Solved

DLLs

Posted on 1997-03-24
1
426 Views
Last Modified: 2010-04-04
I just got a great answer about a Dll question.
So Heres another one .
if I have 2 dll's both have the same function names
when I load the dll's as so :

Hinst := LoadLibrary('c:\files\mikes\projects\dll\project1.dll');
if Hinst > 32 then;
   begin
    FPointer := GetProcAddress(Hinst, 'EntryPoint');
      if FPointer <> Nil then
        begin
          MyProc := proc(FPointer);
          try
            MyProc(MainMenu1);;
          except
           FreeLibrary(HInst);
           ShowMessage('Error in Calling EntryPoint in DLL');
          end;
       end;
     end;

Hinst := LoadLibrary('c:\files\mikes\projects\dll\DLL2.dll');
if Hinst > 32 then;
   begin
    FPointer := GetProcAddress(Hinst, 'EntryPoint');
      if FPointer<> Nil then
        begin
          MyProc := proc(FPointer);
          try
            MyProc(MainMenu1);
          except
           FreeLibrary(HInst1);
           ShowMessage('Error in Calling EntryPoint in DLL');
          end;
       end;


     end;
what the dlls do are they loads two menu Items. This works the two deffernt menu  do load but when I click on the first menu item(first dll that loaded) it runs the right function. when I click on the 2nd menu item(the 2nd dll that loaded) it runs the first menu item not the 2nd?

Both dll have the same function names but the function do differnt things. can anyone explain this to be because I thought if the dlls load in there own memory space the function address would be differnt even if they were name the same. well I quest I'm wrong?

--------------- Code for Dll --------------------------------------
//both dlls are the same except for the showmessage()
//which is in the  DynaClick() procedure.
uses
  Menus, Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs;

type
  TEvent = procedure(Sender: TObject) of object;
  TSomeClass = Class
  procedure DynaClick(Sender: TObject);
end;

 var
  NewMenu : TMenuItem;
  SomeClass : TSomeClass;
  Event : TEvent;

procedure TSomeClass.DynaClick(Sender: TObject);
begin
  showMessage('Its Dll 2');
end;

procedure EntryPoint(AMenu: TMenu); export; stdcall;
var
  NoItem  : TMenuItem;
begin
   //create a event handler...
  SomeClass := TSomeClass.Create;
   //assign Event to DynaClick to be pass to the menu Onclick event...
 Event := SomeClass.DynaClick;

 NoItem := AMenu.Items[AMenu.Items.Count - 1];
 NewMenu := TMenuItem.Create(NoItem);
 NewMenu.Caption := 'DLL2 Menu';
 NewMenu.OnClick := Event;
 NoItem.Insert(NoItem.Count, NewMenu);
 SomeClass.Free;
end;

exports
   EntryPoint;

0
Comment
Question by:mikec459
[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
1 Comment
 
LVL 3

Accepted Solution

by:
sperling earned 100 total points
ID: 1334940
Hmmm... Start with removing the SomeClass.Free from your EntryPoint function. That won't help, but the menuitems OnCLick will call a method of a destroyed object.

Everytime you, or VCL code, calls TMenuItem.Create, a new unique word is reserved as the "Command ID" of the menu item. This "Command ID" is passed on to Windows, and when you click an item, windows passes the command ID back to the VCL, which then again uses this ID to determine what TMenuItem.OnCLick it should call.
The problem is that the method the VCL uses to allocate these unique IDs are local to the application and the DLLs. This means that when you call TMenuItem.Create in the first DLL the menu item will allocate the first unique command ID within the DLL. And so will DLL 2, meaning you get two menu items with the same ID.

Try redesigning a bit:

Have your DLL export a function, "MenuItemClicked" or something.
Declared like this:
  procedure MenuItemClicked; export; stdcall;

Create the menuitem in the app, and pass the item to EntryPoint.

EntryPoint should set the caption, help context and so on of the TMenuItem. In addition, include this line:

  AMenuItem.Tag := INTEGER(@MenuItemClicked);


The application should set the OnClick event for all created menu items to a common procedure, e.g. DLLMenuItemClicked.

procedure TForm1.DLLMenuItemClicked(Sender : TObject);
type
  TClickProc = procedure; stdcall;
var
  ClickProc : TClickProc;
begin
  @ClickProc := POINTER(TMenuItem(Sender).Tag);
  ClickProc;
end;


This scheme should work, although I haven't tested it. Leave me a comment if you get trouble...
0

Featured Post

On Demand Webinar - Networking for the Cloud Era

This webinar discusses:
-Common barriers companies experience when moving to the cloud
-How SD-WAN changes the way we look at networks
-Best practices customers should employ moving forward with cloud migration
-What happens behind the scenes of SteelConnect’s one-click button

Question has a verified solution.

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

In this tutorial I will show you how to use the Windows Speech API in Delphi. I will only cover basic functions such as text to speech and controlling the speed of the speech. SAPI Installation First you need to install the SAPI type library, th…
Have you ever had your Delphi form/application just hanging while waiting for data to load? This is the article to read if you want to learn some things about adding threads for data loading in the background. First, I'll setup a general applica…
Michael from AdRem Software explains how to view the most utilized and worst performing nodes in your network, by accessing the Top Charts view in NetCrunch network monitor (https://www.adremsoft.com/). Top Charts is a view in which you can set seve…
Do you want to know how to make a graph with Microsoft Access? First, create a query with the data for the chart. Then make a blank form and add a chart control. This video also shows how to change what data is displayed on the graph as well as form…

688 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