TweetFollow Us on Twitter

When Wild Animals Bite

Volume Number: 18 (2002)
Issue Number: 10
Column Tag: Mac OS X

When Wild Animals Bite

Or How To Workaround Cocoa bugs

by Andrew C. Stone

Of the last 50 articles I have written about Cocoa and Mac OS X, I think 49 have extolled the virtues of object oriented programming and the unparalleled advantages of using the dynamic runtime of Objective C. You might think I'd been fed some KoolAid, and you might not be too far off. But effects and mileage will vary.

The question that might arise in your mind is "Aren't there any serious drawbacks to using such a high level system?". And the answer to that would be the same as the drawbacks to any complex system: "Yes - Beware of Bit Rot", the inevitable complexification of simple architectures over time as more people work on it.

Once upon a time, the entire Cocoa development system was in the hands of a few able engineers, which kept it focused and robust between system releases. However, with Mac 10.2, aka Jaguar, we've seen a new and dangerous trend. Components that have been working almost flawlessly for over ten years have been "re-plumbed" without enough real world testing, and this can cause trouble for applications which push the envelope. Sometimes the pressure to release a new version is greater than the ability to do adequate quality control, so all of this is quite forgivable.

The same features that seem like an advantage can turn into a disadvantage! Since a Cocoa application links against the runtime AppKit and Foundation frameworks, when improvements are made to a subsystem framework, your application, even unrecompiled, will take advantage of these improvements. For example, Mac OS X 10.2's text system introduced 3 new tab types: decimal, right aligned, and centered tabs. Users of our page layout and web authoring program, Create(R), now automatically have access to these features under 10.2 - even with versions compiled under 10.1. By the same token, some changes in the subsystem framework can break existing, unrecompiled applications.

Because of the relatively small number of Cocoa engineers at Apple compared to the number of traditional Carbon engineers, there has been an increasing tendency to "pollute" our Cocoa purity with underlying Carbon implementations, and consequently, unexpected results can ensue! In Object Oriented theory, all objects are so well encapsulated and isolated that one can just swap out implementations of components and everything should just work. Reality just doesn't conform to these simplistic expectations.

When Carbon Met Cocoa

In the last several years of shipping and maintaining OS X applications, I've found that most of the problems have come up where traditional Mac OS 9 technologies have been shoehorned into the Cocoa model. The interstice between them is riddled with the same ambiguities that bedevils any organization that is a hybrid of philosophies and techniques. Cocoa's AppleScript implementation is an example of this - from the outside, it looks neat and clean, but getting it to work just right is a lot tougher than normal Cocoa programming tasks.

One object whose plumbing was changed in 10.2 is the NSPrintInfo - an object which maintains information about page size, orientation, margins and selected printer. The backend Print Manager grew out of the Carbon Tioga effort and is coded in C and C++. In 10.1, you could set the page size to any value (ideal for custom page sizes) with the simple invocation:

   [myPrintInfo setPaperSize:NSMakeSize(someWidthInPoints, someHeightInPoints)];

And the printInfo dutifully obeyed. This is useful for designing large scale posters to be printed offsite or for web sites with long content. However, in Jaguar, new behavior was introduced which attempts to see if that size is "valid" for the given printer. To be fair to the Apple engineers, I can see how this might be useful. But from my point of view, it broke the existing version of Create(R)! Luckily, since our corporate philosophy is free upgrades downloadable via the Internet, some quick coding, testing and uploading would solve the problem.

This new validation behavior occurs whenever "setPaperSize:" is called, and in the case of Create(R), that's when the document is unarchived from a file. So, when you open an old Create document with a custom size, the old size is lost forever, and all of a sudden, size "A4" is chosen! What's worse is that any attempt to even read this paper size, such as with the public NSPrintInfo API call -(NSSize)paperSize or even -objectForKey on the dictionary returned from -(NSMutableDictionary)dictionary will also trigger this new validation behavior.

Redemption Song

So, what's the workaround? Somehow, we'll find Cocoa's redemption! For any flaw that comes in a shipping OS, there are ALWAYS tricky ways in Cocoa to do post-ship fixes! Once again, Objective C Categories save us from getting egg on our digital faces.

