Listen to an object. If the data of this object changes, it will be sent to the listener to trigger the callback function.
[ addObserver:self forKeyPath:@"data" options:NSKeyValueObservingOptionNew|NSKeyValueObservingOptionOld context:NULL];
This is the registration listening. This @"data" is used as an identifier to facilitate the identification of callback functions.
-(void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context
{
if([keyPath isEqualToString:@"data"])
{
= [ valueForKey:@"data"];
}
}
This is the callback function, which distinguishes which object changes and then gives corresponding processing
-(void)viewWillDisappear:(BOOL)animated{
[ removeObserver:self forKeyPath:@"data"];
}
Since you have registered to listen, remember to release the listener
The following is the complete example code
//
//
// First
//
// Created by shanreal-iOS on 17/10/16.
// Copyright © 2017. All rights reserved.//
#import ""
#import ""
@interface ViewController ()
@property(nonatomic,strong)UILabel* label;
@property(nonatomic,strong)UIButton* btn;
@property(nonatomic,strong)TestBean* bean;
@end
@implementation ViewController
- (void)viewDidLoad {
[super viewDidLoad];
// Do any additional setup after loading the view.
= [[TestBean alloc]init];
[ setValue:@"1" forKey:@"data"];
= [[UILabel alloc]initWithFrame:CGRectMake(10, 30, 100, 30)];
= [UIColor blackColor];
= [ valueForKey:@"data"];
[ addSubview:];
= [[UIButton alloc] initWithFrame:CGRectMake(10, 100, 200, 30)];
[ setTitleColor:[UIColor blackColor] forState:UIControlStateNormal];
[ setTitle:@"chanage data" forState:UIControlStateNormal];
[ addTarget:self action:@selector(clickAction) forControlEvents:UIControlEventTouchUpInside];
[ addSubview:];
}
-(void)viewWillAppear:(BOOL)animated{
[ addObserver:self forKeyPath:@"data" options:NSKeyValueObservingOptionNew|NSKeyValueObservingOptionOld context:NULL];
}
-(void)clickAction{
int data = [[ valueForKey:@"data"] intValue]+1;
= [NSString stringWithFormat:@"%d",data];
}
-(void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context
{
if([keyPath isEqualToString:@"data"])
{
= [ valueForKey:@"data"];
}
}
-(void)viewWillDisappear:(BOOL)animated{
[ removeObserver:self forKeyPath:@"data"];
}
@end
#import <Foundation/>
@interface TestBean : NSObject{
NSString* data;
}
@property(nonatomic,assign)int id;
@property(nonatomic,strong)NSString* data;
@end
#import ""
@implementation TestBean
@end
The above example of the KVO of iOS monitoring callback mechanism is all the content I share with you. I hope you can give you a reference and I hope you can support me more.