TweetFollow Us on Twitter

Window Barrier
Volume Number:4
Issue Number:1
Column Tag:ABC's of C

Breaking the Four Window Barrier

By William Rausch, Kennewick, WA

It seems that every good Macintosh example program (of a text editor, graphics program, or whatever) is hung up on the idea of four windows. Of course, those that aren’t such good example programs only use one window! This limit always seems to be a result of the unnecessary use of global data structures.

Most multi-window Macintosh example programs contain some lines that look like:

WindowPtr some_windows[how_many];
data_structure some_data[how_many];

where how_many is defined to be four. The programmer will claim that it is easy to change this number to be as large as necessary, and the application can be easily recompiled. That is fine for the programmer, but what about the end user. He is stuck with whatever number the programmer happens to choose. If the programmer happens to choose a number of windows and data structures that perfectly fits a 512K Macintosh, then the user is probably not able to take advantage of the extra memory of a Macintosh Plus, much less a Macintosh with even more memory.

In actuality, it is not necessary to predefine any number of windows, or the data structures that are associated with them. Since the Macintosh has an operating system that knows all about windows and how to keep track of them, it makes little sense for the application programmer to duplicate this effort.

The window data structure contains a 32-bit field called refCon which Inside Macintosh describes as “the window’s reference value field, which the application may store into and access for any purpose”. One such purpose, which is mentioned but not demonstrated in many books on Macintosh programming, is to store a handle to some application specific data structure which contains the information that is pertinent to that window.

Since every event given to an application by the Event Manager will contain a pointer to the window concerned, there is no need for the application to keep an array of WindowPtrs; and since each window contains a refCon field, there is no need to keep an array of data structures. Instead, allocate the necessary space for the data structure at the time the new window is created, and put its handle in the refCon field of the window’s data structure. Then, whenever an event is processed, just pass the WindowPtr along to the functions which are going to process the event. These functions then can get access to the data structure when they need it.

The code fragments which follow demonstrate the concepts described:

enum window_type
  {
  type_a,
  type_b,
  type_c
  };

typedef union
  {
  struct
    {
    ...         /* type_a window data */
    } a;
  struct
    {
    ...         /* type_b window data */
    } b;
  struct
    {
    ...         /* type_c window data */
    } c;
  } content,*content_ptr,**content_hndl;

typedef struct 
  {
  enum window_type xxx;   /* optional, appl. specific */
  content_hndl yyy;   /* could include union directly */
  ...
  } window_data, *data_ptr, **data_hndl;

...

make_window(type)
enum window_type type;
  {
  WindowRecord *a_window;
  data_hndl a_data;
  content_hndl a_content;
  ...

  a_window = 
    (WindowRecord *)NewWindow(...);
  a_data = 
    (data_hndl)NewHandle(sizeof(w_data));
  a_content = (content_hndl)NewHandle
                       (sizeof(content));
  (**a_data).xxx = type;
  (**a_data).yyy = a_content;
  a_window->refCon = (long)a_data;
  ...
  }

...

event_loop()
  {
  EventRecord the_event;
  WindowPtr which_window;
  int window_code;
  ...

  while (TRUE)
    {
    if (GetNextEvent(everyEvent, 
                     &the_event))
      {
      switch (the_event.what)
        {
        case mouseDown:
        window_code = FindWindow
                      (the_event.where, 
                       &which_window);
        switch (window_code)
          {
          case inSysWindow:
          SystemClick(&the_event,
                      which_window);
          break;
          
          case inContent:
          process_window(which_window);
          break;

          ...
          }
        break;

        ...
        }
      }
    else
      {
      }
    }
  }

...

process_window(the_window)
WindowRecord *the_window;
  {
  data_hndl the_data;
  ...

  the_data = 
      (data_hndl)(the_window->refCon);
  switch ((**the_data).xxx)
    {
    case type_a:
    process_a_window(the_window);
    break;

    case type_b:
    process_b_window(the_window);
    break;

    case type_c:
    process_c_window(the_window);
    break;
    }
  ...
  }

This general technique may, in some very particular cases, slow things down a little. Generally, this won’t be the case because most applications spend a majority of their time processing NULL events. If you wanted to speed things up a little bit and still maintain the dynamic allocation capabilities of this programming approach, use just one globally declared WindowPtr and one data_handle and just update them to always point at the window/data_structure that the current event refers to. Then you wouldn’t have to pass the event’s WindowPtr to the called function(s).

Of course, most applications need to be able to find all of their windows at times, e.g., when Quitting the application so that changes can be saved, or when updating the windows. At those times, it is still possible to avoid using a global array merely by calling FrontWindow() and following the linked list of pointers stored in the nextWindow field of the window’s data structure.

