Learn Objective-C: Day 1

Welcome to my series on coming to grips with the awesome language that is Objective-C. Throughout this small series of articles, my aim is to take you from no prior experience with Objective-C to using it confidently in your own applications. This isnʼt a rush job – so donʼt expect to just skim through the basics and be away – weʼll be going through not just the bare essentials, but also the best practices you can apply to ensure your code is the best it can be. Letʼs jump straight in!

What is Objective-C?

If youʼre reading this series then Iʼll hazard a guess that you already know, but for those of you who donʼt, donʼt worry as by the end of this part youʼll know what it is back-to-front and inside-out.

Objective-C is an object oriented language which lies on top of the C language (but I bet you guessed that part!). Itʼs primary use in modern computing is on Mac OS X as a desktop language and also on iPhone OS (or as it is now called: iOS). It was originally the main language for NeXTSTEP OS, also known as the operating system Apple bought and descended Mac OS X from, which explains why its primary home today lies on Appleʼs operating systems.

Because Objective-C is a strict superset of C, we are free to use C in an Objective-C file and it will compile fine. Because any compiler of Objective-C will also compile any straight C code passed into it, we have all the power of C along with the power of objects provided by Objective-C.

If youʼre a little confused at this point, think of it this way: everything C can do, Objective-C can do too, but not the other way around.

Creating A Cydia Repository/Source For iOS! [Covering Everything A-Z]

This tutorial will explain the process of creating a Cydia repository from start to finish. We will cover everything from the initial preparation all the way to the hosting and publishing of your Cydia repository. This tutorial will get moderately technical and is not recommended for users who are new to computers or new to the whole jailbreaking scene. I will provide support for this tutorial through the comments section, but you can also contact me directly at: jaden@ijailbreak.com

Cocoa: Binding. GUI application without outlets

Outlet in Cocoa is a persistent reference to a GUI control. For example, it is a common way to create the outlet to the text field and change the text in this field via the outlet. Now, in 64-bit Xcode, you add a property with IBOutlet keyword, synthesize it, and set new text via that property:

1. In interface declaration:

@property (retain) IBOutlet NSTextField * text;

2. In the implementation section:

@synthesize text;

3. Set new text to the text field:

text.stringValue = @"Hello, World!";

4. Get value:

NSString* str = text.stringValue;

Cocoa: show Alert

Show Alert in a Cocoa application:

- (IBAction)showAlert:(id)sender

{

NSString *question = NSLocalizedString(@"Do you see this alert?", 

   @"Let's verify that I see this question");

NSString *info = NSLocalizedString(@"I hope, I see this alert", 

           @"Here is an info");

NSString *cancelButton = NSLocalizedString(@"Cancel", 

   @"Cancel button title");

NSAlert *alert = [[NSAlert alloc] init];

[alert setMessageText:question];

[alert setInformativeText:info];

[alert addButtonWithTitle:cancelButton];

NSInteger answer = [alert runModal];

[alert release];

alert = nil;

}

Cocoa: NSScanner

sscanf is a standard C function. We use it so rarely, but it exists and can be the fastest method to parse a string. In order to remind I post this short program that uses sscanf to retrieve two float number from a string:

#include <stdio.h>

int main (int argc, const char * argv[]) 
{
    float x, y;
    const char* string = "3.1415 6.28";
    sscanf(string, "%f %f", &x, &y);
    printf("x = %.4f, y = %.2f\n", x, y);
    return 0;
}

Template program to learn Cocoa graphics

The standard way to learn new programming language is very boring for me - endless reading of heavy books, typing useless programs that calculates factorials,... Since my student times, since GWBASIC I begin from the graphics, simple graphic, rectangles, circles - the graphic primitives. When I know how to draw them, I can go on and learn the basic language constructions, language semantic and programming techniques.
This way works for me in my Cocoa period. In this post I'd like to show two methods to create a template project that allows to learn the Cocoa graphical primitives. This template can grow in your hands and become a real Cocoa (or Coco Touch) application.
As any Cocoa application this application has a main window and a view inside. That's all. First method uses Interface Builder. The second one fully ignores the Interface Builder.

