The xcode debugger (debugger) cannot locate the exception and throw points.

Xcode debugger (debugger) cannot locate the exception throw point
This book has mentioned multiple times: "When an application throws an exception, the debugger will executeCodeStop at the exception throw point ". In the current version of ios sdk,
During application debugging, xcode's debugger may not stop the Execution Code at the exception throw point. If you encounter such problems, refer to the following solutions.
Select the breakpoint navigation Panel (command + 6 ).
Click the + button in the lower left corner of the Panel. In the new pop-up menu, select the first item "add exception breakpoint ...".

In the new window, do not make any changes. Click the done button.

Thanks http://www.iosprogrammingbook.com/