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Volume Number:9
Issue Number:7
Column Tag:Pascal Workshop

Related Info: Dialog Manager Event Manager List Manager

Dab-hand Dialogs from Darkest Africa

We describe, design, develop and distribute a decent DialogKeyFilter

By Mike O’Hanlon, Cape Town, South Africa

Note: Source code files accompanying article are located on MacTech CD-ROM or source code disks.

About the author

Mike O’Hanlon has been programming the Macintosh on a hobby basis for about 4 years. Anything starting with O’ is likely to be his. O’Tools, O’Heap, O’Files, O’Fonts, O’Help, O’Clock, O’List and O’Tree are examples. He believes his most useful effort to date has been O’Structures - a Data Structures library written in Object Pascal. He thinks C is for the birds. His other preoccupations are his wife, skiing and off-roading in a Land Rover.


I don’t want to be derogatory, but it’s dawning on this developer that our Dialogs are looking decidedly disadvantaged. They’re definitely in the Doldrums.

I’m a user interface fanatic, and hopelessly biased towards the Macintosh, so I get upset when another environment (like Windows) develops a tweak that gives it an edge over the Mac.


In the case of the ubiquitous Modal Dialog, the improvement we should learn from Microsoft is that of allowing keyboard shortcuts for any enabled buttons, checkboxes and radio buttons presented in the dialog. The mouse is great, but sometimes the keyboard is much more convenient. You know the kind of thing: you’ve yanked up a “Find...” dialog using Command-F; you’ve typed the word you want to find, and you want to hit Command-W to toggle the “Whole Words” checkbox. With most applications, you can’t; you have to leave the keyboard and switch to the mouse.

Let’s call these shortcuts Dialog Control keys - to distinguish them from other types of keyboard shortcut like Menu Command keys, and ‘Type Selection’ of items in a List box (see Inside Macintosh Vol. VI, page 2-25).

It’s notable that Microsoft’s own applications for the Mac do implement this feature. The way I see it, Excel and Word are in any event the most popular Macintosh applications, and in effect this legitimizes such an extension to the Mac user interface.


It’s also in keeping with recent keyboard shortcuts introduced by Apple, such as Command-D for the ‘DeskTop’ button in the standard file Open... dialog.

The other day, I got down to implementing this in my own applications. Once I got started, it wasn’t as difficult as I’d thought.

The challenge was to program it in a general purpose fashion and thereby avoid any App-specific code. I think I have succeeded in this, to the extent that if you use a resource editor to alter the titles of dialog controls (e.g. to create a foreign language version of your program), the keyboard shortcuts adapt themselves without any additional work.

So, to try and ensure that the Mac interface isn’t left behind, here are some explanatory notes and the code - which I hereby place in the public domain, hoping that the idea will be adopted by mainstream tool developers such as Symantec (in the THINK Class Libraries) and Bowers Development (in AppMaker).


The original Mac designers cleverly envisaged this kind of thing, and provided a neat hook for developers in the form of the filterProc parameter to the ModalDialog toolbox call.

The default system filter simply maps a few basic keys (Return, Enter, Esc etc.) to certain pre-defined dialog items. What I have done is implemented my ideas for Dialog Control keys entirely inside a much fuller-function filter procedure which you can specify in any ModalDialog call. I have called the thing DialogKeyFilter. There’s nothing else: no additional resources, no global variables, and no heap blocks. I have kept it as self-contained as possible.


The basic principle in the filter is to interpret a key depression as a mouse click on the lowest numbered dialog item which is an enabled Control, and which has a title in which the first capitalized (upper case) letter matches the user’s key stroke. The idea is that the user should be able to use the A key for an “Add” button, the G key for a “Grid Lines” checkbox, the L key for a “Left Aligned” or “align Left” radio button etc. (I’ll come to whether or not the Command key is needed in a moment).


But we have to be careful in several respects. Firstly, the user interface guidelines defined by Apple (I.M. Vol. VI, page 2-26) have already allocated two keyboard equivalents each for the default button (normally OK) and Cancel - namely Enter/Return and Esc/Command-period. For this reason, and because of possible confusion with the Copy (Edit menu) command, it makes sense not to associate Command-C with Cancel. Also, we only allocate an alphabetic Dialog Control key to the dialog’s default item if there is no other dialog item sharing the same first capitalized letter. For example, if the default item is ‘OK’, but there is also an ‘Outline’ button, the ‘O’ key (or Command-O) is interpreted as ‘Outline’, not ‘OK’.

