CODEWITHSUNDEEP
ioscocoa-touch
Andrew
Andrew

Reputation: 8563

How to return a nil CGFloat?

I'd like to return nil to tableView:heightForFooterInSection: but that's not allowed. Is there a way to return nil as a CGFloat?

Why are you doing this?
I'm testing how a tableView will behave with a mix of Titles and Views as sectionFooters. For one footer I need to use a custom view, but for another footer I have 3 or 4 sentences of text and I like how the system styles it and sizes the footer to fit. But as soon as I implement heightForFooterInSection (which is required by viewForFooterInSection), the footer with the title no longer auto-resizes to fit the given text. I'm trying to avoid building a custom view for the straight text.

Upvotes: 5

Views: 5441

Answers (4)

Duck
Duck

Reputation: 35963

I am late for the party but this may be useful to someone.

Like others said, you cannot return nil to primitives but you can do one of two things, to differentiate a non-set value from a set one.

  1. Use NSNotFound

    - (CGFloat)calculateHeight {
   // calculate height...

   if (heightInvalid) return NSNotFound;
   else return validFloatValue;

}

NSNotFound is a huge number defined by Apple and used by them on some operations. Then you can check for that, like:

if ([self calculateHeight] == NSNotFound) ...
  1. Use NSNumber

Instead of returning a CGFloat make your function return a NSNumber.

      - (NSNumber *)calculateHeight {
         // calculate height...

         if (heightInvalid) return nil;
         else return @(validFloatValue);

      }

Then, you can return nil.

When receiving the value you do:

NSNumber *myHeightNumber = [self calculateHeight];
if (!myHeightNumber) NSLog(@"height is invalid... do something");
else myHeight = [myHeightNumber floatValue];

I hope that helps.

Upvotes: 1

Monolo
Monolo

Reputation: 18253

As mentioned by others, there is no such thing as a nil for floats.

However, the Department of Ugly Hacks brings you: The NaN - "NaN" being a special reserved value of the float bit pattern representing "Not a Number".

No clue what a UITableView will make of a NaN, but in other situations it can be a way to specify that a float variable does not have a value.

If you won't tell anyone where you got the idea, here is the code:

CGFloat myNan = nanf(NULL);

Upvotes: 3

Janardan Yri
Janardan Yri

Reputation: 751

Short answer: no.

Long answer: 'nil' is a pointer to nothing, used in place of a pointer to an object. CGFloat is a scalar datatype, not an Objective-C class, and is not generally used with pointers (or it would be CGFloat *).

Upvotes: 2

Lily Ballard
Lily Ballard

Reputation: 185691

There's no such thing as nil for primitive values. You could try returning 0.0f, but I don't know how UITableView responds to that. It may just hide the view entirely. Presumably if you want to return a custom view for one footer, you need to return a custom view for all footers.

Upvotes: 7

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