Objective-Cでカテゴリ拡張およびUtilクラスによる空文字列チェック ref: http://qiita.com/YusukeHosonuma/items/999d47a269435d094210

file0.txt

if ([someString length])

NSString+Additions.m

#import "NSString+Additions.h"

@implementation NSString (Additions)

- (BOOL)isNotEmpty {
    return [self length] > 0;
}

@end

StringUtils.m

#import "StringUtils.h"

@implementation StringUtils

+ (BOOL)isEmpty:(NSString*)string {
    return string == nil || [string length] == 0;
}

+ (BOOL)isNotEmpty:(NSString*)string {
    return ![StringUtils isEmpty:string];
}

@end

XCTest

- (void)test_StringUtils_isEmpty
{
    XCTAssertFalse([StringUtils isEmpty:@"foo"]);
    XCTAssertTrue ([StringUtils isEmpty:@""]);
    XCTAssertTrue ([StringUtils isEmpty:nil]);
}

- (void)test_StringUtils_isNotEmpty
{
    XCTAssertTrue ([StringUtils isNotEmpty:@"foo"]);
    XCTAssertFalse([StringUtils isNotEmpty:@""]);
    XCTAssertFalse([StringUtils isNotEmpty:nil]);
}