iOS Development

Rules of Swift Initializers

2017-04-27T22:19:00.004-04:00

Rule 1: A designated initializer must call its immediate superclass designated initializer

Rule 2: A convenience initializer must calls initializers of the same class

Rule 3: A convenience initializers must ultimately call the designated initializer

Simple Case:

Complex Case

Reference

https://developer.apple.com/library/content/documentation/Swift/Conceptual/Swift_Programming_Language/Initialization.html

Constructs in Objective C and Swift

2017-04-23T17:06:00.005-04:00

Classes, Structs and Enums are called Constructs and all three of them allow your program to store, organize or manipulate data in different ways with different capabilities.

Classes

General Purpose, flexible construct that becomes the building blocks of your program code.
Have properties and methods that provide data storage and functionality to constructs
Can use inheritance
Can use initializers and de-initializers when setup or tear down when they are created or destroyed.

Structs

Structs in Swift can have Properties and Methods (Swift Only)
Can use initializers (Swift Only)
No Inheritance
Passed by copy ( this can be advantage/disadvantage based on the needs)

Enums:

Way to group related elements
Can include functions (Swift only)
Can use initializers (Swift only)

Operators in Objective C and Swift

2017-04-23T16:45:00.002-04:00

Common for Objective C and Swift

Assignment Operator ( = )
Arithmetic Operator

addition +,
Subtraction -,
Multiplication *,
Division /

Remainder (Modulo) Operator %
Unary plus operator (+), Unary minus operator (-), unary operator is prepended directly on the value it operates on.
compound assignment/short hand operators (x+=y, x-=y, x*=y, x/=y, x%=y, x&=y, x|=y, x^=y)
Increment (++) & decrement operator (—) {int x=9, int y: y= ++x , y = - - x } (Removed in Swift 3)
Relational/Comparison operators

Equal to (a == b)
Not equal to (a != b)
Greater than (a > b)
Less than (a < b)
Greater than or equal to (a >= b)
Less than or equal to (a <= b)

Logical Operator

Logical Not (!a)
Logical AND (a && b)
Logical OR (a || b)

Ternary Conditional Operator ( if condition? expression 1 : expression 2 )

Swift Only

Range Operator

Closed Range Operator '1…10', includes 1 and 10 in this range.
Half Open Range Operator '1..~10 , includes 1 but not 10

Nil-Coalescing Operator (x??y)

The nil-coalescing operator (x ?? y) unwraps an optional x if it contains a value, or returns a default value y if x is nil. The expression a is always of an optional type. The expression y must match the type that is stored inside x.

The nil Coalescing operator is shorthand for the below code:

x != nil ? x! : y

The code above uses the ternary conditional operator and forced unwrapping (x!) to access the value wrapped inside a when x is not nil, and to return x otherwise. The nil-coalescing operator provides a more elegant way to encapsulate this conditional checking and unwrapping in a concise and readable form.

Guard in Swift

2017-04-23T15:50:00.000-04:00

Guard statement is similar to IF statement except the fact that body of code executes when the condition in guard statement is evaluated to false.

var citizenAge:Int //Declare a variable of type Integer

citizenAge = 65

guard citizenAge < 60 else {

// Here citizen age is 65, the guard condition is evaluated to false and the below statement is executed.

print("Senior Citizen")

return
}

print("Not a Senior Citizen") // this is executed when guard condition is true.

Guard Statement can also be used for optional binding

var playerScore:Int? //Declare a variable a of type Optional Integer, which might or might not have value (for e.g if player did not bat, he might not have any score)

func updatePlayerScore (playerScore:Int?){

guard let score = playerScore else {

print(“Player did not bat“)

return

}

print("Player score is \(score)")

}

Unlike if statement values assigned in the Guard statement are still available after the Guard statement through out the remaining scope that encloses the Guard Statement
Guard Statement are typically written at the top of the enclosing scope

Swift Data Types

2017-04-23T14:53:00.001-04:00

There are two fundamental data types in Swift

Value Types

Int, Floating-Points, Booleans, Characters, Strings , Arrays, Dictionaries and Tuples (which are implemented as Structures)
Optionals (which are implemented as Enumerations)

Reference Types

Classes
Functions and Closures

Optionals in Swift

2017-04-23T14:48:00.002-04:00

var a : Int // create a swift variable of type int

var b = a + 10 //compiler will thrown an error because a is not initialized

Alternative to above

When your using ‘?”/optional , that means your explicitly telling the compiler that a may or may not have the value.

var a : Int?

var b = a! + 5 // the compiler suggest to unwrap the optional, this is called force unwrapping and program will crash if in case a does not have value so force unwrapping of optionals is always dangerous and should not do it unless your sure about var holding a value.

then what is the safe way to deal with optionals? answer is optional binding

if let nonOptionalValue = a {

var b = nonOptionalValue + 5 // if a is nil, this statement is not executed and force unwrapping is not required in this case because we knew that a is not nil and has a value for sure.

}

Pointers

2017-04-23T14:37:00.001-04:00

In Objective C all objects are referenced using pointers:

A pointer is a variable which stores memory address instead of value itself.

how big is int, 4 bytes

how big is char, 1 byte

how big is String, image or video? we often don’t know and it might even change during our program so we need more flexible way to manage objects and pointers are one way of allowing us to do that.

Using pointers allows us to pass around the objects (just by passing around the address of object) without having need to copy them which is time consuming and inefficient

E.g. NSString* welcomeString;

NSDate* todayDate;

welcomeString = @“Welcome to Objective C”;

Here the string 'Welcome to Objective C’ string is not directly stored in ‘welcomeString’ instead the address/memory location of 'Welcome to Objective C' is stored in ‘welcomeString which is contrary to 'int highScore = 100’ where ‘highScore’ variable directly stores value. ( this is because objects are more complex than primitive types)

if you want to make and use of simple object, we need pointers to reference them.

