Delphi: Stream your objects

Delphi's forms demostrate that it can stream objects to and from files. How can you use this to stream your own objects? It took me a day to blunder through this so I thought I'd share.

• Derive your objects from TComponent. TPersistent is more trouble than it is worth, but see http://www.undu.com/Articles/990609d.html if you really want to.


• Register each class that will be saved. e.g.

  initialization
     Classes.RegisterClass(TRichClipboardContent);

• To save an object to a stream:

  stream.WriteComponent(c);

• Delphi will save your published properties.


• Override GetChildren in any objects that have sub-objects you want to save.


• Also override GetChildOwner in such objects, otherwise all objects will be owned by the root component when they are read back in.


• To read them back in:

  c := stream.ReadComponent(nil);

Want to see what's in a stream? Convert it to the text format used in modern .dfm files:

var
   text_stream: TMemoryStream;
   terminator: Char;
begin
   text_stream := TMemoryStream.Create;
   stream.Seek(soFromBeginning, 0);
   ObjectBinaryToText(stream, text_stream);
   terminator := #0;
   debug_stream.Write(terminator, 1);  // Add null terminator
   OutputDebugString(PChar(debug_stream.Memory));