How to Access a Field of an Unknown Class if the Field Exists

Question

It's a very poorly worded question because I'm not exactly sure how to put it into words that are of appropriate number for a title. Read on for a better explanation. (Using Unity API, C#)

Basically, I have an AI class in a spaceship game. I can assign the AI a target GameObject, and the AI will look in the direction of and chase after it's target. I would like to make the AI be able to strafe in circles around the target. Since the AI always faces its target, I can simply TransformDirection(Vector2.left/right) and it will orbit the target nicely, but if the target is moving it always breaks orbit.

To combat this, I want to add the target's velocity to the strafe velocity of the AI. However, I have different classes for the player's ship and the AI ships whom also might be targeted by another AI. All of my ship classes have a field for the ship's velocity, but since they are different classes, I thought I may access the velocity field by doing a GetComponent() and passing some sort of predicate => T has a Vector2 field named "velocity". Is there some way to achieve this?

Answer 1

You have 3 options I can think of:

Inheritance, all possible target types inherit from single base classclass TargetBase : MonoBehaviour with velocity property, probably the most efficient solution

target.GetComponenet<TargetBase>().velocity

Introduce interface IHasVelocity, implement the interface in target classes and filter for components that implement it, decent solution especially from code style viewpoint

((IHasVelocity)target.GetComponenets().ToList().Single(c => c is IHasVelocity)).velocity

Using reflection, the most flexible but also more dangerous, possibly also least efficient solution

target.GetComponenets().ToList().Select(c => { 
  Vector2? value;
  c.GetType().GetProperty("velocity").GetValue(value, null)
  return value; }).Single(v => v != null).Value

all solution will also work with fields with only minor changes. Code syntax not tested.

Answer 2

Check whether the target has changed its position within the last frame and then add that change to your AI's transform.

//after doing the stuff you need to do, check the changes and add those up
if(lastPos != target.transform.position && currentlyCirclingTheTarget)
{
    transform.position = transform.position + (target.transform.position - lastPos);
    lastPos = target.transform.position
}

I'm not sure if this will work exactly as I think it will but you should be able to incorporate the logic into your own code if it doesn't work perfectly.

(This will only work well if you want the AI to lock on to your target and stay within a certain distance, if you have different maximum speeds for different units, this will mean a slower AI will be faster when it locks on to a faster target.)