CamelCase 下划线并返回到 Objective-C

Question

我正在寻找一种简单、有效的方法来将 CamelCase 中的字符串转换为下划线表示法（即 MyClassName -> my_class_name）并在 Objective C 中再次转换回来。

我当前的解决方案在 NSMutableStrings 上涉及很多 rangeOfString、characterAtIndex 和 replaceCharactersInRange 操作，而且简直丑到要命 :) 似乎必须有更好的解决方案，但我不确定这是什么。

我宁愿不只为这个用例导入正则表达式库，但如果其他方法都失败了，这是一种选择。

Answer 1

Chris 对 RegexKitLite 的建议很好。这是一个出色的工具包，但使用NSScanner 可以轻松完成。在+uppercaseLetterCharacterSet 和+lowercaseLetterCharacterSet 之间交替使用-scanCharactersFromSet:intoString:。要返回，您可以改用 -scanUpToCharactersFromSet:，使用其中只有一个下划线的字符集。

Answer 2

这些怎么样：

NSString *MyCamelCaseToUnderscores(NSString *input) {
    NSMutableString *output = [NSMutableString string];
    NSCharacterSet *uppercase = [NSCharacterSet uppercaseLetterCharacterSet];
    for (NSInteger idx = 0; idx < [input length]; idx += 1) {
        unichar c = [input characterAtIndex:idx];
        if ([uppercase characterIsMember:c]) {
            [output appendFormat:@"_%@", [[NSString stringWithCharacters:&c length:1] lowercaseString]];
        } else {
            [output appendFormat:@"%C", c];
        }
    }
    return output;
}

NSString *MyUnderscoresToCamelCase(NSString *underscores) {
    NSMutableString *output = [NSMutableString string];
    BOOL makeNextCharacterUpperCase = NO;
    for (NSInteger idx = 0; idx < [underscores length]; idx += 1) {
        unichar c = [underscores characterAtIndex:idx];
        if (c == '_') {
            makeNextCharacterUpperCase = YES;
        } else if (makeNextCharacterUpperCase) {
            [output appendString:[[NSString stringWithCharacters:&c length:1] uppercaseString]];
            makeNextCharacterUpperCase = NO;
        } else {
            [output appendFormat:@"%C", c];
        }
    }
    return output;
}

一些缺点是它们确实使用临时字符串在大小写之间进行转换，并且它们没有任何首字母缩写词的逻辑，因此 myURL 将导致 my_u_r_l。

Answer 3

试试这个魔法：

NSString* camelCaseString = @"myBundleVersion";
NSRegularExpression *regex = [NSRegularExpression regularExpressionWithPattern:@"(?<=[a-z])([A-Z])|([A-Z])(?=[a-z])" options:0 error:nil];
NSString *underscoreString = [[regex stringByReplacingMatchesInString:camelCaseString options:0 range:NSMakeRange(0, camelCaseString.length) withTemplate:@"_$1$2"] lowercaseString];
NSLog(@"%@", underscoreString);

输出：my_bundle_version

Answer 4

如果您关心的只是代码的可见性，您可以使用您已经设计的方法为NSString 创建一个类别。这样，你只会看到一次丑陋的烂摊子。 ;)

例如：

@interface NSString(Conversions) {
     - (NSString *)asCamelCase;
     - (NSString *)asUnderscored;
}

@implementation NSString(Conversions) {
     - (NSString *)asCamelCase {
          // whatever you came up with
     }
     - (NSString *)asUnderscored {
          // whatever you came up with
     }
}

编辑：在 Google 快速搜索后，我找不到任何方法，即使是在纯 C 语言中也是如此。但是，我确实找到了一个有用的框架。它被称为RegexKitLite。它使用内置的 ICU 库，所以它只在最终的二进制文件中增加了大约 20K。

Answer 5

这是我对 Rob 答案的实现：

@implementation NSString (CamelCaseConversion)

// Convert a camel case string into a dased word sparated string.
// In case of scanning error, return nil.
// Camel case string must not start with a capital.
- (NSString *)fromCamelCaseToDashed {

    NSScanner *scanner = [NSScanner scannerWithString:self];
    scanner.caseSensitive = YES;

    NSString *builder = [NSString string];
    NSString *buffer = nil;
    NSUInteger lastScanLocation = 0;

    while ([scanner isAtEnd] == NO) {

        if ([scanner scanCharactersFromSet:[NSCharacterSet lowercaseLetterCharacterSet] intoString:&buffer]) {

            builder = [builder stringByAppendingString:buffer];

            if ([scanner scanCharactersFromSet:[NSCharacterSet uppercaseLetterCharacterSet] intoString:&buffer]) {

                builder = [builder stringByAppendingString:@"-"];
                builder = [builder stringByAppendingString:[buffer lowercaseString]];
            }
        }

        // If the scanner location has not moved, there's a problem somewhere.
        if (lastScanLocation == scanner.scanLocation) return nil;
        lastScanLocation = scanner.scanLocation;
    }

    return builder;
}

@end

Answer 6

这是基于以上所有内容的另一个版本。这个版本处理额外的表格。特别是通过以下测试：

camelCase => camel_case
camelCaseWord => camel_case_word
camelURL => camel_url
camelURLCase => camel_url_case
CamelCase => camel_case

