Index: Ringtoets/DuneErosion/src/Ringtoets.DuneErosion.Service/DuneErosionBoundaryCalculationActivity.cs
===================================================================
diff -u -r0144d7112d94bff39e8f8abda70b5178955a8c93 -rb633ec894f0b9c1878e978b24a0c870480fd604b
--- Ringtoets/DuneErosion/src/Ringtoets.DuneErosion.Service/DuneErosionBoundaryCalculationActivity.cs	(.../DuneErosionBoundaryCalculationActivity.cs)	(revision 0144d7112d94bff39e8f8abda70b5178955a8c93)
+++ Ringtoets/DuneErosion/src/Ringtoets.DuneErosion.Service/DuneErosionBoundaryCalculationActivity.cs	(.../DuneErosionBoundaryCalculationActivity.cs)	(revision b633ec894f0b9c1878e978b24a0c870480fd604b)
@@ -42,11 +42,13 @@
         /// Creates a new instance of <see cref="DuneErosionBoundaryCalculationActivity"/>.
         /// </summary>
         /// <param name="duneLocation">The <see cref="DuneLocation"/> to perform the calculation for.</param>
-        /// <param name="failureMechanism">The <see cref="DuneErosionFailureMechanism"/> that holds information about the contribution and
-        /// the general inputs used in the calculation.</param>
-        /// <param name="hydraulicBoundaryDatabaseFilePath">The hydraulic boundary database file that should be used for performing the calculation.</param>
+        /// <param name="failureMechanism">The <see cref="DuneErosionFailureMechanism"/> that holds 
+        /// information about the contribution and the general inputs used in the calculation.</param>
+        /// <param name="hydraulicBoundaryDatabaseFilePath">The hydraulic boundary database file that 
+        /// should be used for performing the calculation.</param>
         /// <param name="norm">The norm to use during the calculation.</param>
-        /// <exception cref="ArgumentNullException">Thrown when any parameter is <c>null</c>.</exception>
+        /// <exception cref="ArgumentNullException">Thrown when <paramref name="duneLocation"/> or
+        /// <paramref name="failureMechanism"/> is <c>null</c>.</exception>
         public DuneErosionBoundaryCalculationActivity(DuneLocation duneLocation,
                                                       DuneErosionFailureMechanism failureMechanism,
                                                       string hydraulicBoundaryDatabaseFilePath,
@@ -66,30 +68,50 @@
             this.hydraulicBoundaryDatabaseFilePath = hydraulicBoundaryDatabaseFilePath;
             this.norm = norm;
 
-            Description = string.Format(Resources.DuneErosionBoundaryCalculationActivity_Calculate_hydraulic_boundary_conditions_for_DuneLocation_with_name_0_, duneLocation.Name);
+            Description = string.Format(Resources.DuneErosionBoundaryCalculationActivity_Calculate_hydraulic_boundary_conditions_for_DuneLocation_with_name_0_,
+                                        duneLocation.Name);
 
             calculationService = new DuneErosionBoundaryCalculationService();
         }
 
-        protected override void PerformCalculation()
+        protected override bool Validate()
         {
-            if (duneLocation.Output != null)
+            if (AlreadyCalculated)
             {
                 State = ActivityState.Skipped;
-                return;
+                return true;
             }
 
-            calculationService.Calculate(duneLocation,
-                                         failureMechanism,
-                                         norm,
-                                         hydraulicBoundaryDatabaseFilePath);
+            return DuneErosionBoundaryCalculationService.Validate(hydraulicBoundaryDatabaseFilePath);
         }
 
+        protected override void PerformCalculation()
+        {
+            if (State != ActivityState.Skipped)
+            {
+                calculationService.Calculate(duneLocation,
+                                             failureMechanism,
+                                             norm,
+                                             hydraulicBoundaryDatabaseFilePath);
+            }
+        }
+
         protected override void OnCancel()
         {
             calculationService.Cancel();
         }
 
-        protected override void OnFinish() {}
+        protected override void OnFinish()
+        {
+            duneLocation.NotifyObservers();
+        }
+
+        private bool AlreadyCalculated
+        {
+            get
+            {
+                return duneLocation.Output != null;
+            }
+        }
     }
 }
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