[IOS] KVC and KVO

I. KVC and KVO
* "KVC": key value Coding * objective: to indirectly modify or obtain object attributes and reduce coupling between programs (classes and classes.
* "KVO": key value Observer (key value observation), Observer mode. (multiple methods are used to detect model changes) * objective: to make a response in a timely manner when an attribute of an object changes.
Ii. Usage of KVC

KVC is called the iOS development platform !!! You can quickly modify object attributes.

* [P1setValue: @ "xxxx" forKeyPath: @ "name"]; modifies the attributes of a specified object. * [arrvalueForKeyPath: @ "book. bookName "]; get object attributes. * KVC can directly obtain the array through the key. * When Using KVC, make sure that the key value exists. * principle: If the KVC value does not contain the specified key value, it automatically enters the internal Member of the object for search.
Iii. Usage of KVC
* KVO is usually used to observe the change of "an attribute of an object" and respond accordingly. (mostly used to observe model data) * one difference between KVO and the notification center: KVO can only stare at an object (working in the current region), and the notification center can traverse through many layers (such as viewController ). * KVO usage steps: * 1. [stuaddObserver: selfforKeyPath: @ "name" options: NSKeyValueObservingOptionNew | NSKeyValueObservingOptionOld context: @ "myObserver"]; * 2. observeValueForKeyPath. this method is automatically called when the specified key value changes * 3. removeObserver. all observer modes have poor performance and need to be removed in time.
Directly run the Code:

//// XNViewController. m // KVC----KVO // Created by neng on 14-6-21. // Copyright (c) 2014 neng. all rights reserved. // # import "XNViewController. h "# import" XNPerson. h "# import" XNStudent. h "# import" XNBook. h "@ interface XNViewController () @ end/*** KVC: Key Value Coding (Key Value encoding) * indirectly Modifies/obtains object attributes to reduce coupling between classes. * KVO: Key Value Observer (Key Value observation) KVO is usually used to observe "an object's attribute" and respond in a timely manner! The NSNotificationCenter is an object that requires the POST "Notification string" (indicating the event type of the listener) to exist, so that the notification center can work! * // @ Implementation XNViewController-(void) viewDidLoad {[super viewDidLoad]; // 1. modify the object attribute [self kvcDemo1]; // 2. for subclass, you can also directly modify [self kvcDemo2]; // 3. modify the book attribute of an object. (This is quite troublesome. Create a book object ). KVC statement [self kvcDemo3]; // 4. obtains the property value of an object. it can be obtained in batches (if it is an array ). [self kvcDemo4]; // KVO demo [self kvoDemo];}-(void) kvoDemo {XNStudent * stu = [[XNStudent alloc] init]; stu. name = @ "xuneng "; // set the listening object // 1 the observed object self // 2 the observed key value path // 3 the observed option // 4 the context: it is usually used to differentiate different observation events [stu addObserver: self forKeyPath: @ "name" options: NSKeyValueObservingOptionNew | NSKeyValueObservingOptionOld context: @ "myObserver"]; stu. name = @ "neng"; // modify // the performance of all observer modes is poor. You need to promptly remove [stu removeObserver: self forKeyPath: @ "name"]; stu. name = @ "xu"; // modify it again after removal}/** this method name is automatically called when the key value of the object specified by KVO changes: observed key value object: observed object change: Modified Dictionary (new and old values) context: Specifies the context passed in when the Observer */-(void) observeValueForKeyPath :( NSString *) keyPath ofObject :( id) object change :( NSDictionary *) change context :( void *) context {NSLog (@ "| -- % @ -- |", keyPath, object, change, context );} /*** modify the object attributes */-(void) kvcDemo1 {// 1. original method. modify the object attribute value XNPerson * p1 = [[XNPerson alloc] init]; p1.name = @ "xuneng"; p1.age = 24; // NSLog (@ "% @, % d ", p1.name, p1.age); NSLog (@" KVC1 demo1 --> % @ ", p1); // directly call the description method. // 2. KVC to modify [p1 setValue: @ "xxxx" forKeyPath: @ "name"]; [p1 setValue: @ "10" forKeyPath: @ "age"]; NSLog (@ "KVC2 demo1 --> % @, % d", p1.name, p1.age);}/*** for subclass, you can also directly change */-(void) kvcDemo2 {// 1. traditional Method XNStudent * p1 = [[XNStudent alloc] init]; // student p1.name = @ "student xuneng"; p1.age = 22; // NSLog (@ "% @, % d ", p1.name, p1.age); NSLog (@" KVC1 demo2 --> % @ ", p1); // directly call the description method. // 2. KVC to modify the subclass [p1 setValue: @ "xxxx" forKeyPath: @ "name"]; [p1 setValue: @ "10" forKeyPath: @ "age"]; NSLog (@ "KVC2 demo2 --> % @, % d", p1.name, p1.age);}/*** modify the book attribute of the object. (This is quite troublesome. Create a book object ). KVC statement */-(void) kvcDemo3 {// 1. traditional Method XNStudent * p1 = [[XNStudent alloc] init]; // student p1.name = @ "student xuneng"; p1.age = 22; XNBook * myBook = [[XNBook alloc] init]; myBook. bookName = @ "iOS"; p1.book = myBook; NSLog (@ "KVC1 demo3 --> % @", p1); // 2. KVC method [p1 setValue: @ "iPhone" forKeyPath: @ "book. bookName "]; // book in the student, bookNameNSLog in the book (@" KVC2 demo3 -- >%@ ", p1);}/*** get the object property value. it can be obtained in batches (if it is an array ). */-(void) kvcDemo4 {XNStudent * p1 = [[XNStudent alloc] init]; // student 1p1. name = @ "student1 xuneng"; p1.age = 24; XNBook * myBook1 = [[XNBook alloc] init]; myBook1.bookName = @ "iOS"; p1.book = myBook1; XNStudent * p2 = [[XNStudent alloc] init]; // student 2p2. name = @ "student2 xuneng"; p2.age = 23; XNBook * myBook2 = [[XNBook alloc] init]; myBook2.bookName = @ "iPhone"; p2.book = myBook2; NSArray * arr = @ [p1, p2]; // 1. normal method to obtain the attributes of objects in the array NSMutableArray * arrBook = [[NSMutableArray alloc] init]; for (XNStudent * stu in arr) {[arrBook addObject: stu. book. bookName];} NSLog (@ "KVC1 demo4 --> % @", arrBook); // 2. obtain the NSLog (@ "KVC2 demo4 --> % @", [arr valueForKeyPath: @ "book. bookName "]);} @ end

Download example source code: Http://download.csdn.net/detail/xn4545945/7571719

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