TweetFollow Us on Twitter

XCMD Libraries
Volume Number:5
Issue Number:6
Column Tag:HyperChat™

XCMD Corner: XCMD Libraries

By Donald Koscheka, Arthur Young & Co., MacTutor Contributing Editor

Modularity and Coupling

As you to explore XCMDs, you should continue to discover new and interesting properties of these routines. Two properties are particularly noteworthy because they lead to code that is usable outside of Hypercard. They are strong modularity and weak coupling.

You determine the modularity of a routine by counting the number of tasks it performs. Strongly modular routines handle one task. If you were writing a spreadsheet program, you would most likely separate the routine that calculates the value of a cell from the routine that displays that value. Combining these functions results in weak modularity. Weakly modular code is hard to debug because you can easily lose track of what the routine is doing at a given point.

Coupling describes how the program interacts with the outside world. Weakly coupled routines operate only on data passed as formal parameters. Weak coupling eliminates harmful side-effects caused by relying on global memory. Weakly coupled programs force you to think over how and when to pass data back and forth.

Well written XCMDs exhibit both strong modularity and weak coupling. Most XCMDs perform one task (strongly modular XCMDs), typically to add a missing feature to Hypertalk. XCMDs interface to Hypertalk using a very strict protocol, passing parameters via the command block record. This protocol coerces weakly coupling in your code.

Software Breadboard

Strong modularity and weak coupling suggest that you can create libraries of useful routines for use both in Hypercard and in programs of your own design. Think of Hypercard as a “Software Breadboard”, a test platform that you plug code into for checkout and debugging. Once working, the routine can be dropped into any application.

An example of a set of routines that play well in this scenario are the calls to the File Manager. Every (non-trivial) application needs to call on the file manager to open a file, access information in the file and then close it. I decided to build my case around accessing a file because Hypercard itself doesn’t handle files “according to Hoyle”. Hypercard violates two precepts of the user interface guidelines when opening a file: (1) The user is required to know the full pathname of a file if it is not in the current working directory and (2) the OpenFile command performs an unexpected action; if it cannot find the file, it creates it!

In order to properly open a file, you first present the user with a dialog that contains the list of files in the current working directory. This dialog allows the user to flip from drive to drive as well as change directories. The standard file package provides you with the “vanilla” get file dialog. When the user selects a file and clicks the “Open” button, your code queries the reply record to discover the file’s name, working directory id and file type.

The working directory id pinpoints which folder contains the document. If you made a killing on Macintosh software and have been away on some deserted island for the past several years, the working directory assumes the role traditionally held by the volume reference number.

Given the file name and working directory, you can reconstruct and return the full pathname to Hypercard so that it can be used by Hypercard’s “open” command (pathname reconstruction is the subject of a future article). However, it’s just as easy to open the file ourselves to ensure that it opens in whatever manner is expected on the Macintosh. The XCMD that opens the file is left as an exercise.

GetFileName XFCN

The XFCN, GetFileName (Listing 1), displays strong modularity - its sole task is to get the name of a file from the user. By relying only on data passed to it formally, it also demonstrates weak coupling. This XFCN provides a general purpose technique for getting the name of a file from the user. GetFileName calls on a routine Called GetFileNametoLoad in HyperUtils.c (listing 2). The prototypes for HyperUtils are found in HyperUtils.h (listing 3). HyperUtils contains a set of re-usable utilities that do not presume the existence of Hypertalk. These routines aren’t encumbered with the XCmdBlkPtr interface.

GetFileNameToLoad accepts as its inputs a list of file types (up to 4) to filter out in the open dialog. If you were writing a text import routine, you might want to present the user with only files of type ‘TEXT’. From Hypercard, you would then invoke GetFileName as:

--1

 Put GetFileName( “TEXT” ) into it;  IF it is not empty then -- User 
selected a file  put item 1 of it into FileName          put item 2 of 
it into FolderID end if 

With little effort, we’ve created a re-usable, general purpose XCMD. Pass the name and the FolderID to any File Manager call that requires the file’s name and volume reference number (aka working directory id). I will call upon this XCMD in future editions of this column so you’ll have ample opportunity to see it action.

