How do I test if a string is empty in Objective C?

Question

How do I test if an NSString is empty in Objective C?

Answer 1

You can check if [string length] == 0. This will check if it's a valid but empty string (@"") as well as if its nil, since calling length on nil will also return 0.

Answer 2

Marc's answer is correct. But I'll take this opportunity to include a pointer to Wil Shipley's generalized isEmpty, which he shared on his blog:

static inline BOOL IsEmpty(id thing) {
return thing == nil
|| ([thing respondsToSelector:@selector(length)]
&& [(NSData *)thing length] == 0)
|| ([thing respondsToSelector:@selector(count)]
&& [(NSArray *)thing count] == 0);
}

Answer 3

The first approach is valid, but doesn't work if your string have blank spaces (@" "). So you must to clear this white spaces before test it.

This code clear all the blank spaces on both sides of one string:

[stringObject stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceCharacterSet] ];

One good idea is create one macro, so you don't have to type this monster line:

#define allTrim( object ) [object stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceCharacterSet] ]

Now you can use:

NSString *emptyString = @"   ";

if ( [allTrim( emptyString ) length] == 0 ) NSLog(@"Is empty!");

Answer 4

You should better use this category:

@implementation NSString (Empty)

    - (BOOL) empty{
        return ([[self stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceAndNewlineCharacterSet]]length] == 0);
    }

@end

Answer 5

One of the best solution I ever seen (better than Matt G's one) is this improved inline function I picked up on some Git Hub repo (sorry I forgot) :

// Check if the "thing" pass'd is empty
static inline BOOL isEmpty(id thing) {
    return thing == nil
    || [thing isKindOfClass:[NSNull class]]
    || ([thing respondsToSelector:@selector(length)]
        && [(NSData *)thing length] == 0)
    || ([thing respondsToSelector:@selector(count)]
        && [(NSArray *)thing count] == 0);
}