TweetFollow Us on Twitter

Chain Events
Volume Number:9
Issue Number:12
Column Tag:Jörg's Folder

Related Info: Event Manager Apple Event Mgr

Apple Event Handlers in MacForth

Changing the main event loop with executable chains

By Jörg Langowski, MacTech Magazine Regular Contributing Author

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

Which Macintosh programming environment - other than Forth - do you know where you can change the main event loop on the fly, plug in new routines or change them while you’re trying them out, or even while your application is running? Maybe Lisp, but certainly none of the development systems (C and C++ of various flavors, Pascal, maybe Fortran and Basic) that account for the majority of all applications on the market. You can solve some of these problems through runtime binding in C++, but for developing a program you still face that edit/compile/link/crash cycle. When I did the example for this column, implementing high-level event support in MacForth, I had plenty of opportunity to appreciate the incremental compiling that Forth offers, together with a good low-level debugger like TMON.

So after having seen how to use Apple events in Fortran and C++, you knew that a Forth example on that subject was just unavoidable. MacForth 4.0, the version that I am still using, does not offer built-in support for high level events. I’m not sure whether the latest 4.2 update does, but I’ll keep you informed as soon as I receive it. Anyway, for the sake of example it is better to use a version that does not support Apple events, because then you can see how to do it.

You remember that an application that supports Apple events has to tell this to the system. There is a bit in the SIZE resource reserved for this purpose. So the first step to make our MacForth kernel high-level event aware is to use ResEdit and set this bit to 1. Now the application’s name will, e.g., be visible in the PPC browser dialog when you select an application to interact with. Now comes the actual work, implementing an Apple event handler in MacForth.

Hooking into the main event loop

Apple events have an event code of 23. Older applications that did not handle Apple events did not check for this code. So how do you persuade the MacForth runtime system to react to high-level events, that is, how does one change the main event loop? (Let’s assume we don’t have access to the source). Easy. MacForth solves this and related problems - like how do you change its behavior on startup and during quit - through the concept of executable chains. These are lists of Forth words that are executed in sequence on various occasions; for instance, the Eventer chain is executed on each pass through the main event loop. There is a standard mechanism to add new Forth words to this chain. If you would add a word to the Eventer chain, all you do is to write Eventer linked followed by your word’s definition (see near the end of the example listing). This word is then automatically linked into the main event loop.

Words linked into the Eventer chain take an event code as a parameter and leave an event code (which may be different from the original one) plus a flag on the stack. The flag tells the system whether the event has been processed (true) or not (false). Thus, we’ll define a word that looks for event code 23 and if it finds it, calls ProcessAppleEvent, the routine that finds the handler corresponding to the Apple event received.

Event handlers

The handlers themselves are installed in a dispatch table through the Forth word Install.Event.Handler (see listing). The parameters to the trap are, from bottom to top of stack:

• the event class specifier (32 bit);

• the event ID (32 bit);

• a pointer to the handler routine (32 bit);

• a reference constant (32 bit);

• a boolean (16 bit) which is true if the handler is installed in the system event dispatch table, false otherwise.

The event class for the required Apple events is ‘aevt’, and the event IDs are ‘oapp’, ‘odoc’, ‘pdoc’, and ‘quit’. We will define handlers for all these events except ‘oapp’.

The address of the handler that is passed to the AEInstallEventHander trap must be a pointer to a routine that follows Pascal calling conventions. Of course, a standard MacForth word doesn’t do that, and you have to define the handler routines in a particular way. MacForth offers two ‘filter routine’ definition words, filter: and ;filter that can be used for that purpose. If you use them instead of : and ; at the start and end of a Forth definition, the resulting word will be callable as a subroutine from machine language. All the word does on execution is to put the entry address of the routine on the stack, which can then be passed as a parameter to a toolbox trap.

The first handler that we’ll write is for the ‘quit’ event. It seems pretty simple; just call ExitToShell and you’re done. But wait we can’t pull the rug from underneath other things that may be going on in the run time system; e.g. open files that have been edited and are not saved, etc. There is a Forth word, bye, that quits the MacForth system gracefully and will for instance present you with the ‘Save Changes ’ dialog box when there are unsaved files. So why not call bye from within the handler? I’ve tried that, with spectacular crashes as a result. This approach does not work because the handler routine would never return correctly, and I guess this leaves things hanging in the air that should be safely fixed on the ground. A safe way to quit is to install a token for a word that quits in the event.filter variable. If this variable is nonzero, MacForth assumes that it contains the pointer to a routine that is called on every pass through the main event loop. We now define a word ciao which resets event.filter to zero and then calls bye, and the quit handler will install the token for this word in event.filter. This way we make sure that ciao is called only once when the ‘quit’ event is received.

