List&Label - HWND of preview form

[uligerhardt 18]

Hello! I want to show a MessageBox from inside a TL21_.OnViewerButtonClicked event handler and need the window handle of the preview form for that. Any idea how to get there?

[FPiette 383]

23 minutes ago, uligerhardt said:

 TL21_

What is it?

 

[Remy Lebeau 1394]

I don't know what kind of control "TL21_" is supposed to refer to, but if it does not expose access to its HWND, one option would be to use a thread-local WH_CBT hook via the Win32 SetWindowsHookEx() function to receive notifications of every HWND that is created by the thread.  For instance, set the hook just before displaying the preview Form, and then release the hook after the Form is ready/closed.  Then you will know every HWND that the preview creates.

[Guest]

On 11/20/2020 at 12:04 PM, uligerhardt said:

Hello! I want to show a MessageBox from inside a TL21_.OnViewerButtonClicked event handler and need the window handle of the preview form for that. Any idea how to get there?

The List & Label report generator extends your application with extensive and convenient print, export and preview functions. You remain independent of programming languages and database formats. You retain control over data transfer and create the interface.

did see this:  https://www.combit.com/  

https://forum.combit.net/t/programmatically-close-the-preview-window/2018

 

if possible, post your code for help us!

Edited November 22, 2020 by Guest

[uligerhardt 18]

On 11/20/2020 at 4:27 PM, FPiette said:

What is it?

 

Sorry, forgot to mention it in the message body. It's the List&Label report component.

Edited November 23, 2020 by uligerhardt

[uligerhardt 18]

Here is the relevant code, a bit condensed:

type
  TPrintLLReportEventHandler = class
  public
    procedure OnViewerButtonClicked(Sender: TObject; Button: TViewerButton; var PerformDefaultAction: Boolean);
  end;

{ TPrintLLReportEventHandler }

procedure TPrintLLReportEventHandler.OnViewerButtonClicked(Sender: TObject; Button: TViewerButton; var PerformDefaultAction: Boolean);
begin
  if Button = vbExit then
  begin
    MessageBox(AWnd, .....); // <= I'd like to get the preview form's window handle here for AWnd
  end;
end;

var
  evh: TPrintLLReportEventHandler;

    evh := TPrintLLReportEventHandler.Create;
    try
      MyLLReportInstance.OnViewerButtonClicked := evh.OnViewerButtonClicked;
      // Show preview here (using LL_PRINT_PREVIEW)
    finally
      evh.Free;
    end;

 

[Remy Lebeau 1394]

Did you try the WH_CBT hook, like I suggested?  For example:

uses
  ..., Windows;

type
  TPrintLLReportEventHandler = class
  private
    FHook: HHOOK;
  public
    constructor Create;
    destructor Destroy; override;
    procedure OnViewerButtonClicked(Sender: TObject; Button: TViewerButton; var PerformDefaultAction: Boolean);
  end;

{ TPrintLLReportEventHandler }

var
  gPrintReportWnd: HWND = 0;

function CBTProc(nCode: Integer; wParam: WPARAM; lParam: LPARAM): LRESULT; stdcall;
begin
  if nCode = HCBT_ACTIVATE then
  begin
    if gPrintReportWnd = 0 then
      gPrintReportWnd := HWND(wParam);
  end;
  Result := CallNextHookEx(0, nCode, wParam, lParam);
end;

constructor TPrintLLReportEventHandler.Create;
begin
  inherited;
  gPrintReportWnd := 0;
  FHook := SetWindowsHookEx(WH_CBT, @CBTProc, HInstance, GetCurrentThreadId);
end;

destructor TPrintLLReportEventHandler.Destroy;
begin
  if FHook <> 0 then
    UnhookWindowsHookEx(FHook);
  gPrintReportWnd := 0;
  inherited;
end;

procedure TPrintLLReportEventHandler.OnViewerButtonClicked(Sender: TObject; Button: TViewerButton; var PerformDefaultAction: Boolean);
begin
  if Button = vbExit then
  begin
    MessageBox(gPrintReportWnd, ...);
  end;
end;

var
  evh: TPrintLLReportEventHandler;
begin
  evh := TPrintLLReportEventHandler.Create;
  try
    MyLLReportInstance.OnViewerButtonClicked := evh.OnViewerButtonClicked;
    // Show preview here (using LL_PRINT_PREVIEW)
  finally
    evh.Free;
  end;
end;

 

[uligerhardt 18]

13 hours ago, Remy Lebeau said:

Did you try the WH_CBT hook, like I suggested?  For example:

uses
  ..., Windows;

type
  TPrintLLReportEventHandler = class
  private
    FHook: HHOOK;
  public
    constructor Create;
    destructor Destroy; override;
    procedure OnViewerButtonClicked(Sender: TObject; Button: TViewerButton; var PerformDefaultAction: Boolean);
  end;

{ TPrintLLReportEventHandler }

var
  gPrintReportWnd: HWND = 0;

function CBTProc(nCode: Integer; wParam: WPARAM; lParam: LPARAM): LRESULT; stdcall;
begin
  if nCode = HCBT_ACTIVATE then
  begin
    if gPrintReportWnd = 0 then
      gPrintReportWnd := HWND(wParam);
  end;
  Result := CallNextHookEx(0, nCode, wParam, lParam);
end;

constructor TPrintLLReportEventHandler.Create;
begin
  inherited;
  gPrintReportWnd := 0;
  FHook := SetWindowsHookEx(WH_CBT, @CBTProc, HInstance, GetCurrentThreadId);
end;

destructor TPrintLLReportEventHandler.Destroy;
begin
  if FHook <> 0 then
    UnhookWindowsHookEx(FHook);
  gPrintReportWnd := 0;
  inherited;
end;

procedure TPrintLLReportEventHandler.OnViewerButtonClicked(Sender: TObject; Button: TViewerButton; var PerformDefaultAction: Boolean);
begin
  if Button = vbExit then
  begin
    MessageBox(gPrintReportWnd, ...);
  end;
end;

var
  evh: TPrintLLReportEventHandler;
begin
  evh := TPrintLLReportEventHandler.Create;
  try
    MyLLReportInstance.OnViewerButtonClicked := evh.OnViewerButtonClicked;
    // Show preview here (using LL_PRINT_PREVIEW)
  finally
    evh.Free;
  end;
end;

 

I tried it just now, and it works AFAICT - I used

GetWindowText(gPrintReportWnd, ...)

to verify. Thanks a lot.