Context Help in .chm file
lazarus / 67-Windows

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Timbo · 2021-09-28 14:39

I'm converting an application developed in Delphi, potentially one of
many. It uses context help in a .chm file, with context numbers set in
the file and the current context number set within the code. This
works correctly with Delphi.

I have a CHMHelpDatabase and LHelpConnector on the main form, and have
initialised them according to the examples, and everything seems to be
working - except that when, for example, the help context is 200, I
get a message, presumably from LHelp, saying "Help context 200 not
found".

As as aside, is there a way I can bypass LHelp and simply invoke the
default CHM file viewer?

Thanks.

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wp · 2021-09-28 15:23

Quote from: Timbo on September 28, 2021, 04:39:09 pmis there a way I
can bypass LHelp and simply invoke the default CHM file viewer?
I don't have a simple example for this, but you could look at the
application LazStats (https://sourceforge.net/p/lazarus-
ccr/svn/HEAD/tree/applications/lazstats/ - download the snapshot if
you don't have svn. No external components are required) which I
modified to use chm help massively. Look at the MainUnit (in folder
"forms"):

- Add the unit htmlhelp to "uses"; it comes with FPC
(packages/winunits-base)

- Add a private method "function HelpHandler(Command: Word; Data:
PtrInt; var CallHelp: Boolean): Boolean;" to the main form which does
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 // Call
HTML help (.chm file)function TOS3MainFrm.HelpHandler(Command: Word;
Data: PtrInt;var  s: String;  ws: UnicodeString;  res: Integer;begin 
if Command = HELP_CONTEXT then  begin    // see:
http://www.helpware.net/download/delphi/hh_doc.txt    ws :=
UnicodeString(Application.HelpFile);    res := htmlhelp.HtmlHelpW(0,
PWideChar(ws), HH_HELP_CONTEXT, Data);  // Data is HelpContext here 
end else  if Command = HELP_COMMAND then  begin    s :=
{%H-}PChar(Data);    // Data is pointer to HelpKeyword here, but the
Windows help viewer does    // not want the KeywordPrefix required for
LHelp.    if pos(HELP_KEYWORD_PREFIX + '/', s) = 1 then      Delete(s,
1, Length(HELP_KEYWORD_PREFIX) + 1);    ws :=
UnicodeString(Application.HelpFile + '::/' + s);    res :=
htmlhelp.HtmlHelpW(0, PWideChar(ws), HH_DISPLAY_TOPIC, 0);  end;   //
Don't call regular help  CallHelp := False;   Result := res <> 0;end;
- In the main form's OnCreate handler, assign it to the
Application.OnHelp event, and set the Application.Helpfile to the name
of your chm file:
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 var 
helpfn: String;begin  ...  helpfn := Application.Location +
'LazStats.chm';  if FileExists(helpfn) then  begin   
Application.HelpFile := helpfn;    Application.OnHelp :=
@HelpHandler;  end  else    MessageDlg('LazStats help file not
found.', mtError, [mbOK], 0);end;
This is for Windows only. Study the real code in the application which
is extended to use the Lazarus-internal help-database instead which -
of course - is cross-platform.

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Timbo · 2021-09-29 10:47

Thanks very much.

I had trouble with line 9 in the second snippet of code, getting an
error for the @.

I fixed it by setting the OnHelp handler for the form using the Object
Inspector instead, and now everything is working perfectly. Thanks
again!

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marcov · 2021-09-29 10:58

Quote from: Timbo on September 29, 2021, 12:47:54 pmThanks very much.

I had trouble with line 9 in the second snippet of code, getting an
error for the @.

That's a difference between $mode delphi and $mode objfpc probably. In
mode delphi just leave it out.