SIGABRT/Unrecognized Selector - objective-c

Question

My app is essentially a collection of cards, each with various messages/information on it. One swipes to go through these cards, generally swiping right. I am currently getting this sig abrt error:
#import <UIKit/UIKit.h>
#import "AppDelegate.h"
int main(int argc, char * argv[]) {
#autoreleasepool {
return UIApplicationMain(argc, argv, nil, NSStringFromClass([AppDelegate class]));
}
}
It also prints, this:
Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[filterPageViewController askForPushNotifications]: unrecognized selector sent to instance 0x7f8b6d0acd80'
*** First throw call stack:
(
0 CoreFoundation 0x000000010fa92d85 __exceptionPreprocess + 165
1 libobjc.A.dylib 0x000000010f506deb objc_exception_throw + 48
2 CoreFoundation 0x000000010fa9bd3d -[NSObject(NSObject) doesNotRecognizeSelector:] + 205
3 CoreFoundation 0x000000010f9e1cfa ___forwarding___ + 970
4 CoreFoundation 0x000000010f9e18a8 _CF_forwarding_prep_0 + 120
5 Lettuce 0x000000010a2780a6 -[DraggableViewBackground cardSwipedRight:] + 2470
6 Lettuce 0x000000010a2d0ad5 -[DraggableView rightAction] + 453
7 Lettuce 0x000000010a2d02ed -[DraggableView afterSwipeAction] + 77
8 Lettuce 0x000000010a2cfe22 -[DraggableView beingDragged:] + 1922
9 UIKit 0x000000010d9c7b28 _UIGestureRecognizerSendTargetActions + 153
10 UIKit 0x000000010d9c419a _UIGestureRecognizerSendActions + 162
11 UIKit 0x000000010d9c2197 -[UIGestureRecognizer _updateGestureWithEvent:buttonEvent:] + 843
12 UIKit 0x000000010d9ca655 ___UIGestureRecognizerUpdate_block_invoke898 + 79
13 UIKit 0x000000010d9ca4f3 _UIGestureRecognizerRemoveObjectsFromArrayAndApplyBlocks + 342
14 UIKit 0x000000010d9b7e75 _UIGestureRecognizerUpdate + 2634
15 UIKit 0x000000010d54448e -[UIWindow _sendGesturesForEvent:] + 1137
16 UIKit 0x000000010d5456c4 -[UIWindow sendEvent:] + 849
17 UIKit 0x000000010d4f0dc6 -[UIApplication sendEvent:] + 263
18 UIKit 0x000000010d4ca553 _UIApplicationHandleEventQueue + 6660
19 CoreFoundation 0x000000010f9b8301 __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION__ + 17
20 CoreFoundation 0x000000010f9ae22c __CFRunLoopDoSources0 + 556
21 CoreFoundation 0x000000010f9ad6e3 __CFRunLoopRun + 867
22 CoreFoundation 0x000000010f9ad0f8 CFRunLoopRunSpecific + 488
23 GraphicsServices 0x00000001107e2ad2 GSEventRunModal + 161
24 UIKit 0x000000010d4cff09 UIApplicationMain + 171
25 Lettuce 0x000000010a2c3f0f main + 111
26 libdyld.dylib 0x000000011012492d start + 1
27 ??? 0x0000000000000001 0x0 + 1
)
libc++abi.dylib: terminating with uncaught exception of type NSException
(lldb)
After some investigating, I have found the problematic code. It is a line within my cardSwipedRight method that is in my draggableviewbackground class (this class functions as a deck, to hold all of the cards) :
[((settingsTableViewController *)([obj.superNavController.viewControllers[obj.profileNum] viewControllers][0])) askForPushNotifications];
This line of code is within an if statement that checks whether this is a "sign me up for notifications card". What I'm confused by, is why xcode associated filterPageView with askForPushNotifications. Not only does filterPageView not have a askForPushNotifications method, but I don't swipe right on filterPageView nor have I viewed it by the time my app crashes.

Answer 1

One receives an unrecognized selector exception when the object to which the selector is sent does not implement/respond to the sent selector. In simple words, if a class A does not implement a method and someone try to call that method on an object of class A, runtime throws an unrecognized selector exception.
When we are not sure whether an object will respond to a selector, we should have a safety check to see if an object responds to intended selector.
For eg.
if ([*obj* respondsToSelector:#selector(*selector*)])
{
[*obj* performSelector:*selector*];
}

Answer 2

unrecognized selector sent to instance comes up when you try to call a method on an object but that method doesn't exist (The corrrect terminology is that you have tried to send a message called "askForPushNotifications" but the settingsTableViewController does not understand it as it(askForPushNotifications) doesn't exit . I am sure you may not have that method in your settingsTableViewController. Please check and let me know if that helped you.
Also, please check with respondsToSelector if the object actually responds to the method askForPushNotifications. It may be the case that
((settingsTableViewController
*)([obj.superNavController.viewControllers[obj.profileNum] viewControllers][0]))
may not be of type SettingsTableViewController. Please check
if [(((settingsTableViewController *)([obj.superNavController.viewControllers[obj.profileNum] viewControllers][0])) respondsToSelector:#selector(askForPushNotifications)]
{
[((settingsTableViewController *)([obj.superNavController.viewControllers[obj.profileNum] viewControllers][0])) askForPushNotifications];
}