How do I test if a string is empty in Objective C?
如何测试Objective C中的NSString是否为空？
You can check if [string length] == 0 . This will check if it's a valid but empty string (@"") as well as if it's nil, since calling length on nil will also return 0.
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);
}
The first approach is valid, but doesn't work if your string has blank spaces ( @" " ). So you must clear this white spaces before testing it.
This code clear all the blank spaces on both sides of the 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!");