You could launch the help file viewer as a separate process, but I think that will make controlling it even more complex. My guess is that the supplied HTML help viewer code is the root cause of your problems. I've always found that code to be extremely low quality.
I deal with that by implementing an OnHelp event handler that I attach to the Application object. This event handler calls the HtmlHelp API directly. I certainly don't experience any of the problems that you describe.
My code looks like this:
unit Help;
interface
uses
SysUtils, Classes, Windows, Messages, Forms;
procedure ShowHelp(HelpContext: THelpContext);
procedure CloseHelpWindow;
implementation
function RegisterShellHookWindow(hWnd: HWND): BOOL; stdcall; external user32;
function DeregisterShellHookWindow(hWnd: HWND): BOOL; stdcall; external user32;
procedure ShowHelp(HelpContext: THelpContext);
begin
Application.HelpCommand(HELP_CONTEXTPOPUP, HelpContext);
end;
type
THelpWindowManager = class
private
FMessageWindow: HWND;
FHelpWindow: HWND;
FHelpWindowLayoutPreference: TFormLayoutPreference;
function ApplicationHelp(Command: Word; Data: THelpEventData; var CallHelp: Boolean): Boolean;
protected
procedure WndProc(var Message: TMessage);
public
constructor Create;
destructor Destroy; override;
procedure RestorePosition;
procedure StorePosition;
procedure StorePositionAndClose;
end;
{ THelpWindowManager }
constructor THelpWindowManager.Create;
function DefaultRect: TRect;
var
i, xMargin, yMargin: Integer;
Monitor: TMonitor;
begin
Result := Rect(20, 20, 1000, 700);
for i := 0 to Screen.MonitorCount-1 do begin
Monitor := Screen.Monitors[i];
if Monitor.Primary then begin
Result := Monitor.WorkareaRect;
xMargin := Monitor.Width div 20;
yMargin := Monitor.Height div 20;
inc(Result.Left, xMargin);
dec(Result.Right, xMargin);
inc(Result.Top, yMargin);
dec(Result.Bottom, yMargin);
break;
end;
end;
end;
begin
inherited;
FHelpWindowLayoutPreference := TFormLayoutPreference.Create('Help Window', DefaultRect, False);
FMessageWindow := AllocateHWnd(WndProc);
RegisterShellHookWindow(FMessageWindow);
Application.OnHelp := ApplicationHelp;
end;
destructor THelpWindowManager.Destroy;
begin
StorePositionAndClose;
Application.OnHelp := nil;
DeregisterShellHookWindow(FMessageWindow);
DeallocateHWnd(FMessageWindow);
FreeAndNil(FHelpWindowLayoutPreference);
inherited;
end;
function THelpWindowManager.ApplicationHelp(Command: Word; Data: THelpEventData; var CallHelp: Boolean): Boolean;
var
hWndCaller: HWND;
HelpFile: string;
DoSetPosition: Boolean;
begin
CallHelp := False;
Result := True;
//argh, WinHelp commands
case Command of
HELP_CONTEXT,HELP_CONTEXTPOPUP:
begin
hWndCaller := GetDesktopWindow;
HelpFile := Application.HelpFile;
DoSetPosition := FHelpWindow=0;//i.e. if the window is not currently showing
FHelpWindow := HtmlHelp(hWndCaller, HelpFile, HH_HELP_CONTEXT, Data);
if FHelpWindow=0 then begin
//the topic may not have been found because the help file isn't there...
if FileExists(HelpFile) then begin
ReportError('Cannot find help topic for selected item.'+sLineBreak+sLineBreak+'Please report this error message to Orcina.');
end else begin
ReportErrorFmt(
'Cannot find help file (%s).'+sLineBreak+sLineBreak+'Reinstalling the program may fix this problem. '+
'If not then please contact Orcina for assistance.',
[HelpFile]
);
end;
end else begin
if DoSetPosition then begin
RestorePosition;
end;
HtmlHelp(hWndCaller, HelpFile, HH_DISPLAY_TOC, 0);//ensure that table of contents is showing
end;
end;
end;
end;
procedure THelpWindowManager.RestorePosition;
begin
if FHelpWindow<>0 then begin
RestoreWindowPosition(FHelpWindow, FHelpWindowLayoutPreference);
end;
end;
procedure THelpWindowManager.StorePosition;
begin
if FHelpWindow<>0 then begin
StoreWindowPosition(FHelpWindow, FHelpWindowLayoutPreference);
end;
end;
procedure THelpWindowManager.StorePositionAndClose;
begin
if FHelpWindow<>0 then begin
StorePosition;
SendMessage(FHelpWindow, WM_CLOSE, 0, 0);
FHelpWindow := 0;
end;
end;
var
WM_SHELLHOOKMESSAGE: UINT;
procedure THelpWindowManager.WndProc(var Message: TMessage);
begin
if (Message.Msg=WM_SHELLHOOKMESSAGE) and (Message.WParam=HSHELL_WINDOWDESTROYED) then begin
//need cast to HWND to avoid range errors
if (FHelpWindow<>0) and (HWND(Message.LParam)=FHelpWindow) then begin
StorePosition;
FHelpWindow := 0;
end;
end;
Message.Result := DefWindowProc(FMessageWindow, Message.Msg, Message.wParam, Message.lParam);
end;
var
HelpWindowManager: THelpWindowManager;
procedure CloseHelpWindow;
begin
HelpWindowManager.StorePositionAndClose;
end;
initialization
if not ModuleIsPackage then begin
Application.HelpFile := ChangeFileExt(Application.ExeName, '.chm');
WM_SHELLHOOKMESSAGE := RegisterWindowMessage('SHELLHOOK');
HelpWindowManager := THelpWindowManager.Create;
end;
finalization
FreeAndNil(HelpWindowManager);
end.
Include that unit in your project and you will be hooked up to handle help context requests. Some comments on the code:
- The implementation of the
OnHelp event handler is limited to just my needs. Should you need more functionality you'd have to add it yourself.
- You won't have
TFormLayoutPrefernce. It's one of my preference classes that manages per-user preferences. It stores away the window's bounds rectangle, and whether or not the window was maximised. This is used to ensure that the help window is shown at the same location as it was shown in the previous session. If you don't want such functionality, strip it away.
ReportError and ReportErrorFmt are my helper functions to show error dialogs. You can replace those with calls to MessageBox or similar.