来了

- (NSString *)fromCamelCaseToDashed3 {
    NSMutableString *output = [NSMutableString string];
    NSCharacterSet *uppercase = [NSCharacterSet uppercaseLetterCharacterSet];
    BOOL previousCharacterWasUppercase = FALSE;
    BOOL currentCharacterIsUppercase = FALSE;
    unichar currentChar = 0;
    unichar previousChar = 0;
    for (NSInteger idx = 0; idx < [self length]; idx += 1) {
        previousChar = currentChar;
        currentChar = [self characterAtIndex:idx];
        previousCharacterWasUppercase = currentCharacterIsUppercase;
        currentCharacterIsUppercase = [uppercase characterIsMember:currentChar];

        if (!previousCharacterWasUppercase && currentCharacterIsUppercase && idx > 0) {
            // insert an _ between the characters
            [output appendString:@"_"];
        } else if (previousCharacterWasUppercase && !currentCharacterIsUppercase) {
            // insert an _ before the previous character
            // insert an _ before the last character in the string
            if ([output length] > 1) {
                unichar charTwoBack = [output characterAtIndex:[output length]-2];
                if (charTwoBack != '_') {
                    [output insertString:@"_" atIndex:[output length]-1];
                }
            }
        } 
        // Append the current character lowercase
        [output appendString:[[NSString stringWithCharacters:&currentChar length:1] lowercaseString]];
    }
    return output;
}

Answer 7

如果您关心代码的速度，您可能希望编写更高性能的代码版本：

- (nonnull NSString *)camelCaseToSnakeCaseString {
    if ([self length] == 0) {
        return @"";
    }
    NSMutableString *output = [NSMutableString string];
    NSCharacterSet *digitSet = [NSCharacterSet decimalDigitCharacterSet];
    NSCharacterSet *uppercaseSet = [NSCharacterSet uppercaseLetterCharacterSet];
    NSCharacterSet *lowercaseSet = [NSCharacterSet lowercaseLetterCharacterSet];

    for (NSInteger idx = 0; idx < [self length]; idx += 1) {
        unichar c = [self characterAtIndex:idx];

        // if it's the last one then just append lowercase of character
        if (idx == [self length] - 1) {
            if ([uppercaseSet characterIsMember:c]) {
                [output appendFormat:@"%@", [[NSString stringWithCharacters:&c length:1] lowercaseString]];
            }
            else {
                [output appendFormat:@"%C", c];
            }
            continue;
        }

        unichar nextC = [self characterAtIndex:(idx+1)];
        // this logic finds the boundaries between lowercase/uppercase/digits and lets the string be split accordingly.
        if ([lowercaseSet characterIsMember:c] && [uppercaseSet characterIsMember:nextC]) {
            [output appendFormat:@"%@_", [[NSString stringWithCharacters:&c length:1] lowercaseString]];
        }
        else if ([lowercaseSet characterIsMember:c] && [digitSet characterIsMember:nextC]) {
            [output appendFormat:@"%@_", [[NSString stringWithCharacters:&c length:1] lowercaseString]];
        }
        else if ([digitSet characterIsMember:c] && [uppercaseSet characterIsMember:nextC]) {
            [output appendFormat:@"%@_", [[NSString stringWithCharacters:&c length:1] lowercaseString]];
        }
        else {
            // Append lowercase of character
            if ([uppercaseSet characterIsMember:c]) {
                [output appendFormat:@"%@", [[NSString stringWithCharacters:&c length:1] lowercaseString]];
            }
            else {
                [output appendFormat:@"%C", c];
            }
        }
    }
    return output;
}

Answer 8

我已将此处找到的答案合并到我的重构库 es_ios_utils 中。见NSCategories.h:

@property(nonatomic, readonly) NSString *asCamelCaseFromUnderscores;
@property(nonatomic, readonly) NSString *asUnderscoresFromCamelCase;

用法：

@"my_string".asCamelCaseFromUnderscores

产生@"myString"

请推动改进！

Answer 9

我碰巧遇到了这个问题，正在寻找一种将 Camel Case 转换为间隔的、用户可显示的字符串的方法。这是我的解决方案，它比用 @" " 替换 @"_" 效果更好

- (NSString *)fromCamelCaseToSpaced:(NSString*)input {
    NSCharacterSet* lower = [NSCharacterSet lowercaseLetterCharacterSet];
    NSCharacterSet* upper = [NSCharacterSet uppercaseLetterCharacterSet];

    for (int i = 1; i < input.length; i++) {
        if ([upper characterIsMember:[input characterAtIndex:i]] &&
            [lower characterIsMember:[input characterAtIndex:i-1]])
        {
            NSString* soFar = [input substringToIndex:i];
            NSString* left = [input substringFromIndex:i];
            return [NSString stringWithFormat:@"%@ %@", soFar, [self fromCamelCaseToSpaced:left]];
        }
    }
    return input;
}

Answer 10

好的，伙计们。这是一个全正则表达式的答案，我认为这是唯一正确的方法：

给定：

NSString *MYSTRING = "foo_bar";

NSRegularExpression *_toCamelCase = [NSRegularExpression 
    regularExpressionWithPattern:@"(_)([a-z])" 
    options:NSRegularExpressionCaseInsensitive error:&error];

NSString *camelCaseAttribute = [_toCamelCase 
    stringByReplacingMatchesInString:MYSTRING options:0 
    range:NSMakeRange(0, attribute.length) 
    withTemplate:@"\\U$2"];

收益 fooBar。

反之：

NSString *MYSTRING = "fooBar";


NSRegularExpression *camelCaseTo_ = [NSRegularExpression 
    regularExpressionWithPattern:@"([A-Z])" 
    options:0 error:&error];

NSString *underscoreParsedAttribute = [camelCaseTo_ 
    stringByReplacingMatchesInString:MYSTRING 
    options:0 range:NSMakeRange(0, attribute.length) 
    withTemplate:@"_$1"];
underscoreParsedAttribute = [underscoreParsedAttribute lowercaseString];

产量：foo_bar。

\U$2 将第二个捕获组替换为自身的大写版本：D

\L$1 然而，奇怪的是，它不会用自己的小写版本替换第一个捕获组:(不知道为什么，它应该可以工作。:/