IOS開發過程中的KVC機制

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作用：提供了另一種  為對象的屬性賦值及讀取對象屬性的編寫代碼的方式

—————Dog.h———————
@interface Dog : NSObject
@property(nonatomic,strong)NSString *name;

@end
－－－－Book.h－－－－
@interface Book : NSObject
@property(nonatomic,strong)NSString *name;
@property(nonatomic)float price;
@end
－－－－Student.h－－－
#import <Foundation/Foundation.h>
#import "Dog.h"
#import "Book.h"

@interface Student : NSObject
{
    float _score;
}
@property(nonatomic,strong)NSString *name;
@property(nonatomic,strong)Dog *dog;
@property(nonatomic,strong)NSArray *books;
@end
－－－Student.m－－－－
@implementation Student
- (instancetype)init
{
    self = [super init];
    if (self) {
        self.dog = [[Dog alloc]init];
        
        Book *b1 = [[Book alloc]init];
        b1.name = @"數學";
        b1.price = 35.5;
        
        Book *b2 = [[Book alloc]init];
        b2.name = @"語文";
        b2.price = 31.8;
        
        self.books = @[b1,b2];
    }
    return self;
}
@end

－－－－ViewController.m－－－－
#import "ViewController.h"
#import "Student.h"
Student *stu = [[Student alloc]init];
    
    //1.為私人成員賦值
    [stu setValue:@98 forKey:@"score"];
    [stu setValue:@"張3" forKey:@"name"];
   
    NSLog(@"%@ %@",[stu valueForKey:@"name"],[stu valueForKey:@"score"]);

    //2.訪問id類型的對象
    id stu2 = [[Student alloc]init];
    [stu2 setValue:@"李4" forKey:@"name"];
    [stu2 setValue:@95.5 forKey:@"score"];

    NSLog(@"%@ %f",[stu2 valueForKey:@"name"],[[stu2 valueForKey:@"score"] floatValue]);
    
    //3.為層級類型的屬性賦值
    [stu setValue:@"ww" forKeyPath:@"dog.name"];
    NSLog(@"%@",stu.dog.name);
    
    //4.使用內建的運算子對數組屬性進行運算
    //擷取所有圖書的價格
    NSLog(@"%@",[stu valueForKeyPath:@"books.price"]);
    //擷取所有圖書的總價sum/平均價格avg/最大價格max/最小价格min
    NSLog(@"%@",[stu valueForKeyPath:@"[email protected]"]);
    //擷取圖書的總數
    NSLog(@"%@",[stu valueForKeyPath:@"[email protected]"]);

 

IOS開發過程中的KVC機制