问题
There's a bug in my app which shows up with the following (partial) stacktrace:
2011-11-25 01:55:59.760 Events2[6650:403] -[Event boolValue]: unrecognized selector sent to instance 0x7fb903928670
To debug this I decided to add a symbolic breakpoint on -[Event boolValue] reasoning that when that selector is sent, the debugger would halt.
However, nothing happens. After setting the breakpoint the app just soldiers on and generates the same exception without halting.
I have defined the breakpoint as follows:
I'm using the LLDB debugger with Xcode 4.2
回答1:
Setting a breakpoint on a selector causes lldb to halt when that selector is executed, not when it is sent. In your case, there is no selector "-[Event boolValue]", therefore this breakpoint will never be hit.
I would set an exception breakpoint on "All Objective-C Exceptions". This will be hit when the "unrecognized selector sent" exception is thrown and you can see where the problem occurs.
回答2:
I was looking for the same answer (symbolic breakpoints) and this link helped: http://www.cocoabuilder.com/archive/cocoa/308967-symbolic-breakpoints.html#308970
You have to follow this pattern (it is also given as a placeholder in Xcode breakpoint editor):
- [name_of_the_class name_of_the_method:]
For example I was looking to see who does set my left bar item and overrides my settings, I used
-[UINavigationItem setLeftBarButtonItem:]
and it worked. Or this one
-[UINavigationController pushViewController:animated:]
回答3:
I would set an Symbolic breakpoint with this symbol -[NSObject doesNotRecognizeSelector:]
which will help us to capture situations where a selector is being invoked against the wrong object.
回答4:
It looks to me like symbolic breakpoints don't work right in LLDB (I'm running the most recent released version of Xcode as of this writing, 4.3.3).
I set a symbolic breakpoint at addAnimation:forKey: in LLDB, and it never gets hit. If I switch my project to GDB, the breakpoint works as expected.
回答5:
Best way to find unrecognized selector call is to create this selector (as category) and put a break point in it.
来源：https://stackoverflow.com/questions/8264193/add-a-symbolic-breakpoint-on-a-selector-in-xcode