Share a data between two units in dynamic loaded BPL.

[CRO_Tomislav 0]

I need a help.
If I make a project with one form and two units a showed basic code is working ok.

unit Prva;

interface

uses
  Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,
  Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.StdCtrls, Vcl.Mask, Vcl.ExtCtrls,
  Vcl.DBCtrls;

type
  TForm1 = class(TForm)
    Button1: TButton;
    Edit1: TEdit;
    procedure Button1Click(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form1: TForm1;

implementation

uses
 Druga;
{$R *.dfm}

procedure TForm1.Button1Click(Sender: TObject);
begin
 Druga.Demo;
end;

end. 

unit Druga;

interface
 uses
  Dialogs;

function Demo:boolean;

implementation
uses
 Prva;

function demo: boolean;
begin
  ShowMessage(Form1.Edit1.Text);
end;


end.

If I press a button on Form1 it run function in Druga.pas and show message with a text filled in Edit1 component.

The problem is If I try to do the same thing with a Form and units which are in dynamic loaded bpl package. It doesn’t work.
It seams that it can’t found a Form or component by its name…

How to solve this?

 

THX in advance

[Lars Fosdal 1866]

I would decouple the action by having a handler.

 

unit Druga;

interface
 uses
  Dialogs;

function Demo:boolean;

type
  TOnShowMessage = reference to procedure;
var
  OnShowMessage: TOnShowMessage;

implementation
// No circular ref here

function demo: boolean;
begin
  if Assigned(OnShowMessage)
  then OnShowMessage
  else raise Exception.Create('Someone forgot to set the OnShowMessage handler');
end;

initalization
  OnShowMessage := nil;
end.

In Prva, I'd connected the handler in f.x. FormCreate;

 

procedure TForm1.FormCreate(sender: TObject);
begin
  Druga.OnShowMessage(Self.MyShowMessage);
end;

procedure TForm1.MyShowMessage;
begin
  ShowMessage(Form1.Edit1.Text);
end;

This avoids the circular unit ref, and since you initialize the handler from the main form, it shouldn't matter if the bpl is dynamically loaded?

If you want to, you can of course also add parameters to the handler to display a text generated in unit Druga or have multiple handlers for different uses.

 

 

[CRO_Tomislav 0]

This is intrested but; 

Exactly my goal is: I inherited a project in Delphi which has a huge units with a lot of code. Mostly of that code is used to create some XML files. Idea is to separate from this unit a code which is generate this XML files to separate units. But for do that I need to access from this (sub)units to Form and grab query results to populate this XML files or even modify and run a querys

As this is doesn’t work "ProfileID.Text := Form1.Query_User.FieldByName('userID').AsString;" in a (sub)unit; do You have some idea what would be elegant solution for this?

[Lajos Juhász 323]

You can send the query as a parameter to the function that generates the XML.

[CRO_Tomislav 0]

(Sub)Unit2 doesn't know for Form1 in code: ProfileID.Text := Form1.Query_User.FieldByName('userID').AsString;

As my form is opened from package by menue item in Main form by: 

procedure TForm_Maom.Button1Click(Sender: TObject);
var
 AClass :TFormClass;
begin
if not IsMDIChildOpen(Form_Glavna,'Form1') then
  begin
   if PackageModule <> 0 then
    begin
     AClass := TFormClass(GetClass('TForm1'));
     if AClass <> nil then TComponentClass(AClass).Create(Self);
    end;
  end;
end;

 

[Pat Foley 54]

One thing about XML is on a treeview each node needs a unique caption so as tabSheets or the parent of control wanted are added a number is added to the node's caption as the forms are added.  

 

Second thing is the Control could have data reference added.  

 

type
  // On the UI controls side carry some data references for convenience
  // the data side could use Dependance Injection to tie in UI controls
  TDataButton = class(TButton)
    Form: TControl;
    Strs: TStrings;
end;

What's neat about MDI you can create a new childform inside a begin..end.  To access the form elsewhere use Application.Screen 

[CRO_Tomislav 0]

15 minutes ago, Pat Foley said:

One thing about XML is on a treeview each node needs a unique caption so as tabSheets or the parent of control wanted are added a number is added to the node's caption as the forms are added.  

 

Second thing is the Control could have data reference added.  

