Reading Moby Dick using Grand Central Dispatch

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// This function blocks until all characters are counted.
void CBRCountCharactersInFileAtPath(NSString *path, unsigned int *characters)
{
    // The dispatch_io_read is an asynchronous call. We use a semaphore to provide synthetic synchronization.
    dispatch_semaphore_t semaphore = dispatch_semaphore_create(0);

    dispatch_queue_t readQueue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
    dispatch_io_t channel = dispatch_io_create_with_path(DISPATCH_IO_STREAM, [path UTF8String], 0, O_RDONLY, readQueue, NULL);

    // SIZE_MAX means keep going until we reach EOF. 
    dispatch_io_read(channel, 0, SIZE_MAX, readQueue, ^(bool done, dispatch_data_t data, int error) {
        if (done) {
            // All bytes have been read. Let's notify that we are done.
            dispatch_semaphore_signal(semaphore);
        } else if (data != NULL) {

            // As we read, we count.
            NSString *string = CBRStringFromDispatchData(data);
            CBRCountCharactersInString(string, characters);
        }
    });

    // Block the calling queue/ thread until the IO read completes (i.e. the channel is "done")
    dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER);

    // What we open, we must close. 
    dispatch_io_close(channel, 0);
}

The above code sets up and executes streaming file IO using Grand Central Dispatch. Now let’s look at the two functions named CBRStringFromDispatchData and CBRCountCharactersInString.

Here is the code used to create a NSString from a dispatch_data_t.

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NSString *CBRStringFromDispatchData(dispatch_data_t data)
{
    size_t dataSize = dispatch_data_get_size(data);
    NSMutableString *string = [[NSMutableString alloc] initWithCapacity:dataSize];
    dispatch_data_apply(data, ^bool(dispatch_data_t region, size_t offset, const void *buffer, size_t size) {
        [string appendFormat:@"%.*s", (unsigned int)size, buffer];
        return true;
    });
    return string;
}

Here is the code that tracks the character counts.

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void CBRCountCharactersInString(NSString *string, unsigned int *characters)
{
    for (unsigned int index = 0; index < [string length]; index++) {
        characters[[string characterAtIndex:index]]++;
    }
}

Sample Program

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#import "CBRCounter.h"

int main(int argc, const char * argv[])
{
    @autoreleasepool {
        unsigned int characters[256] = {0};
        CBRCountCharactersInFileAtPath(@"/path/to/mobydick.txt", characters);
        CBRPrintCharacterCount(characters);
    }
    return 0;
}

Printing the Character Counts

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void CBRPrintCharacterCount(unsigned int *characters)
{
    // This example only prints the "printable" characters. 
    for (unsigned int character = ' '; character <= '~'; character++) {
        NSLog(@"%c: %d", (char)character, characters[character]);
    }
}

Example Output

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A: 2725
B: 1466
C: 1184
D: 802
E: 1361
F: 864
G: 751
H: 1497
I: 3641
J: 261
K: 185
L: 959
M: 782
N: 1241
O: 1050
P: 1158
Q: 323
R: 895
S: 2277
T: 2568
U: 284
V: 181
W: 1326
X: 25
Y: 360
Z: 38

Verify the Counts

I verified my program’s results using TextEdit.

1. Open “Moby Dick” in TextEdit
2. Type Command+F
3. Deselect “Ignore Case”
4. Select “Contains”
5. Enter Character
6. View TextEdit’s Result

This is exactly what sparse checkouts enable.

Here are the steps to create a “sparse” Git local repository that only includes the “Completion” scripts.

Step 1: Create a directory.

I named mine git-completion. You can name the directory whatever you want.

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mkdir git-completion
cd git-completion

Step 2: Initialize a Git repository

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git init

Step 3: Enable Sparse Checkouts

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git config core.sparsecheckout true

Step 4: Tell Git which directories you want

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echo contrib/completion/ >> .git/info/sparse-checkout

Or you can modify the .git/info/sparse-checkout file directly. Either way is fine.

Step 5: Add the remote

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git remote add -f origin https://github.com/git/git.git

Final Step: Fetch the files

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git pull origin master

You should now have the contrib/completion directory. No other Git source files exist in your local copy.

Sourcing the files

Update your .bashrc file.

