How do I debug with NSLog(@”Inside of the iPhone Simulator”)?

There’s a far more convenient way to trace with log messages in Xcode, and that’s using Breakpoint Actions.

On the line of code where you’d be tempted to add a printf or NSLog, set a breakpoint, then control-click it and choose “Edit Breakpoint”. In the blue bubble that appears, click the + button on the right to open the Breakpoint Actions:
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Enter your log text there. Any expression that can be printed in the Debugger can be used when delimited by @ signs.

For debugging Objective-C it’s generally more useful to choose “Debugger Command” from the popup and enter ‘po [[object method] method]’ to print the description string of an Objective-C object or the result of a method call.

Make sure to click the “Continue” checkbox at the top right so execution continues after the log.

Advantages of this over NSLog and printf:

  • It’s on the fly. You don’t have to
    recompile and restart to add or edit
    log messages. This saves you a lot of
  • You can selectively enable and
    disable them. If you learn enough
    from one, but its spew is
    interfering, just uncheck its Enabled
  • All the output is generated on your
    Mac, never on the iPhone, so you
    don’t have to download and parse
    through logs after the fact.
  • The chance of shipping console spew
    in your application is significantly

Also check out the Speak button; it’s great for debugging full-screen apps where you can’t see the debug log.

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