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

Cyberduck 4.7.1 - 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
PDFpen 7.2 - Edit and annotate PDFs with...
We're also offering PDFpenPro for 30% off! PDFpen allows users to easily edit PDF's. Add text, images and signatures. Fill out PDF forms. Merge or split PDF documents. Reorder and delete pages. Even... Read more
Skype 7.9.746 - Voice-over-internet phon...
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
Apple GarageBand 10.1 - Complete recordi...
The new GarageBand is a whole music creation studio right inside your Mac -- complete with keyboard, synths, orchestral and percussion instruments, presets for guitar and voice, an entirely... Read more
Duplicate Annihilator 5.7.7 - Find and d...
Duplicate Annihilator takes on the time-consuming task of comparing the images in your iPhoto library using effective algorithms to make sure that no duplicate escapes. Duplicate Annihilator... Read more
OS X Server 4.1.3 - For OS X 10.10 Yosem...
Designed for OS X and iOS devices, OS X Server makes it easy to share files, schedule meetings, synchronize contacts, develop software, host your own website, publish wikis, configure Mac, iPhone,... Read more
Firefox 39.0 - Fast, safe Web browser. (...
Firefox offers a fast, safe Web browsing experience. Browse quickly, securely, and effortlessly. With its industry-leading features, Firefox is the choice of Web development professionals and casual... Read more
pwSafe 4.1 - 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
Kodi 15.0.rc1 - Powerful media center to...
Kodi (was XBMC) is an award-winning free and open-source (GPL) software media player and entertainment hub that can be installed on Linux, OS X, Windows, iOS, and Android, featuring a 10-foot user... Read more
Coda 2.5.11 - One-window Web development...
Coda is a powerful Web editor that puts everything in one place. An editor. Terminal. CSS. Files. With Coda 2, we went beyond expectations. With loads of new, much-requested features, a few surprises... Read more

This Week at 148Apps: June 29-July 3, 20...
Into July 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 above the... | Read more »
Sonic Runners Guide
Despite its flaws, Sonic Runners' platforming action is actually quite fun. Though it can be a little more complicated than old-school Sonic games. Here's how to make sure you're up to speed when jumping in. [Read more] | Read more »
Rage of Bahamut is Giving Almost All of...
The App Store isn't what it used to be back in 2012, so it's not unexpected to see some games changing their structures with the times. Now we can add Rage of Bahamut to that list with the recent announcement that the game is severely cutting back... | Read more »
Adventures of Pip (Games)
Adventures of Pip 1.0 Device: iOS iPhone Category: Games Price: $4.99, Version: 1.0 (iTunes) Description: ** ONE WEEK ONLY — 66% OFF! *** “Adventures of Pip is a delightful little platformer full of charm, challenge and impeccable... | Read more »
Divide By Sheep - Tips, Tricks, and Stre...
Who would have thought splitting up sheep could be so involved? Anyone who’s played Divide by Sheep, that’s who! While we’re not about to give you complete solutions to everything (because that’s just cheating), we will happily give you some... | Read more »
NaturalMotion and Zynga Have Started Tea...
An official sequel to 2012's CSR Racing is officially on the way, with Zynga and NaturalMotion releasing a short teaser trailer to get everyone excited. Well, as excited as one can get from a trailer with no gameplay footage, anyway. [Read more] | Read more »
Grab a Friend and Pick up Overkill 3, Be...
Overkill 3 is a pretty enjoyable third-person shooter that was sort of begging for some online multiplayer. Fortunately the begging can stop, because its newest update has added an online co-op mode. [Read more] | Read more »
Scanner Pro's Newest Update Adds Au...
Scanner Pro is one of the most popular document scanning apps on iOS, thanks in no small part to its near-constant updates, I'm sure. Now we're up to update number six, and it adds some pretty handy new features. [Read more] | Read more »
Heroki (Games)
Heroki 1.0 Device: iOS Universal Category: Games Price: $7.99, Version: 1.0 (iTunes) Description: CLEAR THE SKIES FOR A NEW HERO!The peaceful sky village of Levantia is in danger! The dastardly Dr. N. Forchin and his accomplice,... | Read more »
Wars of the Roses (Games)
Wars of the Roses 1.0 Device: iOS Universal Category: Games Price: $4.99, Version: 1.0 (iTunes) Description: | Read more »

Price Scanner via MacPrices.net

Apple refurbished Mac minis available startin...
The Apple Store has Apple Certified Refurbished 2014 Mac minis available starting at $419. Apple’s one-year warranty is included with each mini, and shipping is free: - 1.4GHz Mac mini: $419 $80 off... 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
Sky Atlas Star Walk 2 App For iPhone And iPa...
Vito Technology, developer of educational apps for Android and iOS, is for a limited time offering free of charge their Star Walk 2, the next generation of the company’s best-selling stargazing guide... Read more
13-inch 1.6GHz MacBook Air on sale for $849,...
Amazon has the 2015 13″ 1.6GHz/128GB MacBook Air on sale for $849.99 including free shipping. Their price is $150 off MSRP, and it’s the lowest price available for this model. Read more
13-inch 2.5GHz MacBook Pro on sale for $999,...
Adorama has the 13-inch 2.5GHz MacBook Pro on sale for $999 including free shipping plus NY & NJ sales tax only. Their price is $100 off MSRP. 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
15-inch Retina MacBook Pros on sale for up to...
B&H Photo has new 2015 15″ Retina MacBook Pros on sale for up to $225 off MSRP including free shipping plus NY sales tax only: - 15″ 2.2GHz Retina MacBook Pro: $1819 $180 off - 15″ 2.5GHz Retina... Read more
RamDisk4Mac App Helps Run Your Mac Faster And...
Ever use a RAM disk? If you’ve come to the Mac in the OS X era, likely not. The Classic Mac OS had a RAM disk function built-in, but that was dropped in the conversion to OS X. What is a RAM disk?... Read more
13-inch 1.6GHz MacBook Air on sale for $849,...
Best Buy has the 2015 13″ 1.6GHz/128GB MacBook Air on sale for $849.99 on their online store this weekend. Choose free shipping or free local store pickup (if available). Sale price for online orders... 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

Jobs Board

*Apple* Solutions Consultant - Retail Sales...
**Job Summary** As an Apple Solutions Consultant (ASC) you are the link between our customers and our products. Your role is to drive the Apple business in a retail Read more
Senior Payments Security Manager - *Apple*...
**Job Summary** Apple , Inc. is looking for a highly motivated, innovative and hands-on senior payments security manager to join the Apple Pay security team. You will Read more
Sr. Technical Services Consultant, *Apple*...
**Job Summary** Apple Professional Services (APS) has an opening for a senior technical position that contributes to Apple 's efforts for strategic and transactional Read more
Sr. Payment Program Manager, *Apple* Pay -...
**Job Summary** Apple Pay is an exciting environment and a…devices in a simple, private and secure way. The Apple Pay Team is looking for an experienced Senior 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.