TweetFollow Us on Twitter

XCMD Corner
Volume Number:4
Issue Number:7
Column Tag:HyperChat®

XCMD Corner

By Donald Koscheka, Apple Computers, Inc.

--Don Koscheka’s XCMD Corner

Last month I introduced XCMD programming. I explained the parameter block and discussed the interface between HyperTalk and the code that you write in either Pascal, “C” or the language of your choice. If you’re an experienced Macintosh programmer, that’s enough information to get started. The designers of HyperCard didn’t stop with just defining the interface for you. They went beyond what might be reasonably expected and provided some HyperTalk programming capabilities to the XCMD programmer. The XCMD programmer gains access to these capabilities through callbacks. Callbacks are procedures and functions that you call from your XCMD. Callbacks literally jump into Hypercard to perform some function.

Once you get the hang of XCMD programming, you’ll come to rely on some of the callbacks quite frequently. For example, Pascal programmers are accustomed to strings that are preceded by a length byte and that have a maximum of 255 characters (the Str255 type in Pascal) while HyperCard uses strings that have no length byte and are terminated with zero ( referred to as Zero-strings, zero-terminated strings or “C” strings). HyperTalk provides callbacks to convert from zero-terminated strings to Pascal and back again. The XCMD programmer can also use callbacks to retrieve and set the contents of fields and global containers as well as to send messages back to Hypercard.

One of the reasons that this access to HyperCard containers is so important is that XCMDs do not have access to the application globals. When Hypercard starts up, it takes control of its application globals and heap just as any application would. With Hypercard in control of the heap, your XCMD becomes a “guest” of Hypercard. You don’t have access to the globals from your XCMD so you’ll need a safe place to store information that you want to keep around.

A good candidate is a global container. Although Hypercard itself prefers to see text strings in containers, it’s not particular about what you put into a container; you can use the SetGlobal callback to put data into a global container, and GetGlobal to retrieve that data. Make sure that you declare any global containers in Hypercard before accessing them in an XCMD. Your XCMD may need to be backward compatible earlier versions of Hypercard that bombed if you called SetGlobal with an undeclared container name.

An interesting example of the use of callbacks is to send a card message back to HyperCard from a callback. The XCMD in listing 1, “SendMeAMessage”, takes one parameter which is the message to send back to HyperCard. Since messages are sent back as Pascal-format strings, we must convert the input string into a pascal string and then call SendCardMessage to send the message. As a matter of form, we set the return value to NIL indicating that this XCMD doesn’t have a result code (Hypercard will interpret NIL as empty).

The first callback that SendMeAMessage invokes, ZeroToPas, converts input parameter 1 from a zero-terminated string to a pascal-string. Input parameters are passed as handles so the parameter needs to be dereferenced one-time to convert the value to a pointer. ZeroToPas also expects you to pass a reference to the pascal-string into which you’ll store the converted Pascal-string. The second callback, SendCardMessage, sends the message back to Hypercard. To invoke this XCMD from a script use the form:

 SendMeAMessage “go next card”

Because Hypercard already handles message passing, this XCMD may not seem terribly useful. Nonetheless, it is a good illustration of callbacks and the technique is useful if you need to alert the user that some asynchronous event has completed.

{1}
{******************************}
{* File: SendMeAMessage.p *}
{******************************}
(******************************
 BUILD SEQUENCE
      (IGNORE LINK WARNINGS)
pascal SendMeAMessage.p
link -m ENTRYPOINT -rt XCMD=65534 
 -sn Main=SendMeAMessage 
 SendMeAMessage.p.o 
 “{Libraries}”Interface.o 
 “{PLibraries}”Paslib.o 
 -o “{xcmds}”testxcmds
******************************)

{$S SendMeAMessage }

UNIT Donald_Koscheka; 

{--------------INTERFACE----------------}
INTERFACE

USES  MemTypes, QuickDraw, OSIntf, ToolIntf, 
 PackIntf, HyperXCmd;

