NSString "nil or empty" check -- is this complete? - objective-c

Question

I was writing a small Category on NSString, and I wanted to know if this method is accurately handles all potential use cases:
Update: to clarify -- I wanted to make sure I'm not missing some oddball case involving character encodings, etc..
#implementation NSString (Helpers)
+(BOOL)stringIsNilOrEmpty:(NSString*)aString {
if (!aString)
return YES;
return [aString isEqualToString:#""];
}
#end
Sample usage:
-(void) sampleUsage {
NSString *emptyString = #"";
NSString *nilString = nil;
NSAssert([NSString stringIsNilOrEmpty:nilString] == YES, #"String is nil/empty");
NSAssert([NSString stringIsNilOrEmpty:emptyString] == YES, #"String is nil/empty");
}
#end

Answer 1

I only use the next conditional and do not even need a category:
if (!aString.length)
{
...
}
Using Objective-C theory, a message to NIL will return nil or zero, so basically you do not have to test for nil.

Answer 2

You can simplify the code by removing conditional:
+(BOOL)stringIsNilOrEmpty:(NSString*)aString {
return !(aString && aString.length);
}

Answer 3

#dasblinkenlight's answer is fine, but a much more readable conditional check I would use is:
NSString *string = ...; // define the string
if ([string length] == 0) {
// Do stuff with the string
} else {
// The string is empty or nil here
}
Very concise and does not require a separate convenience function definition. It's easy enough to remember.
EDIT: #Michael G. Emmons posted this as the last comment to that answer... credit to him but I'm listing this as an answer in its own right.

Answer 4

Some examples of this sort of "is not empty or blank" tests as a category on NSString.
// Please note that in general I advocate using a prefix on category methods
// to avoid category collisions. I've not done this here for clarity.
// The #interface is also excluded from this example for brevity.
#implementation NSString (MyAdditions)
- (BOOL)isNotEmpty
{
return [self length] != 0;
}
- (BOOL)isNotBlank
{
if ([self isNotEmpty])
{
NSCharacterSet *nonWhitespaceSet = [[NSCharacterSet whitespaceAndNewlineCharacterSet] invertedSet];
NSRange range = [self rangeOfCharactersFromSet:nonWhitespaceSet];
return range.location != NSNotFound;
}
return NO;
}
#end

Answer 5

Simply Check your string length
> if (!yourString.length){
> //your code } a
message to NIL will return nil or 0, so no need to test for nil :).
Happy coding ...

Answer 6

Make sure to check for spaces, trim white spaces before calculating length.
+(BOOL)stringIsNilOrEmpty:(NSString*)aString {
return !aString || [[aString stringByTrimmingCharactersInSet:
[NSCharacterSet whitespaceCharacterSet]] length] == 0;
}