KVC鍵值編碼
鍵值編碼中基本使用-valueForKey:和-setValue:forKye:方法。你可以像對象發送消息並且傳遞你想要訪問的熟悉名稱的鍵值作爲參數。
KVC方法會首先查找以參數命名的getter、setter方法,如果沒有提供getter、setter方法,KVC方法會直接尋找_name和name的實例變量。
// book.h
@interface ZZBook : NSObject
@property (nonatomic,copy) NSString *name;
@end
// book.m
@implementation ZZBook
@end
// person.h
@class ZZBook;
@interface ZZPerson : NSObject
@property (nonatomic,copy) NSString *name;
@property (nonatomic,assign) int age;
@property (nonatomic,strong) ZZBook *book;
@end
// person.m
@implementation ZZPerson
@end
// main.m
int main(int argc, const char * argv[]) {
ZZPerson *p1 = [[ZZPerson alloc] init];
p1.name = @"人1";
p1.age = 18;
ZZBook *book = [[ZZBook alloc] init];
book.name = @"書1";
p1.book = book;
ZZPerson *p2 = [[ZZPerson alloc] init];
// KVC賦值
[p2 setValue:@"人1" forKey:@"name"];
[p2 setValue:@19 forKey:@"age"];
ZZPerson *p3 = [[ZZPerson alloc] init];
p3.name = @"人3";
p3.age = 20;
// 取值
NSString *name = [p1 valueForKey:@"name"];
int age = [[p1 valueForKey:@"age"] intValue];
NSLog(@"%@",name);
NSDictionary *dic = [p1 dictionaryWithValuesForKeys:@[@"name",@"age"]];
NSLog(@"%@",dic);
NSArray *persons = @[p1,p2,p3];
// 整體訪問
NSArray *names = [persons valueForKey:@"name"];
NSLog(@"%@",names);
// 帶路徑
NSLog(@"%@",[p1 valueForKeyPath:@"book.name"]);
return 0;
}
注意:KVC需要解析字符串來計算答案,說以運行效率會比較低,而且編譯器無法做錯誤檢查,有可能會在運行時出錯。
KVO鍵值觀察者
可以監聽一個對象的屬性,當這個對象的屬性發生變化時,會收到一個消息。
//person.h
@interface ZZPerson : NSObject
@property (nonatomic, copy) NSString *name;
@property (nonatomic, copy) NSString *add;
@end
//person.m
@implementation ZZPerson
@end
//viewControl.m
@interface ViewController ()
@property (nonatomic, strong) ZZPerson *p;
@end
@implementation ViewController
- (ZZPerson *)p{
if (_p == nil) {
_p = [[ZZPerson alloc] init];
_p.name = @"名字";
_p.add = @"地址1";
}
return _p;
}
- (void)viewDidLoad {
[super viewDidLoad];
// Do any additional setup after loading the view, typically from a nib.
[self.p addObserver:self forKeyPath:@"add" options:NSKeyValueObservingOptionOld context:nil];
}
//實現KVO方法
/**
* 當監控的某個屬性的值改變了就會調用
*
* @param keyPath 屬性名(哪個屬性改了?)
* @param object 哪個對象的屬性被改了?
* @param change 屬性的修改情況(屬性原來的值、屬性最新的值)
* @param context void * == id
*/
- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary<NSString *,id> *)change context:(void *)context {
NSString *name = [object valueForKey:@"name"];
NSString *add = [object valueForKey:@"add"];
NSLog(@"%@ has a new add: %@", name, add);
NSLog(@"%@", change);
}
- (void)didReceiveMemoryWarning {
[super didReceiveMemoryWarning];
// Dispose of any resources that can be recreated.
}
- (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event {
self.p.add = @"地址2";
}
- (void)dealloc
{
// 移除觀察者
[self.p removeObserver:self forKeyPath:@"age"];
}
@end
先添加一個對對象Person的add屬性的觀察,觀察者爲控制器對象。
[self.p addObserver:self forKeyPath:@"add" options:NSKeyValueObservingOptionOld context:nil];
實現KVO方法
- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary<NSString *,id> *)change context:(void *)context;
當控制器收到觸摸事件的時候,改變了person的add屬性,person會向控制器發送KVO的消息,然後調用方法。