Is it possible (read: easy) to reload all of the properties of a form and
all of its owned components at runtime. What I am hoping for is something
similar to

InitInheritedComponent(Self, TForm);

This unfortunately does not work as the streaming system seems to want to
recreate rather than just reload the components. When I dig into the VCL I
seem to get stuck at TReader.ReadProperty which seems to do most of the
work I am after, but which is alas declared private.

Has anyone found or invented a better way to handle this than coming up
with my own TReader like class?

Todd Sankey
Todd.San...@HMX.Honeywell.com

Procedure TPersistentForm.ReadState(Reader ?); Override;
Begin
  Reader.OnSetName:= ReaderSetName;
  Inherited ReadState(..);
End;

Procedure TPersistentForm.ReaderSetName(Component, Name ?);
Begin
// Free any DFM loaded component, allowing the run-time
// read component to take its place

  FindComponent(Name).Free;
End;

Then you can save your form by simply calling

  aStream.WriteComponent(aForm);

and recreate it by calling

  aForm:= aStream.ReadComponent(Nil) as TForm;

Andrew

I had investigated this approach. It definitely will work, but there are
three reasons I have not gone this path straight off:
  1) In this case, the constructors and destructors of some of the
components have significant side-effects that I would much rather avoid.
  2) I still have to do all the work of getting the form resource, creating
a stream, creating a reader and initializing the streaming process.
  3) While I certainly could do 2) without great difficulty, it does fairly
tightly couple with the current VCL implementation of streaming, which I
would also rather avoid.

Is there a method for streaming in the properties without creating the
components unless they do not already exist?

Andrew Stewart <astew...@strobes.co.nz> wrote in article
<358F8131.74365...@strobes.co.nz>...

Function LoadPersistentForm(Const FileName:String):TForm;
Begin
  With TFileStream.Create(FileName, fmOpenRead) do
    Try
      Result:= ReadComponent(Nil) as TForm;
    Finally
      Free;
    End;
End;

Procedure SavePersistentForm(Const FileName:String; Const Form:TForm);
Begin
  With TFileStream.Create(FileName, fmCreate) do
    Try
      WriteComponent(Form);
    Finally
      Free;
    End;
End;

You may want to avoid streaming certain components on the form, such as
menus and popup-menus, so that you are free to modify the menu heirarchy
in future versions. Each form can handle that on a case by case basis
with some work.

If the components that have major side effects in their constructors can
only exist one-to-a-form, then you could raise an exception in the
constructor if the form already has one on it, before causing the
side-effects. The streaming mechanism can be hooked relatively easily to
continue on after an 'expected' known exception has occurred.

Andrew