NSString&NSMutableString常用操作梳理

作者：弦苦 授权本站转载。

上一篇梳理了NSArray&NSMutableArray常用操作，这次来梳理一下Objective-C中每天都要用到的字符串处理类——NSString。

Objective-C中的NSString/NSMutableString类似MFC中的CString，封装了字符串的日常基本操作。

1.创建初始化（Initialization&Creation）

1.1 常量字符串（literal string）

NSString*constString = @"Hello, World!";

变量constString并不是真正包含一个字符串对象，而指向内存中字符串对象的指针（地址），我们称之为对象标识符。

以下示例中，字面量@“Hello, World!”存储在文字常量区。指针constString1和constString2都指向它，它们在编译时生成的真实类型是NSConstantString(继承关系链——:NSSimpleCString:NSString)。

Objective-C里没有包或者命名空间，靠前缀来区分，NS是“NeXTSTEP”的缩写。

CF是“CoreFoundation”的缩写。CFString可以看做是NSString的C底层实现。

Foundation库（Foundation.framework/Foundation.h）是有Cocoa框架提供的基本数据管理和服务功能的Objective-C接口，而Core Foundation库 (CoreFoundation.framework/CoreFoundation.h) 则是Cocoa底层实现，提供了C语言层面的接口。

以下介绍不可变字符串两种初始化创建方法。

After an immutable string has been initialized in the following way, it cannot be modified.

1.2 Initializing an String(NS_DESIGNATED_INITIALIZER)

- (instancetype)init NS_DESIGNATED_INITIALIZER;

- (instancetype)initWithCoder:(NSCoder*)aDecoder NS_DESIGNATED_INITIALIZER;

// 从UNICODE C String中选取定长字符初始化NSString对象

- (instancetype)initWithCharacters:(const unichar*)characters length:(NSUInteger)length;

// 从UTF8 C String初始化NSString对象

- (instancetype)initWithUTF8String:(const char*)nullTerminatedCString;

// 从C String初始化NSString对象，指定编码格式。

- (instancetype)initWithCString:(const char*)nullTerminatedCString encoding:(NSStringEncoding)encoding;

// 从另一个NSString初始化新的NSString对象

- (instancetype)initWithString:(NSString*)aString;

// 从NSData指定编码格式初始化NSString对象

- (instancetype)initWithData:(NSData*)data encoding:(NSStringEncoding)encoding;

// 从C Buffer指定编码格式初始化NSString对象

- (instancetype)initWithBytes:(const void*)bytes length:(NSUInteger)len encoding:(NSStringEncoding)encoding;

// 可变参格式化初始化NSString对象

- (instancetype)initWithFormat:(NSString*)format, ... NS_FORMAT_FUNCTION(1,2);

比较常用的有以下几个：

// 从UTF8 C String初始化NSString对象

- (instancetype)initWithUTF8String:(constchar *)nullTerminatedCString;

// 从C String初始化NSString对象，指定编码格式（例如NSUTF8StringEncoding）。

- (instancetype)initWithCString:(constchar *)nullTerminatedCString encoding:(NSStringEncoding)encoding;

// 从C Buffer指定编码格式初始化NSString对象

- (instancetype)initWithBytes:(constvoid *)bytes length:(NSUInteger)len encoding:(NSStringEncoding)encoding;

// 可变参格式化初始化NSString对象

- (instancetype)initWithFormat:(NSString *)format, ...NS_FORMAT_FUNCTION(1,2);

示例：

//NSString* string = [[NSString alloc] initWithFormat:@"Hello, %s","World!"];

NSString* string = [[NSString alloc] initWithFormat:@"Hello, %@", @"World!"];

NSLog(@"string= %@", string);

