CODEWITHSUNDEEP
delphiado
Precastwig
Precastwig

Reputation: 13

Delphi invalid pointer operation using ADO

When calling this code more than once (It's called on the change of a combobox), I'm getting the error "Operation not allowed when the object is open" on the second change and on the third onwards i'm getting "invalid pointer operation".

if loadfile.Database <> nil then  
    loadfile.Database.destroy;  
Loadfile.Database := Tdatabase.create(CardSets.Text, false);  
LoadFile.Database.create(CardSets.Text, false);         
refreshlist;

The create code is just

DataSource :=   
    'Provider=Microsoft.Jet.OLEDB.4.0' +   
    ';Data Source=' + Path +  
    ';Jet OLEDB:Engine Type=5';   
with MainWindow do  
begin   
    ADOConnection.ConnectionString := Datasource;   
    ADOConnection.LoginPrompt := False;   
end;

And refreshlist just updates a visual list of the data in the database.

I've looked at some similar stackoverflow questions but i am unable to see how the answers could help my problem.

Side question, When to use .Destroy or .Free? .Free in this case just gives a different error.

Thanks.

Upvotes: 1

Views: 706

Answers (1)

Ken White
Ken White

Reputation: 125620

First, you're calling Create twice; the second is unnecessary:

if loadfile.Database <> nil then  
    loadfile.Database.destroy;  
Loadfile.Database := Tdatabase.create(CardSets.Text, false);  // First call
LoadFile.Database.create(CardSets.Text, false);               // Second call

Change your code to simply:

LoadFile.Database.Free;
LoadFile.Database := TDatabase.Create(CardSets.Text, False);

Second, never directly call Destroy. Use Free instead, as it checks first for an unassigned pointer and then calls Destroy if it's safe to do so. TObject.Free is basically this code:

procedure TObject.Free;
begin
  if Self <> nil then
    Destroy;
end;

Upvotes: 2

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