Strange error with ODBC

[Jonah86]

Hello. I posted this problem in the ODBC board as well...but I figured maybe someone here has encountered this before, so maybe they can help.

**copied from the ODBC board**
I have an app I made with delphi that accesses a MySQL database, I have an ODBC connection set up for this purpose. Now, sometimes when I close the Delphi app it gives me this error: "Exception EAccessViolation in module IDODBC32.DLL" and references some memory addresses. Now this happens on any computer I run the app on, and only happens sometimes. It's completely random in appreance, when this error occurs. I can't even begin to imagine what could be causing this.

Any suggestions would be greatly appreciated.

**End ODBC post**

The thing is, it only happens when I go to close the app, after I hit Exit. It happens on ANY form, and after seemingly ANY possible combination of actions within the app. It just seems totally random. Aggrivating.

 

[VintageWine]

Is everything in your app being closed/freed properly?

Suggest creating an afterclose event for the TDatabase/TADOConnection or whatever you are using and see whether or not it triggers when you exit your app.

Good luck
Simon

 

[Jonah86]

What, exactly, is the best way to exit the program. I'm just using application.terminate at thie point in time, I'm not sure what else I should be doing to ensure that the application is closed/freed properly.

I'm using BDE, by the way. Connecting to MySQL, not sure if that makes a difference.

Thanks for your reply.

 

[whosrdaddy]

application.terminate is IMHO not a good to way to close your application. use the close method of your form.

what I always do is use the formcreate and formclose methods that belongs the main form. something like this :


procedure TFrm_main.InitApplication;

begin
AppClosing:=False;
LOpenChannels:=TStringList.Create;
Assert(LOpenChannels <> nil,'');
CreateChannelList;
end;


procedure TFrm_main.DestroyApplication;
begin
AppClosing:=True;
FreeAndNil(LOpenChannels);
WritePreferencesToRegistry(INT_PREF_MAIN); // save main preferences
end;

procedure TFrm_main.FormCreate(Sender: TObject);
begin
InitApplication;
end;


procedure TFrm_main.FormClose(Sender: TObject; var Action: TCloseAction);
begin
DestroyApplication;
end;

 

[svanels]

I suspect that you use a TmainMenu with an exit option, and there are 2 ways to close your apllication:
1) with your exit option
2) Clicking the close icon on the form (A 3^rd option is hitting the power button).

To synchronize the behaviour of the two methods:

procedure TMainForm.FormCloseQuery(Sender: TObject; var CanClose: Boolean);
begin
if MessageDlg('Exit My Info System ?',
mtConfirmation, [mbYes, mbNo],0) = mrNo then
Canclose:= False;
end;
This is invoked by using the close icon on the main form X

Delphi take cares of all the clean-up stuff and this ishandled by the OnCloseQuery event

To make this code available to your exit button or menu item:

Drop a TActionList on your mainform, open the ActionList editor, add an action called MyClose

In the OnExecute event key in:

if CloseQuery then close;

I had similar experiences with access violations using the plain Close command in my exit menu item

Regards










Steven van Els
SAvanEls@cq-link.sr

 

[VintageWine]

whosrdaddy and Steven both offer valuable contributions. I offer this in addition.

I always have one autocreate form (the MainForm). Delphi will create and open that form. When you close it (Call Close method from button/menu or click close icon) Delphi closes the application in an orderly manner.

For all other forms either:
Make the owner the MainForm, they will then be freed in
an orderly manner before the MainForm is freed.
OR
Set the owner to nil on creation
Put Action:=caFree in the OnClose event
Make sure that the form is closed before closing the application.

You've got plenty of options now.
Simon