Example 6: Logging a bad graphic cell

Uses OnGraphicError so a corrupt or unrecognized image is reported somewhere useful, instead of just being silently left blank in the grid.

Scenario

A Photo field declared as ftGraphic. Some rows have leftover data from a previous, unsupported image format. The cell should stay blank - there is no image to show - but the problem should be visible in the application log rather than only in the grid appearing empty.

Note: This only applies to a true ftGraphic field. A plain BLOB field opted in via DetectBlobImages that fails to decode is treated as an expected outcome, not a malfunction - the cell falls back to showing the field’s own display text, and OnGraphicError does not fire for it at all. See DetectBlobImages.

The handler

procedure TfrmOrders.GridGraphicError(Column: TColumn; const Msg: string);
begin
  AppLog.Warn(Format('Failed to decode image in %s, record %s: %s',
    [Column.FieldName, Table.FieldByName('ID').AsString, Msg]));
end;

Why it works this way

• The cell is already handled: this event only reports the failure - the grid always leaves the cell blank on a decode failure whether or not this event is assigned. There is nothing to “recover” from inside the handler itself.
• Fires per repaint, like any other draw-time event: on a fast-scrolling grid, the same bad row can log repeatedly as it scrolls in and out of view. If that is a concern, keep a small set of already-logged record IDs (or field values) and skip logging ones already seen in this session, rather than writing to a log file on every repaint.
• Msg is short and not localized - currently always the fixed text 'Unsupported graphic format', not something meant to be shown to an end user directly. Still worth logging as-is rather than a hardcoded string of your own, since a future version could make it more specific without changing the handler’s signature. Show a separate, translated message to the user if the application needs to say something in the UI about it.

See Also

• OnGraphicError
• DetectBlobImages
• TEgDBGridGraphicErrorEvent
• Examples