Is it possible to stop on a breakpoint in an instance of an object?

I've tried creating a breakpoint within a class definition, stopping on the message sent to an object instance, hoping it would 开发者_Go百科then jump to the class code and allow me to walk through line by line and see the values of the local variables.

However, I'm going to venture out and say "no, this should not be possible", as there could be multiple instances of the class in memory. If someone could give a better explanation, that would be grand.

(As a side note, my alternative is excessive NSLogging of the runtime data.)

Yes, it is possible! You can add a condition to a breakpoint:

http://d.pr/yZVB+ http://d.pr/pWOB+

The program will only pause at this breakpoint when the condition is satisfied. You could choose a condition such as self == _myGlobalInstanceOfInterest.

If you don't want to store the instance in a variable, you might, for example, start the breakpoint without a condition — and then when you figure out which instance you want as the program is running, use p myObject to get the address, and then just set the condition to use the that address (such as self == 0x8badf00d).

I take it you want to break upon a message being sent to a particular instance?

Read the Xcode documentation on breakpoints and watchpoints. Basically, you can set a condition on a breakpoint so that it will automatically continue if self isn't the instance you're interested in.

Assuming you're talking about something like this:

- (void)eatAPieceOfFruit: (NSFruit *)fruit {
    NSString * fruitType = [fruit species];
    BOOL hasSeeds = [fruit hasSeeds];

    NSInteger deliciousnessRating = [self enjoymentOfFruitType: fruitType];
    NSString * reactionToEating = [self phraseForFruitType: fruitType];

    // Breakpoint set here

}

The debugger has access to and knows the name of any variable that's in scope -- any variable that you would be able to use in the actual code at the line where you broke, you can also get to via the debugger. So, at the debugger prompt, type:

po reactionToEating

(that's "po" for "print object"), or the name of any other local variable to see what it is. If you want to call a method on an object that's in scope you can do so:

print (int)[reactionToEating length]
po [reactionToEating capitalizedString]