Class field lost value!

[WojTec]

Delphi-Quellcode:

var
  Index: Integer;
  Layer: TCustomFilterLayer;
begin
  Index := lbLayers.ItemIndex;

  if Index <> - 1 then
  begin
    if lbLayers.Items.Objects[Index] is TCustomFilterLayer then
    begin
      Layer := lbLayers.Items.Objects[Index] as TCustomFilterLayer;

      if Layer is TBrightnessAdjustmentLayer then
      begin
        Layer := Layer as TBrightnessAdjustmentLayer;

        with TBrightnessLayerEditor.Create(Layer) do
        begin
          SetAmount(vtInteger, -100, 100, TBrightnessAdjustmentLayer(Layer).Amount); // Here is something wrong :(

          // Here is ok
        end;
      end;
    end;
  end;
end;

So, I create some graphic tool with layers.
There is problem with this procedure: when - TBrightnessAdjustmentLayer(Layer).Amount is always 0 (default from Create()), also if is setup other value... Other parameters from TCustomFilterLayer are ok. Why and how to fix? Layer is display with correct setting.

[alzaimar]

Please describe what the loop is doing... Or should be doing.

[WojTec]

When I click on list item should be open editor for object stored in this item.
Window is opening, but field in stored object don't have values setted early, but default form their class constructor.

In oder word I wanna edit object stored in list items.

[alzaimar]

So why do you create another TBrighnessAdjustmentLayer then?
This should work (I removed the 'create' and got rid of some begin/end and other unimportant stuff):

Delphi-Quellcode:

var
  Index: Integer;
  Layer: TCustomFilterLayer;
begin
  Index := lbLayers.ItemIndex;

  if Index <> - 1 then
    if lbLayers.Items.Objects[Index] is TCustomFilterLayer then begin
      Layer := lbLayers.Items.Objects[Index] as TCustomFilterLayer;
      if Layer is TBrightnessAdjustmentLayer then
          SetAmount(vtInteger, -100, 100, TBrightnessAdjustmentLayer(Layer).Amount);
    end;
end;

[WojTec]

Where I create 2nd object? T*Editor is just descendant of TForm (it's more complicated structure, but base class for any editor is TForm) where I have controls to edit layer ;)

I did that I set values in editor contructor.

But I still don't understand why this value is zero? Before constructor is ok, in constructor is ok, after constructor is not ok... (only this field is bad, fields from previous classes are ok at all).

[mkinzler]

Here you're creating a new instance

Delphi-Quellcode:

with TBrightnessLayerEditor.Create(Layer) do

[WojTec]

Why here is created new obj? In this form constructor is reintroduced and assigning parameter to private filed. So, how to change it to do not make new obj and just work on existing one?

[mkinzler]

In Delphi a constructor can be called als "normal" class method. But then you have to call it on an instance! You call it on a class, so the constructor creates a new instance.
Try

Delphi-Quellcode:

    Layer.Create(<Params>);

[WojTec]

But

Delphi-Quellcode:

with TBrightnessLayerEditor.Create(Layer) do

isn't Layer constructor, TBrightnessLayerEditor is just window.
In this case is also created next Layer instance?

[mkinzler]

Yes

Delphi-Quellcode:

TBrightnessLayerEditor.Create(Layer)

creates a new instance of TBrightnessLayerEditor because TBrightnessLayerEditor is a class and not an object!