iOS native plugin. Linker Error

Hi guys. I'm trying to learn native plugin calls for unity > ObjC by writing a few simple functions and I'm running into an error when trying to build. I'm no Objc expert and yet the error seems deceptively simple:

Undefined symbols for architecture armv7:
"_Crap", referenced from:
RegisterMonoModules() in RegisterMonoModules.o
ld: symbol(s) not found for architecture armv7
clang: error: linker command failed with exit code 1 (use -v to see invocation)


Heres the Objc code----------

*----PT3.h
#import <Foundation/Foundation.h>

@interface PT3: NSObject
{
}
-(int)Crap: (int)c;
@End
-----------------------------------------------------------------------------
*---PT3.m
#import <Foundation/Foundation.h>
#import "PT3.h"

@implementation PT3 : NSObject

-(int)Crap: (int)c
{
// Just returning an int value
return s * s;
}

@End

In unity I'm following the automatic plugin integration by dragging the .h and .m files into the Asset/Plugins/IOS Folder and then using a tester c# script to load and call the Objc file:

Code (CSharp):

1. using UnityEngine;
2. using System.Collections;
3.  
4. using System.Runtime.InteropServices;
5.  
6. public class test : MonoBehaviour {
7.  
8.     public GUIText textObj;
9.     public GUITexture textureObj;
10.  
11.  
12.     [DllImport ("__Internal")]
13.     private static extern int Crap(int c);
14.  
15.     void Update ()
16.     {
17.         if(Input.touchCount > 0)
18.         {
19.             if(textureObj.HitTest(Input.GetTouch(0).position))
20.             {
21.                 CrapMaker(94);
22.             }
23.         }
24.         else
25.         {
26.             if(textureObj.HitTest(Input.mousePosition))
27.             {
28.                 CrapMaker(94);
29.             }
30.         }
31.     }
32.  
33.  
34.     public void CrapMaker(int c)
35.     {
36.         textObj.text = "Didnt Work";
37.         int pow = 0;
38.  
39.         #if UNITY_IPHONE
40.         if (Application.platform == RuntimePlatform.IPhonePlayer)
41.         {
42.             pow = Crap(c);
43.             textObj.text = pow.ToString();
44.         }
45.         #endif    
46.    
47.     }
48. }

Ofc whether or not that code works is irrelevant because i cant even build to test. Any ideas?
I'm using xcode 6.1 and Unity 4.5.5.p2

I've tried a few things like wrapping the functions in extern"C"{} and changing the .m to a .mm but in that case i get different error where the xcode is unable to find the method declaration for the CrapMaker() function

 

You can't call Objective-C from Unity, you need to create a C wrapper. See here: http://chrisbaltzer.com/blog/Native-Plugins-101/

 

Fantastic reply! Almost seems that blog post was borne of my question. Thanks.
Now I can start on phase 2.

 

It was, lol. But, I've been meaning to write it for a while, and the same question gets asked a lot, so I figured it was time!