example

[self performSelector:@selector(imageSpawn:withEvent:) withObject:senderObject withObject:eventObject];

So ideally you should use above method for two parameter parsing or encapsulate the data you want to send along into some single Objective C object (e.g. a NSArray, a NSDictionary, some custom Objective C type) and then pass it through the[NSObject performSelector:withObject:afterDelay:]

Example

NSDictionary *dictionary = [[NSDictionary alloc] init];
[dictionary setObject:senderObject forKey:@"sender"];
[dictionary setObject:eventObject forKey:@"event"];
[self performSelector:@selector(imageSpawn:withEvent:) withObject:dictionary afterDelay:3.0];

Upvotes: 1

Martin R
Martin R

Reputation: 539745

- (void) imageSpawn:(id) sender withEvent:(UIEvent *) event

is a method with 2 arguments, and its selector is

@selector(imageSpawn:withEvent:)

However,

performSelector:withObject:afterDelay:

must only be used with methods that have zero or one argument. So you can either replace your method by

- (void) imageSpawn:(id) sender

and call

[self performSelector:@selector(imageSpawn:) withObject:nil afterDelay:3];

or use GCD methods:

double delayInSeconds = 3.0;
dispatch_time_t popTime = dispatch_time(DISPATCH_TIME_NOW, (int64_t)(delayInSeconds * NSEC_PER_SEC));
dispatch_after(popTime, dispatch_get_main_queue(), ^(void){
    [self imageSpawn:nil withEvent:nil];
});

The advantage is much better argument and type checking.

Upvotes: 2

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