delphi Activex and parented forms error

Question

i try to fix up my activex project and i had errors , i have 2 forms in my activex project first form hold tmemo and button to call second form as parented form every thing works fine till now but i cannot set any record from second form to first form control always get access violation so i decided to show result before set tmemo.text control in the first form and actually result is showing but but cannot be set into the first form here is my project code

unit main1;

{$WARN SYMBOL_PLATFORM OFF}

interface

uses
  Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs,
  ActiveX, AxCtrls, embed_TLB, StdVcl, Vcl.StdCtrls;

type
  Tform1 = class(TForm, Iform1)
    Button1: TButton;
    Memo1: TMemo;
    procedure Button1Click(Sender: TObject);
    procedure FormCreate(Sender: TObject);
  private
    { Private declarations }


  protected
    { Protected declarations }

  public
    { Public declarations }
    procedure showEmo(L,T:Integer);

  end;

  var
  Form1 : Tform1;

implementation

uses ComObj, ComServ, main2;

{$R *.DFM}

{ Tform1 }

procedure Tform1.Button1Click(Sender: TObject);
var
  Rect: TRect;
begin
  GetWindowRect(Self.button1.Handle, Rect);
  showEmo(Rect.Left + 70,(Rect.Top - 290));
end;

procedure Tform1.FormCreate(Sender: TObject);
begin
  Form2 := TForm2.Createparented(0);
end;

procedure TForm1.showEmo(L,T:Integer);
var
  Rect: TRect;
begin
  try
    GetWindowRect(button1.Handle, Rect);
    begin
      Form2.FormStyle := fsStayOnTop;
    end;
    Form2.Left := L;//Rect.Left;
    Form2.top := T;//Rect.Top - emo.Height;
  finally
    Form2.Visible := not (Form2.visible);
  end;

end;

initialization
  TActiveFormFactory.Create(
    ComServer,
    TActiveFormControl,
    Tform1,
    Class_form1,
    0,
    '',
    OLEMISC_SIMPLEFRAME or OLEMISC_ACTSLIKELABEL,
    tmApartment);
end.

Form 2

unit main2;

interface

uses
  Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,
  Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.OleCtrls, SHDocVw_EWB, EwbCore,
  EmbeddedWB, MSHTML_EWB, Vcl.StdCtrls;

type
  TForm2 = class(TForm)
    ewbpage: TEmbeddedWB;
    load: TMemo;
    procedure FormCreate(Sender: TObject);
    procedure ewbpageBeforeNavigate2(ASender: TObject; const pDisp: IDispatch;
      var URL, Flags, TargetFrameName, PostData, Headers: OleVariant;
      var Cancel: WordBool);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form2: TForm2;

implementation

uses main1;

{$R *.dfm}

procedure TForm2.ewbpageBeforeNavigate2(ASender: TObject; const pDisp: IDispatch;
  var URL, Flags, TargetFrameName, PostData, Headers: OleVariant;
  var Cancel: WordBool);
  var
  MousePos: TPoint;
  HtmlElement: IHTMLElement;
  iHTMLDoc: IHtmlDocument2;
begin
  if Pos('#sm',URL)>0 then
  begin
    if Supports(ewbpage.Document, IHtmlDocument2, iHTMLDoc) then
    begin
      if GetCursorPos(MousePos) then
      begin
        MousePos := ewbpage.ScreenToClient(MousePos);
        HtmlElement := iHTMLDoc.ElementFromPoint(MousePos.X, MousePos.Y);
        if Assigned(HtmlElement) then
          showmessage(HtmlElement.getAttribute('id', 0));
        form1.Memo1.Text :=  HtmlElement.getAttribute('id', 0);
        Cancel := True;
        Self.Close;
      end;
    end;
  end;
end;

procedure TForm2.FormCreate(Sender: TObject);
begin
  ewbpage.LoadFromStrings(load.Lines);
end;

end.

and the question is why i get this error

Access violation at address 07C734FC in module 'EMBEDA~1.OCX'. Read of address 000003B4.