关于格式化规范，参考String Format Specifiers。

• %@：OC对象描述（description）。

• %d/%D：带符号32位整数（int），NSInteger：%ld，size_t：%zd。

• %u/%U：无符号32位整数（unsigned int），NSUInteger：%lu。

• %o/%O：无符号32位整数（unsigned int）的八进制格式。

• %x/%X：无符号32位整数（unsigned int）的十六进制格式。

• %c：8位无符号字符（unsigned char）。如果非ASCII码则以八进制“\\ddd”或十六进制“\\udddd”格式显示字符值。

• %C：16位UNICODE字符（unichar）。如果非ASCII码则以八进制“\\ddd”或十六进制“\\udddd”格式显示字符值。

• %f：64位浮点数（double）

1.3 Creating an String(autorelease)

// 创建一个字符串独享，其值为空

+ (instancetype)string;

示例：

NSString* constString = @"";

NSString* string = [NSString string];

BOOL bPointerEqual = constString==string; // NO

BOOL bContentEqualTo = [constString isEqualTo:string]; // YES

BOOLbEqualToString = [constString isEqualToString:string]; // YES

以下是一些便利构造方法：

// initWithString对应的类方法

+ (instancetype)stringWithString:(NSString *)string;

// initWithCString:encoding对应的类方法

+ (instancetype)stringWithCString:(const charchar *)cString encoding:(NSStringEncoding)enc;

// initWithCharacters:length: 对应的类方法

+ (instancetype)stringWithCharacters:(const unichar *)characters length:(NSUInteger)length;

// initWithUTF8String对应的类方法

+ (instancetype)stringWithUTF8String:(const charchar *)nullTerminatedCString;

// initWithFormat对应的类方法

+ (instancetype)stringWithFormat:(NSString *)format, ... NS_FORMAT_FUNCTION(1,2);

+ (instancetype)localizedStringWithFormat:(NSString *)format, ... NS_FORMAT_FUNCTION(1,2);

比较常用的有以下几个：

// initWithCString:encoding对应的类方法

+ (instancetype)stringWithCString:(constchar *)cString encoding:(NSStringEncoding)enc;

// initWithUTF8String对应的类方法

+ (instancetype)stringWithUTF8String:(constchar *)nullTerminatedCString;

// initWithFormat对应的类方法

+ (instancetype)stringWithFormat:(NSString *)format, ...NS_FORMAT_FUNCTION(1,2);

2.访问字符串（Querying）

2.1 字符串长度（字符数组大小）

// Thenumber of Unicode characters in the receiver.

@property (readonly) NSUInteger length;

示例：

NSString* constString1 = nil;

NSString* constString2 = @"";

NSString* constString3 = @"Hello, World!";

NSString* constString4 = @"哈喽,世界!"; // 汉字+半角标点混合

NSLog(@"constString1[size,length] = [%zd, %zd]", sizeof(constString1),constString1.length); // [8,0]

NSLog(@"constString2[size,length] = [%zd, %zd]", sizeof(constString2),constString2.length); // [8,0]

NSLog(@"constString3[size,length] = [%zd, %zd]", sizeof(constString3),constString3.length); // [8,13]

NSLog(@"constString4[size,length] = [%zd, %zd]", sizeof(constString4),constString4.length); // [8,6]

以上可知string.length可用来判空：如果length为零，则表示字符串对象为nil或为不包含任何字符。

2.2 字符（字符数组元素）

// 获取指定索引位置/范围的字符（集）

- (unichar)characterAtIndex:(NSUInteger)index;

- (void)getCharacters:(unichar *)buffer range:(NSRange)aRange;

示例：

unichar ch = [constString3 characterAtIndex:7];

NSLog(@"ch = %c", ch); // W

unichar* cBuf = malloc(sizeof(unichar)*constString3.length);

[constString3 getCharacters:cBuf];

NSString* stringFromCharacters1 = [[NSString alloc] initWithCharacters:cBuf length:constString3.length];

NSLog(@"stringFromCharacters1 = %@", stringFromCharacters1); // @"Hello, World!"

[stringFromCharacters1 release];

[constString3 getCharacters:cBuf range:NSMakeRange(7, 6)];

NSString* stringFromCharacters2 = [NSString stringWithCharacters:cBuf length:constString3.length];

NSLog(@"stringFromCharacters2 = %@", stringFromCharacters2); // @"World! World!"