PROCEDURE EntryPoint( paramPtr: XCmdPtr);

{----------IMPLEMENTATION--------------}
IMPLEMENTATION
{$R-}
 
TYPE
 Str31  = String[31];
 
PROCEDURE SendMeAMessage(paramPtr:XCmdPtr);
 FORWARD;

{-------------- EntryPoint --------------}
PROCEDURE EntryPoint(paramPtr: XCmdPtr);
 BEGIN
 SendMeAMessage(paramPtr);
 END;

{------------ SendMeAMessage ------------}
PROCEDURE SendMeAMessage(paramPtr: XCmdPtr);
VAR
 theMessage : Str255;
 
{$I XCmdGlue.inc }
 
BEGIN {*** Body of XCMD ***}
 ZeroToPas( paramPtr^.params[1]^, theMessage );
 SendCardMessage( theMessage );
 paramPtr^.returnValue := NIL;
END; {*** Body of XCMD ***}
END.

Listing 1. SendACardMessage

XCMDs can also use callbacks to get the contents of a field or a global container. Listing 2, GetHomeInfo, uses two new callbacks (1) GetFieldByNum, to get the contents of background field 1 on the home card and (2) SetGlobal to set the contents of some global container.

GetHomeInfo Takes one parameter, the name of the global container to set. First, convert the parameter to a pascal-string. Next, use a series of callbacks to push the current card and go to the home stack. Once we get to the home stack, we call GetFieldByNum to get field data. The first parameter that GetFieldByNum takes is set to TRUE if you want to retrieve the contents of a card field and set to FALSE to retrieve the contents of a background field. The second parameter is the number of the field to retrieve. Alternatively, you could use GetFieldByID if you knew the id of the field or GetFieldByName if you knew the name.

GetFieldByNum returns a handle to the zero-terminated data that was stored in background field 1 of the home card. We then invoke SetGlobal to set the contents of the global container to whatever is stored in fieldData. Finally, we pop the current card to get back to where we started. A typical invocation of this XCMD is:


{2}
 global myData
 GetHomeInfo “myData”



PROCEDURE GetHomeInfo(paramPtr: XCmdPtr);
VAR
 globalName : Str255;
 fieldData: Handle;
 
{$I XCmdGlue.inc }
 
BEGIN
 WITH paramPtr^ DO
 BEGIN
 ZeroToPas( params[1]^, globalName );
 SendCardMessage( ‘Push Card’ );
 SendCardMessage( ‘Go Home’);
 
 fieldData := GetFieldByNum( FALSE, 1 );
 SetGlobal( globalName, fieldData );
 
 SendCardMessage( ‘Pop Card’);
 returnValue := NIL;
 END;
END;

Listing 2. Get Home Info.

So far I’ve showed you XCMDs that don’t do anything that you can’t already do in HyperTalk. A key feature of XCMD programming is that you can write your own commands to augment or add capabilities to Hypercard. Listing 3, “FCreateXFCN”, lets you create a file of any type from HyperCard. This XFCN demonstrates how XCMDs provide greater access to the toolbox than is available to the HyperTalk script writer.

FCreateXFCN introduces two new callbacks. NumToStr returns a result code to the script. NumToStr converts a signed long integer to a pascal-format string. If you don’t want a signed entity, use LongToStr instead which will convert the long integer without regard to sign.

The second callback introduced in this XFCN is PasToZero which takes a pascal format string and returns handle to a zero-terminated string. PasToZero is a handy way of copying from a pascal-string back to a zero-terminated string to return text to Hypercard.

I wrote the XFCN in “C” to show the difference in formats between Pascal and “C” XCMDS and to provide a template for “C” programmers. An important difference is that the parameter list, params, starts at index 0 for “C” and index 1 for Pascal.

FCreateXFCN first converts parameter 1 (params[0]) into a pascal-string and then moves the first four bytes of parameters 2 and 3 into the variables creator and type respectively. These two variables are of type OSType which is a special Macintosh type containing four consecutive ASCII characters. All four characters in this type are significant.

