OC Language -04-OC language-core syntax

One, dot syntax

1> Basic Use

• Point syntax is essentially a call to the Set method/get method

2> Use note

• If it appears to the right of the assignment operator, it is converted to the Get method at execution time
• If it appears to the left of the assignment operator, it is converted to the Set method when executed
• You cannot use self with self in a set, get method, which can cause a dead loop.

Ii. Property and Synthesize keywords

1> @property

1. Role

   ① 自动生成某个成员变量的set方法和get方法

2. Use note

   ① 只能出现在@interface中② 可以使用逗号运算符为多个同类型的成员变量生成setter和getter③ 为了与点语法匹配，使用@property的成员变量不要以下划线开头④ @property可以同时完成@synthesize的任务⑤ @property默认生成的成员变量是@private类型的以下划线开头

2> @synthesize

1. Role

   ① 自动生成某成员变量的setter和getter的实现② 可以指定要访问的成员变量的名字，通常是以下划线开头

2. Use note

   ① 只能出现在@implimentation中② 可以使用都好运算符同时生成多个setter和getter的实现③ 若未指定要访问的成员变量，默认会访问生成@synthesize后名字一  样的成员变量④ 若访问的成员变量未找到，将会自动生成@private类型的以下划线  开头（或与@synthesize后名字一样的）的成员变量 

III. type of ID

1> Basic Meaning

• Universal pointer that can point to any OC object
• Can be understood as NSObject *

2> Use note

• ID does not add a symbol * when defining a variable, which itself already contains

Iv. Construction Methods

1> effect

• Used to initialize the object, returning an initialized object

2> about +new methods

1. +new equivalent to +alloc method and-init method

2. +alloc method and-init method

   ① +alloc方法1）返回值为id类型2）为对象分配内存空间，并返回该对象② -init方法1）返回值为id类型2）初始化当前对象，并返回初始化好的对象

3> steps to override the-init method

1. Call Super's-init method

   ① 初始化父类中的成员变量和其他属性② 返回当前对象，并赋值给self③ 根类将isa指针初始化为最初调用init方法的类

2. Initializing a subclass member variable

3. Returns the Initialized object

4> Custom-init method

1. Applicable occasions

   ① 当初始化成员变量时，需要将成员变量初始化不同的值，通常需要自定义-init方法，将指定的值作为-init方法的参数

2. Specification

   ① 一定是对象方法，以-开头② 返回值一定是id类型③ 方法名一定以init开头

V. Classification (category)

1> effect

• Extend some methods for a class without changing the original class
• Usually works with large classes, the different types of methods of the classes are written in different classifications

2> definition

• The definition of a classification is similar to the definition of a class, with parentheses following the class name to indicate the name of the category
• Classification is usually named by module

3> Use note

• Classification can only be extended to a class and cannot be extended by member variables
• member variables in the original class can be accessed in the implementation of the classification method
• The method of implementing the original class in the classification will invalidate the implementation of the method in the original class.
• When a method is called, it is first found in the taxonomy, then found in the original class, and finally in the parent class.
• When more than one taxonomy of the original class finds a method, it is preferred to find it in the last compiled category

Six, NSString class

1> NSString * with char *

1. NSString *

   NSString \*指向OC字符串对象的指针② NSString是OC字符串类封装了字符串相关操作的方法

2. char *

   char \*创建的是指向C语言字符或字符串的指针② char \*只能存储字符指针或字符串指针，没有相关操作

2> NSString and Nsmutablestring

• The string object created by NSString is immutable, and the string object created by Nsmutablestring can be changed

Methods of 3> NSString

2. Two methods that a subclass of NSString must implement

   ① -length 对象方法，获取字符串的长度② -characterAtIndex: 对象方法，获取字符串指定索引位置的字符

4. Initialize method

   ① +(NSString*)stringWithString: 类方法，创建一个字符串常量，在  Xcode6.0中已经没有该方法，用字符串常量直接创建② +(NSString*)stringWithFormat: 类方法，合成一个新的字符串③ -(NSString*)initWithString: 对象方法，在字符串对象初始化时，为其赋值一个字符串常量④ -(NSString*)initWithFormat: 对象方法，在字符串对象初始化时，为其赋值一个新合成的字符串

