Hi, I don't use data aware controls too often, but as I'm updating a legacy application I have to use them.

Please take a look at this code. DataModule1.SQLQuery1 is a simple "select * from customers limit 10". What I want to accomplish is the refreshing of a DBGrid *without losing the focused row*, that's why I use a TBookmark.

To me, the code looks correct, but I'm getting a SIGSEGV while assigning the bookmark. I must add the error only happens the 2nd or 3rd time this method is called:

var
   lOldStatus: string;
   lBookmark : TBookmark;
begin
   lOldStatus := StatusBar1.Panels[1].Text;
   StatusBar1.Panels[1].Text := 'Updating...';
   lBookmark := DataModule1.SQLQuery1.Bookmark;
   DataModule1.SQLQuery1.DisableControls;
   DataModule1.SQLQuery1.Close;
   DataModule1.SQLQuery1.Open;
   DataModule1.SQLQuery1.EnableControls;
   DataModule1.SQLQuery1.Bookmark := lBookmark; <-- Random SIGSEGV
   StatusBar1.Panels[1].Text := lOldStatus;
end;

El 01/11/15 a les 13:25, Leonardo M. Ram? ha escrit:

To me, the code looks correct, but I'm getting a SIGSEGV while assigning the bookmark. I must add the error only happens the 2nd or 3rd time this method is called:

I suppose that's because the bookmark is only valid while the query is opened, buy you close it between getting the bookmark and setting it.

Bye

Also: in my experience in Delphi closing with DisableControls active is a bad idea. I have seen cases, when components are still referencing old field instances.

2015-11-01 13:06 GMT-03:00 Luca Olivetti :

Yes. In TBufDataset, the bookmark references the internal buffer memory. As soon dataset is closed, the memory may change

Luiz

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El 01/11/15 a las 09:25, Leonardo M. Ram? escribi?:

Hi, I don't use data aware controls too often, but as I'm updating a legacy application I have to use them. ...

I finally solved this by getting the value of a primary key, then after TSQLQuery.refresh I do a locate for that key, works like a charm.

What I don't get is what's the purpouse of TBookmark, I thought it was made for solving the problem I had.

Leonardo.

El 03/11/15 a les 00:58, Leonardo M. Ram? ha escrit:

What I don't get is what's the purpouse of TBookmark, I thought it was made for solving the problem I had.

Yes, but only if you leave the dataset open.

Bye

Bookmarks are only valid until the dataset closes. I will add this to the documentation.

Michael.

El 03/11/15 a las 04:40, Michael Van Canneyt escribi?:

Ok, but apart from Closing/Opening or Refresh, is there any other way to reload a dataset without closing it? TSqlQuery.Refresh also loses the Bookmark.

Regards,
Leonardo.

No, there is not.

Michael.

Even if you could reload it, I'd have thought that the only valid way of positioning would be by locating against a column (preferably known to have an index). After all, the content of the table might have had gross changes due to the actions of other users, and potentially the layout might have changed.

I find myself moving away from data-aware controls and instead executing queries in a background thread, to try to avoid UI glitches while the backend's doing its stuff.