TweetFollow Us on Twitter

May 94 - Handling Preferences

Handling Preferences

Bob Hablutzel

I have something new for you this month. So far, all my articles have been MacApp-based. This month, I am going to present a generic C++ class. Actually; if you get the source code diskettes, you will get two versions of this generic class - one for the standard system header files, and one for the MacApp 3.0.1 header files. The differences are syntactic and minor; I'm just saving you the work of making the changes yourself.

The Issue

The problem to solve this month is handling user preferences. One of the marks of a good Macintosh program is the maintenance of a preference file in the preferences folder. This file can contains the information that describes how the user has customized the application for the way they work.

In general, this information can be neatly captured in resources. The data is fairly small, and usually broken into chunks that different parts of the application access. The code I present here handles preferences as resources.

Let's talk briefly about the zen of preferences. Preferences may or may not have default values. The user's company name, for example, is rarely defaulted. (The user's name can-and should-be obtained from the name entered under Sharing Setup). The color for comments in code could, however, be defaulted; the user has the option of overriding this default.

There needs to be a place for storing these default values. Generally, the application resource fork is the best, most convenient place for this. This is simply done by storing the preset preference resource in the application; when the application goes to access the preference it will be found in the application until a new resource is created in the preference file.

For saving changed resources, however, the application resource fork cannot be used. Since applications might be run from a read only volume, such as file servers; any attempt to write to the application would fail. Also, remember that in a server environment there might be multiple users of a single copy of an application. We want the preferences from each user to remain separate and distinct.

We are then left with two different strategies: one for reading and one for writing. When reading, the code needs to first look in the preference file, if any, and then in the application. Reads should not fail if the preferences file is not there. When writing, the code needs to write the resource directly to the preferences file, creating it if necessary. Additionally, the code needs to check to see if there is an existing preference resource in the preference file; this resource will need to be deleted if it exists.

The class I have written is designed to be generic. In particular, it makes no assumptions about the failure handling mechanism of the framework you are using. It therefore does not signal errors in any coherent manner. Read errors are signaled by returning a NULL handle; write operations fail silently.

This is probably not as bad a situation as you might think. Remember that preferences are generally fairly lightweight data. The application can execute without reading or writing preference information; it will simply use default information instead. (Of course, if the application is counting on a default preference resource to be there, and it's not, there might be problems. But this case means that the application resource fork is not in the state the application assumes it is in, which is probably a problem in any case).

It would be fairly trivial to enhance this code with failures, if you had the interest. If enough people tell me they are interested in a failure handler based version of this code, I will write it for inclusion in a future source diskette.

The Class

This class is used by declaring a stack based object of class CPreferencesHandler. The class takes a single argument, which is the ident of a resource of type 'Prfl'. This resource describes the resource file in case the preferences handle needs to create the file; it includes the name of the file, the type and creator, and the script system. The file will be created in the preferences folder, as specified by a FindFolder call. The resource also includes a string to include in the file for the Finder to display when the file is clicked upon.

The reason that the file name needs to be included is that the user might well change the name of the application. We don't want to have the problem of losing the preferences file if the user does so. So we make sure we always look for the same file. The file type and creator are needed because the Human Interface Guidelines say that the application should not be launched if the preferences file is double clicked upon. Since the preferences file is not the same as the document type for the application, the application will most likely get confused anyhow. So the recommended tactic is to register a creator for the preferences file and never create an application that can open this type. Then, when the Finder goes to open the file, it will fail, and post up the string specified as part of the 'Prfl' resource. This string will let the user know that the file could not be opened as it is a preference file.

Once the object has been declared, reading and writing preference resources is trivial. To read, the ReadPreference method is invoked. This opens the preference file, if any, and attempts to read the resource. If the resource or preference file could not be read, then the method attempts to read from the application. If the resource could not be found in either place, NULL is returned.

Writing resource is just as easy. In the case of writing, the handle is passed along with the type and ident of the resource. The preference file is created, if necessary, and any old copies of the resource are deleted.

A couple of final notes. This class is a little inefficient in a number of ways. First, it insists on continually opening and closing the resource file for each read/write. Also, it does not check to see if the file is already open before opening it; this could lead to the file getting closed behind someone's back. I have an idea for fixing both these problems, but that is next months column. Preferences files are special enough that these limitations should not prevent you from using the class as it is, and I promise that the interfaces for the class will not change when the new version comes out.

In any case, these classes reduce the headache of preferences files down to a couple of simple calls; the class hides all the complexity (as it should). I have found these classes to be extremely useful; I hope you will too.

