[fpc-pascal] Saving user created component structure to LFM file

Martin Friebe fpc at mfriebe.de
Mon Jan 12 00:43:18 CET 2009

Hi, I have a problem saving a certain component struicture to an LFM
(lazarus) file and read it back.

since a good amount of code is in FPC, I am not sure which list to go to?

There is classes/writer.inc with has TBinaryObjectWriter. This is where
things go first.
Then, later this gets translated into text. This translation seems to be
stricter in terms of  what can be nested.

Anyway the problem is, that if I want to save a component (that can be
of different class/classes) then I can use WriteComponent. But only if I
am in a Component that is itself written with WriteComponent.

In the final LFM it seems a Component can only be nested in an other
component. It does not seem to be possible to put it in:
- Not in a subcomponent (because a subcomponent does not write it's
class, but just the properties that are visible for the class given by
the property
     property Foo: TPanel read .. write ...
     Foo.Name = 'abc'
     Foo.Top = 1
- Not in a TCollection, or at least I havent managed. Also again a
TCollection is restricted to one classs for all Items
- Not Using DefineProperties
  All propwerties with define property are of the kind
      Name = Value
  I can add a list, but even inside the list I can not write a component

What I want to archive is theFollowing. I have

TMainComponent = class (foo)
   property Options : TPersitentBar read  x write x;

If It has to be it can be a TComponent, with SubComponent in
Problem 1)   Options is always created in the constructor, it can not be
stored as a nested Component in the LFM. If it was, it would exist twice
(once created in the constructor, and once loaded from the lfm)

TPersitentBar should have a list of components, variable number, and
different subclasses (could inherit from TPersistent, only Component if
it makes it easier)

How can I get this list saved into the lfm? Each item has a diff class,
and diff properties, so they must saved via WriteComponent. (Which does
not work for DefineProerties)

And of course a default list of items is created in the constructor, so
I need to detect if they are loaded, and remove the defaults.

Any Idea?

Example of the final structure (if only it was valid)

object MainComp1 : TMainComponent
      Options.AllowFoo = 1
      Options.AllowABC = 2
      object Options.SubOptionsForCars : TCarOptions
          MAxCar = 4
      object Options.SubOptionsForTrains : TTrainOptions
          MAxTrain = 1

Best Regards

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