Changing Intraweb IWFrames at runtime

I've a simple IntraWeb test project, My Unit1 has an IWform with 3 regions: header, body & footer as below:

type
  TIWForm1 = class(TIWAppForm)
    Body_Region: TIWRegion;
    Header_Region: TIWRegion;
    Footer_Region: TIWRegion;
  public
  end;

implementation

{$R *.dfm}


initialization
  TIWForm1.SetAsMainForm;

end.

My Unit2 and Unit3 are an IWFrame and they have a button only as below:

type
  TIWFrame2 = class(TFrame)
    IWFrameRegion: TIWRegion;
    Button1: TButton;
  private
    { Private declarations }
  public
    { Public declarations }
  end;

implementation

{$R *.dfm}

end.

(unit3 same as unit2)

Now, I can assign a frame to the body region easily at design time by dropping Frames form the tool plate to that region.

The problem is how can I change it at runtime to unit3 Frame?

If I try to add it to type section like this

type
  TIWForm1 = class(TIWAppForm)
    Body_Region: TIWRegion;
    Header_Region: TIWRegion;
    Footer_Region: TIWRegion;

    MyFram2: TIWFrame2; // added here

    procedure IWAppFormShow(Sender: TObject);
  public
  end;

the system tries to remove it!

if I force to keep it to use it as

Body_Region.Parent := MyFram2;

I got nothing in the body region!

if I add it manually at design time I got the same declaration, I got it working but I cannot change it!

am I missing something here or it is impossible to do so?

btw I'm on Delphi Berlin 10.1 and IW14.1.12.

Solution

The "removal" of the declared field is not an IntraWeb thing, but a Delphi "feature". Declare it like this, inside a "private" section otherwise it will be treated as published:

TIWForm1 = class(TIWAppForm)
  Body_Region: TIWRegion;
  Header_Region: TIWRegion;
  Footer_Region: TIWRegion;
  procedure IWAppFormCreate(Sender: TObject);  // use OnCreate event
private
  FMyFram2: TIWFrame2; // put it inside a "Private" section. 
  FMyFram3: TIWFrame3;
public
end;

Remove OnShow event and use OnCreate event instead. Create your frame instances inside the OnCreate event, like this:

procedure TIWForm1.IWAppFormCreate(Sender: TObject);
begin
   FMyFram2 := TIWFrame2.Create(Self);  // create the frame
   FMyFram2.Parent := Body_Region;      // set parent
   FMyFram2.IWFrameRegion.Visible := True;  // set its internal region visibility.

   // the same with Frame3, but lets keep it invisible for now  
   FMyFram3 := TIWFrame3.Create(Self);
   FMyFram3.Parent := Body_Region;           
   FMyFram3.IWFrameRegion.Visible := False;

   Self.RenderInvisibleControls := True;  // tell the form to render invisible frames. They won't be visible in the browser until you make them visible
end;

Then you can make one visible and the other invisible setting Frame.IWFrameRegion visibility as shown above.