Make Better Things

They are all zeros, the difference lies in their types

-> NULL is a generic pointer value ((void*)0, to be specific). It points to 0×0.
-> nil is an id. So its points to a non-existent objective-c object
-> Nil is a non-existent objective-c class
-> [NSNull null] is an object that’s meant to stand in for nil in situations where nil isn’t allowed. For example, you can’t have a nil value in an NSArray. So if you need to represent a “nil”, you can use [NSNull null]

Also there is no ‘null’ in the objective c its ‘NULL’ not ‘null’. ‘null’ exist in Java or in C# not in Objective-C

Ever wondered how the NSString’s +stringWithFormat: method work? How you can pass endless arguments in it?

Well methods that take variable arguments are known as variadic methods.

Here is an example of such a method

Declare variable argument function in your .h file as below

- (void) appendObjects:(id) firstObject, ...; // This method takes a nil-terminated list of objects.

Here is the definition in .m file –

- (void) appendObjects:(id) firstObject, ...
{
     id eachObject;
     va_list argumentList;
     if (firstObject) // The first argument isn't part of the varargs list,
     {
           [self addObject: firstObject];// so we'll handle it separately.
           va_start(argumentList, firstObject); // Start scanning for arguments after firstObject.
           while (eachObject = va_arg(argumentList, id)) // As many times as we can get an argument of type "id"
           {
               [self addObject: eachObject]; // that isn't nil, add it to self's contents.
           }
           va_end(argumentList);

     }

}

Here is a good compilation of links useful in learning iOS development

1) Blogs on iPhone development

http://www.cimgf.com/

http://mycodeteacher.com/

http://iphonedevelopment.blogspot.com/

http://iphoneincubator.com/blog/

http://iphone.zcentric.com/

http://iphoneproghelp.blogspot.com/ (Programming Tutorial)
http://icodeblog.com/ (Programming Tutorial)

http://idevrecipes.com/

2) iPhone Source Code

http://www.theiphonedev.com/SourceCode/tabid/143/Default.aspx

3) Community

http://www.iphonekicks.com/

https://devforums.apple.com/

http://iphonedevsdk.com/

4) News

http://mobileorchard.com/

http://theappleblog.com/

5) Jail breaking/Hacking

http://theiphoneproject.org/

6) Open source libraries and Applications

http://www.codingventures.com/2008/12/useful-open-source-libraries-for-iphone-development/#more-43

http://www.sourcemac.com/

http://www.codeplex.com/

Face Detection: http://niw.at/articles/2009/03/14/using-opencv-on-iphone/en
Bar Code: Is there a barcode recognition framework for iOS?
Rating: http://github.com/eisernWolf/TouchCustoms

http://github.com/erica/iphone-3.0-cookbook-

Is there a gallery of reusable iPhone components on the web?

http://mattgemmell.com/source

http://www.cocoacontrols.com/

http://open.iphonedev.com/

http://www.opensourceresources.org/

http://www.raywenderlich.com/tag/sample-code

Three 20: http://github.com/facebook/three20
Tapku Library: http://github.com/devinross/tapkulibrary

7) Topic-wise
App Store: https://developer.apple.com/appstore/resources/approval/guidelines.html
GIF Support: http://stackoverflow.com/questions/1379818/how-can-i-make-an-animated-gif-with-the-iphone-sdk
In App Purchase: http://www.sixtemia.com/journal/2009/08/12/using-store-kit-framework/
IP Address: http://www.iphonedevsdk.com/forum/iphone-sdk-development/5293-get-current-ip-address.html
Page Curl Animation: What iPhone OS APIs could I use to implement a transition animation similar to the iBook page flip transition?
TTF Font http://github.com/zynga/FontLabel
Rotate Label: http://iphonedevelopment.blogspot.com/2009/12/better-two-finger-rotate-gesture.html
Speech Recognition – 1: http://cmusphinx.sourceforge.net/
Speech Recognition – 2: http://www.politepix.com/openears/
Operation and Thread: http://www.cimgf.com/2008/02/16/cocoa-tutorial-nsoperation-and-nsoperationqueue/
Web service: http://icodeblog.com/2008/11/03/iphone-programming-tutorial-intro-to-soap-web-services/
Code Analyzer: http://clang.llvm.org/StaticAnalysis.html
Game Center: http://mobile.tutsplus.com/tutorials/iphone/ios-sdk-game-center-achievements-and-leaderboards-part-1/
SMS Chat: https://github.com/acani/AcaniChat
Rotating Knob: https://github.com/hollance/MHRotaryKnob

8 ) Game Development with Cocos2D

http://code.google.com/p/cocos2d-iphone/

http://blog.sapusmedia.com/search/label/cocos2d

http://iphonesdkdev.blogspot.com/2009/01/xcode-template-for-cocos2d.html

http://monoclestudios.com/cocos2d_whitepaper.ht

http://lethain.com/entry/2008/oct/03/notes-on-cocos2d-iphone-development/

http://lethain.com/entry/2008/oct/20/touch-detection-in-cocos2d-iphone/

Open GL: http://web.me.com/smaurice/AppleCoder/iPhone_OpenGL/Archive.html

9) Drawing Charts and Graphs

http://code.google.com/p/core-plot/

http://code.google.com/p/s7graphview/

http://github.com/duivesteyn-enterprises/deSimpleChart

http://www.rgraph.net/ (Will work on UIWebView only)
http://sebkade.wordpress.com/2010/05/06/basic-graph-class-for-iphone/ (a blog where demo is given to create a graph)