 

type
  // On the UI controls side carry some data references for convenience
  // the data side could use Dependance Injection to tie in UI controls
  TDataButton = class(TButton)
    Form: TControl;
    Strs: TStrings;
end;

What's neat about MDI you can create a new childform inside a begin..end.  To access the form elsewhere use Application.Screen 

XML is not a problem, Accessing to Quer1 on MDI Form1 is a problem...

Can You provide me an example for Application.Screen to access a Query1 on a MDI form Form1?

[Lars Fosdal 1866]

Isolate your business logic from the UI. Use an intermediate class to pass the data around.

[Pat Foley 54]

 This should yield control asked for. 

 

procedure TTaskMaster.findControl(AtaskDetail: TInstruction; var AC: TControl);
var
  ff, ii : integer;
  sForm, sControl: string;
begin
  with AtaskDetail do
  begin
    if Control <> nil then
      AC := Control
    else
    begin
      sForm := controlForm + ' not found.';
      sControl := controlName + ' not found.';
      //screens move about on windows list top window usually 0 :(
      for ff := 0 to Screen.FormCount - 1 do
      if Screen.Forms[ff].name = controlform then
      begin
        sform := controlForm;
        with Screen.Forms[ff] do begin
          for ii := 0 to componentcount - 1 do
          if Components[ii].Name = ControlName then
          begin
            sControl := controlName + ' comps ' + ii.ToString;
            Control := Components[ii] as Tcontrol;
            //onBS(False, format('Item %d Found %s',[ii,controlName]));
            break;
          end
          //else//if name
          //run := false;
          //  onBS(False, format('Item %d not found %s',[ii,  controlName]));
        end;// with screen forms
      end;  //if screen.forms
      onBS(False, sForm + ' ' + sControl);
    end;// else
  end;//with taskdetail
end;

What TInstruction is

  TInstruction = class  //position in Db
    Atom: PAtom;
    Control: TControl;
    ControlForm: string;   //3
    ControlName: string;   //2
    Description: string;//6
    //Nu: integer;       //0
    Kind: string;     //1  was integer
    KindNU: integer;
    referenceValue: Double;//5
    tagName: string;    //4
    tagValue: Double;   //no data in table
  end;

 

[CRO_Tomislav 0]

THX

 

[Pat Foley 54]

You might to study and use this to move cursor to control being selected.  I want to add it to IDE <F6> or <Ctrl>.  function it only jumps to selection without any animation 🙂  

procedure TTaskmaster.moveMouse(AtaskDetail: TInstruction);
var
  x, y, MouseXError, MouseYError: integer;
  ControlCenter: Tpoint;
  AC: TControl;
begin
  findControl(AtaskDetail, AC);
  if not assigned(AC) then exit;

  if assigned(AC.Parent) then
    AC.Parent.Show;
  AC.Show;

  x := AC.ClientOrigin.X + AC.width div 2;
  y := AC.ClientOrigin.y + AC.height div 2;
  begin
    MouseXError := round(1.12 *(x - mouse.CursorPos.X));
        MouseYError := round(1.12 * (y - mouse.cursorPos.y));
//            MouseXError := min(MouseXError, 10 * sign(MouseXError));
//                MouseYError := min(MouseYError,  10 * sign(MouseYError));
    controlCenter.X := mouse.CursorPos.x + MouseXError;
    controlCenter.Y := Mouse.CursorPos.y + mouseYError;
    mouse.CursorPos := ControlCenter;
  end;
  repeatTask := (abs(MouseXError) > 7) or (abs(MouseYError) > 7);
end;

 

[PeterBelow 260]

On 7/2/2025 at 9:06 AM, CRO_Tomislav said:

I need a help.
If I make a project with one form and two units a showed basic code is working ok.

unit Prva;

interface

uses
  Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,
  Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.StdCtrls, Vcl.Mask, Vcl.ExtCtrls,
  Vcl.DBCtrls;

type
  TForm1 = class(TForm)
    Button1: TButton;
    Edit1: TEdit;
    procedure Button1Click(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form1: TForm1;

implementation

uses
 Druga;
{$R *.dfm}

procedure TForm1.Button1Click(Sender: TObject);
begin
 Druga.Demo;
end;

end. 

