IOS KVC (Key-Value Coding)

IOS KVC (Key-Value Coding)
Common usage: Getting values
ValueForKey: valueForKeyPath based on the property name:[Person valueForKeyPath: @ "car. price"]) ValueForUndefinedKey throws an exception by default. You can rewrite this function for error handling (rarely used) to modify the value.
SetValue: forKey: setValue: forKeyPath: setValue: forUndefinedKey: setNilValueForKey: When nil is set for non-Class Object Attributes, an exception dictionary to model is thrown by default.
SetValuesForKeysWithDictionary: Code on dictionary-to-model conversion:

Define a HSCar class

/// HSCar. h // KVC /// Created by hans on 15/7/13. // Copyright©2015 hans. All rights reserved. // # import
  
   
@ Interface HSCar: NSObject/** name */@ property (nonatomic, copy) NSString * name;/** price */@ property (nonatomic, assign) double price; @ end
  

Define a HSBook class

/// HSBook. h // KVC /// Created by hans on 15/7/13. // Copyright©2015 hans. All rights reserved. // # import
  
   
@ Interface HSBook: NSObject/** title */@ property (nonatomic, copy) NSString * name;/** price */@ property (nonatomic, assign) double price; @ end
  

Define a heat map class

/// HSPerson. h // KVC /// Created by hans on 15/7/13. // Copyright©2015 hans. All rights reserved. // # import
  
   
@ Class HSCar; @ interface HSPerson: NSObject/** name */@ property (nonatomic, copy) NSString * name;/** age */@ property (nonatomic, copy) NSString * age;/** vehicle */@ property (nonatomic, strong) HSCar * car; @ end
  

/// HSPerson. m // KVC /// Created by hans on 15/7/13. // Copyright©2015 hans. all rights reserved. // # import heaterson. h @ implementation HSPerson {// weight 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 @ interface ViewController () @ end @ implementation ViewController-(void) viewDidLoad {[super viewDidLoad]; HSPerson * person = [HSPerson new]; person. name = @ hans; person. age = 23; person. car = [HSCar new]; person. car. name = @ Lamborghini; person. car. price = 10000000.0;/** valueForKey: */NSLog (@ name: % @ age: % @, [person valueForKey: @ name], [person valueForKey: @ age]); // 22:32:02. 356 KVC [54356: 872650] name: hans age: 23/** valueForKeyPath: */NSLog (@ name: % @ price: % @, [person valueForKeyPath: @ car. name], [person valueForKeyPath: @ car. price]); // 22:51:27. 075 KVC [54669: 885579] name: Lamborghini price: 10000000/** setValue: forKey: */[person setValue: @ hanshhh forKey: @ name]; [person setValue: @ 100 forKey: @ age]; NSLog (@ name: % @ age: % @, [person valueForKey: @ name], [person valueForKey: @ age]); // 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]); // 22:56:36. 336 KVC [54767: 888926] name: Ferrari price: 9999999/** change private attributes */[person setValue: @ (120) forKeyPath: @ _ weight]; [person showWeight]; // 23:01:15. 151 KVC [54847: 892122] weight: 120.000000/** dictionary-to-model * // 1. simple conversion of NSDictionary * dict1 ={@ name: @ Hans, @ age: @ 23,}; [person setValuesForKeysWithDictionary: dict1]; NSLog (@ name: % @, age: % d, person. name, person. age); // 23:04:20. 298 KVC [54943: 895092] name: Hans, age: 23 // 2. complex model conversion (Note: person. A car cannot be converted and will become a dictionary object. It is actually a simple pointer assignment.) NSDictionary * dict2 =@{@ name: @ hanhahaha, @ age: @ 23, @ car: @ {@ name: @ Lamborghini, @ price: @ 10000000},}; [person setValuesForKeysWithDictionary: dict2]; NSLog (@ % @, person. car); // 23:10:32. 310 KVC [55019: 899474] {// name = U5170U535aU57faU5c3c; // price = 10000000; //}/** other operations */HSBook * book1 = [HSBook new]; book1.name = @; book1.price = 51.0; HSBook * book2 = [HSBook new]; book2.name = @ out of control; book2.price = 40.0; HSBook * book3 = [HSBook new]; book3.name = @; 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]); // 23:20:43. 434 KVC [55171: 905643] 3 // 23:20:43. 434 KVC [55171: 905643] 50.333333333333333333333333333333333333 // 23:20:43. 435 KVC [55171: 905643] 40 // 23:20:43. 435 KVC [55171: 905643] 60}-(void) didReceiveMemoryWarning {[super didreceivemorywarning]; // Dispose of any resources that can be recreated .} @ end