You can try out the ‘quit’ handler by using any of the tools to send an Apple event to other applications (there is a Hypercard stack and an Apple event test application available on the Apple ETO CD-ROM, and I’m sure there are public domain programs floating around in cyberspace). You’ll see that MacForth quits, and if there is any open file with unsaved changes, opens the dialog that asks you whether you want to save the changes. I had some problems with the quit handler when I used it in connection with the extended editor (see my last Forth column), and don’t know the reason for sure, but with the standard Sibley editor it works alright.

The other two handlers are for opening and printing documents from the finder. They are very similar, and one could easily modify this so that only one handler is called for both purposes, the switch between open and print behavior being done through the reference constant that is passed when the handler is installed.

These handlers are direct translations from the proposed ‘odoc’ and ‘pdoc’ handlers in Inside Mac vol. 6. First, we get the parameter descriptor out of the Apple event that corresponds to a list of files to be opened or printed. The keyword for this descriptor is ‘list’. The descriptor returned consists of two 32-bit words, the first one containing the parameter type (‘list’), the second one a handle to this parameter. The address of the descriptor is then passed to a routine that counts the number of items in the list (CountItems), and then a loop is executed that steps an index starting at 1 to the number of items, and opens - or prints - each item. The information about the file to be opened is obtained through the routine Get.Nth.Ptr which gets the data corresponding to the n-th item out of a descriptor list. The parameters taken by the trap, AEGetNthPtr, used in this routine are the following:

• a pointer to the descriptor list (32 bits);

• the number of the desired item (32 bits);

• the type of the desired item (32 bits);

• a keyword if one is associated with the descriptor record (32 bits);

• the descriptor type of the item returned (32 bits);

• a pointer to the data buffer (32 bits);

• the maximum size of the data to be returned (32 bits);

• the address of a variable that contains the actual size of the data returned (32 bits).

We call this trap with our descriptor list as a parameter, and specifying that we want the data to be returned in the format of a file system specifier (‘fss ’). Actually, the information about the files to be processed in the ‘odoc’ and ‘pdoc’ Apple events is in the format of alias records, which allows file aliases to be processed transparently. If we specify as the desired type ‘fss ’, the Apple Event manager will automatically ‘coerce’ the alias data to the FSS format, thus resolve the alias. You don’t have to worry about this, all that’s important is that the buffer myFSS contains the volume reference number (16 bits), the directory ID (32 bits), and the file name (63 byte string), in that order. After the successful call to GetNthPtr, this information is extracted from the buffer and used to call either of two routines: se.open$ for opening a file in a new editor window, or (paper) for printing it.

After all these preliminaries, try and load the Forth code, and then drag a few files from the finder to the MacForth item, or select the print command. You’ll see how it works. If it doesn’t, make sure that you have modified your SIZE resource with ResEdit so that the high-level events bit is set.

Things to be resolved

There remain quite a few things that could still be done, for instance, I haven’t told you how to install Apple event handlers in a stand-alone MacForth application, or how to handle other types of Apple events. In fact, I have a very nice project: to install a ‘dosc’ handler in MacForth that interprets Forth code that is sent from other applications, and send back the result in text form. Sort of a Forth tool server. But this is something that you may find in a later column. Until then, happy threading.

