How to create TDictionary containing weak references to interfaces in delphi - delphi

Question

I want to create an Tinterfacedobject that contains (ao) two properties ObjectLinks and ObjectBacklinks. Objectlinks contains interface references to other objects, ObjectBacklinks contains the reverse of those links
Both properties consist of a TWeakIntfDictionary = class(TDictionary)
The Backlinks property is maintained in the ObjectLinks.ValueNotify event
To make sure the interface referecnes are removed from the dictionary when the original object is free'd, a notification algorith (same as TFmxObject uses) is put into place
As suspected I'm running into all kinds of circular reference problems when creating so many references to the same interfacedobjects :( but i can't seem to get out of this problem. When the FreeNotification is called from the object being destroyed, everything goes fine until it return fro the FreeNOtification. At that point the .Destroy of the object is called again :-(
{1 Dictionary of interfaces (using weak references) using Free notification }
TWeakIntfDictionary = class(TDictionary<int64, IInterface>, IFreeNotificationMonitor)
protected
procedure ValueNotify(const Value: IInterface; Action: TCollectionNotification); override;
public
procedure FreeNotification(aObject: TObject);
end;
implementation
procedure TWeakIntfDictionary.FreeNotification(aObject: TObject);
var
lObj: TPair<int64, IInterface>;
begin
//Object is going to be destroyed, remove it from dictionary
for lObj in Self do
begin
if (lObj.Value as TObject).Equals(aObject) then
begin
Remove(lObj.Key);
Break;
end;
end;
end;
procedure TWeakIntfDictionary.ValueNotify(const Value: IInterface; Action: TCollectionNotification);
var
lDestrIntf: IFreeNotificationBehavior;
begin
// When a TObject is added to the dictionary, it must support IDestroyNotification
// This dictionary is than added to the notificationlist of the TObject
if Supports(Value, IFreeNotificationBehavior, lDestrIntf) then
case Action of
cnAdded: begin
lDestrIntf.AddFreeNotify(Self);
lDestrIntf._Release;
end;
cnRemoved,
cnExtracted: begin
lDestrIntf.RemoveFreeNotify(Self);
end;
end
else
raise EWeakInftDictionaryException.Create('Object added to TWeakIntfDictionary does not support IFreeNotificationBehavior');
inherited;
end;
Anyone know of a existing implementation of a WeakReferences Dictionary?
Anyone any suggestions how to solve this ?

Answer 1

Found the solution in the following code
procedure TWeakIntfDictionary.FreeNotification(aObject: TObject);
var
...
begin
//Object is going to be destroyed, remove it from dictionary
lSavedEvent := FDict.OnValueNotify;
FDict.OnValueNotify := nil;
lRemoveList := TList<TKey>.Create;
try
for lPair in FDict do
begin
pointer(lIntf) := lPair.Value;
if (lIntf as TObject) = aObject then
lRemoveList.Add(lPair.Key);
end;
pointer(lIntf):=nil; // avoid _release for the last item
for lKey in lRemoveList do
FDict.Remove(lKey);
finally
FDict.OnValueNotify := lSavedEvent;
lRemoveList.Free;
end;
end;