September 1st, 2010
I ran into the following weird compile error recently:
compile error:
1071: Syntax error: expected a definition keyword (such as function) after attribute override, not protected.
in relation to the following code:
override
protected function createChildren():void {}
The solution?
override protected function createChildren():void {}
Don’t even get me started.
Posted in: Tools
August 30th, 2010
Just a quick checklist to get up to speed when your APN certificates expire.
aps_developer_identity.cer) in your default keychain..p12 file will be saved .p12 file will be saved .pem style certificates, run this:
$ openssl pkcs12 -in apn_cert.p12 -out apn_cert.pem -nodes $ openssl pkcs12 -in apn_key.p12 -out apn_key.pem -nodes
.pem files in the right location accessible by your application server that will be sending the Push notifications.Now push notifications should be up and running once again.
Posted in: iPhone and iPad dev
August 28th, 2010
At this point you should be able to rebuild the app.
Posted in: Tools, iPhone and iPad dev
July 25th, 2010
What’s the difference between the Binary and Bitstring types in Erlang? Well, a bitstring is a sequence of bits of any length; a binary is a sequence of bits where the number of bits is evenly divisible by 8. (So any binary is also a bitstring.)
Some examples:
1> <<2#11110000:5>>.
< <16:6>>
2> <<2#11110000:6>>.
< <48:6>>
3> erlang:is_bitstring(<<2#11110000:6>>).
true
4> erlang:is_binary(<<2#11110000:6>>).
false
5> erlang:is_bitstring(<<2#11110000:8>>).
true
6> erlang:is_binary(<<2#11110000:8>>).
true
In the Erlang bit syntax there are 2 clarifying (?) type synonyms:
bytes == binary
bits == bitstring
which are basically telling you to think of binaries as sequence of bytes, and bitstrings as sequence of bits. Quite obvious right? Well, it wasn’t for me at first.
It’s also worth noting how binaries and bitstrings are converted into text strings. Given the binary <<16#50>> storing the letter ‘P’,
7> <<16#50>>
<<"P">>
8>erlang:bitstring_to_list(<<16#50>>). #I could've used binary_to_list()
"P" %great!
9>erlang:bitstring_to_list(<<16#50:5>>).
[<<16:5>>] %mmh...
The result of command #9 is not exactly what I had imagined. Yes, it’s a list, but it’s certainly not a text string, and I was expecting a text string. Why was I expecting a text string if the API is named bitstring_to_list() ? Because if I was in the middle of coding a text manipulation algorithm and called bitstring_to_list(), I would probably (wrongly) assume that it would do some magic and transform any bitstring in a usable text string. Why? Because we are used to treat text strings as lists. Why? Because we don’t have APIs that mention “strings”: all the builtin APIs only mention lists. That’s the problem. We are using a list API as if it was a string API, when a generic list is not necessarily a string.
Posted in: Erlang, Functional Programming
July 21st, 2010
If you are changing the title of a UIButton programmatically, you will naturally use the method setTitle:forState:. Easy enough… well, sort of. What do you put in the state parameter?
My first reaction was “I’m going to put all possible states since I just want the button title to change no matter what.” So I blindly bit-OR‘ed all the possible values defined in the docs.
[myButton setTitle:@"New Title"
forState:UIControlStateNormal | UIControlStateHighlighted | UIControlStateDisabled | UIControlStateSelected];Sound reasonable right? Wrong. If you do that here, your button title is probably not going to change at all. The problem is that the “normal” state (per Apple docs that’s “enabled, not selected, not highlighted”) is defined as such:
enum {
UIControlStateNormal = 0,
UIControlStateHighlighted = 1 << 0,
UIControlStateDisabled = 1 << 1,
UIControlStateSelected = 1 << 2,
...
}
so if you bit-OR all of them you are actually going to set the title for ALL states EXCEPT the “normal” (most common) state!
Sigh…
Posted in: iPhone and iPad dev
May 26th, 2010
I don’t know why but Erlang bit syntax always confused me. I always skipped it while reading the docs, until, well, now that I need it. I should say this is not meant to be an exhaustive how-to by any means. It’s just a collection of notes, but howto sounded better. :) There are better guides out there. [Reference docs too.]
Anyway. Here’s some binary data in Erlang:
<<16#1192c05a:32>>
What does all this mean? Let’s analyze it, left to right.
16# This specifies we want to express the number in base 16.:32 Size specification: this tells erlang to consider 32 units, which in our case means 32 bits, since we are dealing with bits.Let’s evaluate it:
86> <<16#2092105a:32>>. <<32,146,16,90>>
What if we forget to specify the size spec? In that case the default will apply and since we’re dealing with an integer type, the default is 8 (bits). For Erlang this means we are going to return the least significant byte:
87> <<16#2092105a>>. <<90>>
Now that we know that, we can get a subset of bits by setting the size accordingly:
88> <<16#2092105a:16>>. <<16,90>> %two least significant bytes
We don’t need to specify a size multiple of 8:
89> <<16#1192FFFF:15>>. <<255,127:7>>
It’s pretty cool how easy it is to slice bytes apart at the bit level. I was sort of surprised that if we slice some internal bits it looks like the bits at the right are moved to the left. E.g. here we take the 4 least significant bits of the first 0xFF:
90> <<16#FF:4,0,16#FF,0>>.
but instead of obtaining:
<<16:4,0,255,0>> F 00 FF 00
we get:
<<240,15,240,0:4>> F0 0F F0 0 [240 == F0]
Also, the value doesn’t need to be a literal, it can be an expression:
91> N = 16#FF00FF01. 4278255361 92> <<N:32>>. <<255,0,255,1>>
And therefore, given some binary data, we can also pattern-match it super easily:
<SourcePort:16, DestinationPort:16, CheckSum:16, Payload/binary>> = SomeBinary.
