iOS开发UI之KVC(取值/赋值) - KVO (观察某个对象的某个属性的改变)

一. KVC : key value coding,通常用来给某一个对象的属性赋值

1. KVC赋值

// 1.1 创建人
LDPerson *p = [[LDPerson alloc] init];
self.person = p;
// 1.2 创建狗
LDDog *dog = [[LDDog alloc] init];
// 1.3 将狗赋值给人
[p setValue:dog forKeyPath:@"dog"];
// 1.4 通过kvc给dog的weight属性赋值 \
赋值时会自动找到人拥有的dog的weight属性
[p setValue:@20.0 forKeyPath:@"dog.weight"];
NSLog(@"books = %@", [p valueForKeyPath:@"dog.weight"]);
[dog print];

2. KVC字典赋值

// 2.1 创建一个字典,person的属性为键,对应赋值
NSDictionary *dict = @{@"name": @"jack", @"age": @"10", @"height": @"1.65"};
// 2.2 通过字典中的键找到person对象属性进行赋值
[p setValuesForKeysWithDictionary:dict];
NSLog(@"name = %@, age = %@, height = %@", [p valueForKeyPath:@"name"], [p valueForKeyPath:@"age"], [p valueForKeyPath:@"height"]);

3. 自定义字典

// 3.1 定义字典
NSDictionary *dict1 = @{@"name": @"jim",
                       @"age": @"20",
                       @"height": @"1.75",
                       @"books": @[@{@"price": @"100"}, @{@"price": @"98"}, @{@"price": @"200"}, @{@"price": @"198"}], @"dog": @{@"weight": @"45.89"}};
// 3.2 kvc赋值
[p setValuesForKeysWithDictionary:dict1];
// 3.3 输出boos中存放的是字典
NSLog(@"books = %@", [p valueForKeyPath:@"books"]);
NSLog(@"dog.weight = %@", [p valueForKeyPath:@"dog.weight"]);
// 3.4 遍历,让books中存放字典
NSMutableArray *arrayM = [NSMutableArray array];
for (NSDictionary *dict in [p valueForKeyPath:@"books"]) {
    LDBook *book = [LDBook bookWithDict:dict];
    [arrayM addObject:book];
}
[p setValue:arrayM forKeyPath:@"books"];
NSLog(@"books = %@", [p valueForKeyPath:@"books"]);

4. KVC取值

NSMutableArray *tempM = [NSMutableArray array];
// 4.1 kvc取出出数组books中price的值
for (LDBook *book in [p valueForKeyPath:@"books"]) {
    [tempM addObject:[book valueForKeyPath:@"price"]];
}
NSLog(@"%@", tempM);
// 4.2 kvc取出数组中price的最大值/最小值/平均值/个数
NSLog(@"Max = %@", [[p valueForKeyPath:@"books"] valueForKeyPath:@"@max.price"]);
NSLog(@"Min = %@", [[p valueForKeyPath:@"books"] valueForKeyPath:@"@min.price"]);
NSLog(@"Avg = %@", [[p valueForKeyPath:@"books"] valueForKeyPath:@"@avg.price"]);
NSLog(@"count = %@", [[p valueForKeyPath:@"books"] valueForKeyPath:@"@count.price"]);

二. KVO : Key Value OBserver (观察者)

通过KVO可以观察某一个对象的属性值发生改变

1. 给Person创建一个观察者,观察Person的name属性

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

2. 修改Person的name的值

[p setValue:@"ldd" forKey:@"name"];

3. 当Person的name的值发生改变时,会回调

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

#pragma mark - 实现KVO回调方法
/**
 *  当对象的属性发生改变会调用该方法
 *
 *  @param keyPath 监听的属性
 *  @param object  监听的对象
 *  @param change  新值和旧值
 *  @param context 额外的数据
 */
- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context
{
    NSLog(@"KeyPath = %@", keyPath);
    NSLog(@"object = %@", object);
    NSLog(@"change = %@", change);
}

4. 当回调完成之后销毁观察者

/**
 *  销毁Person的观察者
 */
- (void)dealloc
{
    [self.person removeObserver:self forKeyPath:@"name" context:nil];
}