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

Air Video Server HD 2.1.0 - Stream video...
Air Video Server HD streams videos instantly from your computer on your iPhone, iPad, iPod touch or Apple TV. No need to worry about converting or transferring files. We took everything that was... Read more
Duplicate Annihilator 5.7.5 - 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
BusyContacts 1.0.2 - Fast, efficient con...
BusyContacts is a contact manager for OS X that makes creating, finding, and managing contacts faster and more efficient. It brings to contact management the same power, flexibility, and sharing... Read more
Capture One Pro 8.2.0.82 - RAW workflow...
Capture One Pro 8 is a professional RAW converter offering you ultimate image quality with accurate colors and incredible detail from more than 300 high-end cameras -- straight out of the box. It... Read more
Backblaze 4.0.0.872 - Online backup serv...
Backblaze is an online backup service designed from the ground-up for the Mac.With unlimited storage available for $5 per month, as well as a free 15-day trial, peace of mind is within reach with... Read more
Little Snitch 3.5.2 - 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
Monolingual 1.6.4 - Remove unwanted OS X...
Monolingual is a program for removing unnecesary language resources from OS X, in order to reclaim several hundred megabytes of disk space. If you use your computer in only one (human) language, you... Read more
CleanApp 5.0 - Application deinstaller a...
CleanApp is an application deinstaller and archiver.... Your hard drive gets fuller day by day, but do you know why? CleanApp 5 provides you with insights how to reclaim disk space. There are... Read more
Fantastical 2.0 - Create calendar events...
Fantastical is the Mac calendar you'll actually enjoy using. Creating an event with Fantastical is quick, easy, and fun: Open Fantastical with a single click or keystroke Type in your event details... Read more
Cocktail 8.2 - General maintenance and o...
Cocktail is a general purpose utility for OS X that lets you clean, repair and optimize your Mac. It is a powerful digital toolset that helps hundreds of thousands of Mac users around the world get... Read more

Pie In The Sky: A Pizza Odyssey (Games)
Pie In The Sky: A Pizza Odyssey 1.0 Device: iOS Universal Category: Games Price: $2.99, Version: 1.0 (iTunes) Description: A game about delivering pizza. In space. | Read more »
Android's Popular OfficeSuite Now A...
Once only available for Android devices, OfficeSuite has finally landed on the app store. The Mobile Systems app lets you view, edit, create, and share Word, Excel, and PowerPoint documents as well as convert them to/from PDFs. It's touted as being... | Read more »
Fast & Furious: Legacy's Creati...
| Read more »
N-Fusion and 505's Ember is Totally...
| Read more »
These are All the Apple Watch Apps and G...
The Apple Watch is less than a month from hitting store shelves, and once you get your hands on it you're probably going to want some apps and games to install. Fear not! We've compiled a list of all the Apple Watch apps and games we've been able to... | Read more »
Appy to Have Known You - Lee Hamlet Look...
Being at 148Apps these past 2 years has been an awesome experience that has taught me a great deal, and working with such a great team has been a privilege. Thank you to Rob Rich, and to both Rob LeFebvre and Jeff Scott before him, for helping me... | Read more »
Hands-On With Allstar Heroes - A Promisi...
Let’s get this out of the way quickly. Allstar Heroes looks a lot like a certain other recent action RPG release, but it turns out that while it’s not yet available here, Allstar Heroes has been around for much longer than that other title. Now that... | Read more »
Macho Man and Steve Austin Join the Rank...
WWE Immortals, by Warner Bros. Interactive Entertainment and WWE, has gotten a superstar update. You'll now have access to Macho Man Randy Savage and Steve Austin. Both characters have two different versions: Macho Man Randy Savage Renegade or Macho... | Read more »
Fearless Fantasy is Fantastic for the iF...
I actually had my first look at Fearless Fantasy last year at E3, but it was on a PC so there wasn't much for me to talk about. But now that I've been able to play with a pre-release version of the iOS build, there's quite a bit for me to talk... | Read more »
MLB Manager 2015 (Games)
MLB Manager 2015 5.0.14 Device: iOS Universal Category: Games Price: $4.99, Version: 5.0.14 (iTunes) Description: Guide your favorite MLB franchise to glory! MLB Manager 2015, officially licensed by MLB.com and based on the award-... | Read more »

