how to create a breakpoint's log message action in xcode?

Question

Been watching a WWDC video today about new features in xCode 4. They have mentioned that it a good idea to use log message actions on breakpoints along with "automatically continue after evaluation actions" enabled to output a variable's value for instance instead of using NSLogs all the time.

lets say I have something like that:

NSLog(@"URL is : %@", userDocumentsURL);

How would I write a log message action to display userDocumentsURL's value? Is it really a good idea to use the above method instead of NSLog?

Answer 1

Create a Breakpoint 'Log Message' action. For the log message include something like:

URL is @(char*) [[userDocumentsURL description] UTF8String]@

Alternatively you can create a breakpoint 'Debugger command' action similar to:

po [NSString stringWithFormat:@"URL is: %@", userDocumentsURL]

I prefer using breakpoint actions for logging, as it's arguably easier to clear out a bunch of breakpoints than it is to remove NSLogs. A possible downside to using breakpoints in this fashion is that they are significantly slower (during debugging) than a direct NSLog.

Answer 2

Here is a similar solution using NSLog, which might be fewer characters than the other solutions.

However, unless you add the void like this:

po (void)NSLog(@"the person name is: %@", p.name)

you will get an annoying "nil" printed out with your log. for example:

(lldb) po NSLog(@"foo")
 nil
2013-06-19 14:42:59.025 TheMove[95864:c07] foo

(lldb) po (void)NSLog(@"foo")
2013-06-19 14:43:10.758 TheMove[95864:c07] foo

If you can live with the nil (I can) it's faster to type and easier to remember just the po

Answer 3

I notice that the edit breakpoints feature, while useful and perhaps modern, does not commit to source control, so does not scale to a team of developers. For this reason, I would say that when working on a team under source control to stick with code-based logging such as NSLog.