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 <Foundation/Foundation.h>
@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具体使用情况:
//
// 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:
