Syntax to check if NSInteger is nil or not? - objective-c

Question

The following is returning an error because evidently I cannot compare an NSInteger or int to nil. Can anyone suggest syntax to do this
NSInteger *lastID = [[NSUserDefaults standardUserDefaults] integerForKey:#"lastID"]==nil ? #1 : [[NSUserDefaults standardUserDefaults] integerForKey:#"lastID"];

Answer 1

NSInteger lastID = [[NSUserDefaults standardUserDefaults] integerForKey:#"lastID"] == 0 ? 1 : [[NSUserDefaults standardUserDefaults] integerForKey:#"lastID"];
NSInteger is a primitive type. nil is for objects. 0 check, checks is your userDefaults' integer value assigned a value. If it didn't assigned, it returns 0.

Answer 2

NSInteger is a primitive type, not an object. I'm quite sure that an NSInteger* is not what you want, but an NSInteger. integerForKey returns an NSInteger, not an NSInteger*.

Answer 3

NSInteger is a primitive, not an NSObject, so any hypothetical comparison to nil would effectively be comparing to numeric zero.
Since you are using the ternary operator to assign lastID to the boxed NSNumber #1 if the result would be nil, then it seems what you want to do is store an NSNumber in the defaults, use objectForKey: to retrieve it, and use integerValue on the retrieved NSNumber to get the primitive value.
If you do indeed want to store primitives, that's fine, but you'll need to change your logic to not expect nil, which is only pertinent to sublcasses of NSObject, basically.
UPDATE: an example app.
#import <Foundation/Foundation.h>
enum {
MyIdTypeUnrecognized = 0,
MyIdTypeInvalid = 1
} myIdType;
int main(int argc, char *argv[]) {
#autoreleasepool {
NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];
NSString *key = #"lastID";
NSInteger lastID = -100;
[defaults removeObjectForKey:key];
NSLog(#"Case 1: should find 0, and set lastID to 1.");
lastID = [defaults integerForKey:key];
lastID = (lastID == MyIdTypeUnrecognized) ? MyIdTypeInvalid : lastID;
NSLog(#"--- lastID:%ld", lastID);
NSLog(#"Case 2: Set lastID to 2, then try to fetch.");
lastID = -100;
[defaults setInteger:2 forKey:key];
[defaults synchronize];
lastID = [defaults integerForKey:key];
lastID = (lastID == MyIdTypeUnrecognized) ? MyIdTypeInvalid : lastID;
NSLog(#"--- lastID:%ld", lastID);
}
}
//2015-09-04 10:04:38.075 nsnotfound[66983:5231434] Case 1: should find 0, and set lastID to 1.
//2015-09-04 10:04:38.076 nsnotfound[66983:5231434] --- lastID:1
//2015-09-04 10:04:38.076 nsnotfound[66983:5231434] Case 2: Set lastID to 2, then try to fetch.
//2015-09-04 10:04:38.076 nsnotfound[66983:5231434] --- lastID:2
I suggested using NSNumber earlier, as your question used a boxed NSNumber -- #1. #1 is simply shorthand for [NSNumber numberWithInteger:1]. If you don't want to use objects, you can definitely use primitives.
The example above uses both zero and one as sentinel values for your "unfound" and "invalid" IDs. All other IDs should be usable by your app logic. I hope this helps.

Answer 4

You can retrieve this number to NSNumber which is an object and that way you can check if it is nil or not.

Answer 5

NSInteger is basically a typecast of Int in 32 bit or long in 64 bit, as you compare int in similar way you can compare NSInteger.It will never be nil.

Answer 6

NSInteger isn't an object, its a primitive type stored as a NSNumber inside NSUserDefaults. Checking for existence of primitive types is a bit tricky, as its non-existence is equivalent to nil or 0. The cleanest way to get its value and get a default value if it doesn't exist is probably this way:
NSNumber *lastID = [[NSUserDefaults standardUserDefaults] objectForKey:#"lastID"] ?: #1;
This would return you lastID if it exists, otherwise you get a NSNumber with a value of 1.