- 浏览: 38777 次
- 性别:
- 来自: 北京
最近访客 更多访客>>
文章分类
最新评论
-
chenniaoc:
http://www.techotopia.com/index ...
objective-c NSString 使用详细指南
Declaring Constant String Objects
A constant string object is declared by encapsulating the string in double quotes (") preceded by an @ sign. For example:
@"This is a constant character string object";
In order to display the current value of a string object using NSLog, simply reference the string using '%@' as follows:
NSLog (@"%@", @"This is a constant character string object");
Even though all we are doing here is creating a constant string object, keep in mind that this is still an object. As such, it has a range of methods that we can call on it. For example string objects have a length method that returns the number of characters in the string. We can, therefore, call this on a constant string object:
int len = [@"Hello" length]; NSLog (@"Length of string = %i", len);
The above code declares a constant string object containing the word "Hello" and calls the length method of object. The result is assigned to an integer variable named len which in turn is displayed using NSLog. When compiled and executed, we get the following output:
Length of string = 5
Constant string objects are actually instantiated from the NSConstantString class which, much like the other classes we will look at in this chapter, is actually a subclass of the NSString class. In practice, given the way that constant strings are used, it is unlikely that you will need to specifically declare your string constants as being of type NSConstantString. It is more likely that you will declare the string as we have done in this section and let the compiler handle the rest.
[edit ] Creating Mutable and Immutable String Objects
Two additional types of Objective-C string objects are mutable and immutable . When you create a string object of type NSString you are creating an immutable string object. This means that once a string has been assigned to the object, that string cannot subsequently be modified in any way.
NSString *string1 = @"This string is immutable";
Mutable string objects, on the other hand, are declared using the NSMutableString class and allow the string contained within the object to be modified using a variety of methods (some of which will be covered in the remainder of this chapter). NSMutableString is a subclass of NSString, which in turn is a subclass of NSObject. Mutable strings cannot be initialized simply by assigning a constant string object as we did above since that will just give us a pointer to an immutable constant string object. Instead, the string constant must be copied into the mutable string object. For example:
NSMutableString *string2 = [NSMutableString stringWithString:@"This string is mutable"];
Once a string has been declared as immutable, the only way to get a mutable version of the string is to create a mutable string object and copy the contents of the immutable string object to it. This can be achieved using the NSMutableString stringWithString class method. For example:
NSString *string1 = @"This is a string"; NSMutableString *string2; string2 = [NSMutableString stringWithString: string1];
Once executed, the above code will create an immutable string object (string1) initialized with the text "This is a string" and an empty pointer to an immutable string object (string2). The stringWithString class method of the NSMutableString class is then called, passing though the immutable string1 as an argument. This method returns a new object containing the immutable string and assigns it to string2. We now have a mutable copy of the immutable string1 object.
[edit ] Getting the Length of a String
The length of the string in a string object can be obtained by accessing the length method of the string object:
NSString *string1 = @"This string is Immutable"; int len = [string1 length]; NSLog (@"String length is %i", len);
The above code fragment will produce the following output when executed:
String length is 24
[edit ] Copying a String
When copying one string object to another it might be tempting to think that you can simply assign the object from one variable to another. For example, if we had two integer variables and wanted to assign the value of one to the other we could simply do the following:
int a = 10; int b; a = b;
After the above code has executed, both variables a and b will contain the value 10 . The same is not, however, true of string objects. Take for example the following code fragment:
NSMutableString *string1; NSMutableString *string2; string1 = [NSMutableString stringWithString: @"This is a string"]; string2 = string1;
What we have achieved here is to create two variables (string1 and string2) that point to the memory location of the same string object. This is because the '*' before the variable names in the declarations indicates that this is a pointer to an object, not an actual object. Any time that we access the object referenced by either of these pointers we will, in fact, be accessing the same object. To prove this, we can make a change using the string2 reference and then display the string associated with both the string1 and string1 object pointers:
NSMutableString *string1; NSMutableString *string2; string1 = [NSMutableString stringWithString: @"This is a string"]; string2 = string1; [string2 appendString: @" and it is mine!"]; NSLog (@"string1 = %@", string1); NSLog (@"string2 = %@", string2);
The above code will display the following output, proving that both string1 and string2 point to the same object since only one reference was modified, yet both show the change:
2009-11-03 14:35:37.731 t[32239:10b] string1 = This is a string and it is mine! 2009-11-03 14:35:37.732 t[32239:10b] string2 = This is a string and it is mine!