at this line

form1.Memo1.Text :=  HtmlElement.getAttribute('id', 0);

why i cannot set result from second form to first form ? what i did wrong here is the full project for better understand

http://www.mediafire.com/download/zn7hzoxze2390a3/embeddedactivex.zip

I suggest that you do some debugging. Find the code that performs the invalid access. — David Heffernan, Mar 29 '15 at 17:08
i already debug the project always raise error at this line `form1.Memo1.Text := HtmlElement.getAttribute('id', 0);` but i can not find any error with it — DelphiStudent, Mar 29 '15 at 19:54
So where is the AV? In the expression on the rhs, or the expression on the lhs. Dig deeper. — David Heffernan, Mar 29 '15 at 20:04
what do you mean is not accessible ? if you can see i included form1 in form2 uses . — DelphiStudent, Mar 29 '15 at 20:47
Including a unit does **not** ensure you have a valid reference to an instance in the global variable. — Sir Rufo, Mar 29 '15 at 21:46
@SirRufo Yes You are correct private variable can't be accessible into another forms , but this is not a private or public variable its a tmemo control.text — DelphiStudent, Mar 30 '15 at 00:04
string in global var working normal but any control inside Tform1 cannot be set from another form, iam try to debug very hardly — DelphiStudent, Mar 30 '15 at 04:17
I am talking about `Form1` variable. There is no guarantee to have a valid reference in that variable just by including the unit — Sir Rufo, Mar 30 '15 at 05:57
Why don't you do what I ask, and debug this further? Don't be helpless. — David Heffernan, Mar 30 '15 at 08:54
i try to do as you told me by debugging very deep .. creating break point , added to watch every thing looks normal no real issues has been detected . — DelphiStudent, Mar 30 '15 at 14:56
@SirRufo so do you have suggestion about that ? because i shared all my project and as you can see every thing is there as it is , until iam doing something very wrong , debugging showing nothing . — DelphiStudent, Mar 30 '15 at 22:13

score 1 · Accepted Answer · answered Mar 31 '15 at 07:01

You will see this issue once you start to format your code properly

procedure TForm2.ewbpageBeforeNavigate2(ASender: TObject; const pDisp: IDispatch;
  var URL, Flags, TargetFrameName, PostData, Headers: OleVariant;
  var Cancel: WordBool);
  var
  MousePos: TPoint;
  HtmlElement: IHTMLElement;
  iHTMLDoc: IHtmlDocument2;
begin
  if Pos('#sm',URL)>0 then
  begin
    if Supports(ewbpage.Document, IHtmlDocument2, iHTMLDoc) then
    begin
      if GetCursorPos(MousePos) then
      begin
        MousePos := ewbpage.ScreenToClient(MousePos);
        HtmlElement := iHTMLDoc.ElementFromPoint(MousePos.X, MousePos.Y);

        // if we have a valid HtmlElement ...
        if Assigned(HtmlElement) 
        then // show a message
          showmessage(HtmlElement.getAttribute('id', 0));

        // now we do not care about if HtmlElement is valid or not
        form1.Memo1.Text :=  HtmlElement.getAttribute('id', 0);

        Cancel := True;
        Self.Close;
      end;
    end;
  end;
end;

To only solve your current access violation you simply put a begin end block around all the lines that will use HtmlElement.

        HtmlElement := iHTMLDoc.ElementFromPoint( MousePos.X, MousePos.Y );

        if Assigned( HtmlElement ) 
        then
          begin
            showmessage( HtmlElement.getAttribute( 'id', 0 ) );
            form1.Memo1.Text := HtmlElement.getAttribute( 'id', 0 );
          end;

But there are some more issues in your code. You should not use the global variables form1 and form2. Instead pass the form instance to the created TForm2 instance or even better a callback method.

adding begin and end will define start and end point thanks for this notice , but this wil not solve my access violation , iam interested in the last sentences , `instead pass the form instance to create TFORM2 even better callback` any example about this ? — DelphiStudent, Mar 31 '15 at 15:30

delphi Activex and parented forms error

1 Answers1