6. Methods for reading strings in a file

   +(NSString*)stringWithContentsOfFile: encoding: error: 类方法

8. Methods for getting strings in the network

   +(NSString*)stringWithContentsOfURL: encoding: error: 类方法

9. Methods for string manipulation

   ① gets the substring of the specified range of the string-(NSString *) Substringwithrange: Object method,nsrange is struct type, return substring ② replace substring within specified range in string with specified string-(NSString *) Stringbyreplacingcharactersinrange:withstring: Object method, the string that returns the row ③ the range of substrings in the parent string-(nsrange) Rangeofstring: Object method, returning  Nsrange type ④ Compare two string contents-(BOOL) isequaltostring: (NSString *) Astring object method, return BOOL type ⑤ compare size of two strings-(  Nscomparisonresult) Compare: (NSString *) Astring object method, return nscomparisonresult enum type ⑥ split string with specified string-(Nsarray *) Componentsseparatedbystring: (NSString *) Separator object method, return nsarray array type pointer     

Vii. Methods of Description

1> Basic Use

• , the corresponding description method is called
• You can override the description method so that it can output the expected information through the class/object name

2> +description and-description

1. +description method

   *类型

2. -description method

   ① 对象方法，默认输出格式为<类名：内存地址>② 返回值为NSString *类型③ 不要在-description方法中用NSLog函数一%@格式输出self

Viii. Types of SEL

1> Basic Use

1. Meaning

   ① SEL本质上是一个指针类型的数据② 保存的是方法的地址

2. Role

   ① 将方法包装成SEL类型的数据② 每个对应一个唯一的SEL类型数据③ 通过SEL类型的数据可以间接调用类/对象方法

2> how the method is called indirectly through the SEL type

1. Indirectly called by method name

   @selector（方法名），返回一个与参数对应的SEL类型的数据② performSelector:(SEL)，通过SEL类型的数据间接的调用类/对象方  法③ performSelector:(SEL) WithObject:(id)，通过SEL类型数据调用含  参数的类/对象方法

2. Indirect invocation by method name in string form

   NSSelectorFromString: 将字符串类型的方法名转换成该方法对应的  SEL类型的数据② NSStringFromSelector: 将SEL类型的数据转换成字符串类型的方法  名③ 通过转化得到到SEL类型数据，再间接调用方法

Use of 3> _cmd

• _cmd represents the SEL type data corresponding to the current method
• Methods cannot be indirectly called through _cmd in a method, which causes a dead loop

Ix. examples

/* 1. Create a person class, properties: Name; 2. The custom Init method, in initialization, is the name 3 for each person object. Add a category containing the motion method to the person class with the name Sports 4. Overriding the-description method, When you make it output the person object, output the Name property of the object 5. Calling methods indirectly via SEL*/#import <foundation/foundation.h>/***** Define Person Class*****/@interface for person:nsobject//@propert declare member variables, and omit @synthesize@property NSString *name;/* Custom constructor method that assigns a value to the member variable name when the person object is initialized*/-(ID) initwithname: (nsstring*) name;//determine whether the names of two people are the same-(void) Issamename: (Person*) p;@end/**Implementation of the *person class***/@implementation person-(nsstring*) description{return self.name;} -(ID) Initwithname: (nsstring*) name{self.name = name; return self;} -(void) Issamename: (Person*) p{/* Call NSString Object method isequaltostring determine whether the names of two people are the same*/if ([Self.name isequaltostring:p.name]) {NSLog (@ "\ n These two names are:%@", self); }//By overriding the description method to output the object's properties through the object name NSLog (@ "\ n the names of these two persons are:%@\t%@", Self, p);}@end/**** Add a category to the person class****/@interface person (Sports)//Add table tennis to the person class this method-(void) playtabletennis;//for the person class to play basketball this method-(void) Playbasketball;@end/*The realization of classification sports of *person**/@implementation person (Sports)-(void) playtabletennis{NSLog (@ "\n%@ is playing table tennis", self);} -(void) playbasketball{NSLog (@ "\n%@ is playing basketball", self);}@end/***** test function Main **** */int Main () { @autoreleasepool {///define two strings to hold two names NSString * str = @ "Tom"; NSString *STR2 = @ "Jack";//define two person objects and invoke the overridden constructor method person Span class= "Hljs-keyword" >*p = [[Person alloc] initwithname:str]; Person *p2 = [[Person alloc] initwithname:str2];//Call method indirectly by method name [P Performselector: @selector (issamename:) WITHOBJECT:P2]; The method is called indirectly through the method name in string form [P performselector:nsselectorfromstring (@ "Playbasketball")];} return 0,                

OC Language -04-OC language-core syntax