复杂的Objective-C字符串替换

Question

我正在尝试编写一个用于字符串转换的泛型方法(目的是为RESTful应用编程接口编写一个解析器)。

消息的目的是转换字符串，如下所示

creationTSZ -> creation_tsz

userId -> user_id

该消息处理转换userId -> user_id，当前低效地循环通过字符串和更改部分。

它还不能处理creationTSZ -> creation_tsz，我认为进一步循环是非常低效的，我想知道有没有更好的方法来做这件事？

可能是Regex？

-(NSString *)fieldsQueryString 
{

    NSArray *fieldNames = [self fieldList];

    /* Final composed string sent to Etsy */
    NSMutableString *fieldString = [[[NSMutableString alloc] init] autorelease];

    /* Characters that we replace with _lowerCase */
    NSArray *replaceableChars = [NSArray arrayWithObjects:
                                 @"Q", @"W", @"E", @"R", @"T", @"Y", @"U", @"I", @"O", @"P", 
                                 @"A", @"S", @"D", @"F", @"G", @"H", @"J", @"K", @"L",
                                 @"Z", @"X", @"C", @"V", @"B", @"N", @"M", nil];

    /* Reusable pointer for string replacements */
    NSMutableString *fieldNameString = nil;

    /* Loop through the array returned by the filter and change the names */
    for(NSString *fieldName in fieldNames) {
        /* Loop if the field is to be omited */
        if ([[self valueForKey:fieldName] boolValue] == NO) continue;
        /* Otherwise change the name to a field and add it */
        fieldNameString = [fieldName mutableCopy];
        for(NSString *replaceableChar in replaceableChars) {
            [fieldNameString replaceOccurrencesOfString:replaceableChar 
                                             withString:[NSString stringWithFormat:@"_%@", [replaceableChar lowercaseString]] 
                                                options:0 
                                                  range:NSMakeRange(0, [fieldNameString length])];
        }
        [fieldString appendFormat:@"%@,", fieldNameString];
        [fieldNameString release];
    }
    fieldNames = nil;

    /* Return the string without the last comma */
    return [fieldString substringToIndex:[fieldString length] - 1];
}

Answer 1

假设您的标识符的结构如下

<lowercase-prefix><Uppercase-char-and-remainder>

您可以使用：

NSScaner *scanner = [NSScanner scannerWithString:fieldName];
NSString *prefix = nil;
[scanner scanCharactersFromSet:[NSCharacterSet lowercaseLetterCharacterSet] intoString:&prefix];
NSString *suffix = nil;
[scanner scanCharactersFromSet:[NSCharacterSet letterCharacterSet] intoString:&suffix];
NSString *fieldNameString = [NSString stringWithFormat:@"%@_%@", prefix, [suffix lowercaseString]];

这将执行字段标识符的转换(但您应该执行一些错误检查，以防前缀或后缀保持为空)。

构建fieldNames列表的最简单方法是将它们添加到NSMutableArray中，然后加入它们：

NSMutableArray *fields = [[NSMutableArray alloc] init];
for (NSString *fieldName in [self fieldList]) {
    // code as above
    [fields add:fieldNameString];
}
NSString *commaFields = [fields componentsJoinedByString:@","];
[fields release];
return commaFields;