Next, let’s consider the Command key. Should its use be made mandatory, or not? It depends on whether the dialog contains editable text or List items. If the cursor is currently in an editable text field, most key depressions must perform their normal input function. In this case we only interpret the key hit as a Dialog Control key if the user has the Command key depressed as well. Even then, we must reserve Command-X, -C and -V for the standard Edit commands.


Incidentally, if the user does a Cut or Copy whilst in the dialog, the filter routine should notify the calling program, so that the latter knows that the scrap is ‘dirty’ and can act accordingly. The DialogKeyFilter routine provided in the source listing does this by setting the event.message field to the constant convertClipboardFlag, so that the developer can test it on return from the ModalDialog call. (The filterProc’s event is a var parameter). It could alternatively be done by having the filter routine set a global variable. Neither are very elegant solutions, and this reveals a deficiency in the filterProc parameter set.


Now, what happens when a dialog contains one or more List boxes? If a List is selected (or is the only dialog item which could receive keyboard events) most key depressions should be interpreted as ‘Type Selection’ in the list. I couldn’t build any generalized List support into DialogKeyFilter because there’s no way of identifying a dialog item as a List (it’s just a special case of User item). So, if you have a List in your dialog box, you’ll have to filter the List first, and then call DialogKeyFilter. (If there’s any demand, I’ll publish a ListKeyFilter as a follow-up supplement to this article).

Here’s the full Dialog key-depression logic. The part to be done in a List filter is in italics:


KeyDown or AutoKey event:
 Enter or Return:
 Set item hit to the default item;
 Esc. or Command-period:
 Set item hit to Cancel; {item 2}
 Tab key:
 Rotate round Editable text/List items;
 Other keys:
 Editable text field selected:
 F2, F3, or F4 depressed:
 It’s an Edit command;
 Not F2, F3 or F4:
 Command key down:
 X, C or V depressed:
 It’s an Edit command;
 A..Z (but not X, C or V):
 Dialog Control key;
 Others keys:
 Command key not down:
 Apply key to the edit field;
 List box item selected:
 A..Z with Command key:
 Dialog Control key;
 Perform ‘Type Selection’;
 No Editable text fields or List boxes:
 A..Z (Command key optional):
 Dialog Control key;
 Other keys:

In the logic above, Dialog Control key means we search the dialog item list for a matching Control. In DialogKeyFilter, I decided not to make the assumption that the upper case letter will necessarily be the first character in the control’s title. This allows you to capitalize another letter (such as the first letter of the second word). It also provides for quirks like Return characters at the start of the item title. (This is a bit obscure, but you might want to do this to make the control’s title invisible, so that it can be overlaid with a fancier static text title - eg to show a ‘Bold’ checkbox with a Bold caption).


The idea of Dialog Control keys is fully applicable to the new System 7 Movable Modal dialogs, and the code given works fine with them. It also works fine with Modeless dialogs, but extension of the idea to Modeless dialogs is arguable: an essential attribute of the Modeless state is that the majority of Menu commands should remain available whilst the dialog is up. If Dialog Control keys are allowed in Modeless dialogs (and assuming that we stick with the Command key as the modifier key), confusion might arise as to whether a shortcut applies to a dialog control or a menu command.

I believe these shortcuts should be allowed in Modeless dialogs. After all, if the Modeless dialog is the frontmost window, then it is presumably the focus of the user’s attention. Nevertheless, if the user hits a Command-key combination which doesn’t match any dialog item, DialogKeyFilter simply returns false, enabling the command to be interpreted in the main event loop as a Menu command. Thus, in a frequently occurring example, Command-Q will still work as Quit even if there is a Modeless dialog as the front window, provided it doesn’t contain an enabled control with a capitalized Q. (In that case, he could still Quit from the keyboard using Esc, Command-Q).


Before closing, here are some things that went through my head, but which I didn’t do. It occurred to me that it might be clever to allocate the Control key instead of Command as the modifier for use with Dialog Controls. The neat things would have been:

• dialog items accessed by Dialog Control keys are in fact always Controls;

• the Control key has been looking for a real job ever since it came on the scene;

• confusion with Menu Commands would have been avoided (and there would have been no argument about shortcuts in Modeless as well as Modal dialogs).

However, many Mac keyboards still don’t have a Control key, and many owners who do have a Control key like to reserve it for use with a macro recorder like QuicKeys.