To actually copy one string object to another string object we must use stringWithString method the NSMutableString class:
NSMutableString *string1; NSMutableString *string2; string1 = [NSMutableString stringWithString: @"This is a string"]; // Initialize string1 string2 = [NSMutableString stringWithString: string1]; // Copy string1 object to string2 [string2 appendString: @" and it is mine!"]; // Modify string2 NSLog (@"string1 = %@", string1); NSLog (@"string2 = %@", string2);
When executed, the appended text appears only in the object referenced by string2 since string2 now references a different object to that referenced by string1:
2009-11-03 14:42:10.426 t[32263:10b] string1 = This is a string 2009-11-03 14:42:10.427 t[32263:10b] string2 = This is a string and it is mine!
[edit ] Searching for a Substring
A common requirement when working with strings is to identify whether a particular sequence of characters appears within a string. This can be achieved using the rangeOfString method. This method returns a structure of type NSRange . The NSRange structure contains a location value providing the index into the string of the matched substring and a length value indicating the length of the match.
NSString *string1 = @"The quick brown fox jumped"; NSRange match; match = [string1 rangeOfString: @"brown fox"]; NSLog (@"match found at index %i", match.location); NSLog (@"match length = %i", match.length);
The NSLog call will display the location and length of the match. Note that the location is an index into the string where the match started and that the index considers the first position in a string to be 0 and not 1. As such, the location in our example will be 10 and the length will be 9.
In the event that no match is found, the rangeOfString method will set the location member of the NSRange structure to NSNotFound . For example:
NSString *string1 = @"The quick brown fox jumped"; NSRange match; match = [string1 rangeOfString: @"brown dog"]; if (match.location == NSNotFound) NSLog (@"Match not found"); else NSLog (@"match found at index %i", match.location);
[edit ] Replacing Parts of a String
Sections of a mutable string may be replaced by other character sequences using the replaceCharactersInRange method. This method directly modifies the string object on which the method is called so only works on mutable string objects.
This method requires two arguments. The first argument is an NSRange structure consisting of the location of the first character and the total number of characters to be replaced. The second argument is the replacement string. An NSRange structure can be created by calling NSMakeRange and passing though the location and length values as arguments. For example, to replace the word "fox" with "squirrel" in our sample mutable string object we would write the following Objective-C code:
NSMutableString *string1 = [NSMutableString stringWithString: @"The quick brown fox jumped"]; [string1 replaceCharactersInRange: NSMakeRange(16, 3) withString: @"squirrel"]; NSLog (@"string1 = %@", string1);
As you may have noted from the above example, the replacement string does not have to be the same length as the range being replaced. The string object and replacement method will resize the string automatically.
[edit ] String Search and Replace
Previously we have covered how to perform a search in a string and how to replace a subsection of a string using the rangeOfString and replaceCharactersInRange methods respectively. The fact that both of these methods use the NSRange structure enables us to combine the two methods to perform a search and replace. In the following example, we use rangeOfString to provide us with an NSRange structure for the substring to be replace and then pass this through to replaceCharactersInRange to perform the replacement:
NSMutableString *string1 = [NSMutableString stringWithString: @"The quick brown fox jumped"]; [string1 replaceCharactersInRange: [string1 rangeOfString: @"brown fox"] withString: @"black dog"];
When executed, string1 will contain the string "The quick black dog jumped".