**** Sidebar ***

//  Declare the preference file data type
typedef struct
{
    OSType                      creator;
    OSType                      type;
    short                       script;
    short                       fileOpenCommentIdent;
    Str31                       fileName;
} PreferencesFileData, *PreferencesFileDataPtr,
    **PreferencesFileDataHandle;

//  Declare our class
class   CPreferencesHandler
{
public:
    CPreferencesHandler(
        short   preferencesFileDataIdent = 128 );
    ~CPreferencesHandler( void );

    //  ReadPreference is called to get a resource from the 
    //  preferences file, if available, or from the application,
    // if available.
    Handle ReadPreference(
        OSType          resourceType,
        short           resourceIdent );

    //  WritePreference is called to write a resource to the
    //  preferences file, creating it if neccessary
    void WritePreference(
        Handle              preference,
        OSType              resourceType,
        short               resourceIdent,
        const Str255&   resourceName );

private:

    //  GetApplicationResource is called to get a resource from the
    //  application file
    Handle GetApplicationResource(
        OSType          resourceType,
        short           resourceIdent );

    //  fPreferencesFileSpec contains the preferences file spec
    FSSpec                          fPreferencesFileSpec;

    //  fSpecificationValid contains TRUE if the specification is
    //  valid - the preferences file name could be found.
    Boolean                         fSpecificationValid;

    //  fPrefData contains a handle to the preferences data
    PreferencesFileDataHandle       fPrefData;
};
 

Community Search:
MacTech Search:

Software Updates via MacUpdate

VOX 2.8.30 - Music player that supports...
VOX just sounds better! The beauty is in its simplicity, yet behind the minimal exterior lies a powerful music player with a ton of features and support for all audio formats you should ever need.... Read more
Default Folder X 5.1.6b3 - Enhances Open...
Default Folder X attaches a toolbar to the right side of the Open and Save dialogs in any OS X-native application. The toolbar gives you fast access to various folders and commands. You just click on... Read more
CleanMyMac 3.8.6 - $39.95
CleanMyMac makes space for the things you love. Sporting a range of ingenious new features, CleanMyMac lets you safely and intelligently scan and clean your entire system, delete large, unused files... Read more
Postbox 5.0.17 - Powerful and flexible e...
Postbox is a new email application that helps you organize your work life and get stuff done. It has all the elegance and simplicity of Apple Mail, but with more power and flexibility to manage even... Read more
Amazon Chime 4.6.5852 - 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
coconutBattery 3.6.3 - Displays info abo...
With coconutBattery you're always aware of your current battery health. It shows you live information about your battery such as how often it was charged and how is the current maximum capacity in... Read more
VueScan 9.5.82 - 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
Thunderbird 52.3.0 - Email client from M...
As of July 2012, Thunderbird has transitioned to a new governance model, with new features being developed by the broader free software and open source community, and security fixes and improvements... Read more
Little Snitch 4.0.2 - Alerts you about o...
Little Snitch gives you control over your private outgoing data. Track background activity As soon as your computer connects to the Internet, applications often have permission to send any... Read more
Thunderbird 52.3.0 - Email client from M...
As of July 2012, Thunderbird has transitioned to a new governance model, with new features being developed by the broader free software and open source community, and security fixes and improvements... Read more

The best games we played this week - Aug...
Another busy week has come to a close. We played a lot of excellent games this week and now it's time to look back and reflect on some our favorites. Here are our picks for the week of August 18. [Read more] | Read more »
War Wings beginner's guide - how to...
War Wings is the newest project from well-established game maker Miniclip. It's a World War II aerial dogfighting game with loads of different airplane models to unlock and battle. The game offers plenty of single player and multiplayer action. We... | Read more »
How to win every 2v2 battle in Clash Roy...
2v2 is coming back to Clash Royale in a big way. Although it's only been available for temporary periods of time, 2v2 has seen a hugely positive fan response, with players clamoring for more team-based gameplay. Soon we'll get yet another taste of... | Read more »
Roll to Win with Game of Dice’s new upda...
Joycity’s hit Game of Dice gets a big new update this week, introducing new maps, mechanics, and even costumes. The update sets players loose on an exciting new map, The Cursed Tower, that allows folks to use special Runes mid-match. If you feel... | Read more »
Bottom of the 9th (Games)
Bottom of the 9th 1.0.1 Device: iOS iPhone Category: Games Price: $4.99, Version: 1.0.1 (iTunes) Description: Play the most exciting moment of baseball in this fast-paced dice and card game! | Read more »
The best apps for viewing the solar ecli...
If you somehow missed the news, many parts of the United States will be witness to a total solar eclipse on August 21 for the first time in over 90 years. It'll be possible to see the eclipse in at least some capacity throughout the continental U... | Read more »
The 5 best mobile survival games
Games like ARK: Survival Evolved and Conan Exiles have taken the world of gaming by storm. The market is now flooded with hardcore survival games that send players off into the game's world with nothing but maybe the clothes on their back. Never... | Read more »
Portal Walk (Games)
Portal Walk 1.0 Device: iOS Universal Category: Games Price: $1.99, Version: 1.0 (iTunes) Description: Portal Walk is adventure and relaxing platform game about Eugene. Eugene stuck between worlds and trying to find way back home.... | Read more »
Technobabylon (Games)
Technobabylon 1.0 Device: iOS Universal Category: Games Price: $4.99, Version: 1.0 (iTunes) Description: City of Newton, 2087. Genetic engineering is the norm, the addictive Trance has replaced almost any need for human interaction,... | Read more »
5 reasons why 2v2 is the best mode in Cl...
Supercell has been teasing fans with 2v2 windows that allow players to team up for limited periods of time. The Summer of 2v2 was just this past July, but players are already clamoring for more of that sweet, sweet team-based action. The fans have... | Read more »

