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IOS KVC (Key-value Coding)

KVC refers to nskeyvaluecoding, an informal Protocol that provides a mechanism to indirectly access the properties of an object

Common use methods:

• Get value

  • Valueforkey: Value based on attribute name

  • Valueforkeypath: Values based on path (e.g.[person valueforkeypath:@ "Car.price"] )

  • Valueforundefinedkey default implementation is to throw an exception, you can override this function to do error handling (less)

• modifying values

  • Setvalue:forkey: Setting values based on attributes

  • Setvalue:forkeypath: Setting values based on path

  • Setvalue:forundefinedkey:

  • Setnilvalueforkey: Called when Nil is set on a non-class object property, throws an exception by default

• Dictionary Turn model

  • Setvaluesforkeyswithdictionary: Dictionary Turn model

On the code:

Define a Hscar class

////  HSCar.h//  KVC////  Created by hans on 15/7/13.//  Copyright ? 2015年 hans. All rights reserved.//#import <Foundation/Foundation.h>@interface HSCar : NSObject/** 名字 */@property (nonatomic, copy) NSString *name;/** 价格 */@propertydouble price;@end

Define a Hsbook

////  HSBook.h//  KVC////  Created by hans on 15/7/13.//  Copyright ? 2015年 hans. All rights reserved.//#import <Foundation/Foundation.h>@interface HSBook : NSObject/** 书名 */@property (nonatomic, copy) NSString *name;/** 价格 */@propertydouble price;@end

Define a Hsperson class

// //HSPerson.h  //KVC  // // Created by Hans on 15/7/13.  //Copyright 2015 Hans. All rights reserved.  // #import  <foundation/foundation.h>< Span class= "hljs-annotation" > @class Hscar;  @interface  Hsperson:nsobject/** name */  @property  ( nonatomic, copy) NSString *name; /** Age */  @property  (nonatomic, copy) NSString *age; /** car */  @property  (Nonatomic, Strong) Hscar *car;  @end  

////  HSPerson.m//  KVC////  Created by hans on 15/7/13.//  Copyright ? 2015年 hans. All rights reserved.//#import "HSPerson.h"@implementation HSPerson{    // 体重    double _weight;}- (void)showWeight{    NSLog(@"weight: %f", _weight);}@end

Implemented in Viewcontroller

////VIEWCONTROLLER.M//KVC////Created by Hans on 15/7/13.//Copyright? 2015 Hans. All rights reserved.//#Import "ViewController.h"#Import "HSPerson.h"#Import "HSCar.h"#Import "HSBook.h"@interfaceViewcontroller ()@end@implementationviewcontroller-(void) Viewdidload {[SuperViewdidload]; Hsperson *person = [HspersonNew]; Person.name = @"Hans"; Person.age = at; Person.car = [HscarNew]; Person.car.name = @"Lamborghini"; Person.car.price =10000000.0;/** valueforkey: */NSLog (@"Name:%@ Age:%@", [Person valueforkey:@"Name"], [Person valueforkey:@"Age"]);//2015-07-13 22:32:02.356 kvc[54356:872650] Name:hans age:23    /** Valueforkeypath: */NSLog (@"name:%@ Price:%@", [Person valueforkeypath:@"Car.name"], [Person valueforkeypath:@"Car.price"]);//2015-07-13 22:51:27.075 kvc[54669:885579] Name: Lamborghini price:10000000    /** setvalue:forkey: */[Person setvalue:@"Hanshhh"forkey:@"Name"]; [Person setvalue:@" the"forkey:@"Age"]; NSLog (@"Name:%@ Age:%@", [Person valueforkey:@"Name"], [Person valueforkey:@"Age"]);//2015-07-13 22:53:54.876 kvc[54709:886954] name:hanshhh age:100    /** Setvalue:forkeypath: */[Person setvalue:@"Ferrari"forkeypath:@"Car.name"]; [Person setvalue:@ (9999999) forkeypath:@"Car.price"]; NSLog (@"name:%@ Price:%@", [Person valueforkeypath:@"Car.name"], [Person valueforkeypath:@"Car.price"]);//2015-07-13 22:56:36.336 kvc[54767:888926] Name: Ferrari price:9999999    /** Changing private properties * /[Person setvalue:@ ( -) forkeypath:@"_weight"]; [Person Showweight];//2015-07-13 23:01:15.151 kvc[54847:892122] weight:120.000000    /** Dictionary Turn model * /    //1. Simple ConversionNsdictionary *dict1 = @{@"Name": @"Hans",                           @"Age": @"All",                           };    [Person Setvaluesforkeyswithdictionary:dict1]; NSLog (@"Name:%@, Age:%d", Person.name, Person.age);//2015-07-13 23:04:20.298 kvc[54943:895092] Name: Hans, Age:23    //2. Complex model conversion (note: Person.car cannot be converted, it becomes a Dictionary object, it is simply a pointer assignment)Nsdictionary *dict2 = @{@"Name": @"Hansha haha",                           @"Age": @"All",                           @"Car": @{                                   @"Name": @"Lamborghini",                                   @"Price": @"10000000"},                            };    [Person Setvaluesforkeyswithdictionary:dict2]; NSLog (@"%@", Person.car);//2015-07-13 23:10:32.310 kvc[55019:899474] {//name = "\U5170\U535A\U57FA\U5C3C";//Price = 10000000;//    }    /** Other Operations * /Hsbook *book1 = [HsbookNew]; Book1.name = @"Netting"; Book1.price =51.0; Hsbook *BOOK2 = [HsbookNew]; Book2.name = @"Out of Control"; Book2.price =40.0; Hsbook *BOOK3 = [HsbookNew]; Book3.name = @"Heterogeneous"; Book3.price =60.0;    Person.books = @[book1, Book2, BOOK3]; NSLog (@"%@", [Person.books valueforkeypath:@"@count"]); NSLog (@"%@", [Person.books valueforkeypath:@"@avg. Price"]); NSLog (@"%@", [Person.books valueforkeypath:@"@min. Price"]); NSLog (@"%@", [Person.books valueforkeypath:@"@max. Price"]);//2015-07-13 23:20:43.434 kvc[55171:905643] 3//2015-07-13 23:20:43.434 kvc[55171:905643] 50.333333333333333333333333333333333333//2015-07-13 23:20:43.435 kvc[55171:905643]//2015-07-13 23:20:43.435 kvc[55171:905643]}- (void) Didreceivememorywarning {[SuperDidreceivememorywarning];//Dispose of any resources, can be recreated.}@end

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