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:];

         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 ;
 }