Designer issues with specialized TFrame classes.
lazarus / 21-General

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papelhigienico · 2025-02-04 22:24

Hi everyone!

I'm creating a new control for PascalSCADA that will mimic a
functionality of other engineering software in Lazarus. Lazarus has a
similar feature (Frames). Knowing this, I started from TFrame, trying
to specialize it to get new functions, but in this way, I'm doing
something wrong in the process.

What I did:

1) Created the specialized TFrame class with the desired properties.

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i  
TFaceplateFrame = class(TFrame)  private    ffaceplatetag:
TPLCStruct;  protected    procedure setfaceplateTag(AValue:
TPLCStruct);  published    property FaceplatePLCTag: TPLCStruct read
ffaceplatetag write setfaceplateTag;  end; 
2) Registered a Lazarus project file descriptor using the function
RegisterProjectFileDescriptor. The class TFaceplateFrameFileDescriptor
inherits from TFileDescPascalUnitWithResource. Below is the
constructor of the file descriptor:

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i constructor
TFaceplateFrameFileDescriptor.Create;begin  inherited Create;  Name :=
'FaceplateFrame'; // do not translate this  ResourceClass :=
TFaceplateFrame;  RequiredPackages := 'pascalscada_hmi'; 
UseCreateFormStatements := True;end; 
What I expect:
After doing the previous steps, when I create a new TFaceplateFrame
(using Lazarus menu File -> New, then choosing FaceplateFrame), the
property FaceplatePLCTag should be visible on newly created
TFaceplateFrame instances, in the TFaceplateFrame designer or even in
TFaceplateFrame instances inside forms.

This happens on a freshly created TFaceplateFrame, but if I close and
reopen the project, the FaceplatePLCTag property of my FaceplateFrame
instances is lost and does not appear in the Object Inspector anymore.

So, someone can tell me what I'm doing wrong?

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MarkMLl · 2025-02-05 11:10

Only edit the initial TFrame descendant. If you attempt to do anything
to one which has been instantiated onto a form you'll end up in a heck
of a mess, which might include having to fix up your .lfm file with a
text editor.

The fact that instantiated frames aren't treated (at least by default)
as read-only is a longstanding niggle with a number of us, who have
learned to grit our teeth and work around the issues by only
instantiating (e.g. into a panel or tabbed control) at runtime.

I'd suggest not referring to "specialisation" in this context, since
the term's been coopted to refer to generics etc.

MarkMLl

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papelhigienico · 2025-02-05 20:26

Hi MarkMLl!

Thank you by your advises. I'm looking for the best way to implement
the desired feature, and for now, extend a TFrame still the best
option. Furthermore, I discovered that I have to register the extented
TFrame class into the IDE Form designer, doing something like this:

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i uses ...,
FormEditingIntf; procedure Register;begin FormEditingHook.RegisterDesi
gnerBaseClass(TFaceplateFrame);end; 

Doing this, I was able to see the new properties added to my TFrame
descendant class, in Frame design or in frame instances, even across
IDE reinitializations.

Now I have to figure out how to hide a propety in frame design time,
but make property visible when Object Inspector is handling a
FaceplateFrame instance.

And sorry by my translations mistakes. I'll try don´t use "specialize"
when I want to say "extend".