Example: Implementing the required Apple events in MacForth 4.0
anew testAE


\ generic interface word to the AE manager

<code AEPack
 popd0, \ pop selector into d0
 MAC Pack8 w,
 next,


\ some AE routines that we need in this example
\ the Pack8 routines all return a 16-bit result,
\ so we have to leave space below the parameters
\ on the stack. Here, we push a 32-bit 0 and later shift the 
\ result code by 16 bit ( hex 10000 / )

hex
: Process.Apple.Event
 0 event.record 021b AEPack 10000 /
;

: Install.Event.Handler  ( AEclass AEID AEproc -- OSErr )      
 0 3 bury ( space for result)
 0 ( refcon ) 0 0 wbury ( false ) 091f ( selector )
 AEPack 10000 /
;

: Get.Param.Desc 
 ( theEvent AEKey DescType AEDesc -- OSErr )
 0 4 bury ( space for result)
 0812 AEPack 10000 /
;

: Count.Items ( DescList theCount -- OSErr )
 0 2 bury ( space for result)
 0407 AEPack 10000 /
;

: Get.Nth.Ptr ( DescList index desiredType theAEKey
 typeCode dataPtr maximumSize actualSize -- OSErr )
 0 8 bury ( space for result )
 100A AEPack 10000 /
;
 
: Dispose.Desc ( AEDesc -- OSErr )
 0 swap 0204 AEPack 10000 /
;
decimal


\ global variables

create myFSS 70 allot
create docList 8 allot


\ the ‘quit’ handler does not call bye directly (this leads to
\ crashes), but just puts a token to a ‘bye’ routine into 
\ EVENT.FILTER. The ‘bye’ routine then sets the filter
\ back to ‘off’ again, so that it won’t be called all over 
\ again in case the user cancels the bye process.

\ our ‘bye’ routine. 

: ciao 
 event.filter off
 bye
;


\ the quit handler itself

filter: AEquit
 locals| refcon reply theEvent |
 token.for ciao event.filter !
;filter


\ ‘odoc’ handler, uses routines from the Sibley editor

filter: AEodoc
 0 0 0 0 
 locals| actualSize descType myKey #items 
 refcon reply theEvent |
 
 theEvent  ascii ---- ( DirectObject )
 ascii list ( AEList ) docList
 Get.Param.Desc 
 if ." GetParamDesc error" cr then
 
 docList addr.of #items  
 Count.Items
 if ." CountItems error" cr then
 
 #items 1+ 1 do
 docList i ascii fss_ addr.of myKey 
 addr.of descType myFSS 70 addr.of actualSize  
 Get.Nth.Ptr
 if ." Get.Nth.Ptr error" cr then
 myFSS 6+ myFSS w@ myFSS 2+ @ se.open$ 
 loop
 
 docList Dispose.Desc
 if ." Dispose.Desc error" cr then
;filter


\ ‘pdoc’ handler, very similar to the ‘odoc’ handler (some
\ code could be factored out here). Uses the printing 
\ routine from ‘Paper’

filter: AEpdoc
 0 0 0 0 
 locals| actualSize descType myKey #items 
 refcon reply theEvent |
 
 theEvent  ascii ---- ( DirectObject )
 ascii list ( AEList ) docList
 Get.Param.Desc 
 if ." GetParamDesc error" cr then
 
 docList addr.of #items  
 Count.Items
 if ." CountItems error" cr then
 
 #items 1+ 1 do
 docList i ascii fss_ addr.of myKey addr.of descType
 myFSS 70 addr.of actualSize  
 Get.Nth.Ptr
 if ." Get.Nth.Ptr error" cr then
 myFSS w@ volref# !
 myFSS 2+ @ ioDir !
 myFSS 6+ (paper) 
 loop
 
 docList Dispose.Desc
 if ." Dispose.Desc error" cr then
;filter

\ space for filter routine return stack
256 allot here 64 - FilterRP !


\ word to install the handlers. We have not provided the 
\ ‘oapp’ handler, but put in there anything you like

: install.req.handlers
   ascii aevt ascii quit AEquit Install.Event.Handler drop
\ ascii aevt ascii oapp AEoapp Install.Event.Handler drop
   ascii aevt ascii odoc AEodoc Install.Event.Handler drop
   ascii aevt ascii pdoc AEpdoc Install.Event.Handler drop
;

\ we need to catch the high level event. MacForth allows to 
\ easily hook new event handlers into the main event loop, 
\ through the Eventer executable chain.
 