An obvious addition to this list an xcmd that asks the user for the name of a file to save by calling SFPutFile. This is a simple modification to GetFileNameToLoad so I’ll leave it as yet another exercise.

After creating enough XCMDs, you’ll soon view them as general purpose routines with a specific interface (XCmdBlkPtr) to HyperTalk. With this in mind, you should have no trouble creating XCMD libraries that can be used in other applications. Get in the habit of separating the Hypertalk interface, including any callbacks, from the action code. The XCMD itself then becomes an interface between HyperTalk and your code.

Listing 1:  GetFileName.c
/********************************/
/* File: GetFileName.c    */
/* */
/* Using Standard File Package*/
/* query the user for the name*/
/* of a file to open, and return*/
/* the name along with the  */
/* working directory id of the*/
/* file.*/
/* Paramters:    */
/* paramCnt = number of types */
/* params[0..3] = the types to   */
/* filter for (see Inside Mac.*/
/* I-523 for details */ 
/* ----------------------------  */
/* To Build:*/
/* (1) Create a project using */
/* this file as well as the */
/* XCMD.Glue.c file. (Set */
/* project type to XCMD (or */
/* XFCN) from the Project menu.  */
/* */
/* (2) Bring the project up to*/
/* date.*/
/* (3) Build Code Resource. */
/* (4) Use ResEdit to copy the   */
/* resource to your stack.*/
/********************************/

#include<MacTypes.h>
#include<OSUtil.h>
#include<MemoryMgr.h>
#include<FileMgr.h>
#include<ResourceMgr.h>
#include<pascal.h>
#include<strings.h>
#include  “HyperXCmd.h”
#include“HyperUtils.h”

pascal void main( paramPtr )
 XCmdBlockPtr  paramPtr;
{
 short  FileWDID;
 short  numTypes;
 short  i;
 SFTypeList typs;
 char   FileName[256];
 char   WDIDString[32];
 char   comma[2];
 
 if( !paramPtr->paramCount )
 numTypes = -1;  /* select all since no type specified */
 else{
 numTypes = paramPtr->paramCount;
 for( i = 0; i < numTypes; i++ )
 BlockMove( *(paramPtr->params[i]), &typs[i], 4L );
 }
 
 *FileName = ‘\0’;
 
 if( GetFileNameToOpen( typs, numTypes, FileName, &FileWDID ) ){
 NumToStr( paramPtr, (long)FileWDID, &WDIDString );
 PtoCstr( WDIDString );
 
 comma[0] = ‘,’; /* for you MPW folk */
 comma[1] = ‘\0’;
 
 strcat( FileName, comma );
 strcat( FileName, WDIDString );
 CtoPstr( FileName );
 }
 paramPtr->returnValue = PasToZero( paramPtr, FileName );
}
Listing 2:  HyperUtils.c

/****************************/
/* HyperUtils.c  */
/* A collection of useful */
/* routines...   */
/****************************/
#include<MacTypes.h>
#include<OSUtil.h>
#include<MemoryMgr.h>
#include<FileMgr.h>
#include<ResourceMgr.h>
#include<StdFilePkg.h>
#include  “HyperXCmd.h”
#include  “HyperUtils.h”

void  CenterWindow( wptr )
 WindowPtrwptr;
/***************************
* Center a window in the current
* screen port.  Note: Does not
* attempt to work with multi-screen
* systems.
*
* This code is inspired by a
* similar routine written by Steve
* Maller in MPW Pascal.  Thanks Steve.
***************************/
{
 short  hWindSize = wptr->portRect.right - wptr->portRect.left;
 short  vWindSize = wptr->portRect.bottom - wptr->portRect.top;
 short  hSize = wptr->portBits.bounds.right - wptr->portBits.bounds.left;
 short  vSize = wptr->portBits.bounds.bottom - wptr->portBits.bounds.top;
 