This approach to creating windows in an application, which I call “fire and forget” (and which could be considered as a small first step towards object oriented programming), will allow your application to create as many new windows (and their associated data structures) as the user desires. It is also a convenient way of manipulating different types of windows in a single application. (It is very easy, for example, to imagine MacDraw and MacWrite in a single application!) Of course, your application has to check available memory each time it tries to create a new window/data structure to make sure there is enough available, but that is a small price to pay for the increased utility the user can get from having a program that “grows” with his hardware.

 

Community Search:
MacTech Search:

Software Updates via MacUpdate

BBEdit 11.6.6 - Powerful text and HTML e...
BBEdit is the leading professional HTML and text editor for the Mac. Specifically crafted in response to the needs of Web authors and software developers, this award-winning product provides a... Read more
Brackets 1.9.0 - Open Source Web design...
Brackets is an Open-Source editor for Web design and development built on top of Web technologies such as HTML, CSS, and JavaScript. The project was created and is maintained by Adobe, and is... Read more
Audio Hijack 3.3.4 - Record and enhance...
Audio Hijack (was Audio Hijack Pro) drastically changes the way you use audio on your computer, giving you the freedom to listen to audio when you want and how you want. Record and enhance any audio... Read more
Tunnelblick 3.7.1a - GUI for OpenVPN.
Tunnelblick is a free, open source graphic user interface for OpenVPN on OS X. It provides easy control of OpenVPN client and/or server connections. It comes as a ready-to-use application with all... Read more
Amazon Chime 4.3.5721 - Amazon-based com...
Amazon Chime is a communications service that transforms online meetings with a secure, easy-to-use application that you can trust. Amazon Chime works seamlessly across your devices so that you can... Read more
Posterino 3.3.7 - Create posters, collag...
Posterino offers enhanced customization and flexibility including a variety of new, stylish templates featuring grids of identical or odd-sized image boxes. You can customize the size and shape of... Read more
Airmail 3.2.9 - Powerful, minimal email...
Airmail is an mail client with fast performance and intuitive interaction. Support for iCloud, MS Exchange, Gmail, Google Apps, IMAP, POP3, Yahoo!, AOL, Outlook.com, Live.com. Airmail was designed... Read more
Arq 5.8.4 - Online backup to Google Driv...
Arq is super-easy online backup for Mac and Windows computers. Back up to your own cloud account (Amazon Cloud Drive, Google Drive, Dropbox, OneDrive, Google Cloud Storage, any S3-compatible server... Read more
Microsoft Remote Desktop 8.0.39 - Connec...
With Microsoft Remote Desktop, you can connect to a remote PC and your work resources from almost anywhere. Experience the power of Windows with RemoteFX in a Remote Desktop client designed to help... Read more
Arq 5.8.4 - Online backup to Google Driv...
Arq is super-easy online backup for Mac and Windows computers. Back up to your own cloud account (Amazon Cloud Drive, Google Drive, Dropbox, OneDrive, Google Cloud Storage, any S3-compatible server... Read more

Latest Forum Discussions

See All

Clash of Clans' gets a huge new upd...
Clash of Clans just got a massive new update, and that's not hyperbole. The update easily tacks on a whole new game's worth of content to the hit base building game. In the update, that mysterious boat on the edge of the map has been repaired and... | Read more »
Thimbleweed Park officially headed to iO...
Welp, it's official. Thimbleweed Park will be getting a mobile version. After lots of wondering and speculation, the developers confirmed it today. Thimbleweed Park will be available on both iOS and Android sometime in the near future. There's no... | Read more »
Pokémon GO might be getting legendaries...
The long-awaited legendary Pokémon may soon be coming to Pokémon GO at long last. Data miners have already discovered that the legendary birds, Articuno, Moltres, and Zapdos are already in the game, it’s just a matter of time. [Read more] | Read more »
The best deals on the App Store this wee...
If you’ve got the Monday blues we have just the thing to cheer you up. The week is shaping up to be a spectacular one for sales. We’ve got a bunch of well-loved indie games at discounted prices this week along with a few that are a little more... | Read more »
Honor 8 Pro, a great choice for gamers
Honor is making strides to bring its brand to the forefront of mobile gaming with its latest phone, the Honor 8 Pro. The Pro sets itself apart from its predecessor, the Honor 8, with a host of premium updates that boost the device’s graphical and... | Read more »
The 4 best outdoor adventure apps
Now that we're well into the pleasant, warmer months, it's time to start making the most of the great outdoors. Spring and summer are ideal times for a bit of trekking or exploration. You don't have to go it alone, though. There are plenty of... | Read more »
Things 3 (Productivity)
Things 3 3.0.1 Device: iOS iPhone Category: Productivity Price: $7.99, Version: 3.0.1 (iTunes) Description: Meet the all-new Things! A complete rethinking of the original, award-winning task manager – with a perfect balance between... | Read more »
Oddball mash-up Arkanoid vs Space Invade...
In a move no one was really expecting, Square Enix has put forth an Arkanoid/Space Invaders mash-up aptly titled Arkanoid vs Space Invaders. The game launched today on both iOS and Android and the reviews are actually quite good. [Read more] | Read more »
Arkanoid vs Space Invaders (Games)
Arkanoid vs Space Invaders 1.0 Device: iOS Universal Category: Games Price: $3.99, Version: 1.0 (iTunes) Description: LAUNCH SALE: GET THE GAME AT 20% OFF! Two of the most iconic classic games ever made meet in Arkanoid vs Space... | Read more »
The best new games we played this week
Things got off to a bit of a slow start this week, but as we steadily creep towards Friday a bunch of great games have started cropping up. If you're looking for a quality new release to play this weekend, we've got you covered. Here's a handy... | Read more »

