Custom Component: to create an event for a field of type TBaseVirtualTree

[Stano 139]

My component contains the field FVirtualTree: TBaseVirtualTree; FVirtualTree is not a subcomponent. There are examples of this. Assigned during design. I need to write an OnChange event for FVirtualTree in the component. It should work like this

When writing a component:

• for FVirtualTree I will create OnChange. I'll write my code

At design runtime

• Assign to component (property VirtualTree) Vst1 (TVirtualStringTree)
• For Vst1 I define the OnChange event

During the runtime

• I change the node - it calls Vst1.OnChange
• I'll do something there
• I call FVirtualTree.OnChange
• Vst1.OnChange completes

I did not find anything about such a case.

[Remy Lebeau 1255]

Is this what you are looking for?

type
  TMyComponent = class(...)
  private
    FVirtualTree: TBaseVirtualTree;
    procedure SetVirtualTree(AValue: TBaseVirtualTree);
    procedure VirtualTreeChange(Sender: TBaseVirtualTree; Node: PVirtualNode);
  protected
    procedure Notification(AComponent: TComponent; Operation: TOperation); override;
  public
    destructor Destroy; override;
  published
    property VirtualTree: TBaseVirtualTree read FVirtualTree write SetVirtualTree;
  end;

destructor TMyComponent.Destroy;
begin
  SetVirtualTree(nil);
  inherited;
end;

procedure TMyComponent.Notification(AComponent: TComponent; Operation: TOperation);
begin
  inherited;
  if (Operation = opRemove) and (AComponent = FVirtualTree) then
    FVirtualTree := nil;
end;

procedure TMyComponent.SetVirtualTree(AValue: TBaseVirtualTree);
begin
  if AValue <> FVirtualTree then
  begin
    if FVirtualTree <> nil then
    begin
      FVirtualTree.OnChange := nil;
      FVirtualTree.RemoveFreeNotification(Self);
    end;
    FVirtualTree := AValue;
    if FVirtualTree <> nil then
    begin
      FVirtualTree.FreeNotification(Self);
      FVirtualTree.OnChange := VirtualTreeChange;
    end;
  end;
end;

procedure TMyComponent.VirtualTreeChange(Sender: TBaseVirtualTree; Node: PVirtualNode);
begin
  // do something...
end;

 

Edited March 22, 2022 by Remy Lebeau

[Stano 139]

Looks like yes. I'll try and let you know.

[Stano 139]

Unfortunately, it's not good. It behaves as if I simply / directly assigned the event to VST. It means:
the TjstVstDBNavigator.VirtualTreeChange procedure is called (Sender: TBaseVirtualTree; Node: PVirtualNode);
MyVst.OnChange is NOT called

[Remy Lebeau 1255]

7 hours ago, Stano said:

Unfortunately, it's not good. It behaves as if I simply / directly assigned the event to VST. It means:
the TjstVstDBNavigator.VirtualTreeChange procedure is called (Sender: TBaseVirtualTree; Node: PVirtualNode);
MyVst.OnChange is NOT called

Correct, because a component event can have only 1 handler assigned at a time.  If you need multiple handlers, you need to chain them together, ie have one handler call the other.  After re-reading your original post, it is not clear to me what exactly you really want, so please clarify, preferably with an actual workflow example.

[Stano 139]

You brought me the following solution, which I originally rejected. That's not how I imagined it. It's the easiest.
Thanks!

procedure TfrmMainForm.jstvst1Change(Sender: TBaseVirtualTree; Node: PVirtualNode);
var
  NodeData: PAddress;
begin
  if not Assigned(Node) then
    Exit;

  NodeData := jstvst1.GetNodeData(Node);
  jstnav1.PKeyValue := NodeData.PKey;
  jstnav1.VirtualTreeChange(Sender, Node);  //  I thought he would be inherited here

 

[Remy Lebeau 1255]

46 minutes ago, Stano said:

You brought me the following solution, which I originally rejected. That's not how I imagined it. It's the easiest.

That new snippet has nothing to do with your proposed VirtualTree property.  So now I am completely lost as to what you really want.  I'm out.  Good luck.

 

[Stano 139]

I gave up the original idea. What I asked here.