 MoveWindow( wptr, 
 ( hSize - hWindSize ) / 2, 
 ( vSize - vWindSize + 20) / 2,
 false
 );
}

void Concat( str1, str2 )
 char *str1;
 char *str2;
/*****************************
* Append string 2 to the end of
* string 1.  Both strings are 
* pascal-format strings.
*
* str1 must be large enough to hold
* the new string and is assumed to 
* be of Type Str255 (a pascal string)
*****************************/
{
 short len1 = *str1; /***number of chars in str 1***/
 short len2 = *str2++;/***number of chars in str 2***/
 char  *temp;  /*** string pointer ***/
 
 *str1 += len2 + 1;/*** add sizes to get new size***/

 temp = str1 + len1 + 1;/*** move to end of str 1***/
 while( len2 ){
 *temp++ = *str2++;/*** add char to temp & move***/
 --len2;/*** until all characters are added***/
 }

}

void  CopyPStr( pStr1, pStr2 )
 char *pStr1;
 char *pStr2;
/****************************
* Copy the contents of pstr1 into
* pstr2.  The strings are assumed 
* to be of type STR255 (length byte
* precedes data 
*
****************************/
{short  i;
 char *tstr;
 
 tstr = pStr2;
 
 for( i = 0; i <= *pStr1; i++ )
 *tstr++ = *pStr1++;
}

short GetFileNameToOpen( typs, typCnt,theName, theWDID )
 SFTypeList typs;
 short  typCnt;
 char   *theName;
 short  *theWDID;
/*****************************
* Invokes SFOpenFile to query the 
* user for the name of a file to 
* open. 
*
* In:   List of types of files to
*filter for (up to 4)
* Out:  fileName if picked in theName
*working directory in theWDID
*nil otherwise
*the file’s volum ref num.
* ( Note that the space for the 
* string must be allocated by the
* caller).
*****************************/
{
 Point  where;
 char   prompt[1];
 SFReplyreply;
 GrafPort *oldPort;
 WindowPtrdlogID;
 
 prompt[0]  = ‘\0’;
 
 /*** Get and put up the standard file ***/
 /*** dialog.  You will only see the file***/
 /*** types that you filtered for.  If ***/
 /*** you filtered for no files, then  ***/
 /*** all files will display***/
 
 GetPort( &oldPort );
 dlogID = GetNewDialog( (short)getDlgID, (Ptr)NIL, (Ptr)UPFRONT );
 
 SetPort( dlogID );
 CenterWindow( dlogID );
 where.h = dlogID->portRect.left;
 where.v = dlogID->portRect.top;
 LocalToGlobal( &where );
 
 SFGetFile( where, prompt, (Ptr)NIL, typCnt, typs, (Ptr)NIL, &reply );
 
 DisposDialog( dlogID );
 SetPort( oldPort );
 
 /*** If the user selected a file, let’s ***/
 /*** get the information about it ***/
 
 if (reply.good){
 *theWDID = reply.vRefNum;
 PtoCstr( (char *)&reply.fName );
 strcpy( theName, &reply.fName  );
 }
 return( reply.good );
}
Listing 3:  HyperUtils.H

/********************************/
/* HyperUtils.H  */
/* Header file for HyperUtils.c  */
/* routines...   */
/********************************/

#define NIL 0L
#define UPFRONT  -1L

void  CenterWindow( WindowPtr wptr );
void  Concat( char * str1, char * str2 );
void  CopyPStr( char * pStr1, char * pStr2 );
short GetFileNameToOpen(SFTypeList typs,short typcnt, char *theName, 
short *theWDID);

NOTE: From Jul 89 Jorg Column

Note on a bug in last month’s article:

Last month’s XFCN, GetFileName, incorrectly returns the working directory id of the file selected from SFGetFile. Change the call to GetFileNameToOpen to Read:

if( GetFileNameToOpen(typs,numTypes,FileName,&FileWDID ) ){
 temp = (long)FileWDID & 0xFFFF;
 NumToStr( paramPtr, temp, &WDIDString );
 PtoCstr( WDIDString );

 
AAPL
$103.30
Apple Inc.
+0.80
MSFT
$45.09
Microsoft Corpora
-0.34
GOOG
$577.33
Google Inc.
+5.73

