iOS開發UI之KVC(取值/賦值) - KVO (觀察某個對象的某個屬性的改變)

一. KVC : key value coding,通常用來給某一個對象的屬性賦值

1. KVC賦值

// 1.1 創建人
LDPerson *p = [[LDPerson alloc] init];
self.person = p;
// 1.2 創建狗
LDDog *dog = [[LDDog alloc] init];
// 1.3 將狗賦值給人
[p setValue:dog forKeyPath:@"dog"];
// 1.4 通過kvc給dog的weight屬性賦值 \
賦值時會自動找到人擁有的dog的weight屬性
[p setValue:@20.0 forKeyPath:@"dog.weight"];
NSLog(@"books = %@", [p valueForKeyPath:@"dog.weight"]);
[dog print];

2. KVC字典賦值

// 2.1 創建一個字典,person的屬性為鍵,對應賦值
NSDictionary *dict = @{@"name": @"jack", @"age": @"10", @"height": @"1.65"};
// 2.2 通過字典中的鍵找到person對象屬性進行賦值
[p setValuesForKeysWithDictionary:dict];
NSLog(@"name = %@, age = %@, height = %@", [p valueForKeyPath:@"name"], [p valueForKeyPath:@"age"], [p valueForKeyPath:@"height"]);

3. 自定義字典

// 3.1 定義字典
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賦值
[p setValuesForKeysWithDictionary:dict1];
// 3.3 輸出boos中存放的是字典
NSLog(@"books = %@", [p valueForKeyPath:@"books"]);
NSLog(@"dog.weight = %@", [p valueForKeyPath:@"dog.weight"]);
// 3.4 遍歷,讓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取出出數組books中price的值
for (LDBook *book in [p valueForKeyPath:@"books"]) {
    [tempM addObject:[book valueForKeyPath:@"price"]];
}
NSLog(@"%@", tempM);
// 4.2 kvc取出數組中price的最大值/最小值/平均值/個數
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 (觀察者)

通過KVO可以觀察某一個對象的屬性值發生改變

1. 給Person創建一個觀察者,觀察Person的name屬性

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

2. 修改Person的name的值

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

3. 當Person的name的值發生改變時,會回調

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

#pragma mark - 實現KVO回調方法
/**
 *  當對象的屬性發生改變會調用該方法
 *
 *  @param keyPath 監聽的屬性
 *  @param object  監聽的對象
 *  @param change  新值和舊值
 *  @param context 額外的數據
 */
- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context
{
    NSLog(@"KeyPath = %@", keyPath);
    NSLog(@"object = %@", object);
    NSLog(@"change = %@", change);
}

4. 當回調完成之后銷毀觀察者

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