[edit ] Deleting Sections of a String
Similar techniques to those described above can be used to delete a subsection of a string using the deleteCharactersInRange method. As with the preceding examples, this method accepts an NSRange structure as an argument and can be combined with the rangeOfString method to perform a search and delete:
NSMutableString *string1 = [NSMutableString stringWithString: @"The quick brown fox jumped"]; [string1 deleteCharactersInRange: [string1 rangeOfString: @"jumped"]];
[edit ] Extracting a Subsection of a String
A subsection of a string can be extracted using the substringWithRange method. The range is specified using an NSRange structure and the extracted substring is returned in the form of an NSString object:
NSMutableString *string1 = [NSMutableString stringWithString: @"The quick brown fox jumped"]; NSString *string2; string2 = [string1 substringWithRange: NSMakeRange (4, 5)]; NSLog (@"string2 = %@", string2);
When executed, the above code will output the substring assigned to string2 ("quick").
Alternatively, a substring may be extracted from a given index until the end of the string using the subStringFromIndex method. For example:
NSMutableString *string1 = [NSMutableString stringWithString: @"The quick brown fox jumped"]; NSString *string2; string2 = [string1 substringFromIndex: 4];
Similarly, the subStringToIndex may be used to extract a substring from the beginning of the source string up until a specified character index into the string.
[edit ] Inserting Text into a String
The insertString method inserts a substring into a string object and takes as arguments the NSString object from which the new string is to inserted and the index location into the target string where the insertion is to be performed:
NSMutableString *string1 = [NSMutableString stringWithString: @"The quick brown fox jumped"]; [string1 insertString: @"agile, " atIndex: 4];
[edit ] Appending Text to the End of a String
Text can be appended to the end of an existing string object using the appendString method. This method directly modifies the string object on which the method is called and as such is only available for mutable string objects.
NSMutableString *string1 = [NSMutableString stringWithString: @"The quick brown fox jumped"]; [string1 appendString: @" over the lazy dog"]; NSLog (@"string1 = %@", string1);
[edit ] Comparing Strings
String objects cannot be compared using the equality (==) operator. The reason for this is that any attempt to perform a comparison this way will simply compare whether the two string objects are located at the same memory location. Let's take a look at this via an example:
NSString *string1 = @"My String"; NSString *string2 = @"My String"; if (string1 == string2) NSLog (@"Strings match"); else NSLog (@"Strings do not match");
In the above code excerpt, string1 and string2 are pointers to two different string objects both of which contain the same character strings. If we compare them using the equality operator, however, we will get a "Strings do not match" result. This is because the if (string1 == string2) test is asking whether the pointers point to the same memory location. Since string1 and string2 point to entirely different objects the answer, obviously, is no.
We can now take this a step further and change the code so that both string1 and string2 point to the same string object:
NSString *string1 = @"My String"; NSString *string2; string2 = string1; if (string1 == string2) NSLog (@"Strings match"); else NSLog (@"Strings do not match");
Now when we run the code, we get a "Strings match" result because both variables are pointing to the same object in memory.
To truly compare the actual strings contained within two string objects we must use the isEqualToString method:
NSString *string1 = @"My String"; NSString *string2 = @"My String 2"; if ([string1 isEqualToString: string2]) NSLog (@"Strings match"); else NSLog (@"Strings do not match");
Another option is to use the compare method (to perform a case sensitive comparison) or the caseInsenstiveCompare NSString methods. These are more advanced comparison methods that can be useful when sorting strings into order.
[edit ] Checking for String Prefixes and Suffixes
A string object can be tested to identify whether the string begins or ends with a particular sequence of characters (otherwise known as prefixes and suffixes). This is achieved using the hasPrefix and hasSuffix methods respectively, both of which return boolean values based on whether a match is found or not.
NSString *string1 = @"The quick brown fox jumped"; BOOL result; result = [string1 hasPrefix: @"The"]; if (result) NSLog (@"String begins with The"); result = [string1 hasSuffix: @"dog"]; if (result) NSLog (@"String ends with dog");
Converting to Upper or Lower Case
The Foundation NSString classes provide a variety of methods for modifying different aspects of case within a string. Note that each of these methods returns a new string object reflecting the change, leaving the original string object unchanged.
