Objective-C

lastmod 2021-04-04created 2014-02-0434 edits

The Objective-C language (often written ObjC) is an object-oriented language that adds Smalltalk-style messaging syntax to the C programming language.

Currently, the language is used in Mac OS X, the operating system of Apple's Macintosh, and in iOS, the operating system of the iPhone. Objective-C is the primary language for using Apple's Cocoa, and was originally the main language of NeXT's NeXTSTEP operating system. Generic Objective-C does not use the libraries mentioned above.

Basic

• (Repost) Basic syntax of Objective C
• ObjectiveC:DefaultClassTemplate: How to write a basic Objective-C class.
• XCode
• XCode:iPhone:Basic - Basics of iPhone app development.
• iOS
• Core MIDI - Communicate with MIDI devices such as hardware keyboards and synthesizers.
• Core Audio
• Apple

List of Objective-C 2.0 @ Compiler Directives

• @class
• @defs
• @protocol @required @optional @end
• @interface @public @package @protected @private @property @end
• @implementation @synthesize @dynamic @end
• @throw @try @catch @finally
• @synchronized @autoreleasepool
• @selector @encode
• @compatibility_alias
• @"string"

CMake compile

• Stackoverflow - CMakeLists.txt for an Objective C Project

When using clang, you can compile objective-c as follows.

cmake_minimum_required(VERSION 2.8)
project(HelloWorld)
set(NAME HelloWorld) 
set(CMAKE_C_FLAGS "-x objective-c")
#set(CMAKE_CXX_FLAGS "-x objective-c++")

set(HEADER_FILES 
    ./uhdplayerengine/HelloWorld/HelloWorld/AppDelegate.h
)
set(SOURCE_FILES 
    ./uhdplayerengine/HelloWorld/HelloWorld/AppDelegate.m
    ./uhdplayerengine/HelloWorld/HelloWorld/main.m
)
set(XIB_FILE
    ./uhdplayerengine/HelloWorld/HelloWorld/Base.lproj/MainMenu.xib
)

add_executable(
    ${NAME}
    MACOSX_BUNDLE
    ${HEADER_FILES}
    ${SOURCE_FILES}
    ${XIB_FILE}
)

set_source_files_properties(
    ${XIB_FILE}
    PROPERTIES
    MACOSX_PACKAGE_LOCATION
    Resources
)

set_target_properties(
    ${NAME}
    PROPERTIES
    MACOSX_BUNDLE_INFO_PLIST
    ./uhdplayerengine/HelloWorld/HelloWorld/HelloWorld-Info.plist
)

target_link_libraries(${NAME}
    "-framework Cocoa"
    "-framework AppKit"
    "-framework CoreData"
    "-framework Foundation"
)

When passing Linker flags, if Foundation is interpreted as -lFoundation, pass it as -Wl,-framework,Foundation.

Framework

• Foundation
• AVFoundation
• CoreVideo
• CoreMedia
• CoreGraphics
• OpenGL
• CoreImage
• AppKit
• CoreFoundation
• Security
• AudioToolbox
• VideoToolbox
• CoreServices
• CGDirectDisplay

Memory management

Explanation of how memory is managed in Objective-C.

Memory management: Favorite site

• Moon's lectures: Memory management Objective-C
• About the retainCount of ObjC objects
• [Recommended] How memory is managed in OBJECTIVE-C ¹
• iOS memory management: retain/release/autorelease

Examples

String formatting

Use the stringWithFormat function of the NSString class.

int i = 1;
NSString *name = @"thefirstsong";
NSString *filename = [NSString stringWithFormat:@"%0d-%@.mp3", i, name];

Converting between NSString and CFStringRef

• Stackoverflow - NSString to CFStringRef and CFStringRef to NSString in ARC?

Typically:

NSString *yourFriendlyNSString = (__bridge NSString *)yourFriendlyCFString;

and

CFStringRef yourFriendlyCFString = (__bridge CFStringRef)yourFriendlyNSString;

Now, if you want to know why the __bridge keyword is there, you can refer to the Apple documentation. There you will find:

• __bridge transfers a pointer between Objective-C and Core Foundation with no transfer of ownership.
• __bridge_retained or CFBridgingRetain casts an Objective-C pointer to a Core Foundation pointer and also transfers ownership to you. You are responsible for calling CFRelease or a related function to relinquish ownership of the object.
• __bridge_transfer or CFBridgingRelease moves a non-Objective-C pointer to Objective-C and also transfers ownership to ARC. ARC is responsible for relinquishing ownership of the object.

NSString → CFString

:

// Don't transfer ownership. You won't have to call `CFRelease`
CFStringRef str = (__bridge CFStringRef)string;

// Transfer ownership (i.e. get ARC out of the way). The object is now yours and you must call `CFRelease` when you're done with it
CFStringRef str = (__bridge_retained CFStringRef)string // you will have to call `CFRelease`

CFString → NSString

:

// Don't transfer ownership. ARC stays out of the way, and you must call `CFRelease` on `str` if appropriate (depending on how the `CFString` was created)
NSString *string = (__bridge NSString *)str;

// Transfer ownership to ARC. ARC kicks in and it's now in charge of releasing the string object. You won't have to explicitly call `CFRelease` on `str`
NSString *string = (__bridge_transfer NSString *)str;

CFString to C string

• Stackoverflow - Converting a CFStringRef to char *

const char *cs = CFStringGetCStringPtr( cfString, kCFStringEncodingMacRoman ) ;
puts( cs ) ; // works

Sample

MotionSensorManager (Geosoft iOS MyCarNavi)

Class for acquiring iPhone motion sensor data.

See also

• Cocoa

Favorite site

• Wikipedia (en) explanation of Objective-C
• A few things to know when using Windows + GNUSTEP + CLANG
• Closure and anonymous functions in Objective-C ²
• Apple - The Objective-C Programming Language ³
• From C++ to Objective-C ⁴

References