If I press a button on Form1 it run function in Druga.pas and show message with a text filled in Edit1 component.

The problem is If I try to do the same thing with a Form and units which are in dynamic loaded bpl package. It doesn’t work.
It seams that it can’t found a Form or component by its name…

How to solve this?

 

THX in advance

One thing too keep in mind is the fact that form variables created by the IDE  do not get assigned any form reference if the unit is part of a package and the form is also not autocreated. If you create the form in code it is your responsibility to assign the created form reference to the variable if you intend to use it (which is a bad idea in the first place IMO).

[Pat Foley 54]

2 hours ago, PeterBelow said:

One thing too keep in mind is the fact that form variables created by the IDE  do not get assigned any form reference if the unit is part of a package and the form is also not autocreated. If you create the form in code it is your responsibility to assign the created form reference to the variable if you intend to use it (which is a bad idea in the first place IMO).

Would not using global variables for any forms and using unique name for forms to use make it a better idea.  To reduce complexity a TreeView is loaded in mainform with nodes referencing the forms being created.  The Treeview can then be parented to the Active form to let the user navigate the app readily. A DM can help surfacing the data through the UI.         

 

[PeterBelow 260]

On 7/4/2025 at 4:22 PM, Pat Foley said:

Would not using global variables for any forms and using unique name for forms to use make it a better idea.  To reduce complexity a TreeView is loaded in mainform with nodes referencing the forms being created.  The Treeview can then be parented to the Active form to let the user navigate the app readily. A DM can help surfacing the data through the UI.         

 

If a "host" application is designed to use form classes implemented in dynamically loaded packages the host app has ( should have) no idea how the form classes are named. To make this into a truely modular and extensible application you need a design like the one used by the RAD Studio IDE. The app only knows where it has to look for extension modules to load (a folder or a registry or other configuration store listing the module file names). The modules register the form classes when loaded into a factory class or list implemented in a statically bound package used by host and all form modules. The host app can then enumerate the available forms using this factory to offer the selection to the user, check if such a form has already been created by searching through the Screen.Forms collection by class name, and, if not found, create an instance using a local variable that cannot be accessed from other parts of the app. If a form reference is needed elsewhere it has to be retrieved from Screen.Forms or another list, e.g. (for MDI child forms) the MDI frame form's MDIChildren collection.

 

Doing it this way decouples the modules and even makes it possible to add modules without having to rebuild the host app. If one of the dynamically loaded forms uses a data module it should override the constructor and check for the presence of the DM before  calling the inherited constructor and create an instance of the DM if necessary. 

 

I have a strict policy of immideately deleting the IDE-created global variables for forms and DMs if these are not part of the host app and are autocreated and live until the app closes. That prevents all manner of problems caused by accessing global references that may not be valid.

Edited July 6 by PeterBelow

[CRO_Tomislav 0]

On 7/6/2025 at 1:01 PM, PeterBelow said:

If a "host" application is designed to use form classes implemented in dynamically loaded packages the host app has ( should have) no idea how the form classes are named. To make this into a truely modular and extensible application you need a design like the one used by the RAD Studio IDE. The app only knows where it has to look for extension modules to load (a folder or a registry or other configuration store listing the module file names). The modules register the form classes when loaded into a factory class or list implemented in a statically bound package used by host and all form modules. The host app can then enumerate the available forms using this factory to offer the selection to the user, check if such a form has already been created by searching through the Screen.Forms collection by class name, and, if not found, create an instance using a local variable that cannot be accessed from other parts of the app. If a form reference is needed elsewhere it has to be retrieved from Screen.Forms or another list, e.g. (for MDI child forms) the MDI frame form's MDIChildren collection.

 

Doing it this way decouples the modules and even makes it possible to add modules without having to rebuild the host app. If one of the dynamically loaded forms uses a data module it should override the constructor and check for the presence of the DM before  calling the inherited constructor and create an instance of the DM if necessary. 

 

I have a strict policy of immideately deleting the IDE-created global variables for forms and DMs if these are not part of the host app and are autocreated and live until the app closes. That prevents all manner of problems caused by accessing global references that may not be valid.

Big THX to all of you !!!

On a base of your information's/instruction's I manage to solve my problem...

Perhaps a Delphi is not a such a scary tool… 😎