[2 days left] What’s wrong with your cloud strategy? Learn why multicloud solutions matter with Nimble Storage.Register Now

x
?
Solved

Creating controls at runtime through DLL

Posted on 2003-12-03
2
Medium Priority
?
314 Views
Last Modified: 2010-04-05
Hi all

please help me to solve the problem

I am unable to create the controls to main form. I am creating these controls through the DLL procedure. Application is raising invalid memory address exception
here is the code

These are replication of my project

DLL Example:

uses
  sharemem,Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs,
  StdCtrls,ImageHlp;


{$R *.RES}


//This is the main procedure i am creating in dll


procedure LoadPlugin(application: TApplication);

begin

   button:=TButton.Create(application.MainForm  );


   button.Caption:='Sudhakar';
   with button do
   begin

        Top:=10;
        Width:=100;
        Height:=100;
        Left:=10;
        parent:=application.mainForm;
        show;
   end;
end;
exports LoadPlugin;



Application Example
____________________

unit Unit1;

interface

uses
  Sharemem,Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs,
  StdCtrls;

type
  TForm1 = class(TForm)
    Button1: TButton;
    procedure Button1Click(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form1: TForm1;

implementation

{$R *.DFM}

function LoadAndRunDLLProcedure( sDLL, sFunc : string ) : boolean;
type
  // define the type of "function"
  // we're calling

  TFunc_Start = procedure(app:TApplication);
var
  Func_Start : TFunc_Start;


  hDll       : THandle;
  FuncPtr    : TFarProc;
  sMsg       : string;
begin
  Result := False;
  hDll   := LoadLibrary(
              PChar( sDLL ) );
  //app:=pApp(application);
  if(hDll > 32)then
  begin
    FuncPtr :=
      GetProcAddress(
        hDll, PChar( sFunc ) );
    @Func_Start := FuncPtr;
    if(nil <> @Func_Start)then
    begin

      Func_Start(application);
      Result := True;
    end else
    begin
      sMsg := 'DLL entry point ' +
              sFunc + ' not found';
      MessageBox(
        0, PChar( sMsg ), 'Error',
        MB_OK );
    end;
    FreeLibrary( hDll );
  end else
  begin
    sMsg := 'File ' + sDLL +
            ' not found';
    MessageBox(
      0, PChar( sMsg ), 'Error',
      MB_OK );
  end;
end;

procedure TForm1.Button1Click(Sender: TObject);
Var
searchResult : TSearchRec;
fileName:String;
begin
                 if FindFirst('*.dll', faAnyFile, searchResult) = 0 then
  begin
    repeat
     fileName:=searchResult.Name;
     LoadAndRunDLLProcedure(
  fileName,
        'LoadPlugin' );

    until FindNext(searchResult) <> 0;

    // Must free up resources used by these successful finds
    FindClose(searchResult);
  end;

end;


end.



0
Comment
Question by:sudhakar_koundinya
[X]
Welcome to Experts Exchange

Add your voice to the tech community where 5M+ people just like you are talking about what matters.

  • Help others & share knowledge
  • Earn cash & points
  • Learn & ask questions
2 Comments
 
LVL 5

Accepted Solution

by:
snehanshu earned 500 total points
ID: 9881624
sudhakar,
  I am not a DLL expert, but here's a solution that works for me (Delphi 7):

1. It seems FreeLibrary( hDll ) is the major cause of your problems: you need to keep the DLL loaded after calling "LoadAndRunDLLProcedure".

function LoadAndRunDLLProcedure( sDLL, sFunc : string ) : boolean;
type
  // define the type of "function"
  // we're calling

  TFunc_Start = procedure(MyCont: TApplication);
var
  Func_Start : TFunc_Start;

  hDll       : THandle;
  FuncPtr    : TFarProc;
  sMsg       : string;

begin
  Result := False;
  hDll   := LoadLibrary(
              PChar( sDLL ) );
  if(hDll > 32)then
  begin

    FuncPtr :=
      GetProcAddress(
        hDll, PChar( sFunc ) );
    @Func_Start := FuncPtr;
    if(nil <> @Func_Start)then
    begin

      Func_Start(Application);
      Result := True;
    end else
    begin
      sMsg := 'DLL entry point ' +
              sFunc + ' not found';
      MessageBox(
        0, PChar( sMsg ), 'Error',
        MB_OK );
    end;
//    FreeLibrary( hDll );//Causes problems: free later
  end else
  begin
    sMsg := 'File ' + sDLL +
            ' not found';
    MessageBox(
      0, PChar( sMsg ), 'Error',
      MB_OK );
  end;
end;

2. In the DLL, "parent:=application.mainForm;" is the culprit. I don't know the whys of these, but you can get-around this problem by replacing parent by parentwindow.

procedure LoadPlugin(MyApp:TApplication);
Var
 Button: TButton;
begin

   button:=TButton.Create(MyApp.MainForm);
   Button.ParentWindow := MyApp.MainForm.Handle;

   button.Caption:='Sudhakar';
   button.Top:=10;
   button.Width:=100;
   button.Height:=100;
   button.Left:=10;

   button.show;

end;



Hope that helps,
...Shu
0
 
LVL 14

Author Comment

by:sudhakar_koundinya
ID: 10015663
Though it not helped me, Explaination is Good

Regards
Sudha
0

Featured Post

Free Tool: Path Explorer

An intuitive utility to help find the CSS path to UI elements on a webpage. These paths are used frequently in a variety of front-end development and QA automation tasks.

One of a set of tools we're offering as a way of saying thank you for being a part of the community.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Introduction The parallel port is a very commonly known port, it was widely used to connect a printer to the PC, if you look at the back of your computer, for those who don't have newer computers, there will be a port with 25 pins and a small print…
In my programming career I have only very rarely run into situations where operator overloading would be of any use in my work.  Normally those situations involved math with either overly large numbers (hundreds of thousands of digits or accuracy re…
Have you created a query with information for a calendar? ... and then, abra-cadabra, the calendar is done?! I am going to show you how to make that happen. Visualize your data!  ... really see it To use the code to create a calendar from a q…
Are you ready to place your question in front of subject-matter experts for more timely responses? With the release of Priority Question, Premium Members, Team Accounts and Qualified Experts can now identify the emergent level of their issue, signal…
Suggested Courses

656 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question