KVO iOS Learning-design mode

KVO is the abbreviation for Key-value observing key-value observation, simply by observing the change of an object's property value by a key. When the observed attribute changes, the Observer is notified (the observer can be the object itself, or it can be another object).

The following is a simulation of the KVO implementation process:

Create a people class that has two properties name,sex

-----------------------the People.h file----------------------------

#import <Foundation/Foundation.h>

@interface Person: nsobject

-(void) changename; Write a method that changes the name value

@property (nonatomic , copy)nsstring *name; Take name as an example to see the change in the name value

@property (nonatomic , copy)nsstring *sex;

@end

-----------------------the PEOPLE.M file----------------------------

#import "Person.h"

@implementation Person

@synthesize Name,sex;

-(void) ChangeName

{

Self . name = @ " I was watched ";

}

@end

To create an observer Peopleobserve class, in which we observe the change of the name value of the People class, it is very simple to implement a method to

-----------------------the PEOPLEOBSERVE.M file----------------------------

#import "PeopleObserve.h"

@implementation Peopleobserve

Monitor the change in the name of the property in person , this parameter is a dictionary of values before and after the name change is saved.

-(void) Observevalueforkeypath: (nsstring *) keypath ofobject: (ID) object change: (nsdictionary *) Change context: (void *) context

{

if ([KeyPath isequaltostring:@ "name"]) {

Use [change Objectforkey:Nskeyvaluechangeoldkey], sometimes do not prompt objectforkey: knock it out.

NSLog (@ "Changhappen old value:%@ New value:%@", [Change Objectforkey:nskeyvaluechangeoldkey],[　　　Change Objectforkey:Nskeyvaluechangenewkey]);

}

}

@end

---------the output in the Peopleobserve class is simulated in the Appdelegate entry class when the name value is changed------------

#import "AppDelegate.h"

#import "Person.h"

#import "PeopleObserve.h"

@implementation appdelegate

-(BOOL) application: (uiapplication *) application didfinishlaunchingwithoptions: (nsdictionary *) Launchoptions

{

self. Window = [[uiwindow alloc] initwithframe: [[UIScreen mainscreen] bounds]];

Override point for customization after application launch.

self. Window. backgroundcolor = [Uicolor whitecolor];

[self. Window makekeyandvisible];

objects that are being monitored

Person *p = [[person alloc] init];

P.name = @ " observed "; First assign a value to the name to see

Peopleobserve *po = [[Personmonitor alloc] init];

//P is the Observer , the PO is the Observer, and when the change is observed , the method is called

[P addobserver:p m forkeypath:@ "name" options: Nskeyvalueobservingoptionnew| Nskeyvalueobservingoptionold context:nil];

[P changename];

The following two ways can change the value of the name, KVC the value of the way

[P setvalue:@ " I was also observed" forkeypath:@ "name"];

[P setValue:@ " I was observed again " Forkey:@ "name"];

return YES;

}

---------------The result of the output-----------------

KVO iOS Learning-design mode