iOS KVO的实现

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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：

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++;

}

iOS KVO的实现

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原文地址：http://www.cnblogs.com/tongyuling/p/4613483.html