Archive for February, 2010

Voices That Matter iPhone Developers Conference 2010

Monday, February 22nd, 2010

I’m still Mac-only, so I still won’t be there, but here’s the information for this year:

  • The conference is in Seattle, Washington on April 24th and 25th.
  • The speakers, including Aaron Hillegass, Jonathan “Wolf” Rentzsch, Erica Sadun, and Eric Buck, will cover many different topics, including Core Data, Core Location and MapKit, in-app purchasing, UI design, and OpenGL ES.
  • Early bird pricing is $200 off until March 12th.
  • If you use the coupon code “PHBLOGS”, you’ll get another $100 off.

(I do still wonder what the “PH” stands for…)

If this sounds good to you, register for the conference.

See also Brent Simmons’s post about it. He wants to play pinball with you.

Easy main-thread performing category

Saturday, February 13th, 2010

Anyone who’s ever had to perform a message on the main thread knows how ugly the code can be:

[obj performSelectorOnMainThread:@selector(receiveAnswer:)
                      withObject:[NSNumber numberWithUnsignedInteger:42]

I’ve written a category that changes the above code to something much simpler:

[[obj performOnMainThread_PRH] receiveAnswer:42];

Notice that not only is the code much easier to read and to write, but you no longer need to box and unbox primitive values.

You can get the code, under a BSD license, from the higher-order main-thread perform repository.

Back when I originally mentioned my creation of the category on Twitter, Dave Dribin replied that he had already written one of his own. His is part of his DDFoundation framework, and requires DDInvocationGrabber (a fork of Jonathan Wight‘s CInvocationGrabber), also part of that framework.

My category requires nothing but Cocoa and is not part of a larger framework. That said, it’s interesting to read in his code how the functionality of the Invocation Grabber makes his implementation nothing but a thin wrapper around it. (Also, his version lets you say waitUntilDone:YES.)

Amadeus Pro’s noise-removal filter

Thursday, February 11th, 2010

Many of you may remember an audio editor named Amadeus II. It turns out that there is a successor to it now, named Amadeus Pro.

One of Amadeus Pro’s features is the ability to remove noise, quickly and simply. Find, within the audio, a patch of nothing but noise, and choose “Sample Noise”. This trains the filter for that audio. Then, select the whole thing (or nothing), and choose “Suppress Noise”.

That’s it. Sample Noise, then Suppress Noise.

Here’s the result, as demonstrated by a 12-second clip from a recording, ripped from cassette, of Haydn’s Symphony #49, “La Passione”:

(This is actually from a quiet section; I amplified it before filtering it so that you can hear the hiss at the start.)

That’s not to say that it only works on music. I’m also using it on the audio for forthcoming CocoaHeads Lake Forest videos.

This feature alone is worth the $40 for this application.

Before anybody mentions Audacity: Yes, Audacity has a Noise Removal tool, but it lacks the It Just Works factor of Amadeus’s noise-remover. Audacity gives you three settings to think about, with names only an audio engineer could love. (“Frequency smoothing”?!) In Amadeus, all you need to tell it is “here’s what noise sounds like. Go kill it.” This (plus a native Mac OS X interface) is worth the money to me.

Cocoa and Cheesesteaks, February 2010

Monday, February 8th, 2010

CocoaHeads Lake Forest is this Wednesday, the 10th, at 7 PM. If you’re attending, let’s have dinner at 6 PM at Philly’s Best in Lake Forest:

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Nearest Neighbor Image Unit

Saturday, February 6th, 2010

I originally wrote this as an application using NSImage (with NSImageInterpolationNone), but decided to rewrite it as an Image Unit. So, here it is.

An introduction to Cocoa and Cocoa Touch

Wednesday, February 3rd, 2010

If you know someone who’s recently taken up programming the Mac or the iPhone (or both), please give them one (or both) of these links:

As a frequent answerer of questions on Stack Overflow, I see certain patterns—not just frequently-asked questions, but also frequently-unasked questions: Things that are biting the questioner that they don’t know about.

Sometimes they’re thinking about things the wrong way (e.g., using property list objects where they should have a model). Sometimes there is a route to a solution (“my app is slow” “run Instruments”), but they don’t know about that route. Often, they’ll use wrong terms that are right on another platform (like “member variable”), like a speaker using their native language’s pronunciation rules when speaking a foreign one.

