Objective C program - throwing an exception

Question

I was testing an app on Xcode and I got this error saying that an exception has been thrown. Using the debugger, I added an exception breakpoint which led me to this:

-(void)viewWillAppear:(BOOL)animated
{
    [super viewWillAppear:animated];

    self.navigationController.delegate = self;

    int index = [[NSUserDefaults standardUserDefaults] integerForKey:@"ChecklistIndex"];
    if (index != -1) {
        Checklist *checklist = [self.dataModel.lists objectAtIndex:index];
        [self performSegueWithIdentifier:@"ShowChecklist" sender:checklist];
    }
}

With this being the highlighted line:

Checklist *checklist = [self.dataModel.lists objectAtIndex:index];

And the debugger said this:

-[__NSArrayM objectAtIndex:]: index 0 beyond bounds for empty array

I'm not too sure how to fix this. If any more information is needed let me know. Thanks.

Uh, what does the error message say???? Did you actually read it?? — Hot Licks
– Hot Licks, Commented Mar 15, 2014 at 22:47
As @HotLicks said, it's pretty self-explanatory. The error is telling you are trying to access index 0 of an empty array, if you attempt an access an index in an array that doesn't exist, you will throw an exception. — Tim
– Tim, Commented Mar 15, 2014 at 22:49
@holex - Try/catch is rarely the answer in Objective-C, especially for this problem. — Hot Licks
– Hot Licks, Commented Mar 16, 2014 at 2:39

Michael Dautermann · Accepted Answer · 2014-03-15 22:49:35Z

1

It looks like your self.dataModel.lists property is empty.

You should look at where you actually set that ".lists" property or "dataModel" property. One of them is not what you think it is.

answered Mar 15, 2014 at 22:49

Michael Dautermann

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1 Comment

WKC Over a year ago

Yep, that sounds right. Turns out because the dataModel property contained no checklists objects in the "lists" array. And this caused the exception. Thanks.

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