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Dynamically creating Datamodule

Posted on 1998-10-04
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Last Modified: 2010-04-03
Hi,

I have an application that needs three datamodules, all of the same type.  Each datamodule will have a different connection (username/password) to a common database.

These three datamodules need to be accessible from everywhere, i.e. global.  I have created a datamodule in the IDE, called Oracle_DM1.  I now want to create three "copies" of it.

The problem is that the first one gets created successfully, but the 2nd and the 3rd ones have a value of nil.

Here's the applicable code fragments...

The project source file...

-----------------------------------------------------------------------------------
program DBG;

uses
  Windows,
  SysUtils,
  Forms,
  Main in 'MAIN.PAS' {MainForm},
  Oracle_DataMod1 in 'Oracle_DataMod1.pas' {Oracle_DM1: TDataModule},
// others deleted here
  DataModStuff in 'DataModStuff.pas';

{$R *.RES}  

begin

  Application.CreateForm(TOracle_DM1, Oracle_DM1);  // seems to be OK
  Application.CreateForm(TOracle_DM1, Oracle_DM2);  // gets a value of nil
  Application.CreateForm(TOracle_DM1, Oracle_DM3);  // gets a value of nil
  Application.CreateForm(TMainForm, MainForm);          // Main Form
  Application.Run;
end.

------------------------------------------------------------------------------------------

unit Oracle_DataMod1;

interface

uses
  Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs,
  Db, OracleData, OraclewwData, Oracle;

type
  TOracle_DM1 = class(TDataModule)
    OracleSession1: TOracleSession;
    OracleLogon1: TOracleLogon;
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Oracle_DM1: TOracle_DM1;
  Oracle_DM2: TOracle_DM1;  // I added this line
  Oracle_DM3: TOracle_DM1;  // I added this line

implementation

{$R *.DFM}

end.

----------------------------------------------------------------------------------------------------------------

Oracle_DM2 and Oracle_DM3 start off as nil but are set to a value when the MainForm.Create is ran. This form has in it's USES clause Oracle_DataMod1.  However, when I access the value of Oracle_DM2, even though the value does exist, or at least the IDE can read it, I get a Read Access Violation, and the app blows up.

I feel that the problem is either in the way I am creating the three data modules or a scoping issue.

Any idea what I am doing wrong? Environment is D3 with NT40

Thanks
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Comment
Question by:gspears060598
2 Comments
 
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Expert Comment

by:pjdb
ID: 1341769
Can you try
Oracle_DM2:=TOracle_DM1.Create(Application);
instead of
Application.CreateForm(TOracle_DM1, Oracle_DM2)

However, you'll have to destroy the object yourself

JDB
0
 
LVL 1

Accepted Solution

by:
RJENKINS earned 100 total points
ID: 1341770
Inherit the second and third DataModules from the original DM
Goto File| New..
and select the tabwith you projects name
thisa will create 3 different Unit files which will have to be saved seperately

Remember only to make changes to the first (original DataModule)
this will keep them in sync

Hope this Helps
RCJ
0

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