To help people over these speed bumps, I’ve composed an introduction for new Cocoa and Cocoa Touch programmers. (Both of the above links redirect to it.)

If any part of it doesn’t help them (i.e., is unclear or wrong), I’d appreciate it if you’d let me know, either here or by email.


Tuesday, February 2nd, 2010

A common question from people new to Objective-C is “why do I have to separately alloc and init? Why can’t I just call one thing and get a fully initialized object?”.

It’s certainly not how other environments do it. Usually, you call one function or class method, and you get an object. Cocoa makes you send two messages: one to the class, then another to the fresh, uninitialized instance you got back. What does Cocoa know that those other environments don’t?

There are two reasons why alloc and init are separate:

  • “NSResponder”* says that sometimes, NeXT wanted to initialize the same object multiple times.

    This is interesting, but horrifying to modern readers. Practically all init methods I’ve seen do not handle the case of initializing the already-initialized; they blindly assign newly created/retained objects to the ivars without checking for existing objects there.

    A bigger problem is when the init method releases the receiver and returns some other object; in the second message, the “other” object may in fact be the receiver (returned from the first message), so [self release] this time would be killing off an object that should stay alive. On the other hand, retaining the object before re-initializing it will create a leak if the object doesn’t release itself. Unpredictable behavior is bad.

  • On the same Stack Overflow question, Darren points out that alloc is shorthand for allocWithZone:; if allocation and initialization were merged in Cocoa, then, to maintain the same functionality, every initializer would need to take a zone parameter, and optionally come in a flavor without one. You can imagine how a proliferation of initializers would ensue.

    This is essentially what the documentation says: “Separating allocation from initialization gives you individual control over each step so that each can be modified independently of the other.” I.e., both steps can be customized, so they must remain separate so that you can customize either or both.

So, there are two practical reasons why Cocoa’s designers separated allocation from initialization.

But let’s revisit this with modern eyes:

  • As I mentioned, in modern Cocoa, initializing an instance again is risky at best. In practice, I don’t think anybody does it, and if anybody does, they probably feel guilty about it and mean to refactor that code “someday”.
  • Nobody uses zones anymore.

That blows those two reasons away.

So, let’s imagine what life would be like if they had never existed in the first place, and allocation and initialization had remained one task:

+ (id) newWithFramistan:(Framistan *)framistan {
    id obj = [super new];
    if (obj) {
        obj->framistan = framistan;
    return obj;

Right away, you can see several advantages:

  • We can name our local variable “framistan”, not “newFramistan” or anything like that.
  • No more assignment in condition (if ((self = …))).
  • No more assignment to self (which should make Wil Shipley happy).
  • Eliminates the problem of [super init] returning a different object, whereupon you would have to release the receiver. Since the receiver is the class, there is nothing for the upstream-initialized object to be different from. If the superclass wants to return an existing object, it can just do that.
  • Related to the first point, we no longer have a name conflict between instance variables and local (especially argument) variables. In init methods, we resolve this conflict with style rules, such as the aforementioned newFramistan for locals or m_framistan for instance variables; in this newWithFramistan: method, the conflict doesn’t exist in the first place.
  • There is never an uninitialized object that the caller could leave lying around. We’ve all seen (or written) code like Foo *foo = [Foo alloc]; [foo init];; in this alternate universe, such faux pas are impossible.

There are trade-offs:

  • It’s one line longer. (Depending on your employers’ level of cluefulness, this may be a small advantage.)
  • Since you’re not in an instance, you have to prefix every instance-variable access with obj->. I can see how this could get tedious; on the other hand, this is what prevents ivar-vs.-local name conflicts.
  • If you use object controllers that automatically prepare their content, they’ll use alloc and init, bypassing this initializer. I’ve never used the automatic-content-preparation feature, so this doesn’t affect me.
  • It’ll be less than familiar to anybody who hasn’t read this post, and it’s certainly a change from currently-typical Cocoa code.
  • Doing this in a subclass of a class that has an unusual designated initializer, such as NSView with its initWithFrame:, could get tricky.

My opinion is mixed. On the one hand, real problems with the init way of doing things are rare for anyone who knows the ropes. On the other hand, it sure is more straightforward, isn’t it?

What do you think?

* Presumably the same one most of us recognize as John C. Randolph, although there’s no direct evidence of this on his SO profile.