MacTech Search:
Community Search:

Software Updates via MacUpdate

TextSoap 7.4.0 - Flexible text editing u...
TextSoap is for people who work with text. TextSoap effortlessly cleans up text from endlessly different formats. Wash away unwanted characters, spaces, tabs. Fix paragraphs with hard returns at the... Read more
NetShade 6.0.2 - Browse privately using...
NetShade is an Internet security tool that conceals your IP address on the web. NetShade routes your Web connection through either a public anonymous proxy server, or one of NetShade's own dedicated... Read more
Mac DVDRipper Pro 5.0 - Copy, backup, an...
Mac DVDRipper Pro is the DVD backup solution that lets you protect your DVDs from scratches, save your batteries by reading your movies from your hard disk, manage your collection with just a few... Read more
pwSafe 3.1 - Secure password management...
pwSafe provides simple and secure password management across devices and computers. pwSafe uses iCloud to keep your password databases backed-up and synced between Macs and iOS devices. It is... Read more
StatsBar 1.8 - Monitor system processes...
StatsBar gives you a comprehensive and detailed analysis of the following areas of your Mac: CPU usage Memory usage Disk usage Network and bandwidth usage Battery power and health (MacBooks only)... Read more
Path Finder 6.5.5 - Powerful, award-winn...
Path Finder is a file browser that combines the familiar Finder interface with the powerful utilities and innovative features. Just a small selection of the Path Finder 6 feature set: Dual pane... Read more
QuarkXPress 10.2.1 - Desktop publishing...
With QuarkXPress, you can communicate in all the ways you need to -- and always look professional -- in print and digital media, all in a single tool. Features include: Easy to Use -- QuarkXPress is... Read more
Skype 6.19.0.450 - Voice-over-internet p...
Skype allows you to talk to friends, family and co-workers across the Internet without the inconvenience of long distance telephone charges. Using peer-to-peer data transmission technology, Skype... Read more
VueScan 9.4.41 - Scanner software with a...
VueScan is a scanning program that works with most high-quality flatbed and film scanners to produce scans that have excellent color fidelity and color balance. VueScan is easy to use, and has... Read more
Cloud 3.0.0 - File sharing from your men...
Cloud is simple file sharing for the Mac. Drag a file from your Mac to the CloudApp icon in the menubar and we take care of the rest. A link to the file will automatically be copied to your clipboard... Read more

Latest Forum Discussions

See All

Modern Combat 5 Gets a Major Multiplayer...
Modern Combat 5 Gets a Major Multiplayer Update Posted by Jessica Fisher on September 2nd, 2014 [ permalink ] Universal App - Designed for iPhone and iPad | Read more »
Alien Creeps TD Review
Alien Creeps TD Review By Jennifer Allen on September 2nd, 2014 Our Rating: :: EXPENSIVE DEFENSESUniversal App - Designed for iPhone and iPad Alien Creeps TD would be a fun if unremarkable Tower Defense game, but its heavy focus on... | Read more »
The Journey Down: Chapter Two Review
The Journey Down: Chapter Two Review By Jennifer Allen on September 2nd, 2014 Our Rating: :: DARK YET ENTICINGUniversal App - Designed for iPhone and iPad It’s a little dark, in every sense of the word, but The Journey Down:... | Read more »
Function Space, a Social Network App for...
Function Space, a Social Network App for Science, Launches on iOS Posted by Ellis Spice on September 2nd, 2014 [ permalink ] | Read more »
Stupidfast – How Taylor Martinez Switche...
How do you make an Endless Running game more than just another Endless Running game? By adding real life prizes to it, of course! That’s the thinking behind StupidFast: a game designed for football enthusiasts, and the brainchild of former college... | Read more »
Little Raiders: Robin’s Revenge Review
Little Raiders: Robin’s Revenge Review By Jennifer Allen on September 2nd, 2014 Our Rating: :: CASUAL RAIDINGUniversal App - Designed for iPhone and iPad Combining simple combat with village building is a potent combination for... | Read more »
Treasure Tombs: Ra Deal Coming from Bulk...
Treasure Tombs: Ra Deal Coming from Bulkypix and Dark Tonic This Fall Posted by Jessica Fisher on September 2nd, 2014 [ permalink ] Dark Tonic and | Read more »
Pirate Bash Review
Pirate Bash Review By Nadia Oxford on September 2nd, 2014 Our Rating: :: BAD PIRATES, GOOD TIMESUniversal App - Designed for iPhone and iPad Pirate Bash’s turn-based battles add an intriguing twist to a typical physics game.   | Read more »
Tiny Tower Vegas Review
Tiny Tower Vegas Review By Jennifer Allen on September 2nd, 2014 Our Rating: :: STEADY DEVELOPMENTUniversal App - Designed for iPhone and iPad Build a huge tower again but Vegas-style in Tiny Tower Vegas.   | Read more »
The Manhattan Project Review
The Manhattan Project Review By Andrew Fisher on September 2nd, 2014 Our Rating: :: ROCKET SCIENCEUniversal App - Designed for iPhone and iPad The Manhattan Project offers a great Euro-style gameplay experience, but it is totally... | Read more »