Eventer Linked
: AEDispatch
 dup
 23 = if
 Process.Apple.Event drop
 drop 0 true
 else
 false
 then
;

\ finally, install the handlers
install.req.handlers

 

Community Search:
MacTech Search:

Software Updates via MacUpdate

Adobe Lightroom 6.1.1 - Import, develop,...
Adobe Lightroom is available as part of Adobe Creative Cloud for as little as $9.99/month bundled with Photoshop CC as part of the photography package. Lightroom 6 is also available for purchase as a... Read more
File Juicer 4.41 - Extract images, video...
File Juicer is a drag-and-drop can opener and data archaeologist. Its specialty is to find and extract images, video, audio, or text from files which are hard to open in other ways. It finds and... Read more
A Better Finder Rename 9.52 - File, phot...
A Better Finder Rename is the most complete renaming solution available on the market today. That's why, since 1996, tens of thousands of hobbyists, professionals and businesses depend on A Better... Read more
OmniFocus 2.2.3 - GTD task manager with...
OmniFocus helps you manage your tasks the way that you want, freeing you to focus your attention on the things that matter to you most. Capturing tasks and ideas is always a keyboard shortcut away in... Read more
TinkerTool 5.4 - Expanded preference set...
TinkerTool is an application that gives you access to additional preference settings Apple has built into Mac OS X. This allows to activate hidden features in the operating system and in some of the... Read more
Tinderbox 6.3.1 - Store and organize you...
Tinderbox is a personal content management assistant. It stores your notes, ideas, and plans. It can help you organize and understand them. And Tinderbox helps you share ideas through Web journals... Read more
Parallels Desktop 10.2.2 - Run Windows a...
Parallels Desktop is simply the world's bestselling, top-rated, and most trusted solution for running Windows applications on your Mac. With Parallels Desktop for Mac, you can seamlessly run both... Read more
Adobe Premiere Pro CC 2015 9.0.1 - Digit...
Premiere Pro CC 2015 is available as part of Adobe Creative Cloud for as little as $19.99/month (or $9.99/month if you're a previous Premiere Pro customer). Premiere Pro CS6 is still available for... Read more
Adobe After Effects CC 2015 13.5.1 - Cre...
After Effects CC 2015 is available as part of Adobe Creative Cloud for as little as $19.99/month (or $9.99/month if you're a previous After Effects customer). After Effects CS6 is still available... Read more
Adobe Creative Cloud 2.2.0.129 - Access...
Adobe Creative Cloud costs $49.99/month (or less if you're a previous Creative Suite customer). Creative Suite 6 is still available for purchase (without a monthly plan) if you prefer. Introducing... Read more

Domino Drop (Games)
Domino Drop 1.0 Device: iOS Universal Category: Games Price: $1.99, Version: 1.0 (iTunes) Description: Domino Drop is a delightful new puzzle game with dominos and gravity!Learn how to play it in a minute, master it day by day.Your... | Read more »
OPERATION DRACULA (Games)
OPERATION DRACULA 1.0.1 Device: iOS Universal Category: Games Price: $5.99, Version: 1.0.1 (iTunes) Description: 25% off launch sale!!! 'Could prove to be one of the most accurate representations of the Japanese bullet hell shmup... | Read more »
Race The Sun (Games)
Race The Sun 1.01 Device: iOS iPhone Category: Games Price: $4.99, Version: 1.01 (iTunes) Description: You are a solar craft. The sun is your death timer. Hurtle towards the sunset at breakneck speed in a futile race against time.... | Read more »
Tap Delay (Music)
Tap Delay 1.0.0 Device: iOS Universal Category: Music Price: $4.99, Version: 1.0.0 (iTunes) Description: Back in the “old days”, producers and engineers created delay and echo effects using tape machines. Tap Delay combines the warm... | Read more »
This Week at 148Apps: July 20-24, 2015
July is Heating Up With 148Apps How do you know what apps are worth your time and money? Just look to the review team at 148Apps. We sort through the chaos and find the apps you're looking for. The ones we love become Editor’s Choice, standing out... | Read more »
Red Game Without A Great Name (Games)
Red Game Without A Great Name 1.0.3 Device: iOS Universal Category: Games Price: $2.99, Version: 1.0.3 (iTunes) Description: The mechanical bird is flying through an unfriendly, Steampunk world. Help it avoid obstacles and deadly... | Read more »
Warhammer: Arcane Magic (Games)
Warhammer: Arcane Magic 1.0.2 Device: iOS Universal Category: Games Price: $9.99, Version: 1.0.2 (iTunes) Description: Engage in epic battles and tactical gameplay that challenge both novice and veteran in Warhammer: Arcane Magic, a... | Read more »
Mazes of Karradash (Games)
Mazes of Karradash 1.0 Device: iOS Universal Category: Games Price: $1.99, Version: 1.0 (iTunes) Description: The city of Karradash is under attack: the monsters of the Shadow Realms are emerging from the depths.No adventurer is... | Read more »
Battle Golf is the Newest Game from the...
Wrassling was a pretty weird - and equally great - little wressling game. Now the developers, Folmer Kelly and Colin Lane, have turned their attention to a different sport: golfing. This is gonna be weird. [Read more] | Read more »
Qbert Rebooted has the App Store Going...
The weird little orange... whatever... is back, mostly thanks to that movie which shall remain nameless (you know the one). But anyway it's been "rebooted" and now you can play the fancy-looking Qbert Rebooted on iOS devices. [Read more] | Read more »

