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

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
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
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

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.