The result code will be empty if no error occurred and the file was created properly, otherwise it will return the OSErr number that occurred. First, convert the result code back to a pascal-string and then call PasToZero to convert that string into a handle to a zero-terminated string.

The XFCN would be more useful if it returned a brief description of the error in English, but I think I’ll leave that as an exercise for the student. Call FCreateXFCN with the following script:

Put FCreateXFCN( “New File Name”, “WILD”,  “STAK” )

The first parameter is the name of the file you wish to create, the second parameter is the creator and the last parameter is the file type. The foregoing invocation will create an empty stack. What can you do with that?

{3}
/*****************************\
*file: FCreateXFCN.c *
\*****************************/

/*****************************
 BUILD SEQUENCE
 
C -q2 -g FCreateXFCN.c
link  -sn Main=FCreateXFCN 
 -sn STDIO=FCreateXFCN 
  -sn INTENV=FCreateXFCN 
  -rt XFCN=300 
  -m FCREATEXFCN 
  FCreateXFCN.c.o 
  “{CLibraries}”CInterface.o 
  -o testXCMDs
 
*****************************/
#include<Types.h>
#include<OSUtils.h>
#include<Memory.h>
#include<Files.h>
#include<Resources.h>
#include  “HyperXCmd.h”

pascal void FCreateXFCN( paramPtr )
 XCmdBlockPtr  paramPtr;
/****************************
* In:   Paramblock:
*param[0] == filename
*param[1] == TYPE
*param[2] == CREATOR
* Out:  result code in returnValue
****************************/
{
char    *fname;
OSType  type, creator;
Str31 str;
char    vName[33];
short   error, vRefnum;

/** coerce the volume reference  ***
***number from the system **/
GetVol( vName, &vRefnum );
 
/**extract the filename from  ***
***the parameter list     **/
fname   = *(paramPtr->params[0]);
BlockMove(*(paramPtr->params[1]),&creator,4 );
BlockMove(*(paramPtr->params[2]),&type,4 );
 
error = Create( fname, vRefnum, 
 creator, type );
 
FlushVol( 0L, vRefnum );
 
if( !error )
 paramPtr->returnValue = 0L;
else{
 NumToStr( paramPtr, (long)error, &str );
 paramPtr->returnValue = 
 PasToZero( paramPtr, &str );
 }
}

#include <XCmdGlue.inc.c>

Listing 3. FCreateXFCN

Although this article covered some of the more frequently used callbacks, my objective was to present you with the spirit of the callback mechanism. You should have no trouble using any of the callbacks that are currently defined in the HyperCard Developer’s ToolKit (available from APDA). The most important lesson here is that before you go off and write an XCMD, check the callback list to see how you might incorporate them into your XCMDs. Try to get the callbacks to do as much work as possible for you so that you can concentrate on the code that you are trying to write.

Next Month: SortList, an XCMD that sorts a field by line.

end HyperChat
 

Community Search:
MacTech Search:

