[SOLVED] Trying to block error dialog and do exception code, but can't
lazarus / 16-Databases

----------------------------------------------------------------------
Elmug · 2012-07-21 06:07

Hi everyone,

I thought I could maybe handle either .bmp or .jpg using a Try/Except
block, but can't seem to get it to work.

As shown below, the error dialog pops and the error has control, with
no chance to the Except code, when the image is .bmp and would like to
handle it with the except code.

Try
  Image1.Picture.Graphic:= TJpegImage.Create;
Except
  Image1.Picture.Graphic:= TBitMap.Create;
End; 
  Image1.Picture.Graphic.LoadFromStream(BS);

Would appreciate help in solving this, if possible.

Thanks!

----------------------------------------------------------------------
taazz · 2012-07-21 07:15

Create does not raise any error, loadfromstream does you need to put
that method in a try except and not the create.

----------------------------------------------------------------------
KpjComp · 2012-07-21 09:26

Like @taazz pointed out, it's the loading that will be raising the
exception.

But you should not really be using Try/Except blocks in this way.

What's I've done in the past is examine the first few bytes of the the
file.  I have some code at work I could dig up, I think it did
JPEG/BMP/PNG detection.  It's the weekend now, so won't be at work
till Monday, if you can wait I'll dig up the detection algorithm. 
It's not very complicated, it usually involves just seeing if the
bytes at XYZ contain ABC sort of thing.

----------------------------------------------------------------------
Elmug · 2012-07-21 14:12

Hi everyone, again, just to report this (I believe important reach):
My application now DOES handle either JPEG or BitMap images in the
same column, Blob-Type, without having to regard imagefile extension,
nor having to decipher Blob-headers.

In my application, the instructions will be to use only .bmp or JPEG
files, which are loaded into the database by means of the loadpicture
dialog. The loading of the image file it is known, does not
discriminate: can load JPEG or .bmp by same code. These two image
types, for me, are the most popular here. But the idea can possibly be
extended to a few other types if needed, I believe.

The usual problem has been, not the loading, but the SHOWING the Blob
image when the Blob column can store Blobs of JPEG or .bmp files. Of
course, the idea can be extended to include other image formats.

The solution achieved is using Exception coding as follows:

Code: [Select]// var
//  BlobField: TField;
//  BS: TStream;

  with SQLQuery1 do
    begin
       BlobField := FieldByName('Pic'); {'Pic' is name of column with
photo}
       BS := CreateBlobStream(BlobField,bmRead);
       Image1.Picture.Graphic:= TJpegImage.Create; {assume is Jpeg}
    Try
       Image1.Picture.Graphic.LoadFromStream(BS); {error if not Jpeg}
      Except {repeat steps for BitMap}
         BS.Free;
         Image1.Picture.Graphic:= nil; {empty}
         BlobField := FieldByName('Pic'); {'Pic' is name of column
with photo}
         BS := CreateBlobStream(BlobField,bmRead);
         Image1.Picture.Graphic:= TBitMap.Create; {bitmap}
         Image1.Picture.Graphic.LoadFromStream(BS);
      end; {Try}
      BS.Free;
    end; {with SQLQuery}

Thanks to taazz for the very good observation on WHERE to do the
exception, and to all others as well.