- capitalizedString
Returns a copy of the specified string with the first letter of each word capitalized and all other characters in lower case:
NSString *string1 = @"The quicK brOwn fox jumpeD"; NSString *string2; string2 = [string1 capitalizedString];
The above code will return a string object containing the string "The Quick Brown Fox Jumped" and assign it to the string2 variable. The string object referenced by string1 remains unmodified.
- lowercaseString
Returns a copy of the specified string with all characters in lower case:
NSString *string1 = @"The quicK brOwn fox jumpeD"; NSString *string2; string2 = [string1 lowercaseString];
The above code will return a string object containing the string "the quick brown fox jumped" and assign it to the string2 variable. The string object referenced by string1 remains unmodified.
- uppercaseString
Returns a copy of the specified string with all characters in upper case:
NSString *string1 = @"The quicK brOwn fox jumpeD"; NSString *string2; string2 = [string1 uppercaseString];
The above code will return a string object containing the string "THE QUICK BROWN FOX JUMPED" and assign it to the string2 variable. The string object referenced by string1 remains unmodified.
Converting Strings to Numbers
String objects can be converted to a variety of number types:
- Convert String to int
NSString *string1 = @"10"; int myInt = [string1 intValue]; NSLog (@"%i", myInt);
- Convert String to double
NSString *string1 = @"10.1092"; double myDouble = [string1 doubleValue]; NSLog (@"%f", myDouble);
- Convert String to float
NSString *string1 = @"10.1092"; float myFloat = [string1 floatValue]; NSLog (@"%f", myFloat);
- Convert String to NSInteger
NSString *string1 = @"10"; NSInteger myInteger = [string1 integerValue]; NSLog (@"%li", myInteger);
Converting a String Object to ASCII
The string contained within a string object can be extracted and converted to an ASCII C style character string using the UTF8String method. For example:
NSString *string1 = @"The quick browen fox"; const char *utfString = [string1 UTF8String]; printf ("Converted string = %s\n", utfString);
发表评论
-
property “assign” and “retain” for delegate
2012-06-25 01:11 11381 Answer active oldest vo ... -
如何从一个方法中返回来自于集合的对象
2012-06-25 00:20 1030- (ImageScrollView *)dequeue ... -
类似Tweetie那种拽下来就refresh的代码
2012-06-22 12:28 772http://github.com/enormego/EGOT ... -
difference between frame and bounds Property
2012-06-17 21:55 1270bounds The bounds rectangle, wh ... -
Apple Offical : View Programming Guide for iOS
2012-06-16 17:06 992https://developer.apple.com/lib ... -
use UINavigationController inside a UITabBarController
2012-06-16 13:39 1548If you want to add a UINavigati ... -
关于ios中bounds与frame
2012-06-16 12:03 19441.ios中的bounds是指相对于视图自己的坐标,所以默认v ... -
Enum常量放入NSArray的方法
2010-09-07 23:14 2471ypedef enum { UIViewAnim ... -
What is Core Data?
2010-08-31 22:03 1336Path to Success The Core Data P ... -
Iphone开发常用软件
2010-07-19 16:41 808粒子特效:particleillusion -
iPhone にインストールされているフォント一覧
2010-07-19 13:21 1549タイトルの通り、iPhone にインストールされているフォン ... -
Cocoaのメモリ管理(3)
2010-07-15 14:42 709保持と解除という方法 ... -
The cocos2d Tips & Tricks
2010-07-02 14:32 1063The cocos2d Tips & Tricks i ... -
Declared Properties
2010-06-30 14:13 876Writability These attributes s ...
相关推荐
Objective-C语言有关NSString的各种用法(创建、截取、判断比较、转化数据类型、拼接、替换…)
展示如何使用Objective-C语言的独有特性以及Foundation框架的众多特性。此外,书中广 泛提供了多种问题的解决方案,包括: ● 使用Xcode进行应用开发 ● 使用字符串、数字与对象集合 ● 使用NSArray、NSString、...
