iOS语法之KVC的使用

#import <Foundation/Foundation.h>

@class Course;
@interface Student : NSObject {
    NSString *name;
    Course *course;
    NSInteger point;
    NSArray *otherStudent;
}

@end

#import <Foundation/Foundation.h>

@interface Course : NSObject {
    NSString *courseName;
}

@end

//
//  ViewController.m
//  testOC
//
//  Created by Benjamin on 1/2/16.
//  Copyright © 2016 Benjamin. All rights reserved.
//

#import "ViewController.h"
#import "Student.h"
#import "Course.h"

@interface ViewController ()

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    
    [self useKey];
    [self useKeyPath];
    [self performCollection];
    [self performDictionary];
}


/**
 *  .m文件也没有实现。name属性没有加property，原来的访问方法就访问不了name属性了。
    使用KVC就可以轻松实现
 */
- (void)useKey {
    Student *student = [[Student alloc] init];
    [student setValue:@"Benjamin" forKey:@"name"];
    NSString *name = [student valueForKey:@"name"];
    NSLog(@"学生姓名：%@", name); //打印 学生姓名：Benjamin
    
    NSLog(@"------------------------------------");
}

/**
 *  使用Keypath(键路径)访问属性
 */
- (void)useKeyPath {
    Student *student = [[Student alloc] init];
    [student setValue:@"Benjamin" forKey:@"name"];
    
    Course *course = [[Course alloc] init];
    [course setValue:@"语文课" forKey:@"courseName"];
    [student setValue:course forKey:@"course"];
    NSString *courseName = [student valueForKeyPath:@"course.courseName"];
    NSLog(@"课程名称：%@", courseName);  //打印 课程名称：语文课
    
    [student setValue:@"数学课" forKeyPath:@"course.courseName"];
    courseName = [student valueForKeyPath:@"course.courseName"];
    NSLog(@"新课程名称：%@", courseName); //打印 新课程名称：数学课
    
    //NSInteger也可以使用NSString包装使用
    [student setValue:@"88" forKey:@"point"];
    NSString *point = [student valueForKey:@"point"];
    NSLog(@"point: %@", point); //打印 point: 88
    
    //推荐用这种方式使用基本数据类型
    [student setValue:[NSNumber numberWithInteger:88] forKey:@"point"];
    NSNumber *newPoint = [student valueForKey:@"point"];
    NSLog(@"newPoint: %@", newPoint);   //打印 newPoint: 88
    
    NSLog(@"------------------------------------");
}

/**
 *  操作集合
    可以使用集合操作计算学生的平均分、最高分、总分、总人数等数据
 */
- (void)performCollection {
    Student *student = [[Student alloc]init];
    [student setValue:@"张三" forKey:@"name"];
    
    Student *s1 = [[Student alloc] init];
    Student *s2 = [[Student alloc] init];
    Student *s3 = [[Student alloc] init];
    [s1 setValue:@"77" forKey:@"point"];
    [s2 setValue:@"88" forKey:@"point"];
    [s3 setValue:@"99" forKey:@"point"];
    NSArray *studentArray = [NSArray arrayWithObjects:s1, s2, s3, nil];
    [student setValue:studentArray forKey:@"otherStudent"];
    NSLog(@"其他学生的成绩: %@", [student valueForKeyPath: @"otherStudent.point"]);
    NSLog(@"共有%@个学生", [student valueForKeyPath: @"otherStudent.@count"]);
    NSLog(@"学生的总分: %@", [student valueForKeyPath: @"otherStudent.@sum.point"]);
    NSLog(@"学生的最高分: %@", [student valueForKeyPath: @"otherStudent.@max.point"]);
    NSLog(@"学生的最低分: %@", [student valueForKeyPath: @"otherStudent.@min.point"]);
    NSLog(@"平均成绩: %@", [student valueForKeyPath: @"otherStudent.@avg.point"]);
    
    /**
     输出结果
     2016-01-04 12:05:46.528 testOC[29855:945179] 其他学生的成绩: (
     77,
     88,
     99
     )
     2016-01-04 12:05:46.529 testOC[29855:945179] 共有3个学生
     2016-01-04 12:05:46.529 testOC[29855:945179] 学生的总分: 264
     2016-01-04 12:05:46.529 testOC[29855:945179] 学生的最高分: 99
     2016-01-04 12:05:46.529 testOC[29855:945179] 学生的最低分: 77
     2016-01-04 12:05:46.529 testOC[29855:945179] 平均成绩: 88
    **/
    
    NSLog(@"------------------------------------");
}

/**
 *  操作字典
 */
- (void)performDictionary {
    NSDictionary *dic = @{@"name": @"jack",
                          @"point": [NSNumber numberWithInteger:12]};
    Student *student = [[Student alloc] init];
    [student setValuesForKeysWithDictionary:dic];
    NSLog(@"姓名为: %@, 分数为: %@", [student valueForKey: @"name"], [student valueForKey: @"point"]);
    
    /**
     结果为
     姓名为: jack, 分数为: 12
     **/
    
    NSLog(@"------------------------------------");
}

/**
    实际使用举例
    利用kvc的这个特性，我们可以访问系统里的一些私有变量。
    例如：在UIPageControl里面有两个私有变量：
    UIImage *_currentPageImage;
    UIImage *_pageImage;
 *  设置pageControl当前显示和未显示到脚标的样式了
 */
- (void)changePageControlImage {
    UIPageControl *pageControl = [[UIPageControl alloc] init];
    [pageControl setValue:[UIImage imageNamed:@"XX"] forKey:@"_currentPageImage"];
    [pageControl setValue:[UIImage imageNamed:@"YY"] forKey:@"_pageImage"];
    UIImage *currentImage = [pageControl valueForKey:@"_currentPageImage"];
    UIImage *pageImage = [pageControl valueForKey:@"_pageImage"];
    NSLog(@"currentImage: %@, pageImage: %@", currentImage, pageImage);
    
    NSLog(@"------------------------------------");
}
@end