KVC 相關(guān)

1 .KVC 的基本使用
kvc 相關(guān)的基本方法包括

設(shè)置屬性值：：：
setValue: forKey: ;
setValue: forKeyPath: ;
獲取屬性值：：：
valueForKey: ;
valueForKeyPath: ;

keyPath 是指可以多層通過路徑設(shè)置屬性或者獲取屬性值

@interface Dog : NSObject
{// 這里的成員變量沒有 set/ get 方法
    @public
    int dog_age; // 一般成員變量
    NSString * dog_food; // 實(shí)例變量
}
@property (nonatomic,copy)NSString * dog_name ; // 屬性
@end

@interface Person : NSObject
{
    @public
    int person_age;
    NSString * person_food;
}
@property (nonatomic,copy)NSString * person_name;

@property (nonatomic,strong)Dog * dog;
@end

// -------------------vc 中調(diào)用
   self.person = [Person new];
   
    [self.person setValue:@"jack" forKey:@"person_name"];
    [self.person setValue:@"三明治" forKey:@"person_food"];
    [self.person setValue:@12 forKey:@"person_age"];

    NSLog(@"person name value is :: %@",[self.person valueForKey:@"person_name"]);
    NSLog(@"person name is :: %@",self.person.person_name);
   
    NSLog(@"person food value is :: %@",[self.person valueForKey:@"person_food"]);
    NSLog(@"person food is :: %@",self.person->person_food);
  
    NSLog(@"person age value is :: %@",[self.person valueForKey:@"person_age"]);
    NSLog(@"person age is :: %d",self.person->person_age);
    
    self.person.dog = [Dog new];
   
    [self.person setValue:@"pretty" forKeyPath:@"dog.dog_name"];
    [self.person setValue:@"狗糧" forKeyPath:@"dog.dog_food"];
    [self.person setValue:@2 forKeyPath:@"dog.dog_age"];

    NSLog(@"person dog name value is :: %@",[self.person valueForKeyPath:@"dog.dog_name"]);
    NSLog(@"person dog name is :: %@",self.person.dog.dog_name);

    NSLog(@"person dog food value is :: %@",[self.person valueForKeyPath:@"dog.dog_food"]);
    NSLog(@"person dog food is :: %@",self.person.dog->dog_food);

    NSLog(@"person age value is :: %@",[self.person valueForKeyPath:@"dog.dog_age"]);
    NSLog(@"person dog age is :: %d",self.person.dog->dog_age);

/*
key::
person name value is :: jack
person name is :: jack
person food value is :: 三明治
person food is :: 三明治
person age value is :: 12
person age is :: 12

keyPath::
person dog name value is :: pretty
person dog name is :: pretty
person dog food value is :: 狗糧
person dog food is :: 狗糧
person age value is :: 2
person dog age is :: 2
*/

通過代碼驗(yàn)證可以得到相關(guān)的結(jié)果：： kvc 通過key /keypath 設(shè)置成員變量得值

2 .kvc的調(diào)用順序
賦值過程：

KVC調(diào)用順序.png

** 1 . 是否包含 setKey：、 _setKey：的方法
（包含：傳參賦值 ; 不包含 -> 2）;

** 2 . 通過判斷 + (BOOL)accessInstanceVariablesDirectly 的值（是否可以直接訪問實(shí)例變量 ,默認(rèn)值 true）
（ture：查找相關(guān)成員變量 -> 3 ; false -> 報(bào)錯(cuò) ：：undefined key）;

** 3 . 成員變量得查找順序 _key , _isKey , key , isKey
（發(fā)現(xiàn)變量：傳參賦值 ; 未發(fā)現(xiàn)變量 -> 報(bào)錯(cuò) ：：undefined key）;

取值過程：

kvc取值.png

3 . kvc 是否調(diào)用kvo？嗅绸？渐夸？
解答：：（kvc修改成員變量、屬性都會(huì)調(diào)用kvo）

@interface Person : NSObject
{
    @public
    int person_age;
}
@property (nonatomic,copy)NSString * person_name;
@end

//________________________ VC 調(diào)用

@interface ViewController ()

@property (nonatomic,strong)Person *person;
@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];

    self.person = [Person new];
    // 設(shè)置初始值
    [self.person setValue:@"jack" forKey:@"person_name"];
    [self.person setValue:@12 forKey:@"person_age"];
    
// 添加監(jiān)聽 name age
    [self.person addObserver:self forKeyPath:@"person_name" options:NSKeyValueObservingOptionOld | NSKeyValueObservingOptionNew context:@"name"];
    [self.person addObserver:self forKeyPath:@"person_age" options:NSKeyValueObservingOptionOld | NSKeyValueObservingOptionNew context:@"age"];
}

- (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event{
// 修改成員變量 瞻鹏、 屬性的值
    [self.person setValue:@"rose" forKey:@"person_name"];
    [self.person setValue:@13 forKey:@"person_age"];
}

- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context
{
    NSLog(@"keyPath:: %@ ; object:: %@ ; change :: %@ ; context :: %@ ",keyPath,object,change,context);
}

- (void)dealloc
{
    [self.person removeObserver:self forKeyPath:@"person_age"];
    [self.person removeObserver:self forKeyPath:@"person_name"];
}
@end
/*
// kvo:: name 
keyPath:: person_name ; object:: <Person: 0x60000371c3c0> ; change :: {
    kind = 1;
    new = rose;
    old = jack;
} ; context :: name

 kvo:: age
keyPath:: person_age ; object:: <Person: 0x60000371c3c0> ; change :: {
    kind = 1;
    new = 13;
    old = 12;
} ; context :: age
*/

這里可以推斷一個(gè)結(jié)論：
kvo的實(shí)現(xiàn)依賴于方法：：willChangeValueForKey 悲立、didChangeValueForKey
推斷 kvc 修改值得時(shí)候調(diào)用順序：：

1 . willChangeValueForKey
2 . 根據(jù)前面講到的查找順序修改 value
3 . didChangeValueForKey

最后編輯于：2018.12.03 16:15:47

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