Price Scanner via MacPrices.net

Apple offering refurbished 27-inch 5K iMacs f...
The Apple Store is offering Apple Certified Refurbished 27″ 3.5GHz 5K iMacs for $2119 including free shipping. Their price is $380 off the price of new models, and it’s the lowest price available for... Read more
16GB iPad mini on sale for $199, save $50
Walmart has 16GB iPad minis (1st generation) available for $199.99 on their online store, including free shipping. Their price is $50 off MSRP. Online orders only. Read more
New 128GB MacBook Airs on sale for $50 off MS...
 B&H Photo has 128GB 11″ and 13″ 2015 MacBook Airs on sale today for $50 off MSRP including free shipping plus NY sales tax only: - 11″ 1.6GHz/128GB MacBook Air (Model #MJVM2LL/A): $849 $50 off... Read more
13-inch 2.6GHz Retina MacBook Pro (refurbishe...
The Apple Store has Apple Certified Refurbished 13″ 2.6GHz/128GB Retina MacBook Pros available for $979 including free shipping. Original MSRP for this model was $1299. Read more
Save up to $600 with Apple refurbished Mac Pr...
The Apple Store is offering Apple Certified Refurbished Mac Pros for up to $600 off the cost of new models. An Apple one-year warranty is included with each Mac Pro, and shipping is free. The... Read more
Samsung Galaxy S 6 and Galaxy S 6 edge U.S. P...
Samsung Electronics America, Inc. has announced the Galaxy S 6 and Galaxy S 6 edge will be available in the U.S. beginning April 10, with pre-orders being accepted now. “We have completely reimagined... Read more
13-inch 2.5GHz MacBook Pro (refurbished) avai...
The Apple Store has Apple Certified Refurbished 13″ 2.5GHz MacBook Pros available for $829, or $270 off the cost of new models. Apple’s one-year warranty is standard, and shipping is free: - 13″ 2.... Read more
Save up to $80 on iPad Air 2s, NY tax only, f...
 B&H Photo has iPad Air 2s on sale for $80 off MSRP including free shipping plus NY sales tax only: - 16GB iPad Air 2 WiFi: $469.99 $30 off - 64GB iPad Air 2 WiFi: $549.99 $50 off - 128GB iPad... Read more
iMacs on sale for up to $205 off MSRP
B&H Photo has 21″ and 27″ iMacs on sale for up to $205 off MSRP including free shipping plus NY sales tax only: - 21″ 1.4GHz iMac: $1019 $80 off - 21″ 2.7GHz iMac: $1189 $110 off - 21″ 2.9GHz... Read more
Färbe Technik Offers iPhone Battery Charge LI...
Färbe Technik, which manufactures and markets of mobile accessories for Apple, Blackberry and Samsung mobile devices, is offering tips on how to keep your iPhone charged while in the field: •... Read more

Jobs Board

DevOps Software Engineer - *Apple* Pay, iOS...
**Job Summary** Imagine what you could do here. At Apple , great ideas have a way of becoming great products, services, and customer experiences very quickly. Bring 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
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
Lead *Apple* Solutions Consultant - Retail...
**Job Summary** Job Summary The Lead ASC is an Apple employee who serves as the Apple business manager and influencer in a hyper-business critical Reseller's store Read more
*Apple* Pay - Site Reliability Engineer - Ap...
**Job Summary** Imagine what you could do here. At Apple , great ideas have a way of becoming great products, services, and customer experiences very quickly. Bring Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.