How to set symbolic breakpoints to identify when an object is registered/unregistered to NSNotificationCenter

SymbolicBreakpoints

-[NSNotificationCenter addObserver:selector:name:object:]
and

-[NSNotificationCenter addObserverForName:object:queue:usingBlock:]
With the condition:

(BOOL)[@"fractionCompleted" isEqualToString:(id)$r8]
and

(BOOL)[@"fractionCompleted" isEqualToString:(id)$rdx]
Then set an action as a Debugger Command:

po $rdx
and

po $rcx
If you're curious about why the registers change, that is because OS X follows the System V ABI for register calling conventions. Arguments for a method go into:

rdi, rsi, rdx, rcx, r8, r9
In that argument order. Because Objective-C messages get compiled into objc_msgsend(receiver, selectorname, argument1, argument2, argument3, argument4)

Informal Protocol KVO symbols:

-[NSObject(NSKeyValueObserverRegistration) addObserver:forKeyPath:options:context:]
-[NSObject(NSKeyValueObserverRegistration) removeObserver:forKeyPath:context:]

Checking type of class of a pointer in register:

(BOOL)[(id)$rdi isKindOfClass:(Class)[EditorImageView class]]