objectAtIndex problem

Coolio098 · 09-10-2010, 07:37 PM

Hey all,

For the life of me I cannot figure out what's wrong with my code. I keep getting the following error in the console:

Code:

[Session started at 2010-09-10 20:33:41 -0400.]
2010-09-10 20:33:48.176 SchoolOne[19977:207] arrayPosition = 0
2010-09-10 20:33:53.021 SchoolOne[19977:207] @
2010-09-10 20:33:53.022 SchoolOne[19977:207] -[__NSArrayI insertObject:atIndex:]: unrecognized selector sent to instance 0x5d543b0
2010-09-10 20:33:53.024 SchoolOne[19977:207] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[__NSArrayI insertObject:atIndex:]: unrecognized selector sent to instance 0x5d543b0'
*** Call stack at first throw:

And it's coming from this code:

Code:

- (IBAction)courseNameConfirm:(id)sender {

	
	for (int i = 0; i < 100; i++) {
		id object1 = [courseData objectAtIndex:arrayPosition];
		if ([[object1 objectAtIndex:i] isEqualToString:@""]) {
			NSLog(@"@", [object1 objectAtIndex:i]);
			[object1 insertObject:[NSArray arrayWithObject:courseNameField.text] atIndex:i];
			break;
		}
	}
	
	[self.tableView reloadData];
	
	
	[gradeSummaryNavigation dismissModalViewControllerAnimated:YES];
}

Now I know arrayPosition returns a value and so does the NSLog ( 0 and @ respectively) which means that the code is correct up until:

Code:

[object1 insertObject:[NSArray arrayWithObject:courseNameField.text] atIndex:i];

any idea?

Duncan C · 09-10-2010, 07:40 PM

Quote:

Originally Posted by Coolio098

Hey all,

For the life of me I cannot figure out what's wrong with my code. I keep getting the following error in the console:

Code:

[Session started at 2010-09-10 20:33:41 -0400.]
2010-09-10 20:33:48.176 SchoolOne[19977:207] arrayPosition = 0
2010-09-10 20:33:53.021 SchoolOne[19977:207] @
2010-09-10 20:33:53.022 SchoolOne[19977:207] -[__NSArrayI insertObject:atIndex:]: unrecognized selector sent to instance 0x5d543b0
2010-09-10 20:33:53.024 SchoolOne[19977:207] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[__NSArrayI insertObject:atIndex:]: unrecognized selector sent to instance 0x5d543b0'
*** Call stack at first throw:

And it's coming from this code:

Code:

- (IBAction)courseNameConfirm:(id)sender {

	
	for (int i = 0; i < 100; i++) {
		id object1 = [courseData objectAtIndex:arrayPosition];
		if ([[object1 objectAtIndex:i] isEqualToString:@""]) {
			NSLog(@"@", [object1 objectAtIndex:i]);
			[object1 insertObject:[NSArray arrayWithObject:courseNameField.text] atIndex:i];
			break;
		}
	}
	
	[self.tableView reloadData];
	
	
	[gradeSummaryNavigation dismissModalViewControllerAnimated:YES];
}

Now I know arrayPosition returns a value and so does the NSLog ( 0 and @ respectively) which means that the code is correct up until:

Code:

[object1 insertObject:[NSArray arrayWithObject:courseNameField.text] atIndex:i];

any idea?

object1 is probably an NSArray instead of an NSMutableArray. NSArrays have fixed contents and can't be changed (mutated) after they are created. NSMutableArray is the variant that supports methods like insertObject:atIndex:

Coolio098 · 09-10-2010, 07:43 PM

Hmmm I have object1 = [courseData objectAtIndex:arrayPosition]; where courseData is a NSMutableArray.

Duncan C · 09-10-2010, 07:51 PM

Quote:

Originally Posted by Coolio098

Hmmm I have object1 = [courseData objectAtIndex:arrayPosition]; where courseData is a NSMutableArray.

CourseData may be a mutable array, but it is an array of arrays, and the innermost arrays appear to be immutable. Add an NSLog statement to your code right before you try to add an object:

NSLog(@"object1 = %@", object1);

That should show the type of the array as well as it's contents. note that NSArray is a "class cluster" where the actual type of array you get is usually different than what you ask for. You should still be able to tell if it is a mutable or immutable variant.

Coolio098 · 09-10-2010, 08:09 PM

I figured out the issue. When I was assigning objects at the beginning of my code i used NSArray not NSMutable array. Thank you Duncan. Now I have a new problem though. The console gives me this error:

Code:

[Session started at 2010-09-10 21:01:50 -0400.]
2010-09-10 21:01:57.222 SchoolOne[20232:207] arrayPosition = 0
2010-09-10 21:02:00.178 SchoolOne[20232:207] @
2010-09-10 21:02:00.180 SchoolOne[20232:207] -[__NSArrayI isEqualToString:]: unrecognized selector sent to instance 0x5903d10
2010-09-10 21:02:00.182 SchoolOne[20232:207] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[__NSArrayI isEqualToString:]: unrecognized selector sent to instance 0x5903d10'
*** Call stack at first throw:

and its occuring in the same place.

Coolio098 · 09-10-2010, 08:14 PM

Never mind i'm an idiot lol. I figured it out. Thanks for the help Duncan!

Duncan C · 09-10-2010, 08:14 PM

Quote:

Originally Posted by Coolio098

I figured out the issue. When I was assigning objects at the beginning of my code i used NSArray not NSMutable array. Thank you Duncan. Now I have a new problem though. The console gives me this error:

Code:

[Session started at 2010-09-10 21:01:50 -0400.]
2010-09-10 21:01:57.222 SchoolOne[20232:207] arrayPosition = 0
2010-09-10 21:02:00.178 SchoolOne[20232:207] @
2010-09-10 21:02:00.180 SchoolOne[20232:207] -[__NSArrayI isEqualToString:]: unrecognized selector sent to instance 0x5903d10
2010-09-10 21:02:00.182 SchoolOne[20232:207] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[__NSArrayI isEqualToString:]: unrecognized selector sent to instance 0x5903d10'
*** Call stack at first throw:

and its occuring in the same place.

Once again, use the debugger or an NSLog statement. It sounds like the object(s) you're trying to compare with isEqualToString is an array, not a string. Set a breakpoint just before that method call and examine the variable. Or, add an NSLog statement that displays the object, as outlined in my previous post.

Note that if you add a breakpoint, you can display the contents of variables in the console without having to resort to NSLog statements.

Use "PO" (short for print_object) to display an object. Use "p" (print) to display a scalar quantity.

musicwind95 · 09-10-2010, 08:26 PM

So apparently I'm not the only one who'd appreciate compiler warnings about a non-mutable object...

Duncan C · 09-10-2010, 09:12 PM

Quote:

Originally Posted by musicwind95

So apparently I'm not the only one who'd appreciate compiler warnings about a non-mutable object...

This is a runtime problem, not a compiler problem.

An object you get from a container object like an array is of type id (pointer of unknown type), so the compiler can't tell if it responds to a particular message.

If you want to make your code completely bulletproof you should put class checking code after extracting an object from an array, dictionary, or set.

If you create an NSArray variable directly, then the compiler WILL warn you if you try to add an object to it.

This code will generate a compiler warning:

Code:

NSArray* fooArray = [NSArray arrayWithObject: @"xxx"];
[fooArray addObject: @"woof"];

This code will not generate a warning, because fooArray is declared as a mutable type.

Code:

NSMutableArray* fooArray = [NSMutableArray arrayWithCapacity: 1];
[fooArray addObject: @"woof"];