Application.Handle missing
lazarus / 31-LCL

----------------------------------------------------------------------
tk · 2014-06-15 23:38

hello,
I have a main program and a DLL both written in Delphi which I am
converting to Lazarus.
Both main program and the DLL use separate VCLs, no runtime packages
used.
In a DLL there is a configuration form which I need to show from the
main program.
The important code in the DLL is:
Code: [Select]function TCom.PropConfig(AAppHandle: THandle): Boolean;
var
  AForm: TConfigForm;
begin
  Result := False;
{$IFnDEF FPC}
  Application.Handle := AAppHandle;
{$ENDIF}
  AForm := TConfigForm.Create(Application);
  try
    ConfigToForm(AForm);
    if AForm.ShowModal = mrOk then
    begin
      FormToConfig(AForm);
      Result := True;
    end
  finally
    AForm.Free;
  end;
end;

function PropConfig(AHandle, AAppHandle: THandle): Boolean; stdcall;
begin
  try
    if TObject(AHandle) is TCom then
      Result := TCom(AHandle).PropConfig(AAppHandle)
    else
      Result := False;
  except
    Result := False;
  end
end;

The important code in the main program is:
Code: [Select]function TPlugin.PropConfig(AHandle, AAppHandle:
THandle): Boolean;
begin
  if Assigned(FFuncPropConfig) then
    Result := FFuncPropConfig(AHandle, AAppHandle)
  else
    Result := False;
end;

// somewhere in the main program there is this call:
MyPlugin.PropConfig(PluginHandle, MainForm.Handle);

This works OK in Delphi, but due to the missing Application.Handle
property in Lazarus (the first IFDEF) the configuration dialog won't
show up.
I am testing on WIndows now but of course I need platform independent
solution for this.

tk

----------------------------------------------------------------------
marcov · 2014-06-16 07:53

IIRC use WidgetSet.AppHandle

----------------------------------------------------------------------
Mike.Cornflake · 2014-06-16 08:18

Bleh, this may not be relevant to you, however you may find something
of interest...   The words dll and apphandle triggered a vague memory
of something I've read on here.   Here's the post - as I say, not sure
if you'll find it relevant, it may be worth a read...

http://forum.lazarus.freepascal.org/index.php/topic,22766.msg140959.ht
ml

----------------------------------------------------------------------
tk · 2014-06-16 09:04

Quote from: marcov on June 16, 2014, 09:53:34 amIIRC use
WidgetSet.AppHandle

Just tried

Code: [Select]{$IFDEF FPC}
  WidgetSet.AppHandle:= AAppHandle;
{$ELSE}
  Application.Handle := AAppHandle;
{$ENDIF}

without success.

Found also this thread http://forum.lazarus.freepascal.org/index.php/t
opic,8321.msg58906.html#msg58906.
Might work, I didn't try yet but seems a little bit weird to me.
I would like to keep the entire form calling logic hidden inside of
the DLL.

----------------------------------------------------------------------
tk · 2014-06-16 11:57

Finally got the form on screen with:
Code: [Select]{$IFDEF FPC}
  WidgetSet.AppHandle:= AAppHandle;
  Application.Initialize;
{$ELSE}
  Application.Handle := AAppHandle;
{$ENDIF}

but it is not shown as modal form, although ShowModal is called.

----------------------------------------------------------------------
tk · 2014-06-16 22:17

Finally I realized there is no clean solution for this in Lazarus.
To show a form in a DLL in the context of the main application would
need a clean and well defined solution how to link the entire LCL
context from the main project (e.g. WidgetSet, Application, Screen
etc.)  to the DLL project. If both the DLL and main project are
written in Lazarus.

I tried to switch the context, i.e. supplant those static instances I
mentioned above from main project into the DLL but this produced
exceptions. I am sure those three are not enough, there are many more,
going deeply into the particular widget set etc.

Finally I encapsulated the DLL call with Screen's DisableForms and
EnableForms methods, which at least disables all forms from the main
project before the DLL modal form is shown:
Code: [Select]function TPlugin.PropConfig(AHandle, AAppHandle:
THandle): Boolean;
var
  List: TList;
begin
  if Assigned(FFuncPropConfig) then
  begin
    List := Screen.DisableForms(nil);
    try
    Result := FFuncPropConfig(AHandle, AAppHandle);
    finally
      Screen.EnableForms(List);
    end;
  end
  else
    Result := False;
end;     

It produces some problems when switching programs with ALT+TAB but
this is the only at least partially clean solution I could find.

Delphi has no explicit solution as well, but somehow supplanting
Application.Handle in the DLL works fine.