Let order generators account for selection changes

OpenRA.Game/Orders/GenericSelectTarget.cs

@@ -18,13 +18,14 @@ namespace OpenRA.Orders
 	public class GenericSelectTarget : UnitOrderGenerator
 	{
 		public readonly string OrderName;
-		protected readonly IEnumerable<Actor> Subjects;
 		protected readonly string Cursor;
 		protected readonly MouseButton ExpectedButton;
 
+		protected IEnumerable<Actor> subjects;
+
 		public GenericSelectTarget(IEnumerable<Actor> subjects, string order, string cursor, MouseButton button)
 		{
-			Subjects = subjects;
+			this.subjects = subjects;
 			OrderName = order;
 			Cursor = cursor;
 			ExpectedButton = button;
@@ -53,7 +54,7 @@ namespace OpenRA.Orders
 				world.CancelInputMode();
 
 				var queued = mi.Modifiers.HasModifier(Modifiers.Shift);
-				yield return new Order(OrderName, null, Target.FromCell(world, cell), queued, null, Subjects.ToArray());
+				yield return new Order(OrderName, null, Target.FromCell(world, cell), queued, null, subjects.ToArray());
 			}
 		}
 
@@ -68,6 +69,11 @@ namespace OpenRA.Orders
 			return true;
 		}
 
+		public override void SelectionChanged(World world, IEnumerable<Actor> selected)
+		{
+			subjects = selected;
+		}
+
 		public override bool ClearSelectionOnLeftClick { get { return false; } }
 	}
 }

OpenRA.Game/Orders/IOrderGenerator.cs

@@ -24,5 +24,6 @@ namespace OpenRA
 		string GetCursor(World world, CPos cell, int2 worldPixel, MouseInput mi);
 		void Deactivate();
 		bool HandleKeyPress(KeyInput e);
+		void SelectionChanged(World world, IEnumerable<Actor> selected);
 	}
 }

OpenRA.Game/Orders/UnitOrderGenerator.cs

@@ -124,6 +124,8 @@ namespace OpenRA.Orders
 			return false;
 		}
 
+		public virtual void SelectionChanged(World world, IEnumerable<Actor> selected) { }
+
 		/// <summary>
 		/// Returns the most appropriate order for a given actor and target.
 		/// First priority is given to orders that interact with the given actors.