Software Updates via MacUpdate

Apple Remote Desktop 3.8 - Remotely cont...
Apple Remote Desktop is the best way to manage the Mac computers on your network. Distribute software, provide real-time online help to end users, create detailed software and hardware reports, and... Read more
NeoOffice 2014.7 - Mac-tailored, OpenOff...
NeoOffice is a complete office suite for OS X. With NeoOffice, users can view, edit, and save OpenOffice documents, PDF files, and most Microsoft Word, Excel, and PowerPoint documents. NeoOffice 3.x... Read more
DesktopLyrics 2.6.6 - Displays current i...
DesktopLyrics is an application that displays the lyrics of the song currently playing in "iTunes" right on your desktop. The lyrics for the song have to be set in iTunes; DesktopLyrics does nothing... Read more
Ember 1.8.3 - Versatile digital scrapboo...
Ember (formerly LittleSnapper) is your digital scrapbook of things that inspire you: websites, photos, apps or other things. Just drag in images that you want to keep, organize them into relevant... Read more
Apple iTunes 12.1 - Manage your music, m...
Apple iTunes lets you organize and play digital music and video on your computer. It can automatically download new music, app, and book purchases across all your devices and computers. And it's a... Read more
LibreOffice 4.4.3 - Free, open-source of...
LibreOffice is an office suite (word processor, spreadsheet, presentations, drawing tool) compatible with other major office suites. The Document Foundation is coordinating development and... Read more
FoldersSynchronizer 4.2.1 - Synchronize...
FoldersSynchronizer is a popular and useful utility that synchronizes and backs-up files, folders, disks and boot disks. On each session you can apply special options like Timers, Multiple Folders,... Read more
Simon 4.0.2 - Monitor changes and crashe...
Simon monitors websites and alerts you of crashes and changes. Select pages to monitor, choose your alert options, and customize your settings. Simon does the rest. Keep a watchful eye on your... Read more
Cocktail 8.1.2 - General maintenance and...
Cocktail is a general purpose utility for OS X that lets you clean, repair and optimize your Mac. It is a powerful digital toolset that helps hundreds of thousands of Mac users around the world get... Read more
Cyberduck 4.6.4 - FTP and SFTP browser....
Cyberduck is a robust FTP/FTP-TLS/SFTP browser for the Mac whose lack of visual clutter and cleverly intuitive features make it easy to use. Support for external editors and system technologies such... Read more

Playworld Superheroes Review
Playworld Superheroes Review By Tre Lawrence on January 30th, 2015 Our Rating: :: HERO CRAFTINGUniversal App - Designed for iPhone and iPad It’s all about the imagination, fighting bad creatures — and looking good while doing so.   | Read more »
Join the SpongeBob Bubble Party in this...
Join the SpongeBob Bubble Party in this New Match 3 Bubble Poppin’ Frenzy Posted by Jessica Fisher on January 30th, 2015 [ permalink ] | Read more »
Handpick Review
Handpick Review By Jennifer Allen on January 30th, 2015 Our Rating: :: TANTALIZING SUGGESTIONSiPhone App - Designed for the iPhone, compatible with the iPad Handpick will make you hungry, as well as inspire you to cook something... | Read more »
Storm the Halls of Echo Base in First St...
Storm the Halls of Echo Base in First Star Wars: Galactic Defense Event Posted by Jessica Fisher on January 30th, 2015 [ permalink ] Universal App - Designed for iPhone and iPad | Read more »
Contradiction Review
Contradiction Review By Tre Lawrence on January 30th, 2015 Our Rating: :: SPOT THE LIEiPad Only App - Designed for the iPad Contradiction is a live action point and click adventure that’s pretty engaging.   Developer: Tim Follin... | Read more »
Unlock Sunshine Girl in Ironkill with th...
Unlock Sunshine Girl in Ironkill with this special 148Apps code Posted by Rob Rich on January 29th, 2015 [ permalink ] Robo-fighter Ironkill has been out on iOS a | Read more »
Crossroad Zombies Review
Crossroad Zombies Review By Jordan Minor on January 29th, 2015 Our Rating: :: CROSSWALKING DEADiPad Only App - Designed for the iPad Crossroad Zombies is a rough draft of a cool genre mash-up.   | Read more »
Blood Brothers 2 – Tips, Cheats, and Str...
War is hell: Is it the kind of hell you want to check out? Read our Blood Brothers 2 review to find out! Blood Brothers 2, DeNA’s follow-up to the original Blood Brothers, is an intriguing card collecting / role-playing / strategy hybrid. There’s... | Read more »
Blood Brothers 2 Review
Blood Brothers 2 Review By Nadia Oxford on January 29th, 2015 Our Rating: :: AN AGGRAVATING RELATIVEUniversal App - Designed for iPhone and iPad Blood Brothers 2 is built on a simple, solid foundation, but its free-to-play system... | Read more »
I AM BREAD, the Toast of the Town, is Ro...
Have you ever dreamt of being deliciously gluten-y? Do you feel passionate about Rye and Wheat? The guys at Bossa Studios do and that is why they are bringing I AM BREAD to iOS soon. The loafy app will feature all the new content that is being... | Read more »

