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

Vienna 3.0.6 :5eaf312: - RSS and Atom ne...
Vienna is a freeware and Open-Source RSS/Atom newsreader with article storage and management via a SQLite database, written in Objective-C and Cocoa, for the OS X operating system. It provides... Read more
Kodi 15.1.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
Bookends 12.5.8 - Reference management a...
Bookends is a full-featured bibliography/reference and information-management system for students and professionals. Access the power of Bookends directly from Mellel, Nisus Writer Pro, or MS Word (... Read more
Chromium 44.0.2403.125 - Fast and stable...
Chromium is an open-source browser project that aims to build a safer, faster, and more stable way for all Internet users to experience the web. Version 44.0.2403.125: This release contains a number... Read more
iMazing 1.2.2 - Complete iOS device mana...
iMazing (was DiskAid) is the ultimate iOS device manager with capabilities far beyond what iTunes offers. With iMazing and your iOS device (iPhone, iPad, or iPod), you can: Copy music to and from... Read more
Audio Hijack 3.2.0 - 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
FontExplorer X Pro 5.0.1 - Font manageme...
FontExplorer X Pro is optimized for professional use; it's the solution that gives you the power you need to manage all your fonts. Now you can more easily manage, activate and organize your... Read more
Calcbot 1.0.2 - Intelligent calculator a...
Calcbot is an intelligent calculator and unit converter for the rest of us. Featuring an easy-to-read history tape, expression view, intuitive conversion, and much more! Features History Tape -... Read more
MTR 5.0.0.1 - The Mac's oldest and...
MTR (was MacTheRipper)--the Mac's oldest and smartest DVD-backup app--is now updated to version 5.001 MTR -- the complete toolbox, not a one-trick, point-and-click extractor. MTR is intended for... Read more
LibreOffice 4.4.5.2 - Free, open-source...
LibreOffice is an office suite (word processor, spreadsheet, presentations, drawing tool) compatible with other major office suites. The Document Foundation is coordinating development and... Read more

Card King: Dragon Wars - Tips, Tricks an...
[Read more] | Read more »
Pac-Man Championship Edition DX has brou...
Bandai Namco has released Pac-Man Championship Edition DX on iOS and Android, which features the classic arcade gameplay that we've all grown to love. Pac-Man Championship Edition DX can be enjoyed in much shorter bursts than the arcade versions... | Read more »
Cosmonautica (Games)
Cosmonautica 1.1 Device: iOS Universal Category: Games Price: $6.99, Version: 1.1 (iTunes) Description: Cast off! Are you ready for some hilarious adventures in outer space? | Read more »
Rescue humanity from a Demon horde in An...
Angel Stone is Fincon's follow up to the massively successful Hello Hero and is out now on iOS and Android. You play as a member of The Resistance, a group of mighty human warriors who have risen up in defiance of the Demon horde threatening to... | Read more »
Gallery Doctor (Photography)
Gallery Doctor 1.0 Device: iOS iPhone Category: Photography Price: $2.99, Version: 1.0 (iTunes) Description: Free up valuable iCloud and iPhone storage with Gallery Doctor, the only iPhone cleaner that automatically identifies the... | Read more »
You Against Me (Games)
You Against Me 1.0 Device: iOS Universal Category: Games Price: $.99, Version: 1.0 (iTunes) Description: A simple game… You. Me. Claim, steal, lock, score, win! | Read more »
Yep, it's True - Angry Birds 2 is O...
The not exactly rumors were true and the birds are back. Angry Birds 2 has come to the App Store and the world will... well I suppose it'll still be the same, but now we have more bird-flinging options! [Read more] | Read more »
You Could Design Your Own Card for Chain...
If you've ever wanted to create your own item, weapon, trap, or even monster for Chainsaw Warrior: Lords of the Night, this is your chance. Auroch Digital is currently holding a contest so that fans can fight to the death (not really) to see which... | Read more »
Bitcoin Billionaire is Going Back in Tim...
If you thought you managed to buy everything there is to buy in Bitcoin Billionaire and make all the money, well you though wrong. Those of you who made it far enough might remember investing in time travel - and it looks like that investment is... | Read more »
Domino Drop (Games)
Domino Drop 1.0 Device: iOS Universal Category: Games Price: $1.99, Version: 1.0 (iTunes) Description: Domino Drop is a delightful new puzzle game with dominos and gravity!Learn how to play it in a minute, master it day by day.Your... | Read more »

