Objective-C 协议和运行时检查方法、类是否存在

协议的声明：

//
//  Person.h
//  TestOC01
//
//  Created by xinye on 13-10-23.
//  Copyright (c) 2013年 xinye. All rights reserved.
//

#import <Foundation/Foundation.h>

@protocol Person <NSObject>


@property (nonatomic,strong) NSString *firstName;
@property (nonatomic,strong) NSString *lastName;
@property (nonatomic,unsafe_unretained) NSUInteger age;

@optional
-(id<Person>) initWithFirstName:(NSString *) firstName
                       lastName:(NSString *) lastName
                            age:(NSUInteger) age;
@required
-(id<Person>) initWithNil;
@end

实现协议：

//
//  Father.h
//  TestOC01
//
//  Created by xinye on 13-10-23.
//  Copyright (c) 2013年 xinye. All rights reserved.
//

#import <Foundation/Foundation.h>
#import "Person.h"

@interface Father : NSObject <Person>

+(void) sayNil;


@end


//
//  Father.m
//  TestOC01
//
//  Created by xinye on 13-10-23.
//  Copyright (c) 2013年 xinye. All rights reserved.
//

#import "Father.h"

@implementation Father
// 实现一个协议，必须实现其@required标记的方法，并且必须@synthesize协议中定义的@requeired属性,协议中定义的方法和属性默认都是@required的
@synthesize firstName,lastName,age;

-(id<Person>) initWithFirstName:(NSString *)_firstName lastName:(NSString *)_lastName age:(NSUInteger)_age
{
    self = [super init];
    if (self) {
        self.firstName = _firstName;
        self.lastName = _lastName;
        self.age = _age;
    }
    
    return self;
}

-(id<Person>) initWithNil
{
    self = [super init];
    return self;
}

+(void) sayNil
{
    NSLog(@"say Nil Method");
}
@end

测试：

//
//  main.m
//  TestOC01
//
//  Created by xinye on 13-10-23.
//  Copyright (c) 2013年 xinye. All rights reserved.
//

#import <Foundation/Foundation.h>
#import "Person.h"
#import "Father.h"


int main(int argc, const char * argv[])
{

    @autoreleasepool {
        
        id<Person> per = [[Father alloc]initWithFirstName:@"张" lastName:@"三" age:111];
        
        NSLog(@"姓名：%@",[[per firstName] stringByAppendingString:per.lastName]);
        NSLog(@"年龄：%li",per.age);
        // 检测是否有实例方法
        if([Father instancesRespondToSelector:@selector(initWithNil)]){
            NSLog(@"*****Father 类中有一个实例方法：initWithNil");
        }else{
            NSLog(@"Father 类中没有initWithNil实例方法");
        }
        
        // 检测是否有类方法
        if([Father respondsToSelector:@selector(sayNil)]){
            NSLog(@"*****Father 类中有sayNil类方法");
        }else{
            NSLog(@"Father 类中没有sayNil类方法");
        }
        
        // 检测是否有实例方法
        if([per respondsToSelector:@selector(initWithFirstName:lastName:age:)]){
            NSLog(@"*****Father 类中有initWithFirstName:lastName:age:实例方法");
        }else{
            NSLog(@"Father 类中没有initWithFirstName:lastName:age:实例方法");
        }
        
        // 检测指定的类是否存在
        if(NSClassFromString(@"NSString") != nil){
            NSLog(@"=========当前版本中存在NSString类");
        }else{
            NSLog(@"$$$$$$$$$当前版本中不存在NSString类");
        }
        if(NSClassFromString(@"NBString") != nil){
            NSLog(@"=========当前版本中存在NBString类");
        }else{
            NSLog(@"$$$$$$$$$当前版本中不存在NBString类");
        }
        
    }
    return 0;
}