Two final deciding factors were that it would often have caused awkward shifting of the modifier finger from Command to Control, and it would have been inconsistent with MS Word and Excel for the Macintosh. It would also have been inconsistent with Windows, which uses the ‘Alt’ key for dialog shortcuts. (The PC’s ‘Alt’ key is normally situated in the same keyboard position as the Mac’s Command key). So on balance the idea was rejected.

I also toyed with more positive visual cueing of Dialog Control keys, but I couldn’t come up with anything that was aesthetically pleasing, didn’t chew up too much dialog real estate and wasn’t a nightmare to implement. So that idea also went out of the window dialog. Anyway the capitalization should be cue enough, and the user is given feedback in the normal way (highlighting, checking etc.).


I hope you can see that I’ve given this a fair amount of thought. However, no code is perfect and I’m sure some of you will be able to suggest improvements. If so, please write to me at the address given below (unfortunately it’s a bit expensive working with CompuServe etc. from South Africa). Please also write to me if you can figure out how to install a filter like this in System 7.0 so that it replaces the default filter procedure which is used whenever a developer supplies nil as ModalDialog’s filterProc. Then it would automatically work for all applications which don’t currently specify a filter routine for dialog boxes. Now that would be clever.

Mike O’Hanlon, Eden House, 49 Eden Road,Claremont, 7700, Cape, South Africa.

function DialogKeyFilter (
         Dialog: DialogPtr;
         var event: EventRecord;
         var itemHit: integer): boolean;
{  Implements “Dialog Control keys” -  }
{  keyboard shortcuts for buttons,     }
{  checkboxes and radio buttons.       }
{            Author: Mike O’Hanlon.    }

  kEnter = chr(3);        {Enter key}
  kReturn = chr(13);      {Return key}
  kEscOrClear = chr(27);  {Esc/Clear}

  KeyX = 7;               {-X = Cut}
  KeyC = 8;               {-C = Copy}
  KeyV = 9;               {-V = Paste}

  KeyF2 = $78;            {F2 = Cut}
  KeyF3 = $63;            {F3 = Copy}
  KeyF4 = $76;            {F4 = Paste}

  filtered: boolean;
  defItem: integer;
  keyChar: char;
  keyCode: Byte;

 function ButtonItem (Item: integer)
        : boolean;
    {uses Dialog: DialogPtr}
{ Checks whether specified item is a   }
{ normal button (not Checkbox/radio).  }
   IType: integer;
   IHandle: Handle;
   IRect: Rect;
  GetDItem(Dialog, Item, IType,
                   IHandle, IRect);
  ButtonItem := BAND(IType, 255 -
   itemDisable) = (ctrlItem + btnCtrl);
 end; {ButtonItem}

 function Enabled (Item: integer)
        : boolean;
    {uses Dialog: DialogPtr}
{ Checks whether the item is enabled.  }
   IType: integer;
   IHandle: Handle;
   IRect: Rect;
  GetDItem(Dialog, Item, IType,
                   IHandle, IRect);
  Enabled := BAND(
              IType, itemDisable) = 0;
 end; {Enabled}

 procedure EditCommand (key: Byte);
     {uses Dialog: DialogPtr}
     {sets event: EventRecord}
     {sets itemHit: integer}
     {sets filtered: boolean}
{ Performs the specified Edit command. }
  itemHit := DialogPeek(Dialog)^.
             editField + 1;
  case key of
   KeyX, KeyF2: 
     if itemHit > 0 then
      event.message :=
   KeyC, KeyF3: 
     if itemHit > 0 then
      event.message :=
     itemHit := 0;
   KeyV, KeyF4: 
  end; {case}
  if itemHit > 0 then
   if Enabled(itemHit) then
    filtered := true;
  if not filtered then
   event.what := nullEvent;
 end; {EditCommand}

 procedure FrameButton (Item: integer);
     {uses Dialog: DialogPtr}
{ Frames the specified (button) item,  }
{ to designate it as the default.      }
   IType: integer;
   IHandle: Handle;
   IRect: Rect;
   savePen: PenState;
  GetDItem(Dialog, Item, IType,
                   IHandle, IRect);
  PenSize(3, 3);
  InsetRect(IRect, -4, -4);
  FrameRoundRect(IRect, 16, 16);
 end; {FrameButton}

