SHUNMIAN

1 Object Hierarchy & Messaging
2 Reference

1 Object Hierarchy & Messaging

Item 6：Understand Properties

@property = _iVar + setter + getter。To prevent @property automatically create _iVar + setter + getter，use @dynamic；To customize your own iVar’s name (not _iVar)，use @synthesis。
@property attribues：atomicity(nonatomic，atomic)，read/write(readwrite，readonly)，memeory-management(assing，strong，weak，copy)，method name(getter，setter)。

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45 //  EOCCat.h
#import <Foundation/Foundation.h>

@interface EOCCat : NSObject
@property(nonatomic,strong) NSString *name0;
@property(nonatomic,strong) NSString *name1;
@property(nonatomic,strong) NSString *name2;

@property(nonatomic,strong,readonly) NSString *nameReadOnly;
@property(nonatomic,copy) NSString *nameCopy;
@property(nonatomic,assign,getter=isMale)BOOL male;
-(instancetype)initWithNameCopy:(NSString *)nameCopy;
-(void)changeNameCopy:(NSString *)nameCopy;
@end


//  EOCCat.m
#import "EOCCat.h"

@interface EOCCat()
@property(nonatomic, strong, readwrite) NSString *nameReadOnly;
@end

@implementation EOCCat
@synthesize name1 =_myName1;
@dynamic name2;

-(instancetype)initWithNameCopy:(NSString *)nameCopy{
    if(self = [super init]){
        _name0 = @"name0";
        _myName1 = @"myName1";
        //_name2 error, since dynamic forbidden its _iVar+setter+getter auto create
        //in init, one cannot use setter, thus [nameCopy copy] is used to conform to _nameCopy's copy attributes
        _nameCopy = [nameCopy copy];
        _nameReadOnly = @"readOnly1";
    }
    return self;
}

-(void)changeNameCopy:(NSString *)nameCopy{
    //nameCopy will be copied to self.nameCopy
    self.nameCopy = nameCopy;
    //self.nameReadOnly can only be changed once it redeclared as readwrite in .m
    self.nameReadOnly = @"readOnyly2";
}

Item 7：Access Instance Variables Primarily Directly When Accessing Them Internally

For external access，property usage is without doubt。
For internal access，use property except in init，setter，getter，dealloc。 Since property encapsulate setter(customization)，getter(lazy instantiate)， memory-managment(_iVar = someValue not retain new value and release old value while self.iVar do) and copy (_iVar = someValue don’t copy it while self.iVar = someValue do if @property with copy)。

Item 8：Understand Object Equality

Object euqality必须实现下面两个方法：用 isEuqal(用于两者比较)；hash用于collection内object的比较，例如set。前者相同的后者必须相同，后者相同的前者不用相同。两者都属于NSObject协议。
对于创建的Class，可以写isEqualToClass方法，例如NSString有isEqualToString，NSArray有isEuqalToArray，NSDictionary有isEuqalToDictionary。可以用isEqualToClass(不需要check类是否相同)来实现isEqual方法(需要check类是否相同，不同返回false)。

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23 -(BOOL)isEqualToPerson:(EOCPerson *)other{
    if(self == other) return YES; //if points to the same instance, return YES
    
    if(![self.firstName isEqualToString:other.firstName]){
        return NO;
    }
    if(![self.lastName isEqualToString:other.lastName]){
        return NO;
    }
    return YES;
}

-(BOOL)isEqual:(id)object{
    if([object isKindOfClass:[self class]]){
        return [self isEqualToPerson:object];
    }else{
        return [super isEqual:object];
    }
}

-(NSUInteger)hash{
    return [self.firstName hash]^[self.lastName hash];
}

Item 9：Use the Class Cluster Pattern to Hide Implementation Detail

类簇可以减少类的种类，子类信息被类簇隐藏，调用者不需要知道子类。比如NSSnumber是一个类簇，如果不使用类簇的话，需要为每一种基本类型都提供一种封装，这样会使类的数量极其庞大，程序员需要记住大量的类，但是如果使用类簇的话，只需要记住NSNumber这一个类就行了，具体使用这个类返回的是什么类型的对象，会在NSNumber类内部做处理和判断，而不需要调用者来关心，调用者只需要知道NSNumber的接口拿来用即可。
Subclass abstract class在类簇里和Subclass normal class是完全不一样的。后者可以是一个空的实现，因为super class已经提供了完整实现；而前者需要实现super class接口的函数，因为这部分在super class里只是一个空壳。

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77 //EOCMployee.h
#import <Foundation/Foundation.h>

typedef NS_ENUM(NSUInteger,EOCEmployeeType){
    EOCEmployeeTypeDeveloper,
    EOCEmployeeTypeDesigner,
    EOCEmployeeTypeFinance,
};

@interface EOCEmployee : NSObject
+(EOCEmployee *)employeeWithType:(EOCEmployeeType)type;
-(void)doWork;
@end



//EOCEmployee.m
#import "EOCEmployee.h"

@interface EOCEmployeeDeveloper : EOCEmployee
@end
@implementation EOCEmployeeDeveloper
-(void)doWork{
    NSLog(@"%@,%@",[self class],NSStringFromSelector(_cmd));
}
@end

@interface EOCEmployeeDesigner : EOCEmployee
@end
@implementation EOCEmployeeDesigner
-(void)doWork{
    NSLog(@"%@,%@",[self class],NSStringFromSelector(_cmd));
}
@end

@interface EOCEmployeeFinance : EOCEmployee
@end
@implementation EOCEmployeeFinance
-(void)doWork{
    NSLog(@"%@,%@",[self class],NSStringFromSelector(_cmd));
}
@end

@interface EOCEmployee()
@property(nonatomic,assign)EOCEmployeeType type;
@end

@implementation EOCEmployee

+(EOCEmployee *)employeeWithType:(EOCEmployeeType)type{
    EOCEmployee *employee;
    switch (type) {
        case EOCEmployeeTypeDeveloper:
            employee = [EOCEmployeeDeveloper new];
            break;
        case EOCEmployeeTypeDesigner:
            employee = [EOCEmployeeDesigner new];
            
        case EOCEmployeeTypeFinance:
            employee = [EOCEmployeeFinance new];
    }
    employee.type = type;
    return employee;
}

-(void)doWork{
    //Subclass implement this.
    //Without class cluster, you need to implement with lots of cumbersome if/else
    if(self.type == EOCEmployeeTypeDeveloper){
        //do developer work
    }else if (self.type == EOCEmployeeTypeDesigner){
        //do designer work
    }else if (self.type == EOCEmployeeTypeFinance){
        //do finance work
    }
}
@end

Item 10：Use Associated Objects to Attach Custom Data to Existing Classes

1.对已有的类进行实例变量扩展可以通过category结合runtime实现，具体有3个方法：objc_setAssociatedObject(id object, void *key, id value, objc_AssociationPolicy policy)，objc_getAssociatedObject(id object, void *key)，void objc_removeAssociatedObjects(id object)。

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20 //EOCPerson+ID.h
#import "EOCPerson.h"

@interface EOCPerson (ID)
@property(nonatomic, strong) NSString *id;
@end

//EOCPerson+ID.m
#import "EOCPerson+ID.h"
#import <objc/runtime.h>
@implementation EOCPerson (ID)

-(void)setId:(NSString *)id{
    objc_setAssociatedObject(self,@selector(id),id,OBJC_ASSOCIATION_RETAIN_NONATOMIC);
}

-(NSString *)id{
    return objc_getAssociatedObject(self,@selector(id));
}
@end