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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）
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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)
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- (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：
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// 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：
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//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)
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// 创建一个字符串独享，其值为空 + (instancetype)string; |
示例：
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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： |
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// 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：
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// 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）
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// Thenumber of Unicode characters in the receiver. @property (readonly) NSUInteger length; |
示例：
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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）
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// 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：
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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
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//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。
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/* 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
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// 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
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// 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
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// 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：
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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
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// 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：
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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：
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- (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
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/* 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）
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// 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）
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/* 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）
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// 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）
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// 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：
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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)
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/* 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
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// 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:@””;
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// 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
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- (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
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// 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
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- (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
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- (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
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/* 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
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// 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：
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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。
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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。
参考：
NSString&NSMutableString常用操作梳理（转）
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原文地址：http://www.cnblogs.com/cc412/p/4688914.html