Cocoa: Implicit Animation

This program will help to begin with the Core Animation.
1. In Xcode create Max OS X Cocoa Application.
2. In the Application delegate implementation file (automatically created by Xcode on Snow Leopard) add a button to the content view:

- (void)applicationDidFinishLaunching:(NSNotification *)aNotification 
{
    // Create new button in content view.
    NSRect frame = NSMakeRect(10, 40, 90, 40);
    NSButton* pushButton = [[NSButton alloc] initWithFrame: frame];
    pushButton.bezelStyle = NSRoundedBezelStyle;
    [pushButton setTitle: @"Move"];
    [self.window.contentView addSubview: pushButton];
    
    // Set the button target and action.
    pushButton.target = self;
    pushButton.action = @selector(move:);
    
    [pushButton release];
}

Save and Load UIImage in Documents directory on iPhone

The following function saves UIImage in test.png file in the user Document folder:

- (void)saveImage: (UIImage*)image
{
    if (image != nil)
    {
        NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, 
                      NSUserDomainMask, YES);
        NSString *documentsDirectory = [paths objectAtIndex:0];
        NSString* path = [documentsDirectory stringByAppendingPathComponent: 
                       [NSString stringWithString: @"test.png"] ];
        NSData* data = UIImagePNGRepresentation(image);
        [data writeToFile:path atomically:YES];
    }
}

Create Bitmap Graphics Context on iPhone

The following function creates an UIImage object:

- (UIImage*)makeImage: (CGRect)rect
{
    CGFloat width = CGRectGetWidth(rect);
    CGFloat height = CGRectGetHeight(rect);
    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
    
    size_t bitsPerComponent = 8;
    size_t bytesPerPixel    = 4;
    size_t bytesPerRow      = (width * bitsPerComponent * bytesPerPixel + 7) / 8;
    size_t dataSize         = bytesPerRow * height;
    
    unsigned char *data = malloc(dataSize);
    memset(data, 0, dataSize);

    CGContextRef context = CGBitmapContextCreate(data, width, height, 
                bitsPerComponent, 
                bytesPerRow, colorSpace, 
                kCGImageAlphaPremultipliedLast | kCGBitmapByteOrder32Big);

    
    CGColorSpaceRelease(colorSpace);
    CGImageRef imageRef = CGBitmapContextCreateImage(context);
    UIImage *result = [[UIImage imageWithCGImage:imageRef] retain];
    CGImageRelease(imageRef);
    CGContextRelease(context);
    free(data);    
    return result;
}

Make a snapshot from an iPhone application

Today I needed to make a snapshot programmatically. I thought it's easy:
[iPhone developer:tips];. Screen Capture using UIGetScreenImage.
Unfortunately, this approach does not work for me. People say that this API is private.
Ok. Let's make our own function.
I will add this function to my application delegate class. It looks so:

@interface myDelegate : NSObject<UIApplicationDelegate>
{
    UIWindow* window;
}

- (void) makeSnapshot;

@end

Cocoa. Date and Time

This small program below detects the current date:

#import <Foundation/Foundation.h>

int main (int argc, const char * argv[]) {
    NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];

     NSDate* today = [[NSDate alloc] init];
     NSLog(@"today is: %@", today);
    
    [today release];        
    [pool drain];
    return 0;
}

In the console you'll see:

run
[Switching to process 12401 local thread 0x3f03]
Running…
2010-03-06 17:05:45.217 DayOfToday[12401:a0f] today is: 2010-03-06 17:05:45 +0200

The Blocks

Apple introduced blocks (a segment of code that can be executed any time) in C and Objective-c. It happened in Mac OS X 10.6. Later on this feature was back-ported to Mac OS X 10.5 and iPhone by Plausible Labs.  The blocks are also called closures, because they close around variables. Also the blocks can be called lambdas.
I'd say that the blocks are the same as the regular function pointers in C. From a very general point of view, the main difference is just the symbol caret (^) before the block name instead of the asterisk (*) before the function pointer. Here is a trivial example: 

#import <Foundation/Foundation.h>

int main (int argc, const char * argv[])
{

    @autoreleasepool {

        void (^now)(void) = ^{ 
            NSDate* moment = [NSDate date];
            NSLog(@"Now: %@", moment);
        };
        
        
        now();
    }
    return 0;
}

The program output is: [Switching to process 41322 thread 0x0] 2011-11-26 18:07:25.202 block4[41322:707] Now: 2011-11-26 16:07:25 +0000 Program ended with exit code: 0 The following program simply creates and synchronously performs a block:

Sort String Array

The following code demonstrates how to sort an array of strings in Objective-C:

#import <Foundation/Foundation.h>

int main (int argc, const char * argv[])
{

    @autoreleasepool {
        
        NSArray *stringsArray = [NSArray arrayWithObjects:
                                 @"string 1",
                                 @"String 21",
                                 @"string 12",
                                 @"String 11",
                                 @"String 02", nil];
        static NSStringCompareOptions comparisonOptions = NSCaseInsensitiveSearch | NSNumericSearch |
        NSWidthInsensitiveSearch | NSForcedOrderingSearch;
        NSLocale *currentLocale = [NSLocale currentLocale];
        NSComparator finderSort = ^(id string1, id string2) {
            NSRange string1Range = NSMakeRange(0, [string1 length]);
            return [string1 compare:string2 options:comparisonOptions range:string1Range locale:currentLocale];
        };
        
        NSArray* sortedArray = [stringsArray sortedArrayUsingComparator:finderSort];
        NSLog(@"finderSort: %@", sortedArray);        
    }
    return 0;
}

This code is taken from iOS Developer Library.