 function NumItems: integer;
    {uses Dialog: DialogPtr}
{ Returns no. of items in item list.   }
   DITLHandle = ^DITLPtr;
   DITLPtr = ^DITL;
   DITL = packed record
     NumItemsLess1: integer;
      {followed by the items, but we...}
      {don’t need them in this function}
    end; {DITL}
  NumItems := DITLHandle(DialogPeek(
   Dialog)^.items)^^.NumItemsLess1 + 1;
 end; {NumItems}

 procedure SetItemHit (Item: integer);
     {uses Dialog: DialogPtr}
     {sets itemHit: integer}
{ Sets itemHit to the specified item & }
{ flashes it if it’s an enabled button.}
   IType: integer;
   IHandle: Handle;
   IRect: Rect;
   Btn: ControlHandle;
   SaveState: Byte;
   finalTicks: longint;
  itemHit := Item;
  if Enabled(Item) & ButtonItem(Item)
   then begin
    GetDItem(Dialog, Item, IType,
                     IHandle, IRect);
    if IHandle <> nil then
      Btn := ControlHandle(IHandle);
      SaveState := Btn^^.contrlHilite;
      HiliteControl(Btn, inButton);
      Delay(6, finalTicks);
      HiliteControl(Btn, SaveState);
     end; {IHandle <> nil}
   end; {Enabled button}
  filtered := true;
 end; {SetItemHit}

 function TestItem (Item: integer;
              Ch: char): boolean;
    {uses Dialog: DialogPtr}
{ Tests the specified dialog item for  }
{ the designated upper case char.      }
   IType: integer;
   IHandle: Handle;
   IRect: Rect;
   ITitle: str255;
   Posn: integer;
  TestItem := false;
  GetDItem(Dialog, Item, IType,
                   IHandle, IRect);
  if IType in [ctrlItem + btnCtrl,
               ctrlItem + chkCtrl,
               ctrlItem + radCtrl] then
   begin {it’s a Control item}
    if IHandle <> nil then
       ControlHandle(IHandle), ITitle);
      if ITitle <> ‘’ then
        for Posn := 1 to length(ITitle)
         if ITitle[Posn] in [‘A’..’Z’]
          then Leave; {for loop}
        if Posn <= length(ITitle) then
         if ITitle[Posn] = Ch then
          if Enabled(Item) then
           TestItem := true;
       end; {ITitle <> ‘’}
     end; {IHandle <> nil}
   end; {it’s a Control item}
 end; {TestItem}

 procedure SearchForItem (Ch: char);
     {sets itemHit: integer}
{ Searches item list for Control with  }
{ specified upper case char. in title. }
   Item: integer;
   Found: boolean;
  itemHit := 0;
  if Ch in [‘a’..’z’] then
    Found := false;
    Ch := chr(ord(Ch) - 32);
                {Convert to Upper case}
    for Item := 1 to NumItems do
     if (Item <> defItem) &
        (Item <> Cancel) then
      if TestItem(Item, Ch) then
        Found := true;
        Leave; {for loop}
    if not found then
     if TestItem(defItem, Ch) then
   end; {key in range ‘a’..’z’}
 end; {SearchForItem}

begin {DialogKeyFilter}
{           The main logic.            }
 filtered:= false;
 defItem:= DialogPeek(Dialog)^.aDefItem;
 if event.what in [keyDown,autoKey] then
   keyChar := chr(BAND(event.message,
   keyCode := BSR((BAND(event.message,
                   keyCodeMask)), 8);
   if keyChar in [kEnter, kReturn] then
   else if keyChar = kEscOrClear then
   else if (BAND(event.Modifiers,
         CmdKey) <> 0) & (keyChar = ‘.’)
   then {Command-period}
   else {not Enter/Return/Esc/Cmd-.}
     if DialogPeek(Dialog)^.
             editField + 1 <> 0 then
      { editable text field exists}
      if keyCode in [KeyF2,KeyF3,KeyF4]
      else if BAND(event.Modifiers,
                    CmdKey) <> 0 then
       if keyCode in [KeyX, KeyC, KeyV]
         {Editable text field exists}
         {and Command Key isn’t down}
         {... so we do nothing here.}
     else {no editable text field}
    end; {not Enter/Return/Esc/Cmd-.}
  end {keyDown, autoKey}
 else if (event.what = updateEvt) then
  if WindowPtr(event.message) = thePort
   if ButtonItem(defItem) then
 DialogKeyFilter := Filtered;
end; {DialogKeyFilter}

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