Interface issue on iOS

I've been trying to track down an issue that only occurs on iOS where functions declared in an interface will not be called correctly through an interface reference. So far I have not been able to reproduce this in a simple case and I am pretty sure I must be using some limitation of AOT compilation that is not throwing any message or error. My code works fine in the Unity Editor and in an OS X build.

I have the following sort of setup (though IWalkingAgent has more to it and CreatureAgent implements a few other interfaces.)

Code (csharp):

1. public interface IWalkingAgent : IMapObject
2. {
3.     int getMoveCost();
4. }
5.  
6. public class CreatureAgent : MonoBehaviour, IWalkingAgent
7. {
8.     public int getMoveCost()
9.     {
10.         Debug.log("Move cost requested.")
11.         return 10;
12.     }
13. }

The behaviour I am getting right now occurs when the second CreatureAgent is created through Resource.load and it behaves as follows:

Code (csharp):

1. CreatureAgent agent = newInstance.getComponent<CreatureAgent>();
2. IWalkingAgent walkingAgent = agent as IWalkingAgent;
3.  
4. //The following line will not print out the Debug message and will return a random number upwards of 140000000.
5. int walkingAgentMoveCost = walkingAgent.getMoveCost();  
6.  
7. //The following line however, will correctly print out the Debug message and will return the correct number of 10.
8. int creatureAgentMoveCost = agent.getMoveCost();

For some reason right now this only occurs on the second instance of the CreatureAgent. The first one, created using the same code, will work correctly. This issue however has moved several times, usually when I introduce code to try and track it down. I have seen it occur on the first instance of a CreatureAgent when trying to set an event delegate. The event was still null after the line in which the delegate was added to it.

I have yet to see any error being thrown when this issue occurs, nor have I been able to see a warning that I think is related. (The only warnings I've seen have been referring to the NCalc library, which I have removed temporarily, and onMouseUp being used.)

I have only been able to find one other post on this issue happening on StackOverflow: http://stackoverflow.com/questions/...tion-using-interface-not-working-in-unity-ios
Though there was no resolution.

Has anyone encountered this sort of issue before? Have I missed a post somewhere? Any help would be appreciated.

 

Maybe you have to declare the functions as virtual / override to make the polymorphism work as expected.

 

Thanks for the suggestion.

I'll double check but I believe those particular methods are not being overridden anywhere. They are just being implemented off the interface. I'll give it a try and let you know what happens.

Though I did find the line of code that seemed to be causing the issue, but its more likely that removing it just moved the issue to someplace I have not found unless anyone can explain to me why the following line would cause chaos.

Code (csharp):

1.  
2. //agent in this case is a reference to a CreatureAgent
3. Debug.Log("Creature that died: " + agent.toString());
4.  

I had that line of code so I could see what was happening on device, before I figured out how to do remote script debugging. After removing it, the issue I described above seems to have gone away. If it was that line it makes sense as to why the issue was moving around as I was doing that in different areas of the code to try and track the issue down, but I still don't see how a toString method could cause it.

Either way I'll put the line back and see if there is anyplace I may have missed placing an override or virtual though Unity seems to warn me about hiding methods if I forget them.

Thanks again.

 

Actually YOU have to declare this function as virtual (on IWalkingAgent) and override (on CreatureAgent) if you want polymorphism to work.

 

I think I need a bit of clarification on your post, perhaps an example.

From what I understand from your post you want me to add the 'virtual' keyword in front of the interface method which isn't actually allowed by the complier. Likewise the 'override' keyword is not allowed in front of an implemented interface method as as the complier cannot locate a function to override.

 

Thanks, I'll work around it until then.

 

What is the estimated date of the release that contains the fix?

 

This sounds like an issue that isn't happening 100% of the time- what other factors would cause it?

Because myself and other developers I know are calling methods via interfaces and we aren't running into any problems.

Is it specifically related to doing the GetComponent<CreatureAgent>() as <IWalkingAgent> ?

 

My company is also having this issue, and it's blocking us from releasing our game on iOS. (A lot of our core gameplay logic uses interfaces, as well as several third-party libraries over which we have little control.) I've had a hard time getting the game playable without removing major features, which is of course unacceptable.

Perhaps Unity could fix this bug ASAP via one of its new patch-releases?

 

Hi, we are experiencing this bug as well and have a major iOS release in 2 weeks. The amount of interfaces we are using in our project (including plugins from the Asset Store) is not minimal and refactoring them all is not a feasible option at this stage. Are you able to provide us with a more accurate estimate of when the fix will be available in 4.5? Thanks

 

So it appears, thank you