Price Scanner via MacPrices.net

touchbyte Releases PhotoSync 3.2 for iOS With...
Hamburg, Germany based touchbyte has announced the release of PhotoSync 3.2 for iOS, a major upgrade to the versatile and powerful app to transfer, backup and share photos and videos over the air.... Read more
Emerson Adds Touchscreen Display and Apple Ho...
Emerson has announced the next evolution of its nationally recognized smart thermostat. The new Sensi Touch Wi-Fi Thermostat combines proven smarthome technology with a color touchscreen display and... Read more
SurfPro VPN for Mac Protects Data While Offer...
XwaveSoft has announced announce the release and immediate availability of SurfPro VPN 1.0, their secure VPN client for macOS. SurfPro VPN allows Mac users to protect their internet traffic from... Read more
13-inch Touch Bar MacBook Pros on sale for $1...
B&H Photo has 13″ MacBook Pros in stock today for up to $150 off MSRP. Shipping is free, and B&H charges NY & NJ sales tax only: - 13″ 2.9GHz/512GB Touch Bar MacBook Pro Space Gray (... Read more
Tuesday deal: $200 off 27-inch Apple iMacs
Amazon has select 27″ iMacs on sale for $200 off MSRP, each including free shipping: - 27″ 3.3GHz iMac 5K: $2099 $200 off MSRP - 27″ 3.2GHz/1TB Fusion iMac 5K: $1799 $200 off MSRP Keep an eye on our... Read more
Five To Six Million 10.5-inch iPad Pro Tablet...
Digitimes’ Siu Han and Joseph Tsai report that upstream supply chain shipments for Apple’s new 10.5-inch iPad Pro have been increasing, with monthly shipment volume expected to hit 600,000 units by... Read more
Georgia Tech Students Win Toyota and Net Impa...
Earlier this year, a team of students at Georgia Tech realized that there was a critical gap in transportation services for people who use wheelchairs, and wondered if the solution could be in the... Read more
13-inch 2.0GHz Space Gray MacBook Pro on sale...
Amazon has the 13″ 2.0GHz Space Gray non-Touch Bar MacBook Pro (MLL42LL/A) on sale for $1299.99 including free shipping. Their price is $200 off MSRP, and it’s currently the lowest price available... Read more
Roundup of 15-inch MacBook Pro sale prices, m...
B&H Photo has the new 2016 15″ Apple Touch Bar MacBook Pros in stock today and on sale for up to $200 off MSRP. Shipping is free, and B&H charges NY & NJ sales tax only: - 15″ 2.7GHz... Read more
15-inch 2.2GHz Retina MacBook Pro on sale for...
B&H Photo has the 2015 15″ 2.2GHz Retina MacBook Pro (MJLQ2LL/A) on sale for $1849 including free shipping plus NY & NJ sales tax only. Their price is $150 off MSRP. Read more

Jobs Board

*Apple* Media Products - Commerce Engineerin...
Apple Media Products - Commerce Engineering Manager Job Number: 57037480 Santa Clara Valley, California, United States Posted: Apr. 18, 2017 Weekly Hours: 40.00 Job Read more
*Apple* Technical Support - Atrilogy (United...
Our direct client is looking for an Apple Technical Support / Apple Help Desk Specialist for a Full Time Direct Hire role in West Los Angeles by Playa Vista, CA Read more
*Apple* Media Products - Commerce Engineerin...
Apple Media Products - Commerce Engineering Manager Job Number: 57037480 Santa Clara Valley, California, United States Posted: Apr. 18, 2017 Weekly Hours: 40.00 Job Read more
Director *Apple* Platform, IS Data Manageme...
…a real difference. Come, shine with us! Astellas is announcing a Director Apple Platform, IS Data Management Lead opportunity in Northbrook, IL. Purpose & Scope: Read more
Director *Apple* ERP Integration Lead - Ast...
…make a real difference. Come, shine with us! Astellas is announcing a Director Apple ERP Integration Lead opportunity in Northbrook, IL. Purpose & Scope: This role Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.