Price Scanner via MacPrices.net

Amazon offers 15-inch 2.2GHz Retina MacBook P...
 Amazon.com has the 15″ 2.2GHz Retina MacBook Pro on sale for $1879 including free shipping. Their price is $120 off MSRP, and it’s the lowest price available for this model from any reseller (except... Read more
Intel Aims to Transform Workplace With 5th-Ge...
Intel Corporation today announced the availability of its 5th generation Intel Core vPro processor family that provides cutting-edge features to enable a new and rapidly shifting workplace. To meet... Read more
iOS App Sharalike Introduces New Instant Smar...
Sharalike slideshow and photo management software for iOS, is making it easier than ever to create shareable meaningful moments with its new instant SmartShow technology. Staying organized is a goal... Read more
Apple Becomes World’s Largest Smartphone Vend...
According to the latest research data from Strategy Analytics, as global smartphone shipments grew 31 percent annually to reach a record 380 million units in the fourth quarter of 2014. Apple became... Read more
Cut the Cord: OtterBox Resurgence Power Case...
Dead batteries and broken phones are two of the biggest issues for smartphone users today. Otterbox addresses both with the new Resurgence Power Case for Apple iPhone 6, promising to make those panic... Read more
13-inch Retina MacBook Pros on sale for up to...
B&H Photo has 13″ Retina MacBook Pros on sale for $200 off MSRP. Shipping is free, and B&H charges NY sales tax only: - 13″ 2.6GHz/128GB Retina MacBook Pro: $1199.99 save $100 - 13″ 2.6GHz/... Read more
15-inch 2.5GHz Retina MacBook Pro on sale for...
 B&H Photo has the 15″ 2.5GHz Retina MacBook Pro on sale for $2319.99 including free shipping plus NY sales tax only. Their price is $180 off MSRP, and it’s the lowest price available for this... Read more
Back in stock: Refurbished iPod nanos for $99...
The Apple Store has Apple Certified Refurbished 16GB iPod nanos available for $99 including free shipping and Apple’s standard one-year warranty. That’s $50 off the cost of new nanos. Most colors are... Read more
Apple lowers price on refurbished 256GB MacBo...
The Apple Store has lowered prices on Apple Certified Refurbished 2014 MacBook Airs with 256GB SSDs, now available for up to $200 off the cost of new models. An Apple one-year warranty is included... Read more
New Good Management Suite Simplifies Enterpri...
Good Technology has announced the availability of the Good Management Suite, a comprehensive cross-platform solution for organizations getting started with mobile business initiatives. Built on the... Read more

Jobs Board

At-Home Chat Specialist- *Apple* Online Stor...
**Job Summary** At Apple , we believe in hard work, a fun environment, and the kind of creativity and innovation that only comes about when talented people from diverse Read more
Sr. Mac Expert- *Apple* Online Store - Apple...
**Job Summary** The World Wide Apple Online Store (AOS) Sales and Service team is looking for motivated, outgoing, and tech savvy individuals who want to offer Apple Read more
*Apple* Solutions Consultant- Retail Sales (...
**Job Summary** The ASC is an Apple employee who serves as an Apple brand ambassador and influencer in a Reseller's store. The ASC's role is to grow Apple Read more
Event Director, *Apple* Retail Marketing -...
…This senior level position is responsible for leading and imagining the Apple Retail Team's global engagement strategy and team. Delivering an overarching brand Read more
At-Home Chat Specialist- *Apple* Online Stor...
**Job Summary** At Apple , we believe in hard work, a fun environment, and the kind of creativity and innovation that only comes about when talented people from diverse Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.