How do I reset the scrolling after removing images in TScrollBox?

Question

I have a Delphi form with a TScrollBox and some TImage components, and the form's scrollbox is not resetting when it's emptied... it appears to be growing every time a new image is thrown in the box.

I would like to reset the scroll range/size to the scrollbox size after I delete the image, before the next one is loaded. Is there a way to do that?

I've tried setting scrollbars invisible, and turning them back on after the next file loads and that doesn't seem to work. Any help greatly appreciated.

Root Cause: So it appears that the image moves its top-left corner to the center of where the image was located in the TScrollBox when the bitmap is freed.

Please provide a Minimal, Complete, and Verifiable example. What does your code and DFM look like? Do you have the TForm.AutoSize set to true or false? The TScrollBox.AutoSize? TImage.AutoSize? It sounds like you are not actually resizing the ScrollBox correctly, so its content area is not shrinking like you expect it to. — Remy Lebeau
ScrollBox1.AutoScroll = true; ScrollBox1.AutoSize := false; image1.AutoSize := True; I may have solved the issue.. will verify this tomorrow. — Joseph Poirier
@JosephPoirier, please rollback your latest edit and put in a separate answer. — LU RD

Joseph Poirier Joseph Poirier · Accepted Answer · 2017-01-24T15:54:29

Root Cause : So it appears that the image moves its top-left corner to the center of where the image was located in the TScrollBox when the bitmap is freed.

Resolution : Move image to top after turning off scrollbars and freeing image, but before loading new image into image object.

Code Sample..

try
  // Reset existing images
  if assigned(Image1.Picture.Bitmap) then
    Image1.Picture.Bitmap.FreeImage; // using .Free eventually caused memory issues
    // .Free should only be in Finally code section for process objects
    // or on Destroy event for program objects

  Image1.Picture.Graphic := TBitmap.Create;
  Image1.Picture.Bitmap := TBitmap.Create;

  // reset Bitmap
  if assigned(bitmap123) then
    bitmap123.FreeImage;

  bitmap123 := TBitmap.Create;

finally
  ScrollBox1.HorzScrollBar.Visible := false;
  ScrollBox1.VertScrollBar.Visible := false;
  Image1.Top := 0; Image1.Left := 0;
  Image1.Refresh;
  Application.ProcessMessages;

  ScrollBox1.HorzScrollBar.Visible := true;
  ScrollBox1.VertScrollBar.Visible := true;
  ScrollBox1.Refresh;

end;
// now images can be loaded 
// and they will appear in the top-left corner of the scrollbox every time.

How do I reset the scrolling after removing images in TScrollBox?

2 Answers