iOS KVO的实现

kvo听说过，之前一直没怎么用，最近用到啦，就学习了一下。

demo介绍：有俩个viewcontroller（a和b），b里有个定时器和一个button，b push到a，a里的textview和label来展示b里属性str变化的值。

代码： 注：在哪add就在哪remove，viewDidLoad里add就dealloc里remove

bController.m

@property (strong,nonatomic)aController * aView;

@property (assign,nonatomic)int str;

- (void)viewDidLoad {

[super viewDidLoad];

self.aView=[[aController alloc]init];

self.str=0;

UIButton * btn=[UIButton buttonWithType:UIButtonTypeCustom];

btn.frame=CGRectMake(100, 100, 100, 100);

[btn setTitle:@"push" forState:UIControlStateNormal];

[btn setBackgroundColor:[UIColor orangeColor]];

[btn setTitleColor:[UIColor whiteColor] forState:UIControlStateNormal];

[btn addTarget:self action:@selector(push) forControlEvents:UIControlEventTouchUpInside];

[self.view addSubview:btn];

[self addObserver:self.aView forKeyPath:@"str" options:NSKeyValueObservingOptionOld |NSKeyValueObservingOptionNew context:nil];

}

//实现监听

-(void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context

{

if ([keyPath isEqual:@"str"]) {

NSLog(@"new str: %@",[change objectForKey:@"new"]);

NSLog(@"old str: %@",[change objectForKey:@"old"]);

}

}

-(void)push

{

NSTimer *myTimer = [NSTimer timerWithTimeInterval:1.0 target:self selector:@selector(timerFired)userInfo:nil repeats:YES];

[[NSRunLoop currentRunLoop] addTimer:myTimer forMode:NSDefaultRunLoopMode];

self.aView.str=self.str;

[self.navigationController pushViewController:self.aView animated:YES];

}

-(void)timerFired

{

self.str++;

}

aController.h

@property (assign,nonatomic)int str;

aController.m

@property (strong,nonatomic)UITextView * textView;

@property (strong,nonatomic)UILabel * label;

- (void)viewDidLoad {

[super viewDidLoad];

self.view.backgroundColor=[UIColor orangeColor];

[self addObserver:self forKeyPath:@"str" options:NSKeyValueObservingOptionOld |NSKeyValueObservingOptionNew context:nil];

UITextView * textView=[[UITextView alloc]initWithFrame:CGRectMake(10, 100, 300, 200)];

textView.backgroundColor=[UIColor whiteColor];

textView.textColor=[UIColor blackColor];

textView.editable=NO;

self.textView=textView;

[self.view addSubview:textView];

UILabel * label=[[UILabel alloc]init];

label.frame=CGRectMake(100, CGRectGetMaxY(textView.frame)+20, 100, 20);

label.backgroundColor=[UIColor orangeColor];

self.label=label;

[self.view addSubview:label];

}

//实现监听

-(void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context

{

if ([keyPath isEqual:@"str"]) {

[self writeToLog:[NSString stringWithFormat:@"%@",[change objectForKey:@"new"]]];

[self.label setText:[NSString stringWithFormat:@"%@",[change objectForKey:@"new"]]];

}

}

-(void)writeToLog:(NSString *)info{

static unsigned int count = 0;

[self.textView setText:[NSString stringWithFormat:@"[ %d ] %@\r\n%@",count,info,self.textView.text]];

count++;

}