10) Map Kit

http://github.com/kishikawakatsumi/MapKit-Route-Directions

http://www.iphonedevsdk.com/forum/iphone-sdk-development/8100-opening-maps-app-given-route-direction.html

http://spitzkoff.com/craig/?p=65

11) Audio Streaming

http://code.google.com/p/indie1031/

http://cocoawithlove.com/2010/03/streaming-mp3aac-audio-again.html

http://code.google.com/p/audiostreamer-meta/

http://github.com/DigitalDJ/AudioStreamer

http://lists.apple.com/archives/coreaudio-api/2009/Jan//msg00143.html

https://bitbucket.org/brentsimmons/ngmovieplayer/ (It’s a code for streaming video using     AVPlayer class. Same code could be applied for streaming audio as well by minor modification)

12) Twitter

http://code.google.com/p/tweetphoto-api-objective-c/

http://tweetphoto-api-objective-c.googlecode.com/files/TweetPhoto.zip

13) Scroll View

http://github.com/andreyvit/ScrollingMadness

14) SQLite

http://code.google.com/p/sqlitepersistentobjects/

http://www.slideshare.net/360conferences/using-sqlite

15) Video
How to play YouTube Movie on an iPhone Application when tapped on UITableViewCell?

http://www.iphonedevsdk.com/forum/iphone-sdk-development/41322-convert-image-sequences-video.html

16) SCM

http://iphonedevelopment.blogspot.com/2009/03/version-control-is-your-friend.html

http://developer.apple.com/tools/subversionxcode.html

Which SCM system for Xcode?

http://www.covertapps.com/development/6-setting-up-your-xcode-scm-repositories

17) Testing: Functional Testing

http://www.gorillalogic.com/fonemonkey

Unit Testing:
i) http://code.google.com/p/google-toolbox-for-mac/
ii)http://developer.apple.com/tools/unittest.html
Automated Testing:
i) http://cocoawithlove.com/2008/11/automated-user-interface-testing-on.html
ii)http://code.google.com/p/uispec/
iii) http://answers.oreilly.com/topic/1646-how-to-use-uiautomation-to-create-iphone-ui-tests/

18) Push Notification

http://blog.boxedice.com/2009/07/10/how-to-build-an-apple-push-notification-provider-server-tutorial/

http://urbanairship.com/

19) Core Data Tutorial for Beginners

http://www.raywenderlich.com/934/core-data-tutorial-getting-started

20) VOIP

http://code.google.com/p/idoubs/

http://code.google.com/p/siphon/

http://github.com/pzion/miumiu

http://www.linphone.org/eng/download/git.html

I strongly recommend not to use iOS version numbers to write conditional code. There is usually a more reliable method of checking whether a particular feature available or not. But if you are in a deadly situation and hardly needed the version number then you can get iOS version number by UIDevice class. Here is the real code –

NSString *currSysVer = [[UIDevice currentDevice] systemVersion];

Here is how you can use this to write conditional code –

// A system version of 3.1 or greater is required to use CADisplayLink. The NSTimer
// class is used as fallback when it isn't available.
NSString *reqSysVer = @"3.1";
NSString *currSysVer = [[UIDevice currentDevice] systemVersion];
if ([currSysVer compare:reqSysVer options:NSNumericSearch] != NSOrderedAscending)
    displayLinkSupported = TRUE;

Above code works great but writing this condition is real pain every time. The solution of this is Macros. We can use Macros in objective c and reduce the line of code in above code.

Here is real code using Macros –

/*
 *  System Versioning Preprocessor Macros
 */ 

#define SYSTEM_VERSION_EQUAL_TO(v)                  ([[[UIDevice currentDevice] systemVersion] compare:v options:NSNumericSearch] == NSOrderedSame)
#define SYSTEM_VERSION_GREATER_THAN(v)              ([[[UIDevice currentDevice] systemVersion] compare:v options:NSNumericSearch] == NSOrderedDescending)
#define SYSTEM_VERSION_GREATER_THAN_OR_EQUAL_TO(v)  ([[[UIDevice currentDevice] systemVersion] compare:v options:NSNumericSearch] != NSOrderedAscending)
#define SYSTEM_VERSION_LESS_THAN(v)                 ([[[UIDevice currentDevice] systemVersion] compare:v options:NSNumericSearch] == NSOrderedAscending)
#define SYSTEM_VERSION_LESS_THAN_OR_EQUAL_TO(v)     ([[[UIDevice currentDevice] systemVersion] compare:v options:NSNumericSearch] != NSOrderedDescending)

And how we can use these Macros to write conditional code –

/*
 *  Usage
 */ 

if (SYSTEM_VERSION_LESS_THAN(@"4.0")) {
    ...
}

if (SYSTEM_VERSION_GREATER_THAN_OR_EQUAL_TO(@"3.1.1")) {
    ...
}

Hope these Macros will save someone’s time.

Multitasking support is enabled by default in all iOS 4+ application. There can be situations where you need to disable this support (if you don’t want your app to run in background).
You can disable multitasking in iOS 4+ app just by adding a key in your info.plist file.

You just need to add this following key (right click on your info.plist file and open as plain text file) –

<key>UIApplicationExitsOnSuspend</key>
	<true/>

If you are using visual editor to edit info.plist file the just click on “+” button and add ‘UIApplicationExitsOnSuspend’ key and press tab key and select the check mark.