change ContactListener from Interface to Abstract Class

Author: NArnott

src/box2dx/Box2D.NetStandard/Dynamics/Contacts/Contact.cs

@@ -318,7 +318,7 @@ public static Contact Create(Fixture fixtureA, int indexA, Fixture fixtureB, int
 			        })!;
 		}
 
-		public void Update(IContactListener listener)
+		public void Update(ContactListener listener)
 		{
 			Manifold oldManifold = m_manifold;
 

…mics/World/Callbacks/IContactListener.cs …amics/World/Callbacks/ContactListener.cssrc/box2dx/Box2D.NetStandard/Dynamics/World/Callbacks/IContactListener.cs renamed to src/box2dx/Box2D.NetStandard/Dynamics/World/Callbacks/ContactListener.cs src/box2dx/Box2D.NetStandard/Dynamics/World/Callbacks/IContactListener.cs renamed to src/box2dx/Box2D.NetStandard/Dynamics/World/Callbacks/ContactListener.cs

@@ -16,19 +16,19 @@ namespace Box2D.NetStandard.Dynamics.World.Callbacks
 	/// <warning>
 	///  You cannot create/destroy Box2DX entities inside these callbacks.
 	/// </warning>
-	public interface IContactListener
+	public abstract class ContactListener
 	{
 		/// <summary>
 		///  Called when two fixtures begin to touch.
 		/// </summary>
 		/// <param name="contact"></param>
-		void BeginContact(in Contact contact);
+		public abstract void BeginContact(in Contact contact);
 
 		/// <summary>
 		///  Called when two fixtures cease to touch.
 		/// </summary>
 		/// <param name="contact"></param>
-		void EndContact(in Contact contact);
+		public abstract void EndContact(in Contact contact);
 
 		/// <summary>
 		///  This is called after a contact is updated. This allows you to inspect a
@@ -44,7 +44,7 @@ public interface IContactListener
 		/// </summary>
 		/// <param name="contact"></param>
 		/// <param name="oldManifold"></param>
-		void PreSolve(in Contact contact, in Manifold oldManifold);
+		public abstract void PreSolve(in Contact contact, in Manifold oldManifold);
 
 		/// <summary>
 		///  This lets you inspect a contact after the solver is finished. This is useful
@@ -56,6 +56,6 @@ public interface IContactListener
 		/// </summary>
 		/// <param name="contact"></param>
 		/// <param name="impulse"></param>
-		void PostSolve(in Contact contact, in ContactImpulse impulse);
+		public abstract void PostSolve(in Contact contact, in ContactImpulse impulse);
 	}
 }

src/box2dx/Box2D.NetStandard/Dynamics/World/ContactManager.cs

@@ -44,7 +44,7 @@ internal class ContactManager
 		internal int m_contactCount;
 		internal ContactFilter m_contactFilter;
 		internal Contact m_contactList;
-		internal IContactListener m_contactListener;
+		internal ContactListener m_contactListener;
 
 		internal ContactManager()
 		{

src/box2dx/Box2D.NetStandard/Dynamics/World/Island.cs

@@ -162,7 +162,7 @@ public class Island
 		internal readonly int m_contactCapacity;
 		private readonly Contact[] m_contacts;
 		private readonly Joint[] m_joints;
-		private readonly IContactListener m_listener;
+		private readonly ContactListener m_listener;
 
 		private readonly Position[] m_positions;
 		private readonly Velocity[] m_velocities;
@@ -173,7 +173,7 @@ public class Island
 		internal int m_contactCount;
 		private int m_jointCount;
 
-		public Island(int bodyCapacity, int contactCapacity, int jointCapacity, IContactListener listener)
+		public Island(int bodyCapacity, int contactCapacity, int jointCapacity, ContactListener listener)
 		{
 			m_bodyCapacity = bodyCapacity;
 			m_contactCapacity = contactCapacity;

src/box2dx/Box2D.NetStandard/Dynamics/World/World.cs

@@ -213,7 +213,7 @@ public void SetContactFilter(ContactFilter filter)
 		///  Register a contact event listener
 		/// </summary>
 		/// <param name="listener"></param>
-		public void SetContactListener(IContactListener listener)
+		public void SetContactListener(ContactListener listener)
 		{
 			m_contactManager.m_contactListener = listener;
 		}