Saving image from Electron app into file

WEB TMS WEB Core
1

delphi 10.3 / TMS WEB Core 1.5.6.0

I'm storing an image inside a database as Base64 string. For testing purpose, I'm trying to store it in a file using a TElectronBinaryDataStream. I know, that I can assign the Base64 image string directly to the stream by

Var
  stream : TElectronBinaryDataStream;
begin
    stream:= TElectronBinaryDataStream.Create();
    stream.Base64:= image_string_base64;
    stream.SaveToFile(FileName);
end;

This is working, I get an image file.

I'm also trying to create a TGraphic object from the base64 image string and then storing it to a stream:

Var
  g : TGraphic;
  stream : TElectronBinaryDataStream;
begin
    stream:= TElectronBinaryDataStream.Create();  
    g:= TGraphic.CreateFromURL(image_string_base64);

    stream.Base64:= g.GetBase64Image;
    stream.SaveToFile(FileName);
end;

Here I get an empty file. Which part is not working?

2

CreateFromURL is an asynchronous function. Calling it will not immediately yield a result on the next line. You might need to handle further processing from OnChange.

3

How to assign the event handler to the TGraphic.OnChange event? I saw in the form source code the method, but can't make it work.

Var
  signature_base64 : string;
  g : TGraphic;
begin
  g:= TGraphic.Create;
  SetEvent(g, self, 'OnChange', 'OnGraphicChanged');

  g.LoadFromURL(signature_base64);

  result:= g;
end;

procedure TForm1.OnGraphicChanged(Sender: TObject);
Var
  g : TGraphic;
  stream : TElectronBinaryDataStream;
begin
  try
    g:= Sender as TGraphic;
    stream:= TElectronBinaryDataStream.Create;

    stream.Base64:= g.GetBase64Image;
    stream.SaveToFile('Image.png');
  finally
    g.free;
    stream.free;
  end;
end;

I tested a version using a TWebImageControl.OnLoaded event for storing the image file, which is working as expected. Why is my code, using the TGraphic object not working?

4

You set it like any Delphi event handler, i.e.
class.OnChange := yourhandler

5

That's what I did first, but it didn't work. In the chrome debugger window I saw this form creation code which is assigning the eventhandler by SetEvent()

ElectronFormCreation

6

please define "didn't work"

7

The assigned event handler procedure wasn't executed