2.3 取C String

//Convenience to return null-terminated UTF8 representation

@property (readonly) __strong const charchar *UTF8String NS_RETURNS_INNER_POINTER;

2.4 取字面值

类似cstdlib中的atoi/atol/strtol/atof。

/* convenience methods all skip initial space characters (whitespaceSet)and ignore trailing characters.

NSScanner can be used for more"exact" parsing of numbers. */

@property (readonly) double doubleValue;

@property (readonly) float floatValue;

@property (readonly) int intValue;

@property (readonly) NSInteger integerValue NS_AVAILABLE(10_5, 2_0);

@property (readonly) long long longLongValue NS_AVAILABLE(10_5, 2_0);

@property (readonly) BOOL boolValue NS_AVAILABLE(10_5, 2_0);

2.5 大小写转换

// 所有字符转换成大写

@property (readonly, copy) NSString *uppercaseString;

// 所有字符转换成小写

@property (readonly, copy) NSString *lowercaseString;

// 每个单词首字母大写，其余字母小写。

@property (readonly, copy) NSString *capitalizedString;

3.查询字符串（Finding）

3.1 查询子串

// 返回查找到包含子串的范围

- (NSRange)rangeOfString:(NSString *)aString;

// 返回查找到包含子串的范围，可指定查询选项（忽略大小写、逆序）

- (NSRange)rangeOfString:(NSString *)aString options:(NSStringCompareOptions)mask;

// 返回查找到包含子串的范围，可指定查询选项（忽略大小写、逆序），可进一步指定查找范围

- (NSRange)rangeOfString:(NSString *)aString options:(NSStringCompareOptions)mask range:(NSRange)searchRange;

3.2 取子串

// 返回从指定索引到结尾的子串

- (NSString *)substringFromIndex:(NSUInteger)from;

// 返回从开头到指定索引的子串

- (NSString *)substringToIndex:(NSUInteger)to;

// 返回从指定范围（开始索引+长度）界定的子串

- (NSString *)substringWithRange:(NSRange)range; // Hint: Use withrangeOfComposedCharacterSequencesForRange: to avoid breaking up composedcharacters

示例：

NSString* prefix = [constString3 substringToIndex:7]; // @"Hello, "

NSString* suffix = [constString3 substringFromIndex:7]; // @"World!"

NSString* substr =[constString3 substringWithRange:NSMakeRange(3,6)]; // @"lo, Wo"

3.3 是否包含子串

// 是否以指定子串开头

- (BOOL)hasPrefix:(NSString *)aString;

// 是否以指定子串结尾

- (BOOL)hasSuffix:(NSString *)aString;

// 是否包含子串，注意只适用于iOS8以上！

- (BOOL)containsString:(NSString *)aString NS_AVAILABLE(10_10, 8_0);

示例：

BOOL bHasPrefix = [constString3 hasPrefix:@"Hello,"]; // YES

BOOL bHasSuffix = [constString3 hasSuffix:@"World!"]; // YES

BOOL bContain= [constString3 containsString:@"lo, Wo"]; // YES

以下为NSString扩展类别（Category）判断是否包含子串的适配接口：

- (BOOL)hasContainStr:(NSString*)subStr

{

if(!subStr) {

return NO;

}

if([self respondsToSelector:@selector(containsString:)]) { // ≥iOS8

return [self containsString:subStr];

} else { //0 ? YES : NO);

}

}

3.4 查询字符集

/* These return the range of the first character from the set in thestring, not the range of a sequence of characters.

*/

- (NSRange)rangeOfCharacterFromSet:(NSCharacterSet *)aSet;

- (NSRange)rangeOfCharacterFromSet:(NSCharacterSet *)aSet options:(NSStringCompareOptions)mask;

- (NSRange)rangeOfCharacterFromSet:(NSCharacterSet *)aSet options:(NSStringCompareOptions)mask range:(NSRange)searchRange;

- (NSRange)rangeOfComposedCharacterSequenceAtIndex:(NSUInteger)index;

- (NSRange)rangeOfComposedCharacterSequencesForRange:(NSRange)range NS_AVAILABLE(10_5, 2_0);

4.比较字符串（Comparing）

// 判断两个字符串内容是否相等

- (BOOL)isEqualToString:(NSString *)aString;

/* In the compare: methods, the range argument specifies the subrange,rather than the whole, of the receiver to use in the comparison.

