NSString is empty - iphone

Question

How do you test if an NSString is empty? or all whitespace or nil? with a single method call?

Answer 1

You can try something like this:
#implementation NSString (JRAdditions)
+ (BOOL)isStringEmpty:(NSString *)string {
if([string length] == 0) { //string is empty or nil
return YES;
}
if(![[string stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceAndNewlineCharacterSet]] length]) {
//string is all whitespace
return YES;
}
return NO;
}
#end
Check out the NSString reference on ADC.

Answer 2

This is what I use, an Extension to NSString:
+ (BOOL)isEmptyString:(NSString *)string;
// Returns YES if the string is nil or equal to #""
{
// Note that [string length] == 0 can be false when [string isEqualToString:#""] is true, because these are Unicode strings.
if (((NSNull *) string == [NSNull null]) || (string == nil) ) {
return YES;
}
string = [string stringByTrimmingCharactersInSet: [NSCharacterSet whitespaceAndNewlineCharacterSet]];
if ([string isEqualToString:#""]) {
return YES;
}
return NO;
}

Answer 3

I use,
+ (BOOL ) stringIsEmpty:(NSString *) aString {
if ((NSNull *) aString == [NSNull null]) {
return YES;
}
if (aString == nil) {
return YES;
} else if ([aString length] == 0) {
return YES;
} else {
aString = [aString stringByTrimmingCharactersInSet: [NSCharacterSet whitespaceAndNewlineCharacterSet]];
if ([aString length] == 0) {
return YES;
}
}
return NO;
}
+ (BOOL ) stringIsEmpty:(NSString *) aString shouldCleanWhiteSpace:(BOOL)cleanWhileSpace {
if ((NSNull *) aString == [NSNull null]) {
return YES;
}
if (aString == nil) {
return YES;
} else if ([aString length] == 0) {
return YES;
}
if (cleanWhileSpace) {
aString = [aString stringByTrimmingCharactersInSet: [NSCharacterSet whitespaceAndNewlineCharacterSet]];
if ([aString length] == 0) {
return YES;
}
}
return NO;
}

Answer 4

I hate to throw another log on this exceptionally old fire, but I'm leery about editing someone else's answer - especially when it's the selected answer.
Jacob asked a follow up question: How can I do this with a single method call?
The answer is, by creating a category - which basically extends the functionality of a base Objective-C class - and writing a "shorthand" method for all the other code.
However, technically, a string with white space characters is not empty - it just doesn't contain any visible glyphs (for the last couple of years I've been using a method called isEmptyString: and converted today after reading this question, answer, and comment set).
To create a category go to Option+Click -> New File... (or File -> New -> File... or just command+n) -> choose Objective-C Category. Pick a name for the category (this will help namespace it and reduce possible future conflicts) - choose NSString from the "Category on" drop down - save the file somewhere. (Note: The file will automatically be named NSString+YourCategoryName.h and .m.)
I personally appreciate the self-documenting nature of Objective-C; therefore, I have created the following category method on NSString modifying my original isEmptyString: method and opting for a more aptly declared method (I trust the compiler to compress the code later - maybe a little too much).
Header (.h):
#import <Foundation/Foundation.h>
#interface NSString (YourCategoryName)
/*! Strips the string of white space characters (inlcuding new line characters).
#param string NSString object to be tested - if passed nil or #"" return will
be negative
#return BOOL if modified string length is greater than 0, returns YES;
otherwise, returns NO */
+ (BOOL)visibleGlyphsExistInString:(NSString *)string;
#end
Implementation (.m):
#implementation NSString (YourCategoryName)
+ (BOOL)visibleGlyphsExistInString:(NSString *)string
{
// copying string should ensure retain count does not increase
// it was a recommendation I saw somewhere (I think on stack),
// made sense, but not sure if still necessary/recommended with ARC
NSString *copy = [string copy];
// assume the string has visible glyphs
BOOL visibleGlyphsExist = YES;
if (
copy == nil
|| copy.length == 0
|| [[copy stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceAndNewlineCharacterSet]] length] == 0
) {
// if the string is nil, no visible characters would exist
// if the string length is 0, no visible characters would exist
// and, of course, if the length after stripping the white space
// is 0, the string contains no visible glyphs
visibleGlyphsExist = NO;
}
return visibleGlyphsExist;
}
#end
To call the method be sure to #import the NSString+MyCategoryName.h file into the .h or .m (I prefer the .m for categories) class where you are running this sort of validation and do the following:
NSString* myString = #""; // or nil, or tabs, or spaces, or something else
BOOL hasGlyphs = [NSString visibleGlyphsExistInString:myString];
Hopefully that covers all the bases. I remember when I first started developing for Objective-C the category thing was one of those "huh?" ordeals for me - but now I use them quite a bit to increase reusability.
Edit: And I suppose, technically, if we're stripping characters, this:
[[copy stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceAndNewlineCharacterSet]] length] == 0
Is really all that is needed (it should do everything that category method does, including the copy), but I could be wrong on that score.

Answer 5

I'm using this define as it works with nil strings as well as empty strings:
#define STR_EMPTY(str) \
str.length == 0
Actually now its like this:
#define STR_EMPTY(str) \
(![str isKindOfClass:[NSString class]] || str.length == 0)

Answer 6

Maybe you can try something like this:
+ (BOOL)stringIsEmpty:(NSString *)str
{
return (str == nil) || (([str stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceAndNewlineCharacterSet]]).length == 0);
}

Answer 7

Based on the Jacob Relkin answer and Jonathan comment:
#implementation TextUtils
+ (BOOL)isEmpty:(NSString*) string {
if([string length] == 0 || ![[string stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceAndNewlineCharacterSet]] length]) {
return YES;
}
return NO;
}
#end

Answer 8

Should be easier:
if (![[string stringByReplacingOccurencesOfString:#" " withString:#""] length]) { NSLog(#"This string is empty"); }