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source ~/Development/git-completion/contrib/completion/git-completion.bash
source ~/Development/git-completion/contrib/completion/git-prompt.sh

By Jason Graves

BLE or Bluetooth ‘Low Energy’ is a fairly new wireless spec designed to connect us to world around us. This includes gathering data from embedded sensors like a thermostat or heart rate monitor, or controlling the lights in your house or unlocking the front door without a key. Apple’s CoreBluetooth framework has been around since iOS 5, but we are only now starting to see many new BLE enabled devices become available. We will cover some of the interesting uses of BLE and how to use CoreBluetooth to create your own apps that can communicate with these devices.

• 6:00pm - Meet/Greet
• 6:15pm - Bluetooth LE
• 7:30pm - Next Meeting Details, Questions / Discussions

St. Louis County Library Headquarters (East Room); (314) 994-3300; (1640 S. Lindbergh Blvd).

Why I Bought AppCode

By Jason Hanson

AppCode, by JetBrains, is what an IDE should be. All the tools I have come to know and love in a ‘grown-up’ IDE for the Objective-C and iOS platform. My productivity, and more importantly, my confidence to refactor, skyrocketed when I started using AppCode. Come learn about some of the powerful features, tips, tricks, and shortcuts AppCode has to offer the iOS developer.

Lighten the load on your teams with Jenkins

By JP Revel

If you’ve ever been part of a software project with a team, it often falls to one person to compile the project when it comes time to deliver. There are lots of problems with this approach. One solution is to set up a CI server, such as Jenkins (formerly Hudson). I will talk about the concept of CI, go over a sample setup, show some configuration and (hopefully) have Jenkins build a project for us.

• 6:00pm - Meet/Greet
• 6:15pm - iOS Tools Talk
• 7:30pm - Next Meeting Details, Questions / Discussions

St. Louis County Library Headquarters (East Room); (314) 994-3300; (1640 S. Lindbergh Blvd).

By Rick Aurbach

While apps with straightforward UI designs can often be implemented effectively using a single storyboard and GUI-based segues, this approach is less effective for large complex UI designs. This talk will discuss techniques for dividing an application’s UI into multiple storyboards and implementing programmatically-generated segues. We will discuss tab bar controllers, embedding sub-controllers into views, popover controllers, and navigation controllers. The talk will hopefully appeal to newbies and veterans alike.

• 6:00pm - Meet/Greet
• 6:15pm - UIStoryboards by Rick Aurbach
• 7:30pm - Next Meeting Details, Questions / Discussions

St. Louis County Library Headquarters (East Room); (314) 994-3300; (1640 S. Lindbergh Blvd).

By Jeff Roberts

The vast majority of developers don’t write unit tests against their applications. The typical design of many iOS applications and the iOS SDK can make it challenging to write tests. We will learn about some basic unit testing principles, mocking with OCMock, asserting with OCHamcrest, swizzling and even cheating with KVO, while keeping score with some helpful utilities like OCUnit2JUnit and code coverage with gcov.

• 6:00pm - Meet/Greet
• 6:15pm - Unit Testing Objective-C Applications by Jeff Roberts
• 7:30pm - Next Meeting Details, Questions / Discussions

St. Louis County Library Headquarters (East Room); (314) 994-3300; (1640 S. Lindbergh Blvd).

By Brian Coyner

LLDB is the default debugger in Xcode on OS X. LLDB supports debugging Objective-C, C, and C++. We will discuss various aspects of the debugger, as well as look at how to utilize LLDB to effectively debug apps.

• LLDB architecture
• Various LLDB commands (setting breakpoints, setting watchpoints, thread control, etc.)
• Using the LLDB Python bridge to “script” a debug session

• 6:00pm - Meet/Greet
• 6:15pm - LLDB by Brian Coyner
• 7:30pm - Next Meeting Details, Questions / Discussions

St. Louis County Library Headquarters (East Room); (314) 994-3300; (1640 S. Lindbergh Blvd).

By Brian Coyner

Brian will discuss 5 things every iOS developer should know. Plus a few bonus items.

• 6:00pm - Meet/Greet
• 6:15pm - 5 Things Every iOS Developer Should Know by Brian Coyner
• 7:30pm - Next Meeting Details, Questions / Discussions

St. Louis County Library Headquarters (East Room); (314) 994-3300; (1640 S. Lindbergh Blvd).

5 Things Every iOS Developer Should Know

By Brian Coyner

Brian will discuss 5 things every iOS developer should know. Plus a few bonus items.

• 6:00pm - Meet/Greet
• 6:15pm - 5 Things Every iOS Developer Should Know by Brian Coyner
• 7:30pm - Next Meeting Details, Questions / Discussions

St. Louis County Library Headquarters (East Room); (314) 994-3300; (1640 S. Lindbergh Blvd).

