Introduction to Objective-C Spring 2013

Goals An introduction to Objective-C As implemented by the Apple LLVM Compiler 4.0 (a.k.a. Clang) Only the basics… See the class web page for references: Reference->Objective-C Most of the references are WRONG about memory management Now ARC takes care of memory management for you!

History Brad Cox created Objective-C in the early 1980s Added object-oriented programming concepts to the C programming language NeXT Computer licensed the language in 1988 Used it to develop the NeXTSTEP operating system, programming libraries and applications for NeXT In 1993, NeXT worked with Sun to create OpenStep, an open specification of NeXTSTEP on Sun hardware

History In 1997, Apple purchased NeXT and transformed NeXTSTEP into MacOS X which was first released in the summer of 2000 Objective-C has been one of the primary ways to develop applications for OS X ever since In 2008, it became the primary way to develop applications for iOS

Objective-C Objective-C adds classes to C through a small set of extensions It is used with two object-oriented frameworks: The Foundation framework contains classes for basic concepts such as strings, arrays and other data structures and provides classes to interact with the underlying operating system The AppKit contains classes for developing applications and for creating windows, buttons and other widgets Together the Foundation and AppKit frameworks are called Cocoa

Objective-C On iOS, AppKit is replaced by UIKit Foundation and UIKit together are called Cocoa touch In this lecture, we focus on the Objective-C language, we’ll see a few examples of the Foundation framework we’ll see examples of UIKit later

Objective-C Objective C is C All of C code will work. Memory management not necessary with ARC Classes are based on Smalltalk syntax It’s a bit, well, weird.

XCode Apple’s development tool Only tool you can use to develop native apps for iOS Makes use of Apple’s Clang compiler Based on LLVM Used to use the gnu compilers, but Apple wanted to extend the compiler without open-sourcing the code LLVM is a highly-optimized compiler Xcode also contains Interface Builder, a tool for creating iOS GUI interfaces via drag ‘n drop.

Example Create a new project as you did with the C++ program. In the first dialog box choose “OS X” and “Application” Choose “Command Line Tool” hit “next” Enter a name. Make sure the “Type” is Foundation Make sure to check the checkbox next to “Create local git repository for this project” when you choose where to locate the project. A project will be created and you’ll get the file “main.m” The “.m” stands for “messages” Insert the code on the next slide

Example #import int main(int argc, const char *argv[]) { NSLog Objective-C!”); } return(0); } // main Instead of include import will ensure that the file is only included once. NSLog is the printf of the Foundation frameworks. Also prints date & time and a newline signifies a NSString. NS = NextStep This is a string class like that found in Java Most Foundation framework classes expect a NSString not a C style string!

Interlude notice that an “M” appears to the right of main.m after you edit it. The M is an aspect of XCode’s git integration. It’s telling you that the file was modified and that (eventually) you can check these changes into the git repository XCode automatically created the git repository for you.

Example 2 #import int main(int argc, const char * argv[]) { char getName[32]; printf("Enter a name: "); scanf("%s", getName); printf(“Hello %s\n”, getName); } return 0; }

Example 2.1 #import int main(int argc, const char * argv[]) { char getName[32]; printf("Enter a name: "); scanf("%s", getName); // Note the use of a “C” string %s !", theName); } return 0; }

Example 2.2 #import int main(int argc, const char * argv[]) { NSString *theName; char getName[32]; printf("Enter a name: "); scanf("%s", getName); theName = [NSString stringWithCString:getName encoding:NSASCIIStringEncoding]; theName); } return 0; } It’s complicated to convert a C string to a NSString! Note the format for NSString NSString is defined in the Foundation framework

Example 3 int main(int argc, const char * argv[]) { BOOL areTheyDifferent; areTheyDifferent = areIntsDifferent (5, 5); NSLog %d and %d different? 5, [NSString areTheyDifferent = areIntsDifferent (23, 42); NSLog %d and %d different? 42, [NSString } return 0; } BOOL is a Foundation type Different from a C language “bool” In Foundation library have constants for BOOL type: YES = 1 NO = 0

Example 3 // returns NO if the two integers have the same // value, YES otherwise BOOL areIntsDifferent (int thing1, int thing2) { if (thing1 == thing2) { return (NO); } else { return (YES); } } // areIntsDifferent

Example 3 // given a YES value, return the human-readable // string "YES". Otherwise return "NO" NSString *boolString (BOOL yesNo) { if (yesNo == NO) { return } else { return } } // boolString