Index: VerpakkingsDefinitie/UI/ProductDetailScherm.pas
===================================================================
diff -u -r606 -r622
--- VerpakkingsDefinitie/UI/ProductDetailScherm.pas	(.../ProductDetailScherm.pas)	(revision 606)
+++ VerpakkingsDefinitie/UI/ProductDetailScherm.pas	(.../ProductDetailScherm.pas)	(revision 622)
@@ -64,11 +64,11 @@
   inherited Create(AOwner, Navigator, ApplicationContext);
 
   self.FProductsContextSubject := ProductsContextSubject;
-  self.FProductsContextSubjectObserver := TSubjectObserver.Create(self);
+  self.FProductsContextSubjectObserver := TSubjectObserver.Create();
   self.FProductsContextSubjectObserver.OnChange := UpdateGuiProduct;
 
   self.FVerpakkingenContextSubject := VerpakkingContextSubject;
-  self.FVerpakkingenContextSubjectObserver := TSubjectObserver.Create(self);
+  self.FVerpakkingenContextSubjectObserver := TSubjectObserver.Create();
   self.FVerpakkingenContextSubjectObserver.OnChange := UpdateGuiVerpakkingen;
 
   self.FProductsAgent := ProductsAgent;
Index: VerpakkingsDefinitie/UI/GevondenProductenScherm.pas
===================================================================
diff -u -r596 -r622
--- VerpakkingsDefinitie/UI/GevondenProductenScherm.pas	(.../GevondenProductenScherm.pas)	(revision 596)
+++ VerpakkingsDefinitie/UI/GevondenProductenScherm.pas	(.../GevondenProductenScherm.pas)	(revision 622)
@@ -39,7 +39,7 @@
 begin
   inherited Create(AOwner, Navigator, ApplicationContext);
   self.FProductSubject := ProductSubject;
-  self.FSubjectObserver := TSubjectObserver.Create(self);
+  self.FSubjectObserver := TSubjectObserver.Create();
   self.FSubjectObserver.OnChange := UpdateGui;
   self.FProductsAgent := ProductsAgent;
 end;
Index: VerpakkingsDefinitie/UI/GebruikerScherm.pas
===================================================================
diff -u -r593 -r622
--- VerpakkingsDefinitie/UI/GebruikerScherm.pas	(.../GebruikerScherm.pas)	(revision 593)
+++ VerpakkingsDefinitie/UI/GebruikerScherm.pas	(.../GebruikerScherm.pas)	(revision 622)
@@ -36,7 +36,7 @@
 begin
   inherited Create(AOwner, Navigator, ApplicationContext);
   self.FGebruikerSubject := GebruikerSubject;
-  self.FGebruikerSubjectObserver := TSubjectObserver.Create(self);
+  self.FGebruikerSubjectObserver := TSubjectObserver.Create();
   self.FGebruikerSubjectObserver.OnChange := UpdateGui;
   self.FUserAgent := UserAgent;
 end;
FishEye: Tag 622 refers to a dead (removed) revision in file `VerpakkingsDefinitie/UI/ObserverPattern.pas'.
FishEye: No comparison available.  Pass `N' to diff?
Index: VerpakkingsDefinitie/VerpakkingsDefinitie.dpr
===================================================================
diff -u -r610 -r622
--- VerpakkingsDefinitie/VerpakkingsDefinitie.dpr	(.../VerpakkingsDefinitie.dpr)	(revision 610)
+++ VerpakkingsDefinitie/VerpakkingsDefinitie.dpr	(.../VerpakkingsDefinitie.dpr)	(revision 622)
@@ -11,7 +11,7 @@
   ZoekProductenScherm in 'UI\ZoekProductenScherm.pas' {FormZoekProducten},
   Util in 'UI\Util.pas',
   GebruikerScherm in 'UI\GebruikerScherm.pas' {FormGebruiker},
-  ObserverPattern in 'UI\ObserverPattern.pas',
+  ObserverPattern in 'Other\ObserverPattern.pas',
   SelectService in 'WS\SelectService.pas',
   ProductsAgent in 'WS\ProductsAgent.pas',
   GevondenProductenScherm in 'UI\GevondenProductenScherm.pas' {FormGevondenProducten},
Index: VerpakkingsDefinitie/VerpakkingsDefinitie.dproj
===================================================================
diff -u -r620 -r622
--- VerpakkingsDefinitie/VerpakkingsDefinitie.dproj	(.../VerpakkingsDefinitie.dproj)	(revision 620)
+++ VerpakkingsDefinitie/VerpakkingsDefinitie.dproj	(.../VerpakkingsDefinitie.dproj)	(revision 622)
@@ -123,7 +123,7 @@
 				<Form>FormGebruiker</Form>
 				<FormType>dfm</FormType>
 			</DCCReference>
-			<DCCReference Include="UI\ObserverPattern.pas"/>
+			<DCCReference Include="Other\ObserverPattern.pas"/>
 			<DCCReference Include="WS\SelectService.pas"/>
 			<DCCReference Include="WS\ProductsAgent.pas"/>
 			<DCCReference Include="UI\GevondenProductenScherm.pas">
Index: VerpakkingsDefinitie/UI/VerpakkingDetailScherm.pas
===================================================================
diff -u -r618 -r622
--- VerpakkingsDefinitie/UI/VerpakkingDetailScherm.pas	(.../VerpakkingDetailScherm.pas)	(revision 618)
+++ VerpakkingsDefinitie/UI/VerpakkingDetailScherm.pas	(.../VerpakkingDetailScherm.pas)	(revision 622)
@@ -89,7 +89,7 @@
   FProductsAgent := ProductsAgent;
   // Observer
   self.FProductVerpakkingSubject := ProductVerpakkingSubject;
-  self.FProductVerpakkingSubjectObserver := TSubjectObserver.Create(self);
+  self.FProductVerpakkingSubjectObserver := TSubjectObserver.Create();
   self.FProductVerpakkingSubjectObserver.OnChange := UpdateGui;
 end;
 
