NSArray index 1 beyond bounds for empty array

Question

-(IBAction)someMethod:(UIStepper *)sender{
    int x=sender.value; //This is an integer from 0-8;
    NSLog(@"%f",sender.value);
    NSArray *rpmValues = [[NSArray alloc]initWithObjects:@"a",@"b",@"c",@"d",@"e",@"f",@"g",@"h",@"i", nil];
    if (x<=[rpmValues count]) {

        myLabel.text = [rpmValues objectAtIndex:x];
    }
    NSLog(@"%i",[rpmValues count]);
}

Above is my code, what I want to do is to change UILabel display by changing UIStepper. This is very straight forward. But when I change press the stepper value, it crashes:

*** Terminating app due to uncaught exception 'NSRangeException', reason: '*** -   [__NSArrayM objectAtIndex:]: index 1 beyond bounds for empty array'
*** First throw call stack:

And the [rpmValue count] is 9. I really got confused. Can anyone help me?

Other than the if statement needing to use < and not <=, this code looks OK. Are you 100% sure the error is coming from this code and not some other place? — rmaddy
– rmaddy, Commented Nov 6, 2012 at 22:42
Setting int x manually to 1 seems to work for me, can you try this? Your NSLog statement is wrong, what does NSLog(@"%d",sender.value); print? Something else must be causing the problem. — WDUK
– WDUK, Commented Nov 6, 2012 at 22:42
The problem is when x = [rpmValues count]. Getting an object at that index does not work as index starts from 0. — jajo87
– jajo87, Commented Nov 6, 2012 at 22:43
You shouldn't be able to get this error message from the code you posted -- I tried it out and it worked fine up until the last item which can be fixed like the comments have said. So, I believe your error is elsewhere. — rdelmar
– rdelmar, Commented Nov 6, 2012 at 23:00
Also, your error is pointing to a mutable array, and rpmValues is immutable. You should add an exception breakpoint to your project, so the line where the error occurs will be highlighted. — rdelmar
– rdelmar, Commented Nov 6, 2012 at 23:15

WDUK · Accepted Answer · 2012-11-06 22:43:40Z

4

That code seems fine (see my comment on the question); your problem could arise from the use of

if (x<=[rpmValues count]) {

This will include the count of the array, which exceeds the index range by one. Use

if (x < [rpmValues count]) {

answered Nov 6, 2012 at 22:43

WDUK

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Tommy · Accepted Answer · 2012-11-06 22:43:54Z

0

At the very least if (x<=[rpmValues count]) should be if (x<[rpmValues count]). Otherwise if you have an array with, say, two entities then you're allowing yourself to access indices 0, 1 and 2 — three possibilities in total.

Is it possible you've set a maximumValue on your stepper of '9' based on similar logic?

answered Nov 6, 2012 at 22:43

Tommy

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