是iOS开发中Objective-C语言基础的NSString操作的总结性文档,里面包含了NSString操作的大部分方法
Objective-C 中 NSString 关于常见 Hash 算法的分类,能对字符串,文件进行 Hash 运算,具备 HMAC 功能。支持的 Hash 算法有:MD5、SHA1、SHA256、SHA512。
Google Objective-C Style Guide 中文版 目录 例子 空格与格式 空格与制表符 行宽 方法声明与定义 方法调用 @public与@private 异常 协议 命名 文件名 Objective-C++ 类名 分类名 Objective-C方法名 变量名 注释 ...
word源码java 这是一个基于Objective-C语言的基础案例集。旨在用于给初学者快速了解Objective-C语言的语法。...这个案例是关于NSString类的基本使用案例。 ocprj7和ocprj7_1 这个案例是关于集合相关类的基
[map setObject:@"c" forKey:@"content"]; 或者 NSMutableArray *list = [[NSMutableArray alloc]init]; NSMutableDictionary *map1 = [[NSMutableDictionary alloc]init]; [map1 setObject:@"a1" forKey:@...
ytoolkit 是 Objective-C 的一个常用开发工具包,包括: 一个快速的base64编码(纯C,及NSData/NSString的category),可以看项目页面的README和代码库里的benchmark,或者在ytoolkitdemo里跑profile一个cocoa附加...
Objective-C学习心得初学objective-c,自己写的一个demo,有不足之处请指正: 效果图:
使用 Objective-C 的运行时反射技术。示例代码:from pyobjus import ObjcClass, ObjcMethod, MetaObjcClass class NSString(ObjcClass): __objcclass__ = 'NSString' __metaclass__ = ...
Objective-C-如何创建和使用NSString最新2017-印地语- 视频:-Yogesh Patel在Objective-C中使用NSString类的介绍。 在本频道中,我将在多部视频中讲授大多数目标C编程语言。 一定要去MyChannel享受视频和不要忘记...
在 Objective-C 中实现的加密库。 AES、SHA、RSA 该库旨在作为以Objective-C方式实施RSA / AES / SHA加密算法的实验。 那里有很多加密库,但我没有找到一个具有纯 Objective-C(或面向对象)API 的库。 这个实现...
主要介绍了Objective-C中使用NSString类操作字符串的方法小结,文中讲到了字符串的分割和拼接等一些常见的用法,需要的朋友可以参考下
JSON Web 令牌的 Objective-c 实现。 在 iOS/MacOS 应用程序上编码和解码 JWT 的简单方法。 哈希算法 SHA256 SHA384 SHA512 应用程序接口 + (NSString *) encodeWithPayload:(NSDictionary *) andKey:...
前几天提前看到了新出的<Objective-C 2.0 程序设计>, 也就是<Programming in Objective-C 2.0(Section Edition)>的中文翻译版, 翻看了几章, 总体上感觉还是不错的. 翻译的质量我觉得比较满意吧. 个人觉得, 对一个还...
objective-c小技巧 1. 使用@property和@synthesize声明一个成员变量,给其赋值是时要在前面加上"self.",以便调用成员变量的setmember方法。 直接调用成员变量并且给其赋值:member=[NSString stringWithFormat...
NSString *string = [[NSString alloc] init]; string = @”i am an iOSDevTip too!”; (3)用initWithString创建字符串 代码如下: NSString *string = [[NSString alloc] initWithString:@”iOSDevTip is here!”...
基础语法:熟悉C语言基础是前提,Objective-C是在C语言的基础上增加了面向对象特性。 面向对象:理解类(Class)、对象(Object)、实例变量(Instance Variables)、方法(Methods)、继承(Inheritance)、封装...
-(NSMutableDictionary *)getObject:(NSString *)elName xmlData:(NSData *)xmlData; -(NSMutableArray *)getList:(NSString *)elName xmlData:(NSData *)xmlData; @end --- XmlResolve.m #import ...