Price Scanner via MacPrices.net

Back To School With The Edge Desk All-in-one...
Back to school is just around the corner, and the ergonomically correct Edge Desk all-in-one portable kneeling desk is ideal for students living in dorms and small apartments, Edge Desk features:... Read more
Norton Core Secure Wi-Fi Router Now Available...
First introduced at the 2017 Consumer Electronics Show (CES), Norton Core, a secure, high-performance Wi-Fi router, fundamentally changed the concept of Wi-Fi routers by making security the primary... Read more
ViewSonic Adds New 27-inch 4K UHD Monitor to...
ViewSonic Corp. has introduced the VP2785-4K, a 27-inch 4K UHD (3840×2160) monitor that delivers precise and consistent color representation and performance to ensure incredible image quality. Built... Read more
Apple now offering Certified Refurbished 2017...
Apple is now offering Certified Refurbished 2017 27″ iMacs for up to $350 off original MSRP. Apple’s one-year warranty is standard, and shipping is free. The following models are available: – 27″ 3.... Read more
13-inch 2.3GHz MacBook Pros on sale for $100...
Amazon has the new 2017 13″ 2.3GHz MacBook Pros on sale today for $100 off MSRP, each including free shipping: – 13″ 2.3GHz/128GB Space Gray MacBook Pro (MPXQ2LL/A): $1199.99 $100 off MSRP – 13″ 2.... Read more
Clearance 2016 13-inch MacBook Airs available...
B&H Photo has clearance 2016 13″ MacBook Airs available for up to $200 off original MSRP. Shipping is free, and B&H charges NY & NJ sales tax only: – 13″ 1.6GHz/128GB MacBook Air (MMGF2LL... Read more
Clearance 21-inch and 27-inch iMacs available...
B&H Photo has clearance 21″ and 27″ Apple iMacs available for up to $500 off original MSRP, each including free shipping plus NY & NJ sales tax only: – 27″ 3.3GHz iMac 5K: $1799 $500 off... Read more
New iOS 11 Productivity Features Welcome But...
The iOS community is in late summer holding mode awaiting the September arrival of the iPhone 8 and iOS 11. iOS 11 public betas have been available for months — number six was released this week —... Read more
Samsung Electronics Launches New Portable SSD...
Samsung Electronics America, Inc. has announced the launch of Samsung Portable SSD T5 – its newest portable solid state drive (PSSD) that raises the bar for the performance of external memory... Read more
TrendForce Reports YoY Gain of 3.6% for 2Q17...
Market research firm TrendForce reports that the global notebook shipments for this second quarter registered a sequential quarterly increase of 5.7% and a year-on-year increase of 3.6%, totaling 39.... Read more

Jobs Board

Development Operations and Site Reliability E...
Development Operations and Site Reliability Engineer, Apple Payment Gateway Job Number: 57572631 Santa Clara Valley, California, United States Posted: Jul. 27, 2017 Read more
Frameworks Engineering Manager, *Apple* Wat...
Frameworks Engineering Manager, Apple Watch Job Number: 41632321 Santa Clara Valley, California, United States Posted: Jun. 15, 2017 Weekly Hours: 40.00 Job Summary Read more
Business Development Manager - *Apple* Medi...
Job Summary Apple Music is a single, intuitive app that...- all in one place. You can stream any Apple Music song, playlist or album, and download it Read more
Development Operations and Site Reliability E...
Development Operations and Site Reliability Engineer, Apple Payment Gateway Job Number: 57572631 Santa Clara Valley, California, United States Posted: Jul. 27, 2017 Read more
Frameworks Engineering Manager, *Apple* Wat...
Frameworks Engineering Manager, Apple Watch Job Number: 41632321 Santa Clara Valley, California, United States Posted: Jun. 15, 2017 Weekly Hours: 40.00 Job Summary Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.