Index: VerpakkingsDefinitie/Other/ObserverPattern.pas
===================================================================
diff -u
--- VerpakkingsDefinitie/Other/ObserverPattern.pas	(revision 0)
+++ VerpakkingsDefinitie/Other/ObserverPattern.pas	(revision 622)
@@ -0,0 +1,82 @@
+// Based on: https://sourcemaking.com/design_patterns/observer/delphi
+unit ObserverPattern;
+
+interface
+
+uses
+  System.Classes;
+
+type
+  TSubjectObserver = class
+  private
+    FEnabled: Boolean;
+    FOnChange: TNotifyEvent;
+  protected
+    procedure Change(Subject: TObject);
+  public
+    constructor Create();
+    property Enabled: Boolean read FEnabled write FEnabled;
+    property OnChange: TNotifyEvent read FOnChange write FOnChange;
+  end;
+
+  TSubject = class
+  private
+    FObservers: TList;
+  protected
+    procedure Change; // Call this method to dispatch change
+  public
+    constructor Create();
+    procedure RegisterObserver(Observer: TSubjectObserver);
+    procedure UnregisterObserver(Observer: TSubjectObserver);
+  end;
+
+implementation
+
+constructor TSubjectObserver.Create();
+begin
+  inherited Create();
+  self.FEnabled := True;
+end;
+
+procedure TSubjectObserver.Change(Subject: TObject);
+begin
+  if Assigned(FOnChange) then
+    FOnChange(Subject);
+end;
+
+constructor TSubject.Create();
+begin
+  inherited Create();
+  FObservers := TList.Create();
+end;
+
+procedure TSubject.Change;
+var
+  Obs: TSubjectObserver;
+  I: Integer;
+begin
+  for I := 0 to FObservers.Count - 1 do
+  begin
+    Obs := FObservers[I];
+    if Obs.Enabled then
+      Obs.Change(self);
+  end;
+end;
+
+procedure TSubject.RegisterObserver(Observer: TSubjectObserver);
+begin
+  if FObservers.IndexOf(Observer) = -1 then
+  begin
+    FObservers.Add(Observer);
+    // Update nieuwe observer
+    if Observer.Enabled then
+      Observer.Change(self);
+  end;
+end;
+
+procedure TSubject.UnregisterObserver(Observer: TSubjectObserver);
+begin
+  FObservers.Remove(Observer);
+end;
+
+end.