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];
}