By examining the header file NSPrintInfo.h, we see a private instance variable (IVAR), _attributes, which is the actual mutable dictionary which holds all the values of the PrintInfo:

@interface NSPrintInfo : NSObject<NSCopying, NSCoding> {
    @private
    NSMutableDictionary *_attributes;
    void *_moreVars;
}

Because the IVAR is designated private, even a subclass cannot access it directly, so subclassing NSPrintInfo won't work. Only a category of the class containing the private IVAR can directly access the variable. Here's a category that can return any set value for paperSize, without triggering the unwanted validation behavior:

@interface NSPrintInfo (peek)

- (NSSize)grabOriginalSize;
@end
@implementation NSPrintInfo(peek)
- (NSSize)grabOriginalSize {
    id obj = [_attributes objectForKey:NSPrintPaperSize];
    return obj? [obj sizeValue]: NSZeroSize;
}
@end

Documents which had no custom page size will return NSZeroSize, which indicates that no extra work will be required. So, here's how we'll use the new category method:

            NSPrintInfo *printInfo = [NSUnarchiver unarchiveObjectWithData:obj];
       // a freshly unarchived PrintInfo still has its old values in the dictionary....
            if (printInfo) {
                NSSize raw = [printInfo grabOriginalSize];
                if (!NSEqualSizes(raw, NSZeroSize)) {   
         // it could have been written
                    // by a 10.1 version of Create
                   [self setUpPrintInfo:printInfo toPaperSize:raw];
                }             
                [self setPrintInfo:printInfo];
            }

Now, all we need to do is fake NSPrintInfo out so that it thinks the custom paper size is valid. To do this, I had to dig into undocumented API using class-dump as explained in several of my last few articles, and even more dreaded by an Objective C coder, into the Carbon header files! It turns out that there is a C function to make custom paper sizes programmatically, which stands to reason because the new Page Setup... panel in Jaguar has a popup option to set custom paper sizes:

OSStatus PMPaperCreate(PMPrinter printer, CFStringRef id, CFStringRef name, double width, double height, const PMPaperMargins *margins, PMPaper *paperP);

And we'll call it like this:

        OSStatus osStatus = PMPaperCreate([[pi printer] _printer], 
(CFStringRef)[NSString stringWithFormat:@"%ld",self], 
(CFStringRef)[NSString stringWithFormat:@"%2.2f X %2.2f",userW,userH],(double) paperSize.width,
(double) paperSize.height, marginPtr, &myPaper);

If PMPaperCreate() returns an OSStatus of 0, then a new PMPaper * object (which you'll need to later release after use) has been created in myPaper. The first parameter, PMPrinter, can be returned from the NSPrintInfo via undocumented NSPrintInfo API, -(PMPrinter)_printer:

[[pi printer] _printer]

Another sweet feature of Cocoa is "toll-free bridging" between Core Foundation objects, such as a CFStringRef and the equivalent Cocoa object, in this case, the NSString. We will cast the NSString parameters to CFStringRef's just to hush the compiler. The other fancy dancing that we're doing is using the pointer to memory of the document object as our uniquing strategy for the second argument, but it could be any string as long as it is a unique identifier:

(CFStringRef)[NSString stringWithFormat:@"%ld",self]

Finally, we'll name the custom page in the user's units by converting the points to their measurement units - these functions are included below.

// these functions are declared here:
#import <CoreServices/CoreServices.h>
#import <ApplicationServices/ApplicationServices.h>
typedef struct OpaquePMPaper *PMPaper;
typedef struct {
    double top;
    double left;
    double bottom;
    double right;
} PMPaperMargins;

OSStatus PMPaperCreate(PMPrinter printer, CFStringRef id, CFStringRef name, double width, double height, const PMPaperMargins *margins, PMPaper *paperP);

- (void)setUpPrintInfo:(NSPrintInfo *)pi toPaperSize:(NSSize)paperSize {
    if (floor(NSAppKitVersionNumber) <= NSAppKitVersionNumber10_1) {
        /* On a 10.1 - 10.1.x system */
   // nothing special to do...
    } else {
        /* 10.2 or later system */
        float userW = convertToUserUnits(paperSize.width);
        float userH = convertToUserUnits(paperSize.height);
        PMPaperMargins margins;
        PMPaperMargins *marginPtr = &margins;   
                        // does C suck or what?
        PMPaper *myPaper;
        // Create uses WYSIWYG full page model:
        margins.top = margins.left = margins.bottom = margins.right = 0.0;
        
        OSStatus osStatus = PMPaperCreate([[pi printer] _printer], (CFStringRef)[NSString 
        stringWithFormat:@"%ld",self], (CFStringRef)[NSString stringWithFormat:@"%2.2f X %2.2f",
        userW,userH],(double) paperSize.width,(double) paperSize.height, marginPtr, &myPaper);
        
     if (osStatus  != 0) {
      // You may want to do something else here:
      NSLog(@"Trouble creating a custom page size: %f by %f",paperSize.width, paperSize.height);
        }
    }
     // on 10.1 this just works:
    [pi setPaperSize:paperSize];
}
// getting user units from an NSUserDefault: - sometimes C is cool!
float
pointsFromUserUnits()
{
    switch([[NSUserDefaults standardUserDefaults] integerForKey:@"MeasurementUnits"]) {
            case 0: return 72.0;
            case 1: return 28.35;
            case 2: return 1.0;
            case 3: return 12.0;
            default: return 72.0;
    }
}
float
convertToUserUnits(float points)
{
    return points/pointsFromUserUnits();
}