By John Haney

Now that iOS 6 is officially released, we can dive into the details of the new features of this update.

• Maps
• Social Framework
• Pass Kit
• Game Center
• Reminders
• In-App Purchase
• and more

• 6:00pm - Meet/Greet
• 6:15pm - A Tour of iOS 6 by John Haney
• 7:30pm - Next Meeting Details, Questions / Discussions

St. Louis County Library Headquarters (East Room); (314) 994-3300; (40 & Lindbergh).

‘Nuff said

• 6:00pm - Meet/Greet
• 6:15pm - Core Animation is Awesome by Brian Coyner
• 7:30pm - Next Meeting Details, Questions / Discussions

St. Louis County Library Headquarters (East Room); (314) 994-3300; (40 & Lindbergh).

Brian Coyner (Xcode Tips and Tricks, Responder Chain) John Haney (View Controller) Other

• 6:00pm - Meet/Greet
• 6:15pm - July “Blast” Talks
• 7:30pm - Next Meeting Details, Questions / Discussions

St. Louis County Library Headquarters (East Room); (314) 994-3300; (40 & Lindbergh).

We will meet again in July for “July Blast” talks. These will be short talks dedicated to small, but useful iOS frameworks/ classes/ methods.

By Brian Coyner

iOS 5 introduced Storyboards. This talk shows how to effectively utilize storyboards to create and visualize your app’s workflows. We will focus on using Storyboards for both iPhone and iPad.

• Introduction
• Building Static and Dynamic UITableViews and UITableViewCells
• Responding to Segue Transitions (including popovers)
• Programmatically Invoking a Segue
• Composing custom iPad scenes with multiple view controllers (includes UIViewController containment)

• 6:00pm - Meet/Greet
• 6:15pm - UIStoryboards Are Awesome! by Brian Coyner
• 7:30pm - Next Meeting Details, Questions / Discussions

St. Louis County Library Headquarters (East Room); (314) 994-3300; (40 & Lindbergh).

Why no header (.h)?

• test cases are, by nature, private implementation details
• no need for a public interface (test cases are never imported by other test cases)
• it is completely legal Objective-C to have the @interface and @implementation in the same file

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//
// BTSPreferredTransferTest.m
//

#import <SenTestingKit/SenTestingKit.h>

@interface BTSPreferredTransferTest : SenTestCase
@end

@implementation BTSPreferredTransferTest

- (void)testSomethingUseful
{
    // Test implementation
}

@end

By Brian Paulsmeyer

This session covers the following Cocos2D topics

• menus, touch input, timers,
• sprites (with actions and animations)
• layers, tiled maps (with scrolling)
• joysticks/button pads,
• particle emitters, projectiles

• 6:00pm - Meet/Greet
• 6:15pm - Cocos2D by Brian Paulsmeyer
• 7:30pm - Next Meeting Details, Questions / Discussions

St. Louis County Library Headquarters (East Room); (314) 994-3300; (40 & Lindbergh).

By Byron Bennett

This session digs into the following Core Data topics:

• Using the new UIManagedDocument
• using Xcode to build an entity model
• executing “fetch requests”
• using NSFetchedResultsController to sync data with a UITableView

• 6:00pm - Meet/Greet
• 6:15pm - Getting Started with Core Data in iOS 5 by Byron Bennett
• 7:30pm - Next Meeting Details, Questions / Discussions

St. Louis County Library Headquarters (East Room); (314) 994-3300; (40 & Lindbergh).

Please let me know if you are interested in participating in this event.

This session will take place on March 1, 2012 (the February meeting) after the main presentation.

By Mark Schisler

The iOS Notification Center is a great way for app developers to notify users of matters which require their urgent attention. However, it can become one of the quickest ways to annoy users via what may be the most obnoxious personal communication medium ever devised by man, prompting users to uninstall your app, or worse write a bad review. This presentation will consider the best practices for implementing notifications as devised by the Apple Guidelines and other notable app experts. From there we will take a look under the hood at the technical details of implementing local and push notifications, including some PaaS options that might help (most notably: Urban Airship and Heroku via the APN on Rails framework.)

NOTE: The February meeting is Thursday, March 1.

• 6:00pm - Meet/Greet
• 6:15pm - What Your Mom Never Told You About Notifications by Mark Schisler
• 7:30pm - Next Meeting Details, Questions / Discussions

St. Louis County Library Headquarters (East Room); (314) 994-3300; (40 & Lindbergh).