How to make a form in a DLL embedded inside my application?

Question

I'm building a form inside a DLL and would like to embed that form inside the host application. Surely I can't simply pass the Parent control into the DLL. But I have to give this DLL form a Parent from the EXE form (inside a TPanel).

How can I make this form inside the DLL embedded inside its host application, aligned as Client within a panel?

What I'm building is a setup module which consists of a tree view on the left half of the form, and an empty placeholder panel on the right, like a snap-in console. Each possible module is represented by a DLL, one corresponding with each node on the tree view.

EDIT

One important thing I didn't mention before, the reason I'm implementing DLL's is because each setup module might be developed in a different language. Most will be Delphi, But the software package which this is based around consists of different applications built in some other languages than Delphi (such as C#). Those developers will design their own setup modules to be integrated.

Not necessarily, the Host and its DLLs are developed in the same Delphi environment — Jerry Dodge, Sep 02 '13 at 18:07
Then use packages. We've discussed this millions of times here. — David Heffernan, Sep 02 '13 at 18:12
Yeah it's tempting, but I like to leave that door open to be cross-language compatible — Jerry Dodge, Sep 02 '13 at 18:13
Then design a plugin interface. Your current plan shuts the door to all, including you. — David Heffernan, Sep 02 '13 at 18:15
I am designing a plugin interface, where each plugin might be developed in a different language than Delphi. — Jerry Dodge, Sep 02 '13 at 18:52
So what about an Active Form: http://docwiki.embarcadero.com/RADStudio/XE3/en/Creating_a_VCL_Forms_ActiveX_Active_Form — David Heffernan, Sep 02 '13 at 18:57
@DavidHeffernan I did consider that but ActiveX is as good as dead lately. Besides I will only need 4 exported functions. If I remember right you yourself had discouraged the use of ActiveX to me back when I was experimenting with it. — Jerry Dodge, Sep 02 '13 at 19:00
ActiveX solves this particular problem. Do you understand the issues with trying to share VCL objects across modules? — David Heffernan, Sep 02 '13 at 19:06
Yes, and that's exactly why I was seeking a solution to set the parent of a form. — Jerry Dodge, Sep 02 '13 at 19:07
There is no solution to that. You cannot set the parent of a control to be a control from a different VCL instance. If you want to do that you have to use packages so that there is a single VCL instance. — David Heffernan, Sep 02 '13 at 19:13
So the Window Handle can't even be passed and used to assign its parent? — Jerry Dodge, Sep 02 '13 at 19:35
That's fragile. Does not play well with window recreation and you still have two VCL instances — David Heffernan, Sep 02 '13 at 19:46
@DavidHeffernan I understand, and I don't intend to pass any VCL objects between the EXE and DLL. — Jerry Dodge, Sep 02 '13 at 20:20
@DavidHeffernan I'm willing to do whatever it takes to make this possible, even if it means taking VCL out of the picture. — Jerry Dodge, Sep 02 '13 at 20:28
You use `SetParent` to set a parent to a window, the api function not of TControl. Then set the `WS_CHILD` flag for the parented window, if it wasn't a child. Then you start struggling with key input, tab order, focus issues etc.. — Sertac Akyuz, Sep 02 '13 at 21:27
Actually I just found a duplicate: http://stackoverflow.com/questions/16912393/show-form-from-dll-in-tscrollbox — Jerry Dodge, Sep 03 '13 at 07:27
For the record I have moved on to encapsulating each form with a common `IInterface` and the DLL only has 3 exported functions: `ShowSetupModal`, `CreateSetup`, and `DestroySetup`, which are used along with `LoadLibrary` and `FreeLibrary`. — Jerry Dodge, Sep 03 '13 at 09:40

score 5 · Accepted Answer · edited Feb 11 '16 at 14:29

I don't know if this will address all the issues (save freeing the form, I would expose functions to do anything external involving the dll form), but this should give a good start:

library testdll;

uses dllunit in 'dllunit.pas' {Form1}, windows;

procedure callform(ParentForm: HWnd);
// simple test, resource management is necessary on the form.
var
  dllform: TForm1;
begin
  dllform := TForm1.Create(nil);
  dllform.Show;
  Windows.SetParent(dllform.Handle, ParentForm);
end;

exports
  callform;

end.


program mainprogram;

procedure callform(ParentHandle: THandle); external 'testdll.dll';

procedure TForm1.Button1Click(Sender: TObject);
  begin
    callform(Panel1.Handle);
  end;

Like was said, there might be other issues once you start adding features to the dll form, but (for me) it's putting the form designed in dllunit.pas into the main form's project with Panel1 as a parent and is operating as expected. But like was said, this was just intended as a start.

Indeed, they're both a `NativeUInt`but the `THandle` is the Delphi RTL representation of it. — Jerry Dodge, Sep 03 '13 at 06:22

score 4 · Answer 2 · answered Sep 02 '13 at 17:59

If the parent is another Delphi program, you could simply make your DLL as a BPL, and then you shouldn't have problems with stuff like this. Have a look at the plugin system in the JVCL for a way to make it easy to plug new functionality into your program with packages.

score 0 · Answer 3 · answered Jul 23 '15 at 17:31

0

Yes, it is the handle, just call it to fill any component like a Groupbox or Panel

answered Jul 23 '15 at 17:31

DarthGodete

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How to make a form in a DLL embedded inside my application?

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