I'd like to set some properties of a TComponent(TForm) through RTTI before TComponent.Loaded is called.

After a call to TMyForm.Create, the component is initiated through the streaming system that calls Loaded.

Is there a way to hook this streaming system so i can change the properties before the call to Loaded?

Luiz

You can use defineproperties for that. You can simply override it in your form and set whatever properties you want. An alternative is overriding 'Loading', which is called at the start.

Michael.

Thanks. But i think that won't help me. I'm creating a instance of a generic TForm (see code below) and than setting the properties after the call to constructor.

I would need that the properties be set after loading the stored properties and before FormClass.Loaded is called but it's to late.

The problem is that Loaded is called inside the constructor call chain. I could create the instance through NewInstance but AFAIK that is too early (before creating the stored/published properties).

var
  Form: TForm;
begin
  //FormClass: TFormClass
  Form := FormClass.Create(Owner);
  SetObjectProperties(Form, FormProperties);
  [..]
end;

Luiz

What do you want to achieve?
Why do you think you have to set a property after loading and before Loaded?

Mattias

Just for convenience.

Currently i'm sending a custom message to notify the form that all properties (stored in lfm plus customized) are initialized so it can take the necessary actions:

  Form.Perform(CM_INIT, 0, 0);

If i find such event/procedure i could get rid of the message sending/receiving.

Not a big issue. I still can use OnShow, CreateWnd but it would not be as intuitive as using Loaded.

Luiz

What is wrong with overriding Loaded ? It is the last thing that is called ?

Michael.

In fact i'd like to use an overrided Loaded in the created TForm. But it occurs to early:

Form := TMyForm.Create;
      [..]//Streaming system
      TMyForm.Loaded; //> occurs before the customized properties are set
MySetPropertiesFunction(Form);//Set the desired properties. Too late to
be recognized by TMyForm.Loaded

I would need :

Form := TMyForm.Create;
      [..]//Streaming system
      //hook streaming to call MySetPropertiesFunction(Form);//Set the
desired properties.
      TMyForm.Loaded; //> i can assume that all properties are set

By looking the TComponent/TReader code i could not figure how to do that, so if i did not missed something it seems is not possible.

I'll look at other solutions.

Luiz

Why does the following not work for you?

procedure TMyForm.Loaded; override;
...
procedure TMyForm.Loaded;
begin
  MySetPropertiesFunction(Self);
  inherited Loaded;
end;

Mattias

Because i don't know before hand what FormClass(TMyForm) is. Also FormClass (TMyForm) does not knows FormProperties

Here's the actual code (calls a generic TForm descendant):

The article: http://lazarusroad.blogspot.com/

function ShowForm(FormClass: TFormClass; Owner: TWinControl;
FormProperties: array of const): TModalResult;
var
  Form: TForm;
begin
  Form := FormClass.Create(Owner);
  try
    SetObjectProperties(Form, FormProperties);
    Form.Perform(CM_INIT, 0, 0);
    Result := Form.ShowModal;
  finally
    Form.Destroy;
  end;
end;

Luiz

The article does not explain why the properties must be set before calling Loaded.

Mattias

If
procedure TMyForm.Loaded;
begin
  inherited;
  if MyBool then
     DoAction;
end;

MyBool will be always false even if called through

ShowForm(TMyForm, nil, ['MyBool', True]);

Luiz

Is this correct:
One of your forms has a design bug, which you can not fix (for whatever reason), so you need a workaround.

I see several solutions:
- Patch and compile your own special version of TReader or LCL.
- modify the lfm at runtime
- modify the VMT at runtime and override Loaded

Mattias

do this ? If the property is published, it's value is in the .lfm file, so what is the point of setting it separately ?

Are you trying to use 'custom TForms' with extra properties? In that case it is easier to simply use Lazarus' or Delphi's support for it. I do it every day; I have many thousands of such forms.

Michael.

It's not intended at a specific case. I just created a way to call generic TForm descendants with generic properties, basically to avoid boilerplate code. It's is already working fine, i'm just trying to avoid an extra notification (the CM_INIT message). I can also use OnShow or CreateWnd. An example:

TEditMyObjectForm = class(TForm)
 [..] //Controls created at design time (stored in the lfm)
published
  //customized property
  property MyObject: TMyObject;
end;

To show that form setting the property MyObject i would do:

Form := TEditMyObjectForm.Create(nil);
try
  Form.MyObject := ObjectX;
  Result :=  Form.ShowModal = mrOk;
finally
  Form.Destroy;
end;

With my function i do:

Result := ShowForm(TEditMyObjectForm, nil, ['MyObject', ObjectX]) = mrOk;

Wow. Not necessary too much. I can live with a message handler ;-)

Luiz

See the previous mail. The property is not in the lfm, it's set at runtime.

Are you trying to use 'custom TForms' with extra properties? In that case it is easier to simply use Lazarus' or Delphi's support for it. I do it every day; I have many thousands of such forms.

I'm interested. Can you show me an example?

Luiz

There is an example in lazarus/components/customform.

I also wrote an article on it. If you're interested, I can send it to you tomorrow.

Michael.

Please send

Luiz