Delphi Form in DLL works, but Delphi Frame - not - delphi

Question

I am trying to create a Form and a Frame in Delphi-made DLL using handles only. The form appears in host application normally, but the frame doesn't appear at all.
What could be wrong?
Below I provide a piece of code that creates both Frame and Window:
library DLL1;
{ Important note about DLL memory management: ShareMem must be the
first unit in your library's USES clause AND your project's (select
Project-View Source) USES clause if your DLL exports any procedures or
functions that pass strings as parameters or function results. This
applies to all strings passed to and from your DLL--even those that
are nested in records and classes. ShareMem is the interface unit to
the BORLNDMM.DLL shared memory manager, which must be deployed along
with your DLL. To avoid using BORLNDMM.DLL, pass string information
using PChar or ShortString parameters. }
uses
System.SysUtils,
System.Classes,
DllMain in 'DllMain.pas',
Winapi.Windows,
Vcl.Forms,
Vcl.Controls {DLLFrame1: TFrame},
DllForm in 'DllForm.pas' {Form1};
{$R *.res}
type
TSingleton = class
private
fra: TDLLFrame1;
frm: TForm1;
class var __instance: TSingleton;
class function __getInstance(): TSingleton; static;
public
class property Instance: TSingleton read __getInstance;
procedure CreateDLLFrame(AppHandle, ParentWindow: HWND);
procedure CreateDLLForm(AppHandle, ParentWindow: HWND);
procedure DestroyDLLFrame();
procedure DestroyDLLForm();
end;
procedure CreateDLLFrame(AppHandle, ParentWindow: HWND); stdcall;
begin
TSingleton.Instance.CreateDLLFrame(AppHandle, ParentWindow);
end;
procedure CreateDLLForm(AppHandle, ParentWindow: HWND); stdcall;
begin
TSingleton.Instance.CreateDLLForm(AppHandle, ParentWindow);
end;
procedure DestroyDLLFrame(); stdcall;
begin
TSingleton.Instance.DestroyDLLFrame();
end;
procedure DestroyDLLForm(); stdcall;
begin
TSingleton.Instance.DestroyDLLForm();
end;
exports
CreateDLLFrame,
CreateDLLForm,
DestroyDLLFrame,
DestroyDLLForm;
procedure TSingleton.CreateDLLFrame(AppHandle, ParentWindow: HWND);
begin
Application.Handle := AppHandle;
fra := TDLLFrame1.CreateParented(ParentWindow);
fra.Show();
end;
procedure TSingleton.DestroyDLLForm();
begin
frm.Free();
end;
procedure TSingleton.DestroyDLLFrame();
begin
fra.Free();
end;
procedure TSingleton.CreateDLLForm(AppHandle, ParentWindow: HWND);
begin
Application.Handle := AppHandle;
frm := TForm1.CreateParented(ParentWindow);
frm.Show();
end;
class function TSingleton.__getInstance(): TSingleton;
begin
if __instance = nil then
__instance := TSingleton.Create();
Result := __instance;
end;
end.
The DLLFrame:
unit DllMain;
interface
uses
Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes,
Vcl.Graphics, Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.StdCtrls, Vcl.ExtCtrls;
type
TDLLFrame1 = class(TFrame)
mmoText: TMemo;
pnlSend: TPanel;
edtSend: TEdit;
btnSend: TButton;
private
public
constructor Create(AOwner: TComponent); override;
end;
implementation
{$R *.dfm}
{ TDLLFrame1 }
constructor TDLLFrame1.Create(AOwner: TComponent);
begin
inherited;
if AOwner = nil then
MessageBox(0, 'Frame owner is NIL', 'Debug', 0)
else
MessageBox(0, PWideChar(AOwner.Name), 'Debug', 0);
end;
end.

Answer 1

Delphi TFrame descend from TWinControl (and thus, TControl), they have an Owner and they have a Parent (often these are the same). The Owner controls the Frame's lifetime while the Parent controls where it's displayed (i.e. which Window handle is to be used). For example, in a VCL app with 2 form units and a frame unit, you could instantiate a Frame having it's owner be the Application object or the the first Form while having it's parent be the second form; the Frame would be displayed on the second form even though it's owner was the first frame.
What is the difference between Owner and Parent of a control?
This little example doesn't use DLLs, but it shows how the frame won't be displayed without a Parent being assigned:
unit CreateFrameAtRunTimeForm;
interface
uses
Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,
Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.StdCtrls;
type
TForm2 = class(TForm)
Label1: TLabel;
Button1: TButton;
Button2: TButton;
procedure Button1Click(Sender: TObject);
procedure Button2Click(Sender: TObject);
private
{ Private declarations }
public
{ Public declarations }
end;
var
Form2: TForm2;
implementation
uses CreateFrameAtRunTimeFrame;
{$R *.dfm}
procedure TForm2.Button1Click(Sender: TObject);
var
F : TFrame3;
begin
F := TFrame3.Create(self);
F.Name := 'Frame'+Random(1000000).ToString;
F.Panel1.Caption := 'Frame '+F.Name;
F.Left := 200;
F.Top := 100;
end;
procedure TForm2.Button2Click(Sender: TObject);
var
F : TFrame3;
begin
F := TFrame3.Create(self);
F.Name := 'Frame'+Random(1000000).ToString;
F.Panel1.Caption := 'Frame '+F.Name;
F.Left := 200;
F.Top := 100;
F.Parent := self;
end;
end.
I'm sure your problem is that the Frame doesn't have a Parent control and I don't think it's possible to set one if you are only passing window handles around.