Conclusion

So now, our printInfo will return the correct new size! Well, the dust hasn't settled entirely, so hopefully this will work and continue to work in the future. Ideally, NSPrintInfo would just "do the right thing" in terms of creating these custom page sizes. The proposed solution doesn't address custom page size uniquing and coalescing of similar-sized pages - but then, I haven't finished coding the solution entirely either! Even the mighty Cocoa has its compatibility weaknesses as it grows, but its native power can even pull the tractor out of the mud when it gets really stuck.


Andrew Stone, founder of Stone Design <www.stone.com>, spends too much time coding and not enough time gardening.

 

Community Search:
MacTech Search:

Software Updates via MacUpdate

Apple iBooks Author 2.5 - Create and pub...
Apple iBooks Author helps you create and publish amazing Multi-Touch books for iPad. Now anyone can create stunning iBooks textbooks, cookbooks, history books, picture books, and more for iPad. All... Read more
TunnelBear 3.0.1 - Subscription-based pr...
TunnelBear is a subscription-based virtual private network (VPN) service and companion app, enabling you to browse the internet privately and securely. Features Browse privately - Secure your data... Read more
ExpanDrive 5.4.0 - Access cloud storage...
ExpanDrive builds cloud storage in every application, acts just like a USB drive plugged into your Mac. With ExpanDrive, you can securely access any remote file server directly from the Finder or... Read more
Opera 40.0.2308.62 - High-performance We...
Opera is a fast and secure browser trusted by millions of users. With the intuitive interface, Speed Dial and visual bookmarks for organizing favorite sites, news feature with fresh, relevant content... Read more
Apple iOS 10.0.2 - The latest version of...
iOS 10 is the biggest release of iOS ever. A massive update to Messages brings the power of the App Store to your conversations and makes messaging more personal than ever. Find your route with... Read more
Herald 7.0 - Notification plugin for Mai...
Note: Versions 2.1.3 (for OS X 10.7), 3.0.6 (for OS X 10.8), 4.0.8 (for OS X 10.9), 5.0.2 (for OS X 10.10), and 6.0.3 (for OS X 10.11) are no longer supported by the developer. Herald is a... Read more
Postbox 5.0.2 - Powerful and flexible em...
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
Yummy FTP Pro 1.11.10 - $29.99
Yummy FTP Pro is an advanced Mac file transfer app which provides a full-featured professional toolkit combined with blazing speeds and impeccable reliability, so whether you want to transfer a few... Read more
Tidy Up 4.1.17 - $29.99
Tidy Up is a full-featured duplicate finder and disk-tidiness utility. Features With Tidy Up you can search for duplicate files and packages by the owner application, content, type, creator,... Read more
Logitech Control Center 3.9.5 - Keyboard...
Logitech Control Center (LCC) is designed to support OS X and allows you to take full advantage of your Logitech keyboard, mouse, or trackball. With the LCC you can: Browse the Internet using... Read more

How to build and care for your team in D...
Before you hit the trail and become a dog sledding legend, there’s actually a fair bit of prep work to be done. In Dog Sled Saga, you’re not only racing, you’re also building and caring for a team of furry friends. There’s a lot to consider—... | Read more »
How to win every race in Dog Sled Saga
If I had to guess, I’d say Dog Sled Saga is the most adorable racing game on the App Store right now. It’s a dog sled racing sim full of adorable, loyal puppies. Just look at those fluffy little tails wagging. Behind that cute, pixelated facade is... | Read more »
Let the war games commence in Gunship Ba...
Buzz Lightyear famously said, “This isn’t flying, this is falling – with style!” In the case of Gunship Battle: Second War, though, this really is flying - with style! The flight simulator app from Joycity puts you in control of 20 faithfully... | Read more »
How to get a high score in Fired Up
Fired Up is Noodlecake Games’ high score chasing, firefighting adventure. You take control of a wayward firefighter who propels himself up the side of a highrise with blasts of water. Sound silly? It is. It’s also pretty difficult. You can’t... | Read more »
NBA 2K17 (Games)
NBA 2K17 1.0 Device: iOS iPhone Category: Games Price: $7.99, Version: 1.0 (iTunes) Description: Following the record-breaking launch of NBA 2K16, the NBA 2K franchise continues to stake its claim as the most authentic sports video... | Read more »
Dog Sled Saga (Games)
Dog Sled Saga 1.0.1 Device: iOS Universal Category: Games Price: $3.99, Version: 1.0.1 (iTunes) Description: A game by Dan + Lisa As a rookie musher, foster a dogsledding team whose skills will grow if they're treated right. Week by... | Read more »
60 Seconds! Atomic Adventure (Games)
60 Seconds! Atomic Adventure 1.2 Device: iOS Universal Category: Games Price: $2.99, Version: 1.2 (iTunes) Description: 60 Seconds! is a dark comedy atomic adventure of scavenge and survival. Collect supplies and rescue your family... | Read more »
Tons of Bullets! (Games)
Tons of Bullets! 1.0 Device: iOS Universal Category: Games Price: $1.99, Version: 1.0 (iTunes) Description: Tons of BulletsA retro 2D pixel platformer infused with tons of bullets and tons of features!Fight as Kenji the Ninja and... | Read more »
Sorcery! 4 (Games)
Sorcery! 4 1.0 Device: iOS Universal Category: Games Price: $4.99, Version: 1.0 (iTunes) Description: *** PLEASE NOTE: Sorcery! 4 requires a minimum of iPad 3 or iPhone 4 *** An epic adventure through a cursed citadel of monsters,... | Read more »
Building the perfect Animation Throwdown...
Animation Throwdown is a casual card game full of plenty of inside jokes from some of your favorite cartoons. It’s accessible as far as card games go, but that’s not to say that it hands your victories to you easily. There’s quite a bit that goes... | Read more »