Price Scanner via MacPrices.net

Back-to-School with Tablet and Smartphone Acc...
Belkin helps you prepare for the coming school year with a wide variety of the latest mobile and tablet accessories to outfit both grade school and college students. The line-up includes charging... Read more
11-inch MacBook Airs on sale for $100 off MSR...
Best Buy has 11-inch MacBook Airs on sale for $100 off MSRP. Choose free shipping or free local store pickup (if available). Sale prices for online orders only, in-store prices may vary: - 11″ 1.6GHz... Read more
iPad Air 2 on sale for up to $100 off MSRP
Best Buy has iPad Air 2s on sale for up to $100 off MSRP on their online store for a limited time. Choose free shipping or free local store pickup (if available). Sale prices available for online... Read more
Sale! 13-inch MacBook Pros on sale for $100 o...
B&H Photo has 13″ MacBook Pros on sale for $100 off MSRP. Shipping is free, and B&H charges NY sales tax only: - 13″ 2.5GHz/500GB MacBook Pro: $999.99 save $100 - 13″ 2.7GHz/128GB Retina... Read more
Sale! Save $100 on 13-inch MacBook Airs this...
B&H Photo has the 13″ 1.6GHz/128GB MacBook Air on sale for $899.99 including free shipping plus NY tax only. Their price is $100 off MSRP, and it’s the lowest price available for this model.... Read more
Worldwide Tablet Market Decline Continues, Ap...
The worldwide tablet market declined -7.0% year-over-year in the second quarter of 2015 (2Q15) with shipments totaling 44.7 million units according to preliminary data from the International Data... Read more
TP-LINK TL-PA8030P KIT Powerline Featuring Ho...
Consumer and business networking products provider TP-LINK is now shipping its TL-PA8030P KIT AV1200 3-Port Gigabit Passthrough Powerline Starter Kit that expands your home’s network over its... Read more
Apple refurbished iPad Air 2s available for u...
The Apple Store has Apple Certified Refurbished iPad Air 2s available for up to $140 off the price of new models. Apple’s one-year warranty is included with each model, and shipping is free: - 128GB... Read more
Updated Apple iPad Price Trackers
We’ve updated our iPad Air Price Tracker and our iPad mini Price Tracker with the latest information on prices and availability from Apple and other resellers. Read more
Apple refurbished 2014 13-inch 128GB MacBook...
The Apple Store has Apple Certified Refurbished 2014 13″ MacBook Airs available starting at $759. An Apple one-year warranty is included with each MacBook, and shipping is free: - 13″ 1.4GHz/128GB... Read more

Jobs Board

*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
Infrastructure Engineer - *Apple* /Mac - Hil...
Infrastructure Engineer - Apple /Mac Job Code: 1608 # of openings: 1 Description Our fortune 500 client is looking to hire an experienced Infrastructure Engineer to join Read more
Executive Administrative Assistant, *Apple*...
…supporting presentation development for senior leadership. * User experience with Apple hardware and software is preferred. Additional Requirements The following list Read more
*Apple* Bus Company is now hirin - Apple Bus...
Apple Bus Company is now hiring school bus drivers in the Pettis County area. Class B CDL preferred. Free training provided. No nights or weekends required. Flexible Read more
*Apple* Certified Mac Technician - Updated 6...
…and friendly, hands-on technical support to customers troubleshooting and repairing Apple /Mac products with courtesy, speed and skill. Use your problem-solving skills Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.