Overview and use of KVO

Source: Internet
Author: User

Reference: Http://blog.csdn.net/yuquan0821/article/details/6646400/

One, overview

KVO, Key-value Observing, provides a mechanism for the object to receive notification when the properties of the specified object have been modified. Simply put, the KVO will automatically notify the appropriate observer when the property of the observed object has been modified each time it is specified.

Second, how to use

The system framework already supports KVO, so programmers are very easy to use.

1. Register, specify the attributes of the viewer,

2. Implementing a callback method

3. Removal of observations (arc not required)

Three, example:

When a property of an object changes, it is displayed on the screen

As in the Money field below

@interface Model: nsobject

@property (nonatomic,assign)int money ;

@end

Registered Observer

[_mymodel addobserver:self forkeypath:@ ' money ' options: Nskeyvalueobservingoptionnew| Nskeyvalueobservingoptionold Context:NULL];

Callback implementation

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

{

_moneyshow. Text = [[nsstring alloc]initwithformat:@ "%d",_mymodel. Money ];

}

Full code

#import "ViewController.h"@interfaceModel:nsobject@property (nonatomic,assign)intMoney ;@end@interfaceViewcontroller () {UILabel*_moneyshow; Model*_mymodel;}@end@implementationViewcontroller- (void) viewdidload {[Super viewdidload]; _moneyshow= [[UILabel alloc]initwithframe:cgrectmake ( -, -, -, -)]; _moneyshow.backgroundcolor=[Uicolor Bluecolor];    [Self.view Addsubview:_moneyshow]; _mymodel=[Model Alloc]init]; _mymodel.money= -;//KVO[_mymodel addobserver:self Forkeypath:@" Money"options:nskeyvalueobservingoptionnew|Nskeyvalueobservingoptionold Context:null]; UIButton*BTN =[[UIButton alloc]init]; Btn.frame= CGRectMake ( -, -, -, -); [BTN Settitle:@"Add Money"Forstate:uicontrolstatenormal]; Btn.backgroundcolor=[Uicolor Redcolor];    [Btn addtarget:self Action: @selector (Addmoney) forcontrolevents:uicontroleventtouchupinside]; [Self.view addsubview:btn];}-(void) Observevalueforkeypath: (NSString *) KeyPath Ofobject: (ID)ObjectChange: (nsdictionary *) Change context: (void*) context{_moneyshow.text= [[NSString Alloc]initwithformat:@"%d", _mymodel.money];}- (void) addmoney{_mymodel.money+= -;}- (void) didreceivememorywarning {[Super didreceivememorywarning]; //Dispose of any resources the can be recreated.}@end

Overview and use of KVO

Contact Us

The content source of this page is from Internet, which doesn't represent Alibaba Cloud's opinion; products and services mentioned on that page don't have any relationship with Alibaba Cloud. If the content of the page makes you feel confusing, please write us an email, we will handle the problem within 5 days after receiving your email.

If you find any instances of plagiarism from the community, please send an email to: info-contact@alibabacloud.com and provide relevant evidence. A staff member will contact you within 5 working days.

A Free Trial That Lets You Build Big!

Start building with 50+ products and up to 12 months usage for Elastic Compute Service

  • Sales Support

    1 on 1 presale consultation

  • After-Sales Support

    24/7 Technical Support 6 Free Tickets per Quarter Faster Response

  • Alibaba Cloud offers highly flexible support services tailored to meet your exact needs.