Easily use HTML Help files in your programs

Problem/Question/Abstract:

Do you long to move from WinHelp to HTML Help in your programs? The unit below converts all WinHelp calls to HTML Help enabling you to upgrade with the minimum of effort.

Answer:

Save this unit to a directory on your Environment Options|Library|Library Path and add to your project uses clause, all WinHelp requests will now be translated to HTML Help. Specify your *.chm file in the Project Options|Application|Help file setting. Context sensitive help will work as normal, use TApplication.HelpCommand to send help commands. eg. Application.HelpCommand(HELP_KEY, DWORD(keyData))

unit dmHTMLHelp;
{Unit to translate WinHelp requests into HTML Help and call the API.}
{Written by Dave Murray, October 2001. dmurray@worldmark.com}
{NOTES:
This unit assigns its own handler to the Application.OnHelp event.
DO NOT assign your own handler to Application.OnHelp.
Also, this unit ignores any form's HelpFile property. (Delphi 4+)}

interface

uses
  Windows, Messages, SysUtils, Forms;

const
  {commands to pass to HtmlHelp(), see HTML Help API Reference}
  HH_DISPLAY_TOPIC = $0000; {open help topic}
  HH_HELP_FINDER = $0000; {backwards compatibility,use HH_DISPLAY_TOPIC instead}
  HH_DISPLAY_TOC = $0001; {select Contents tab in nav pane}
  HH_DISPLAY_INDEX = $0002; {select Index tab + search for keyword}
  HH_DISPLAY_SEARCH = $0003; {select Search tab in nav pane}
  HH_SET_WIN_TYPE = $0004;
  HH_GET_WIN_TYPE = $0005;
  HH_GET_WIN_HANDLE = $0006;
  HH_ENUM_INFO_TYPE = $0007;
  HH_SET_INFO_TYPE = $0008;
  HH_SYNC = $0009;
  HH_RESERVED1 = $000A; {not currently implemented}
  HH_RESERVED2 = $000B; {not currently implemented}
  HH_RESERVED3 = $000C; {not currently implemented}
  HH_KEYWORD_LOOKUP = $000D;
  HH_DISPLAY_TEXT_POPUP = $000E; {display string resource/text in a popup}
  HH_HELP_CONTEXT = $000F; {display topic for context number}
  HH_TP_HELP_CONTEXTMENU = $0010; {text popup help, same as HELP_CONTEXTMENU}
  HH_TP_HELP_WM_HELP = $0011; {text popup help, same as HELP_WM_HELP}
  HH_CLOSE_ALL = $0012; {close all windows opened by caller}
  HH_ALINK_LOOKUP = $0013; {ALink version of HH_KEYWORD_LOOKUP}
  HH_GET_LAST_ERROR = $0014; {not currently implemented}
  HH_ENUM_CATEGORY = $0015;
  HH_ENUM_CATEGORY_IT = $0016;
  HH_RESET_IT_FILTER = $0017;
  HH_SET_INCLUSIVE_FILTER = $0018;
  HH_SET_EXCLUSIVE_FILTER = $0019;
  HH_INITIALIZE = $001C;
  HH_UNINITIALIZE = $001D;
  HH_PRETRANSLATEMESSAGE = $00FD;
  HH_SET_GLOBAL_PROPERTY = $00FC;

function HtmlHelp(hwndCaller: THandle; pszFile: PChar; uCommand: cardinal; dwData:
  longint): THandle; stdcall;

implementation

function HtmlHelp(hwndCaller: THandle; pszFile: PChar; uCommand: cardinal; dwData:
  longint): THandle; stdcall; external 'hhctrl.ocx' name 'HtmlHelpA'; {external API call}

type
  TdmHTMLHelp = class(TObject) {encapsulates function}
    function ApplicationHelp(Command: Word; Data: Longint; var CallHelp: Boolean):
      Boolean;
  end; {TdmHTMLHelp..}

function TdmHTMLHelp.ApplicationHelp(Command: Word; Data: Longint; var CallHelp:
  Boolean): Boolean;
{translates WinHelp commands to HTMLHelp commands + calls API}
var
  HCommand: word;
begin
  {make sure VCL doesn't activate WinHelp + function succeeds}
  CallHelp := false;
  result := true;
  {translate WinHelp > HTMLHelp}
  case Command of
    HELP_CONTENTS:
      begin
        HCommand := HH_DISPLAY_TOC;
        Data := 0;
      end; {HELP_CONTENTS..}
    HELP_CONTEXT: HCommand := HH_HELP_CONTEXT;
    HELP_CONTEXTPOPUP: HCommand := HH_HELP_CONTEXT;
    HELP_FINDER: HCommand := HH_DISPLAY_TOPIC;
    HELP_KEY: HCommand := HH_DISPLAY_INDEX;
    HELP_QUIT:
      begin
        HCommand := HH_CLOSE_ALL;
        Data := 0;
      end; {HELP_QUIT..}
  else
    begin {default}
      HCommand := HH_DISPLAY_TOPIC;
      Data := 0;
    end; {default..}
  end; {case Command..}
  {call HTML Help API}
  HtmlHelp(Application.MainForm.Handle, PChar(Application.HelpFile), HCommand, Data);
end; {function TdmHTMLHelp.ApplicationHelp}

var
  HTMLHelper: TdmHTMLHelp;

initialization
  {create object + assign event handler}
  HTMLHelper := TdmHTMLHelp.Create;
  Application.OnHelp := HTMLHelper.ApplicationHelp;
finalization
  {free event handler + object}
  Application.OnHelp := nil;
  HTMLHelper.Free;
end.