The range is not applied to the search string. For example, [@"AB"compare:@"ABC" options:0 range:NSMakeRange(0,1)] compares"A" to "ABC", not "A" to "A", and will return NSOrderedAscending.

*/

// 比较字符串，如果相同返回NSOrderedSame；如果不相同，返回第一个不相同的字符值比较结果（NSOrderedAscending、NSOrderedDescending）

- (NSComparisonResult)compare:(NSString *)string;

// 比较字符串，可指定比较选项（忽略大小写、逆序、按十进制值）

- (NSComparisonResult)compare:(NSString *)string options:(NSStringCompareOptions)mask;

// 比较字符串，可指定比较选项（忽略大小写、逆序、按十进制值），可进一步指定查找范围

- (NSComparisonResult)compare:(NSString *)string options:(NSStringCompareOptions)mask range:(NSRange)compareRange;

// 比较字符串，可指定查询选项（忽略大小写、逆序、按十进制值），可进一步指定查找范围，可进一步按照本地化比较

- (NSComparisonResult)compare:(NSString *)string options:(NSStringCompareOptions)mask range:(NSRange)compareRange locale:(id)locale; //locale arg used to be a dictionary pre-Leopard. We now accept NSLocale. Assumes the current locale if non-nil and non-NSLocale. nil continues to mean canonical compare, which doesn't depend on user's locale choice.

// 相当于compare:string options:NSCaseInsensitiveSearch

- (NSComparisonResult)caseInsensitiveCompare:(NSString *)string;

// 按照本地化比较

- (NSComparisonResult)localizedCompare:(NSString *)string;

// 以上两个版本组合

- (NSComparisonResult)localizedCaseInsensitiveCompare:(NSString *)string;

5.替换子串（Replacing）

/* Replace all occurrences of the target string in the specified range with replacement. Specified compare options are used for matching target. IfNSRegularExpressionSearch is specified, the replacement is treated as a template, as in the corresponding NSRegularExpression methods, and no other options can apply except NSCaseInsensitiveSearch and NSAnchoredSearch.*/

- (NSString *)stringByReplacingOccurrencesOfString:(NSString *)target withString:(NSString *)replacement options:(NSStringCompareOptions)options range:(NSRange)searchRange NS_AVAILABLE(10_5, 2_0);

/* Replace all occurrences of the target string with replacement. Invokes the above method with 0 options and range of the whole string.*/

- (NSString *)stringByReplacingOccurrencesOfString:(NSString *)target withString:(NSString *)replacement NS_AVAILABLE(10_5, 2_0);

/* Replace characters in range with the specified string, returning new string.*/

- (NSString *)stringByReplacingCharactersInRange:(NSRange)range withString:(NSString *)replacement NS_AVAILABLE(10_5, 2_0);

6.衍生字符串（Deriving）

// 当前字符串追加aString生成返回一个新的NSString对象。

- (NSString *)stringByAppendingString:(NSString *)aString;

- (NSString *)stringByAppendingFormat:(NSString *)format, ... NS_FORMAT_FUNCTION(1,2);

7.拆分字符串（Separate & Join Components）

// NSString::componentsSeparatedByString接口按照分割字符（子串）来切分字符串：NSString->NSArray

- (NSArray *)componentsSeparatedByString:(NSString *)separator;

- (NSArray *)componentsSeparatedByCharactersInSet:(NSCharacterSet *)separator NS_AVAILABLE(10_5, 2_0);

// NSArray::componentsJoinedByString接口将多个字符串（字符串数组）以衔接字符连接：NSArray->NSString

- (NSString *)componentsJoinedByString:(NSString *)separator;

以下代码示例将字符串按分隔符拆分，然后按分隔符衔接复原：

NSString* originString = @"do-do-sol-sol-la-la-sol";

