iOS - KVO 简单应用

KVO（键值监听）全称 Key Value Observing。使用KVO可以实现视图组件和数据模型的分离，视图作为监听器，当模型的属性值发生变化后，监听器可以做相应的处理。KVO的方法由NSKeyValueObserving协议提供，同样NSObject已经实现了该协议，因此几乎所有的对象都可以使用KVO。

使用KVO操作常用的方法如下：

注册制定路径的监听器： addObserver: forKeyPath: option: context:

删除制定路径的监听器：removeObserver: forKeyPath:

触发监听时的方法：observeValueForKeyPath: ofObject: change: context:

引入的三方头文件：

#import "ReactiveObjC.h"

#import "MJExtension.h"

声明的属性：

@interface ViewController ()

@property(nonatomic, strong) UITextField *textField;

@property(nonatomic, strong) UILabel     *lableRetValue;

@end

实现方法：

- (void)viewDidLoad {

    [super viewDidLoad];

    // Do any additional setup after loading the view, typically from a nib.

    self.view.backgroundColor = [UIColor whiteColor];

    self.person = [[Person alloc] init];

    [self.person addObserver:self forKeyPath:@"str" options:NSKeyValueObservingOptionNew context:nil];

    [self.textField.rac_textSignal subscribeNext:^(NSString * _Nullable x) {

        [self.person setValue:x forKey:@"str"];

    }];

}

-(void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary<NSKeyValueChangeKey,id> *)change context:(void *)context{

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

        self.lableRetValue.text = [change valueForKey:@"new"];

    }

}

-(UILabel *)lableRetValue{

    if (!_lableRetValue) {

        _lableRetValue = [UILabel new];

        _lableRetValue.layer.borderColor = [UIColor redColor].CGColor;

        _lableRetValue.layer.borderWidth = .f;

        _lableRetValue.textAlignment = NSTextAlignmentCenter;

        [self.view addSubview:_lableRetValue];

        [_lableRetValue mas_makeConstraints:^(MASConstraintMaker *make) {

            make.top.equalTo(self.view).offset();

            make.centerX.equalTo(self.view);

            make.width.equalTo(self.view).multipliedBy(0.6);

            make.height.offset();

        }];

    }

    return _lableRetValue;

}

-(UITextField *)textField{

    if (!_textField) {

        _textField = [UITextField new];

        _textField.placeholder = @"请输入内容";

        _textField.keyboardType = UIKeyboardTypeNumberPad;

        _textField.textAlignment = NSTextAlignmentCenter;

        _textField.backgroundColor = [UIColor grayColor];

        [self.view addSubview:_textField];

        [_textField mas_makeConstraints:^(MASConstraintMaker *make) {

            make.top.equalTo(self.lableRetValue.mas_bottom).offset();

            make.centerX.equalTo(self.view);

            make.width.equalTo(self.view).multipliedBy(0.7);

            make.height.offset();

        }];

    }

    return _textField;

}

巴特西

iOS - KVO 简单应用

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