How do I tell if TDBImage my has been erased/emptied?

问题

I have a TDBImage control on my form.

Users can CTRL-V images in to it. They can also CTRL-X in the control to clear the image.

When I later try to take the contents of that TDBImage as save it to my database I get memory access violations, in particular when I generate the memory stream.

Naturally my first inclination is to see if the TDBImage is somehow empty before I do this (and clear the database field my self). But I can't seem to find a way to detect if the control has been CTRL-X'ed by the user.

Here's a very condensed version of what my existing code looks like if it helps.

var
  photo: TDBImage;
  photoValue: TPicture; 
  photoStream: TMemoryStream;
  updateQuery: TOraQuery;
begin
  // ....
  // It gets through here without complaint
  photoValue := photo.Picture;

  // It fails on this line
  photoValue.Graphic.SaveToStream(photoStream);
  updateQuery.paramByName('picture').ParamType := ptInput;
  updateQuery.paramByName('picture').AsOraBlob.LoadFromStream(photoStream);
  updateQuery.ExecSQL;
  // ...
end;

How can I detect an empty/CTRL-Xed TDBImage control?

回答1:

You can check if the Graphic property is nil, like so

 if DBImage1.Picture.Graphic<>nil then 
   //do something

来源：https://stackoverflow.com/questions/32656587/how-do-i-tell-if-tdbimage-my-has-been-erased-emptied