iOS 使用hash判断字符串是否为空

+ (BOOL)notEmptyString:(NSString *)string {
    if (!string) {
        return NO;
    }
    
    static NSSet *emptySet;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        emptySet = [NSSet setWithObjects:@"", @"null", @"(null)", @"<null>", @"NULL", nil];
    });
    
    if ([emptySet containsObject:string]) {
        return NO;
    }
    
    if ([string isKindOfClass:NSNull.class]) {
        return NO;
    }
    
    //去掉空格之后长度为0
    if (0 == [string stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceCharacterSet]].length) {
        return NO;
    }
    
    return YES;
}

参考链接：何为代码质量？——用脑子写代码