Price Scanner via MacPrices.net

Duplicate Sweeper Free On Mac App Store For O...
To celebrate the launch of Apple’s latest macOS Sierra, Stafford, United Kingdom based Wide Angle Software has announced that its duplicate file finder software, Duplicate Sweeper, is now available... Read more
13-inch Retina MacBook Pros on sale for up to...
B&H Photo has 13″ Retina Apple MacBook Pros on sale for up to $150 off MSRP. Shipping is free, and B&H charges NY tax only: - 13″ 2.7GHz/128GB Retina MacBook Pro: $1174.99 $125 off MSRP - 13... Read more
Evidence Surfaces Pointing To New A10X Chip F...
Citing a job description for a Project Lead position at Apple’s Austin, Texas engineering labs, Motley Fool’s Ashraf Eassa deduces that development is progressing well on Apple’s next-generation in-... Read more
Check Print’R for macOS Allows Anyone to Easi...
Delaware-based Match Software has announced the release and immediate availability of Check Print’R 3.21, an important update to their easy-to-use check printing application for macOS. Check Print’R... Read more
Apple refurbished 11-inch MacBook Airs availa...
Apple has Certified Refurbished 11″ MacBook Airs (the latest models), available for up to $170 off the cost of new models. An Apple one-year warranty is included with each MacBook, and shipping is... Read more
Apple refurbished 15-inch Retina MacBook Pros...
Apple has Certified Refurbished 2015 15″ Retina MacBook Pros available for up to $380 off the cost of new models. An Apple one-year warranty is included with each model, and shipping is free: - 15″ 2... Read more
Major Version 5 Release Of Free myTuner Radio...
AppGeneration Software has announced the release of myTuner Radio 5.0.1, an important update to their live radio app for iOS and Android platforms. With myTuner Radio, you can listen to more than 30,... Read more
TheAppStore Searches And Filters iOS And macO...
Boston based InchWest has announced the official launch of TheAppStore, a free web based service that lets users search iOS and Mac apps on the web without iTunes or the App store. TheAppStore... Read more
2TB Time Capsule on sale for $199, save $100
Amazon has 2TB Apple Time Capsules on sale for $199 including free shipping. Their price is $100 off MSRP. Choose Amazon as the seller when making your purchase, rather than a third party seller. Read more
12-inch 1.2GHz Rose Gold Retina MacBook on sa...
Amazon.com has the 2016 12″ 1.2GHz Rose Gold Retina MacBook on sale for $1254.02 including free shipping. Their price is $345 off MSRP, and it’s the lowest price available for this model from any... Read more

Jobs Board

Senior *Apple* Administrator - Pratt Instit...
POSITION SUMMARY: Directs the coordination and standardization of campus-wide Apple systems, including planning, analysis and implementation of Apple -related Read more
Restaurant Manager (Neighborhood Captain) - A...
…in every aspect of daily operation. WHY YOU'LL LIKE IT: You'll be the Big Apple . You'll solve problems. You'll get to show your ability to handle the stress and Read more
*Apple* Retail - Multiple Positions- Napervi...
Job Description: Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, Read more
US- *Apple* Store Leader Program - Apple (Un...
…Summary Learn and grow as you explore the art of leadership at the Apple Store. You'll master our retail business inside and out through training, hands-on 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
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.