Variable getting released between calls

Question

I am developing a tweak for iOS using Logos/Theos.

I need to store the last two characters the user has typed in at all times.

My code for this is:

static NSString *lastTwoChars = [[NSString alloc] init];
...
if (lastTwoChars.length < 2) {
    lastTwoChars = [lastTwoChars stringByAppendingString:text];
} else {
    lastTwoChars = [lastTwoChars stringByAppendingString:text];
    lastTwoChars = [lastTwoChars substringFromIndex:1];
}
...

(In this scope, text is the last character they entered in the keyboard)

This code works fine, until I press a third character. After a very long time of trial and error, I found that it is because the variable lastTwoChars is getting released, and becoming a different object.

I cannot figure out how to keep the object from being deallocated and changing to another object. I've tried to retain the variable, but either I'm doing it wrong, or that won't work.

Any help would be greatly appreciated.

The methods you are using do, indeed, return a new `NSString` object. Are you using ARC or MRC? — Droppy, Aug 08 '16 at 19:46
@Droppy Whatever the default is. I never configured it to be different. — Campbell Cole, Aug 08 '16 at 19:54

Campbell Cole · Answer 1 · 2016-08-11T22:54:58.820

-1

Alright. I finally figured it out. Thanks to Droppy for hinting at the problem.

I fixed it by retaining the new strings:

if (lastTwoChars.length < 2) {
    lastTwoChars = [[lastTwoChars stringByAppendingString:text] retain];
} else {
    lastTwoChars = [[lastTwoChars stringByAppendingString:text] retain];
    lastTwoChars = [[lastTwoChars substringFromIndex:1] retain];
}

I didn't know that stringByAppendingString and substringFromIndex were creating new NSString objects, so thanks again to Droppy.

EDIT: I thought this may be a memory leak, but Droppy confirmed it was.

This is my new code:

if (lastTwoChars.length < 2)
{
    lastTwoChars[lastTwoChars.length] = (unichar) text;
}
else
{
    lastTwoChars[0] = lastTwoChars[1];
    lastTwoChars[1] = (unichar) text;
}

edited Aug 11 '16 at 22:54

answered Aug 08 '16 at 23:20

Campbell Cole

37
1
9

1

So now you've got a memory leak... If you always want the last 2 characters then why not use `static unichar lastTwoChars[2];`? – Droppy Aug 09 '16 at 06:05
@Droppy I didn't think of that, thanks. I edited the answer. Does that look about right? – Campbell Cole Aug 11 '16 at 22:57
1

No, not at all. You need `[text characterAtIndex:index]`, where you need to calculate `index`. – Droppy Aug 12 '16 at 06:03
@Droppy I ended up figuring that out earlier. It works now. Thanks for the help. – Campbell Cole Aug 13 '16 at 07:34

Variable getting released between calls

1 Answers1