more helpful ID lookup error messages

encompass-cs/ComponentManager.cs

@@ -167,17 +167,38 @@ namespace Encompass
 
         internal IComponent GetComponentByID(Guid componentID)
         {
-            return IDToComponent[componentID];
+            if (IDToComponent.ContainsKey(componentID))
+            {
+                return IDToComponent[componentID];
+            }
+            else
+            {
+                throw new ComponentNotFoundException("Component with ID {0} does not exist.", componentID);
+            }
         }
 
         internal Type GetComponentTypeByID(Guid componentID)
         {
-            return componentIDToType[componentID];
+            if (componentIDToType.ContainsKey(componentID))
+            {
+                return componentIDToType[componentID];
+            }
+            else
+            {
+                throw new ComponentNotFoundException("Component with ID {0} does not exist.", componentID);
+            }
         }
 
         internal Guid GetEntityIDByComponentID(Guid componentID)
         {
-            return componentIDToEntityID[componentID];
+            if (componentIDToEntityID.ContainsKey(componentID))
+            {
+                return componentIDToEntityID[componentID];
+            }
+            else
+            {
+                throw new ComponentNotFoundException("Component with ID {0} does not exist.", componentID);
+            }
         }
 
         internal void MarkAllComponentsOnEntityForRemoval(Guid entityID)

encompass-cs/ComponentMessageManager.cs

@@ -277,17 +277,38 @@ namespace Encompass
 
         internal IComponent GetComponentByID(Guid componentID)
         {
-            return componentIDToComponent[componentID];
+            if (componentIDToComponent.ContainsKey(componentID))
+            {
+                return componentIDToComponent[componentID];
+            }
+            else
+            {
+                throw new ComponentNotFoundException("Component with ID {0} does not exist.", componentID);
+            }
         }
 
         internal Type GetComponentTypeByID(Guid componentID)
         {
-            return componentIDToType[componentID];
+            if (componentIDToType.ContainsKey(componentID))
+            {
+                return componentIDToType[componentID];
+            }
+            else
+            {
+                throw new ComponentNotFoundException("Component with ID {0} does not exist.", componentID);
+            }
         }
 
         internal Guid GetEntityIDByComponentID(Guid componentID)
         {
-            return componentIDToEntityID[componentID];
+            if (componentIDToEntityID.ContainsKey(componentID))
+            {
+                return componentIDToEntityID[componentID];
+            }
+            else
+            {
+                throw new ComponentNotFoundException("Component with ID {0} does not exist.", componentID);
+            }
         }
     }
 }

encompass-cs/EntityManager.cs

@@ -1,5 +1,7 @@
+using System.Linq;
 using System;
 using System.Collections.Generic;
+using Encompass.Exceptions;
 
 namespace Encompass
 {
@@ -35,7 +37,14 @@ namespace Encompass
 
         public Entity GetEntity(Guid id)
         {
-            return IDToEntity[id];
+            if (IDToEntity.ContainsKey(id))
+            {
+                return IDToEntity[id];
+            }
+            else
+            {
+                throw new EntityNotFoundException("Entity with ID {0} does not exist.", id);
+            }
         }
 
         public void MarkForDestroy(Guid entityID)

encompass-cs/Exceptions/ComponentNotFoundException.cs

@@ -0,0 +1,12 @@
+using System;
+
+namespace Encompass.Exceptions
+{
+    public class ComponentNotFoundException : Exception
+    {
+        public ComponentNotFoundException(
+            string format,
+            params object[] args
+        ) : base(string.Format(format, args)) { }
+    }
+}

encompass-cs/Exceptions/EntityNotFoundException.cs

@@ -0,0 +1,12 @@
+using System;
+
+namespace Encompass.Exceptions
+{
+    public class EntityNotFoundException : Exception
+    {
+        public EntityNotFoundException(
+            string format,
+            params object[] args
+        ) : base(string.Format(format, args)) { }
+    }
+}