Price Scanner via MacPrices.net

Apple refurbished iPads available for up to $...
Apple is offering Certified Refurbished iPad Airs for up to $140 off MSRP. Apple’s one-year warranty is included with each model, and shipping is free. Stock tends to come and go with some of these... Read more
Are We Now In The Post-Post-PC Era?
A longtime and thoroughgoing laptop aficionado, I was more than a little dismayed by Steve Jobs’s declaration back in 2010 when he sprang the iPad on an unsuspecting world. that we’d entered a “post-... Read more
PC Outlook Improves, But 2014 Shipments Still...
According to the International Data Corporation (IDC) Worldwide Quarterly PC Tracker, worldwide PC shipments are expected to fall by -3.7 percent in 2014. To hat’s actually an improvement from the... Read more
IDC Lowers Tablet Sales Projections for 2014...
Following a second consecutive quarter of softer than expected demand, International Data Corporation (IDC) has lowered its worldwide tablet plus 2-in-1 forecast for 2014 to 233.1 million units. The... Read more
Apple now offering refurbished 21-inch 1.4GHz...
The Apple Store is now offering Apple Certified Refurbished 21″ 1.4GHz iMacs for $929 including free shipping plus Apple’s standard one-year warranty. Their price is $170 off the cost of new models,... Read more
Save $50 on the 2.5GHz Mac mini, on sale for...
B&H Photo has the 2.5GHz Mac mini on sale for $549.99 including free shipping. That’s $50 off MSRP, and B&H will also include a free copy of Parallels Desktop software. NY sales tax only. Read more
Save up to $300 on an iMac with Apple refurbi...
The Apple Store has Apple Certified Refurbished iMacs available for up to $300 off the cost of new models. Apple’s one-year warranty is standard, and shipping is free. These are the best prices on... Read more
The Rise of Phablets
Carlisle & Gallagher Consulting Group, a businesses and technology consulting firm focused solely on the financial services industry, has released an infographic depicting the convergence of... Read more
Bad Driver Database App Allows Good Drivers t...
Bad Driver Database 1.4 by Facile Group is a new iOS and Android app that lets users instantly input and see how many times a careless, reckless or just plain stupid driver has been added to the... Read more
Eddy – Cloud Music Player for iPhone/iPad Fre...
Ukraine based CapableBits announces the release of Eddy, its tiny, but smart and powerful cloud music player for iPhone and iPad that allows users to stream or download music directly from cloud... Read more

Jobs Board

*Apple* Retail - Multiple Positions (US) - A...
Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, you're also the Read more
*Apple* Retail - Multiple Positions (US) - A...
Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, you're also the Read more
*Apple* Retail - Multiple Positions (US) - A...
Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, you're also the Read more
*Apple* Retail - Multiple Positions (US) - A...
Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, you're also the Read more
Senior Event Manager, *Apple* Retail Market...
…This senior level position is responsible for leading and imagining the Apple Retail Team's global event strategy. Delivering an overarching brand story; in-store, Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.