Logicsaurus Rex Logicsaurus Rex - 2 months ago 12
iOS Question

NSUInteger oddities with for loops

I use AppCode to tweak the code I've written in XCode. AppCode does awesome code inspections, and tells you where things can be improved.

One of the frequent inspections I come across points out that

[SomeObjCFrameworkClass objectAtIndex]
is expecting an
NSUInteger
which is in fact true...

- (ObjectType)objectAtIndex:(NSUInteger)index


however, I keep finding myself getting screwed by trying to follow this advice and change my
int
s to
NSUInteger
s.

For example, here's one piece of code that exploded when I did this change...

-(void)removeBadge
{
if ([[theButton subviews] count]>0)
{
NSUInteger initalValue = [[theButton subviews] count]-1;
//Get reference to the subview, and if it's a badge, remove it from it's parent (the button)
for (NSUInteger i=initalValue; i>=0; i--) {

if ([[[theButton subviews] objectAtIndex:i] isMemberOfClass:[MKNumberBadgeView class]])
{
[[[theButton subviews] objectAtIndex:i] removeFromSuperview];
[theButton setTitleColor:[UIColor lightTextColor] forState:UIControlStateNormal];
}
}
}
}


Any idea why this is happening.
There is a clue in the debug data pictured below, but I can't make sense of it.

enter image description here

Answer

NSUInteger in unsigned, so i>=0 condition in your for loop always evaluates to YES. After i reach 0, on next iteration you will get integer underflow, and i becomes NSUIntegerMax.

Updated: As far as I can tell from your code, there is no reason in processing subviews in reverse order. So, you can simply do

for (NSUInteger i=0; i<theButton.subviews.count; i++)

Otherwise, you can use something like

if (0 == i) {
    break;
}

inside your loop or use do/while for example.

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