What name should I use for exception name of NSException, in Objective-C?

Question

I want to use +[NSException exceptionWithName:reason:userInfo:].

But what string should I use for argument Name:?

Should exception name be unique in the project?
Or I can use @"MyException" for all of my exception?

And I don't know what exception name is used for.
Where are exception names used?

Answer 1

You can use the name in in @catch (NSException *theErr).

@catch (NSException *theErr)
{
    tst_name = [theErr name];
    if ([tst_name  isEqualToString:@"name"])
}

what string should I use for argument Name:?

Anything meaningful.

Should exception name be unique in the project?

No.

Or I can use @"MyException" for all of my exception?

Yes, but you should use meaningful names.

- (void)applicationDidFinishLaunching:(NSNotification *)aNotification {
    // Insert code here to initialize your application 
    NSNumber *tst_dividend, *tst_divisor, *tst_quotient;
    // prepare the trap
    @try
    {
        // initialize the following locals
        tst_dividend = [NSNumber numberWithLong:8];
        tst_divisor = [NSNumber numberWithLong:0];

        // attempt a division operation
        tst_quotient = [self divideLong:tst_dividend by:tst_divisor];

        // display the results
        NSLog (@"The answer is: %@", tst_quotient);
    }
    @catch (NSException *theErr)
    {
        // an exception has occured
        // display the results
        NSLog (@"The exception is:\n name: %@\nreason: %@"
               , [theErr name], [theErr reason]);
    }
    @finally
    {
        //...
        // the housekeeping domain
        //...
    }
}

- (NSNumber *)divideLong:(NSNumber *)aDividend by:(NSNumber *)aDivisor
{
    NSException *loc_err;
    long     loc_long;

    // validity check
    loc_long = [aDivisor longValue];
    if (loc_long == 0)
    {
        // create and send an exception signal
        loc_err = [NSException 
                   exceptionWithName:NSInvalidArgumentException
                   reason:@"Division by zero attempted" 
                   userInfo:nil];
        [loc_err raise]; //locate nearest exception handler, 
        //If the instance fails to locate a handler, it goes straight to the default exception handler. 
    }
    else
        // perform the division
        loc_long = [aDividend longValue] / loc_long;

    // return the results
    return ([NSNumber numberWithLong:loc_long]);
}

Take a look at Understanding Exceptions and Handlers in Cocoa

Answer 2

Ultimately, the intent of adding an exception in this way is to detect a problem as soon as possible, report it, and allow diagnosis.

As such, whether you choose an exception name unique to your project, or specific to the problem (i.e. line of source, method) is dependent on which will provide you with the best diagnostic information.

Exception names can be shared across your apps, as they will be reported by app to identify where the exception originated from.