OC中的Selector小解

SEL 类成员方法的指针

可以理解 @selector()就是取类方法的编号,它的行为基本可以等同C语言的中函数指针,只不过C语言中,可以把函数名直接赋给一个函数指针,而Objective-C的类不能直接应用函数指针,这样只能做一个@selector()语法来取.

它的结果是一个SEL类型.这个类型本质是类方法的编号(函数地址).

下面给出两个例子,来简单实现selector的两个用法:

test1():模拟不同情境下,执行对象不同的方法;

test2():用选择器来实现对不同字段进行排序.

//
//  main.m
//  Selector
//
//  Created by MacroHong on 9/22/13.
//  Copyright © 2013 MacroHong. All rights reserved.
//

#import <Foundation/Foundation.h>
#import "Dog.h"
#import "Student.h"


void test1(void); // 选择器相当于函数指针变量
void test2(void); // 利用选择器给不同字段排序

int main(int argc, const char * argv[]) {
    @autoreleasepool {
//        test1(); // 选择器相当于函数指针变量
        test2(); // 利用选择器给不同字段排序
        
    }
    return 0;
}


void test1(void) {
    Dog *dog = [[Dog alloc] init];
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Warc-performSelector-leaks"
    //定义并给选择器赋值
    
    SEL sel = @selector(run);
    // 利用选择器运行相应的方法
    [dog performSelector:sel]; // 相当于运行 [dog run];
    
    sel = @selector(jump);
    [dog performSelector:sel];
    
    sel = @selector(bark);
    [dog performSelector:sel];
    
    
#pragma clang diagnostic pop // ARC中加此三句可以消去内存泄露的警告
    
}

void test2(void) {
    NSArray *names = @[@"Tim", @"Bob", @"Alice", @"Ferry", @"Kitty"];
    NSMutableArray *stus = [[NSMutableArray alloc] init];
    
    for (NSString *name in names) {
        Student *stu = [[Student alloc] init];
        stu.name = name;
        stu.age = arc4random() % 90;
        stu.score = arc4random() % 100;
        
        [stus addObject: stu];
    }
//        [students sortUsingSelector:@selector(olderThanStudent:)];//年龄排序
//        [students sortUsingSelector:@selector(nameAfterStudent:)];//姓名排序
        [stus sortUsingSelector:@selector(scoreLowerThanStudent:)];//成绩排序

    for (Student * stu in stus) {
        NSLog(@"name:%@ age:%ld score:%ld", stu.name, stu.age, stu.score);
        
    }
    
}

//
//  Dog.h
//  Selector
//
//  Created by MacroHong on 9/22/13.
//  Copyright © 2013 MacroHong. All rights reserved.
//

#import <Foundation/Foundation.h>

@interface Dog : NSObject

-(void)bark;

-(void)run;

-(void)jump;

@end

//
//  Dog.m
//  Selector
//
//  Created by MacroHong on 9/22/13.
//  Copyright © 2013 MacroHong. All rights reserved.
//

#import "Dog.h"

@implementation Dog

-(void)bark {
    NSLog(@"Dog Won~ Won~");
}

-(void)run {
    NSLog(@"Dog run...");
}

-(void)jump {
    NSLog(@"Dog jump...");
}

@end

//
//  Student.h
//  Selector
//
//  Created by MacroHong on 9/22/13.
//  Copyright © 2013 MacroHong. All rights reserved.
//

#import <Foundation/Foundation.h>

@interface Student : NSObject


@property (copy) NSString * name;
@property NSInteger age;
@property NSInteger score;

/**
 年龄排序
 */
-(BOOL) olderThanStudent:(Student *)anotherStudent;

/**
 成绩排序
 */
-(BOOL) scoreLowerThanStudent:(Student *)anotherStudent;

/**
 姓名排序
 */
-(BOOL) nameAfterStudent:(Student *)anotherStudent;

@end

//
//  Student.m
//  Selector
//
//  Created by MacroHong on 9/22/13.
//  Copyright © 2013 MacroHong. All rights reserved.
//

#import "Student.h"

@implementation Student

-(BOOL) olderThanStudent:(Student *)anotherStudent {
    return self.age > anotherStudent.age;
}

-(BOOL) scoreLowerThanStudent:(Student *)anotherStudent {
    return self.score < anotherStudent.score;
}

-(BOOL) nameAfterStudent:(Student *)anotherStudent {
    return ([self.name compare:anotherStudent.name] == NSOrderedDescending);
}

@end