NSArray* components = [originString componentsSeparatedByString:@"-"]; // 拆分

NSLog(@"components = %@", components);

NSString* recoverString = [components componentsJoinedByString:@"-"]; //复原

NSLog(@"recoverString = %@", recoverString);

8.可变字符串（NSMutableString）

8.1 Initializing an String(NS_DESIGNATED_INITIALIZER)

/* In addition to these two, NSMutableString responds properly to allNSString creation methods.*/

- (NSMutableString *)initWithCapacity:(NSUInteger)capacity;

+ (NSMutableString *)stringWithCapacity:(NSUInteger)capacity;

8.2 set/append aString

// Replaces the characters of the receiver with those in a given string.aString must not be nil.

- (void)setString:(NSString *)aString;

setString类似于对retain propery的赋值（setter）。

字符串置为空串：=@””或setString:@””;

// Adds to the end of the receiver the characters of a given string.aString must not be nil

- (void)appendString:(NSString *)aString;

- (void)appendFormat:(NSString *)format, ... NS_FORMAT_FUNCTION(1,2);

8.3 insert/replace

- (void)insertString:(NSString *)aString atIndex:(NSUInteger)loc;

// 替换

- (void)replaceCharactersInRange:(NSRange)range withString:(NSString *)aString;

- (NSUInteger)replaceOccurrencesOfString:(NSString *)target withString:(NSString *)replacement options:(NSStringCompareOptions)options range:(NSRange)searchRange;

8.4 delete

// 删除指定位置、指定长度的子串

- (void)deleteCharactersInRange:(NSRange)range;

9.文件、URL与字符串

9.1 从指定文件读取内容到字符串

- (instancetype)initWithContentsOfFile:(NSString *)path encoding:(NSStringEncoding)enc error:(NSError **)error;

+ (instancetype)stringWithContentsOfFile:(NSString *)path encoding:(NSStringEncoding)enc error:(NSError **)error;

9.2 从指定url读取（下载）内容到字符串

- (instancetype)initWithContentsOfURL:(NSURL *)url encoding:(NSStringEncoding)enc error:(NSError **)error;

+ (instancetype)stringWithContentsOfURL:(NSURL *)url encoding:(NSStringEncoding)enc error:(NSError **)error;

9.3 将字符串内容写到指定url/path

/* Write to specified url or path using the specified encoding.*/

- (BOOL)writeToURL:(NSURL *)url atomically:(BOOL)useAuxiliaryFileencoding:(NSStringEncoding)encerror:(NSError **)error;

- (BOOL)writeToFile:(NSString *)path atomically:(BOOL)useAuxiliaryFileencoding:(NSStringEncoding)encerror:(NSError **)error;

10.字符串化

10.1 NSString & Class

// 获取某个对象的具体类名，传入[obj class]，相当于[objclassName]

FOUNDATION_EXPORT NSString *NSStringFromClass(Class aClass);

// 基于类名获取类

FOUNDATION_EXPORT Class NSClassFromString(NSString *aClassName);

示例：

NSLog(@"[constString2 className] = %@", [constString2 className]); // __NSCFConstantString

NSLog(@"NSStringFromClass([constString2 class]) = %@", NSStringFromClass([constString2class])); //__NSCFConstantString

NSLog(@"object_getClassName(constString2) = %s", object_getClassName(constString2));// __NSCFConstantString

// 返回C字符串格式的类名

const char* className = class_getName([obj class]);

10.2 NSString & SEL

类似的还有NSStringFromSelector/NSSelectorFromString。

Class _alertManager = NSClassFromString([NSString stringWithFormat:@"_UIAlertManager"]);

SEL methodSel = NSSelectorFromString([NSStringstringWithFormat:@"topMostAlert"]);

if ([_alertManager respondsToSelector:methodSel])

{

id topView = objc_msgSend(_alertManager, methodSel);

}

10.3 NSString & CGPoint/CGSize/CGRect

NSStringFromCGPoint/CGPointFromString、NSStringFromCGSize/CGSizeFromString、 NSStringFromCGRect/CGRectFromString。