There’s more to Erlang bit syntax than this, but I’ll stop here for now.
Posted in: Erlang, Functional Programming
May 22nd, 2010
After working for about 2 years in a startup, one thing sticks out the most compared to a “normal job” at a more established technology company: the meaning of “proactivity.” While I’ve always thought of myself as a proactive person, I don’t think I knew the real meaning of the word while working for big companies.
Example. Suppose you discover a problem in the system you are building/maintaining. Well, at a large company sometimes you have the luxury of simply ignoring the problem. Depending how “skilled” you are in the fine art of bullshitting people, you may succeed into making them believe that (1) it’s not your fault, (2) “somebody else will fix it.” It’s pretty sad.
If you do that at a startup, you’re guaranteed to have it backlash at you one way or another, sooner or later. When other people find out, YOU are going to have to fix it if it’s your code, and if not you, YOU are going to have to help others fix it. Obviously not fixing it is not an option. If noone else finds out immediately, it’s even worse. It will be a tour de force the next day to repair all the damage the bug has caused in the mean time, without even considering the effort to actually fix the bug.
But there’s an even bigger backlash. If you don’t take charge at a startup, you’re subject to the implicit mocking of your coworkers, who will resent your laziness like an insult. You will lose reputation immediately. This is probably the biggest motivation to fix things. The “reward” is big, because people will thank you and they will not be faking their gratitude. In a big company people might thank you (often without meaning it), or might even resent you because your warning revealed a flaw in their code.
Posted in: Startup Life
May 16th, 2010
While testing out older versions of a Cocoa app — Smultron, a developer text editor which used to work great but now it’s very buggy — I stumbled upon the error:
“The managed object model version used to open the persistent store is incompatible with the one used to create the persistent store”
Apparently this is a Core Data error. To fix it you will have to remove some files Core Data builds, which are usually stored in ~/Application Support/. Differently from what mentioned elsewhere, they are not always XML files. In the case of Smultron they looked like binary files named Smultron*.smultron.
For free apps that are installed via drag and drop (no installer) it’s probably safe to wipe out the whole $HOME/Application Support/APPNAME folder contents. It wasn’t there the first time you launched the app after all. However, payed apps may install license info there, and apps with installers may install other stuff there as well, so one must be careful.
In my case, I removed the whole content of ~/Application Support/Smultron and the error disappeared once I relaunched the app.
Posted in: Tools
April 14th, 2010
Some time ago I noticed that editing text of a medium sized MXML file had gotten extremely slow in Flash Builder 4. With ‘extremely slow’ I mean a painful lag between key presses: you type (or delete) 3 characters, you see one appearing, wait one second, a second one appears and so on. Unbearable. I had just imported my project from Flex Builder 3 and there were no problems there.
Cause? Workarounds?
The problem was that under the Project > Properties > Flex Build Path > Source Path tab I had added a few paths to the source code of some libraries I am using, including Flex. I was using this to jump into the code during debugging. Turns out if you are already linking to those libraries, you can add the path to their source code in the Source Attachment disclosure field of that library under the Project > Properties > Flex Build Path > Library Path tab.
Then remove it from the Source Path tab: the text editor will all of a sudden become super fast. As it should be. The less source paths you have under the Source Paths tab the faster it will be. You’ll still be able to jump into the library source with F3 when needed.
An Adobe employee on the Adobe forums seems to imply there may be some issues with doing this, but after a few weeks I have seen none.
Posted in: Tools
April 3rd, 2010
Cory Doctorow nailed it about the iPad:
“The iStore lock-in doesn’t make life better for Apple’s customers or Apple’s developers. As an adult, I want to be able to choose whose stuff I buy and whom I trust to evaluate that stuff. I don’t want my universe of apps constrained to the stuff that the Cupertino Politburo decides to allow for its platform. And as a copyright holder and creator, I don’t want a single, Wal-Mart-like channel that controls access to my audience and dictates what is and is not acceptable material for me to create.”
What kind of spell did Jobs cast on us to make us accept these terms? A computer where we have almost no control on it, yet we want to pay for it?
What is happening to computing?
Around 10 years ago we were horrified by TCPA and Palladium and Trusted Computing and all those future DRM technologies that evoked a really sinister aura of devices whose content we’d be unable to control. But… this is it! It is happening! It has already happened with the iPhone actually. At that time I imagined the killer app that would make this possible was going to be entertainment, and here it is. Everybody loves to be entertained. Now you have a fast and sleek device for it. With a great, “approved” user experience.
The genius here is that Apple understood that to make this happen — to have people accept it — they had to invent a brand new class of devices. Nobody will accept a classic computer with those locked-in limitations. And since the iPad is “revolutionary” and fast, sexy, beautiful, with an engaging UI, people will feel compelled to accept the compromise.
Apple invented a beautiful new device to do whatever the fuck they want, no matter how dirty. But they left the hackers out. Mind you, this is the same company (but is it really?) who made the Apple II+, which shipped with schematics.
Posted in: Design
just the letter e @ cubelogic dot o-r-g
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