objective-C 中如何判断一个类中有没有定义某个方法

C#中可以通过反射分析元数据来解决这个问题，示例代码如下：

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using System; using System.Reflection;   namespace Hello {     class Program     {         static void Main(string[] args)         {             if (IsMethodDefined(typeof(Utils), "HelloWorld"))             {                 Console.WriteLine("Utils类中有方法HelloWorld");             }             else             {                 Console.WriteLine("Utils类中没有方法HelloWorld");             }             Console.ReadKey();         }             /// <summary>         /// 判断一个类中有无"指定名称"的方法         /// </summary>         /// <param name="type"></param>         /// <param name="methodName"></param>         /// <returns></returns>         static bool IsMethodDefined(Type type,string methodName)         {             bool result = false;             foreach (MemberInfo m in type.GetMembers())             {                 if (m.Name == methodName)                 {                     result = true;                     break;                 }             }             return result;         }     }       public static class Utils     {         public static void HelloWorld()         {             Console.WriteLine("Hello World!");         }     } }

在obj-C中，则是通过选择器selector来判断的

Sampe.h

#import <Foundation/Foundation.h>
@interface Sample : NSObject {
}
-(void) print:(NSString*) msg;
@end

Sample.m

#import "Sample.h"
@implementation Sample
-(void) print:(NSString*) msg
{
	NSLog(@"%@",msg);
}
@end

main函数:

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

int main (int argc, const char * argv[]) {
    
	NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];
	
	Sample *s = [Sample new];	
	
	if ([s respondsToSelector:@selector(print:)]) //这一行就是判断实例s中有没有方法print
	{
		[s print:@"Hello World"];
	}
	else
	{
		NSLog(@"%@",@"Sample类中没有定义方法print");
	}
	
	[s release];
	
    [pool drain];
    return 0;
}