How to set a conditional breakpoint in Xcode based on an object string property?

Question

I'm looking to be able to have the debugger break when it reaches a particular string match. As an example, I might have something like this:

Foo myObj = [self gimmeObj];

myObj might have a property called 'name'. I want the debugger to stop on the assignment when [myObj.name isEqualToString:@"Bar"];

How can I set my conditional breakpoint in Xcode to do that?

Answer 1

I'm not sure if this will work, but you can try setting a breakpoint at that line of code, open up the debugger console (Cmd+Shift+R), and type

condition N (int)[[myObj name] isEqualToString:@"Bar"]

Where N is replaced by the number of the breakpoint (an integer).

Answer 2

If you mutate myObj.name using the setter, you can add a symbolic breakpoint on -[MyObjClass setName:] either from the Debugger Console or from the Run->Manage Breakpoints->Add Symbolic Breakpoint menu in Xcode. If not (why not? you probably shouldn't be modifying the instance variable directly except in the designated initializer or dealloc) you can set a watchpoint in gdb (use the Debugger Console in Xcode once the debugger is running). This page explains how. I don't believe Xcode exposes a UI for setting watchpoints without using the Debugger Console.

Answer 3

You can set a conditional break point it Xcode by setting the breakpoint normally, then control-click on it and select Edit Breakpoint (choose Run -> Show -> Breakpoints).

In the preakpoint entry, there is a Condition column.

Now, there are several issues to keep in mind for the condition. Firstly, gdb does not understand dot syntax, so instead of myObj.name, you must use [myObj name] (unless name is an ivar).

Next, as with most expressions in gdb, you must tell it the type of return result, namely "bool". So set a condition like:

(bool)[[myObj name] isEqualToString:@"Bar"]

Often it is actually easier to just do this in code by temporarily adding code like:

if ( [myObj.name isEqualToString:@"Bar"] ) {
    NSLog( @"here" );
}

and then setting the break point on the NSLog. Then your condition can be arbitrarily complex without having to worry about what gdb can and can't parse.