Price Scanner via MacPrices.net

12-inch MacBooks in stock for $20 off, save o...
Adorama has 12″ Retina MacBooks in stock for $20 off MSRP including free shipping plus NY & NJ sales tax only. For a limited time, Adorama will include a free Apple USB-C to USB Adapter, free 4-... Read more
College Student Deals: Additional $100 off Ma...
Take an additional $100 off all MacBooks and iMacs at Best Buy Online with their College Students Deals Savings, valid through August 8, 2015. Anyone with a valid .EDU email address can take... Read more
2015 13-inch 2.7GHz Retina MacBook Pro on sal...
B&H Photo has the new 2015 13″ 2.7GHz/128GB Retina MacBook Pro on sale today for $1199 including free shipping plus NY sales tax only. Their price is $100 off MSRP. Read more
2.8GHz Mac mini available for $988, includes...
Adorama has the 2.8GHz Mac mini available for $988, $11 off MSRP, including a free copy of Apple’s 3-Year AppleCare Protection Plan. Shipping is free, and Adorama charges sales tax in NY & NJ... Read more
Updated Mac Price Trackers
We’ve updated our Mac Price Trackers with the latest information on prices, bundles, and availability on systems from Apple’s authorized internet/catalog resellers: - 15″ MacBook Pros - 13″ MacBook... Read more
High-Precision Battery Fuel Gauge IC Extends...
Renesas Electronics Corporation has announced its new lithium-ion (Li-ion) battery fuel gauge IC, the RAJ240500, designed to extend battery life for connected mobile devices such as tablets, notebook... Read more
27-inch 3.3GHz 5K iMac on sale for $1799, $20...
B&H Photo has the 27″ 3.3GHz 5K iMac on sale for $1799 including free shipping plus NY tax only. Their price is $200 off MSRP, and it’s the lowest price available for this model from any Apple... Read more
Twelve South Free Dual Screen Backgrounds Co...
Twelve South has posted a second collection of travel Desktop photos, noting: For the Twelve South team, a vacation is never just a vacation. It’s a time to try out new prototypes on the road, visit... Read more
Apple Refurbished iMacs available for up to $...
The Apple Store has Apple Certified Refurbished iMacs available for up to $380 off the cost of new models. Apple’s one-year warranty is standard, and shipping is free: - 27″ 3.5GHz 5K iMac – $1949 $... Read more
Tablets: Why Microsoft’s Surface Is Soaring W...
In contrast to Apple’s record fiscal third quarter reported this week, Microsoft had a miserable latest quarter with its revenues falling by 5.1 percent, hammered by ongoing weak PC demand, and... Read more

Jobs Board

*Apple* Retail - Multiple Positions (US) - A...
Job Description: Sales. Specialist - Retail Customer Service and Sales. Transform Apple Store visitors into loyal Apple customers. When customers enter the store, Read more
*Apple* Retail - Multiple Positions (US) - A...
Job Description: Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, Read more
*Apple* Retail - Multiple Positions (US) - A...
Job Description: Sales. Specialist - Retail Customer Service and Sales. Transform Apple Store visitors into loyal Apple customers. When customers enter the store, Read more
*Apple* Customer Experience (ACE) Leader - A...
…management to deliver on business objectives Training partner store staff on Apple products, services, and merchandising guidelines Coaching partner store staff on Read more
Project Manager - *Apple* Pay Security - Ap...
**Job Summary** The Apple Pay Security team is seeking a highly organized, results-driven Project Manager to drive the development of Apple Pay Security. If you are Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.