手动设定实例变量的KVO实现监听

如果将一个对象设定成属性,这个属性是自动支持KVO的,如果这个对象是一个实例变量,那么,这个KVO是需要我们自己来实现的.

以下给出源码供君测试:

Student.h 与 Student.m

////  Student.h//  SuperNotification////  Copyright (c) 2014年 Y.X. All rights reserved.//#import 
    
     @interface Student : NSObject{    NSString  *_age;}- (void)setAge:(NSString *)age;- (NSString *)age;@property (nonatomic, strong) NSString  *name;@end
    

////  Student.m//  SuperNotification////  Copyright (c) 2014年 Y.X. All rights reserved.//#import "Student.h"@implementation Student@synthesize name = _name;- (void)setName:(NSString *)name{    _name = name;}- (NSString *)name{    return _name;}// 手动设定KVO- (void)setAge:(NSString *)age{    [self willChangeValueForKey:@"age"];    _age = age;    [self didChangeValueForKey:@"age"];}- (NSString *)age{    return _age;}+ (BOOL)automaticallyNotifiesObserversForKey:(NSString *)key{    // 如果监测到键值为age,则指定为非自动监听对象    if ([key isEqualToString:@"age"])    {        return NO;    }        return [super automaticallyNotifiesObserversForKey:key];}@end

////  RootViewController.m//  SuperNotification////  Copyright (c) 2014年 Y.X. All rights reserved.//#import "RootViewController.h"#import "Student.h"@interface RootViewController ()@property (nonatomic, strong) Student *student;@end@implementation RootViewController- (void)viewDidLoad{    [super viewDidLoad];    // 创建学生对象    _student = [Student new];        // 监听属性name    [_student addObserver:self               forKeyPath:@"name"  // 属性                  options:NSKeyValueObservingOptionNew | NSKeyValueObservingOptionOld                  context:nil];        // 监听实例变量age    [_student addObserver:self               forKeyPath:@"age"   // 实例变量                  options:NSKeyValueObservingOptionNew | NSKeyValueObservingOptionOld                  context:nil];        _student.name = @"YouXianMing"; // 改变名字    _student.age  = @"18";          // 改变年龄}- (void)observeValueForKeyPath:(NSString *)keyPath                      ofObject:(id)object                        change:(NSDictionary *)change                       context:(void *)context{    NSLog(@"%@", change);}@end

这个是手动实现KVO需要注意的地方: