iOS字符串不为空判断

- (BOOL)isEmptyStr:(NSString *)string{
    if ( ![string isKindOfClass:[NSString class]]) {
        return YES;
    }
    if (string == nil || string == NULL) {
        return YES;
    }
    if ([string isKindOfClass:[NSNull class]]) {
        return YES;
    }
    if ([[string stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceCharacterSet]] length]==0) {
        return YES;
    }
    if ([string isEqualToString:@"<null>"]) {
        return YES;
    }
    if ([string isEqualToString:@"(null)"]) {
        return YES;
    }
    if ([[string lowercaseString] isEqualToString:@"null"]) {
        return YES;
    }
    return NO;
}