Accelerometer. It's simple

The simplest way to use accelerometer in an iPhone application is UIAccelerometer class:

    UIAccelerometer* accelerometer = [UIAccelerometer sharedAccelerometer];

This code above shows how to get the accelerometer instance in the code.
The following line sets up the update interval:

    [accelerometer setUpdateInterval: 1.0 / 10.0f];

    [accelerometer setDelegate:self];

each 0.1 second the accelerometer will update the program that implements delegate method:

 - (void)accelerometer:(UIAccelerometer *)acel didAccelerate:(UIAcceleration *)aceler 

{

    NSLog(@"acceleration.x = %+.6f", aceler.x);

    NSLog(@"acceleration.y = %+.6f", aceler.y);

    NSLog(@"acceleration.z = %+.6f", aceler.z);

}

Do not forget to add UIAccelerometerDelegate, for example, to a view controller class:

Objective-C. Class Extensions.

Few years ago, I was writing my first program in Objective-C, I was surprised that there is no way to add a private method to my class. Encapsulation, one of the basic principles of the OO programming, does not work in Objective-C? Unbelievable.
I found a way to declare a private category in the class main implementation class:

@interface MyClass (Private)
- (void)privateMethod;
@end

Once, by mistake, probably because of this annoying spell checker helping to type code in Xcode, I forgot the category name:

@interface MyClass ()

- (void)privateMethod;

@end

Singleton in iOS Programming

What Apple says about Singleton: 
Cocoa Core Competencies.Singleton 
Creating a Singleton Instance 

What other people say: 
Singletons in Cocoa/Objective-C 
Implementing a Singleton in iOS 
Implementing a Singleton in Objective-C / iOS 
Singleton Classes 
A note on Objective-C singletons 
Singletons, AppDelegates and top-level data. 

A long discussion about it in Stackoverflow: What does your Objective-C singleton look like?

Add Settings to an iOS project

Just find a very nice article about the subject: 
Adding a settings bundle to an iPhone App 

Please pay attention on the paragraph "Even defaults need defaults…" - that's what I needed in my app. Recently I found out that the default values I set for the settings do not work - a boolean parameter is always NO and does not matter that I set it to YES. This boolean parameter gets its default value only when the user opens the application settings for the first time. This article proposes a solution.

The source documentation in the iOS Developer Library: 
Preferences and Settings Programming Guide 

iOS Developer Library proposes an example: FunHouse. Here is a method from this sample:

+ (void)setupDefaults

{

    NSDictionary *userDefaultsValuesDict;

    userDefaultsValuesDict=[NSDictionary dictionaryWithObject:

              [NSNumber numberWithBool:NO] forKey:@"useSoftwareRenderer"];

    

    // set them in the standard user defaults

    [[NSUserDefaults standardUserDefaults] 

              registerDefaults:userDefaultsValuesDict];

}

Find all words in a sentence

This is one of the first samples in Mac OS X Developer Library. I found it in Cocoa Fundamental Guide

#import <Foundation/Foundation.h>

int main(int argc, const char * argv[])

{

    @autoreleasepool {

        

        NSArray *param = [[NSProcessInfo processInfo] arguments];

        NSCountedSet *cset = [[NSCountedSet alloc] initWithArray:param];

        NSArray *sorted_args = [[cset allObjects]

                                sortedArrayUsingSelector:@selector(compare:)];

        NSEnumerator *enm = [sorted_args objectEnumerator];

        id word;

        while (word = [enm nextObject]) {

            printf("%s\n", [word UTF8String]);

        }

        

        [cset release];

        

    }

    return 0;

}

Objective-C. Read text file.

This small program reads the text file:

#import <Foundation/Foundation.h>

int main (int argc, const char * argv[]) 
{
    NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];

    NSString* fileName = @"text.txt";
    NSString *fileString = [NSString stringWithContentsOfFile: fileName];

    NSArray *lines = [fileString componentsSeparatedByString:@"\n"];    

    [pool drain];
    return 0;
}