Note: Explicit use of pointers in Swift is not required unlike Objective C. e.g let someInstance = SomeClass ( ) whereas in objective C it is SomeClass *someInstance = [SomeClass alloc] init];

Structures in Objective C and Swift

2017-04-23T14:28:00.000-04:00

Structure is a complex data type which contains individual elements which defer in type.

There are many situations in programming where discrete types have to be identified together as one unit. In this situations we make use of Struct.

Structs are used to represent a record, Suppose you want to keep track of your books in a Library. you might want to track the following attributes about each book.

Struct Book {

Title

Author

Subject

Book ID

};

Struck Person {

Name

Age

Height

Weight

Gender

Color

};

Individual elements of Struct are referred to as members

Unlike Objective C, classes in Swift, structures can have methods, properties, initializers, and conform to protocols. The main difference between classes and structures is that classes are passed by reference, while structs are passed by value.

Set vs Array

2017-04-23T14:04:00.000-04:00

The main difference is that NSArray is an ordered collection and NSSet is an unordered list of unique elements.

Set

Primarily access items by comparison

E.g let ingredients = [“Tea Powder”, “Sugar”, “Hot Water”, “Milk”, "Cardamom"]

if ingredients.contains(“Cardamom”) {

print(“It is Cardamom Tea”)
}

unordered
does not allow duplicates

Array

Can access items by Index
Ordered
Allow duplicates

Dynamic Typing & Dynamic Binding:

2017-04-23T13:52:00.001-04:00

Dynamic Typing in Objective C means that the class of an object type id is unknown at the compile time and is discovered at the run time based on the message sent to the Object.

Dynamic typing allows us to declare a variable that is capable of storing any type of object regardless of its class origin, this is achieved using the Objective C id type, the id type is a special, general purpose data type that can be assigned an object of any type.

Dynamic binding takes this one step further by allowing methods on object type id to be called without prior knowledge of the type of an object currently assigned to the variable.

Different states of an iOS app

2017-04-23T13:40:00.001-04:00

Different states of an iOS app:

Not Running
Inactive
active
Background
Suspended

1. Not Running

App is usually in this state when it is not launched yet or was running but was terminated by the system

2. Inactive

App is running in the foreground but is currently not receiving any user events (it may be executing other code though), App usually enter into this state only briefly as it transitions into different state.

3. Active

App is in the Foreground and receiving user events. This is normal mode for foreground apps.

4. Background

App is in the background and executing code. Most app enters into this state briefly on their way to being suspended. However the app that request the extra execution time may remain in this state for a period of time.

5. Suspended

App is in the background but not executing code. The system moves apps to this state automatically and does not notify them before doing so, while suspended app remains in memory but does not execute any code

When a low memory condition occurs, the system may purge suspended apps without notice to make more space for foreground app.

Apps must be prepared for termination to happen any time and should not wait to save user data to perform other critical tasks. Suspended apps receives no notification when they are terminated.

if the app is currently running in the background and not suspended, the system calls applicationWillTerminate: of its app delegate prior to termination. The system does not call this method when the device reboots.

Swift Only Features

2017-04-23T13:31:00.000-04:00

Below are the features introduced in swift and not present in Objective C

'repeat while' which is conceptually equal to 'do while' in C/Objective C
guard statement
'Any' (keyword using which arrays dicts can store objects of discrete type)
'fallthrough' (using which we can allow implicit fall-through in switch statement which is not default in Swift unlike Objective C)
'AnyObject' conceptually equivalent to id in Objective C
Optionals
Tuples
Range Operator

About Swift

2017-04-23T13:22:00.000-04:00

Swift is the safe, interactive and concise language. Following are the notable things in Swift language for objective C developers.

Explicit pointer usage is not required in Swift unlike Objective C
No semicolon is needed at the end of the statement
Conditional expression is not necessarily included in parenthesis for if, while, do while, switch statements
print() is used to print messages to the console in swift
var and let are two important keywords in swift programming language
var is used to create mutable object variables and let is used to create immutable object variables in Swift
var should be either initialized or type defined. if you creating variables in the class context, you must initialize variables using default/custom initializers.
Do while not allowed in Swift instead use repeat while which is conceptually equivalent.
Just like Objective C, multiple inheritance is not supported by Swift, however a Swift class can conform to multiple protocols.
String interpolation in Swift is a way to construct a new string value from a mix of constants, variables, literals, and expressions by including their values in a string literal. Each item you include in a string literal is wrapped in a pair of parenthesis prefixed by a backslash.
Swift does not support implicit conversion of values E.g var i = 4 cannot be changed to i = 4.5 during some point in the program.
Swift infers the data type implicitly based on the initialized values
functions in swift are conceptually equivalent to methods in objective C
Arrays are zero based and accessed using sequence of integers.
Arrays are strongly typed/type safe (all the elements in the array should be of same data type unless using “Any" keyword)
Dictionaries are strongly typed in Swift (elements in dictionary is accessed using unique key)
All the keys in the dictionary should be specific type and all the values in the dictionary should of specific type. All the keys and values of dictionary can be of same type but the number of types dictionary can accommodate is restricted to two unless using “Any” keyword
Switch statement in swift must be exhaustive, can provide ranges of values ( closed range operator and half open range operator). No automatic implicit fall though unlike Objective C- code , but can be achieved by writing fallthrough control transfer statement.

How to Localize iOS Apps

2013-07-03T14:13:00.000-04:00

Localization?

The practice of adjusting a product functional properties and characteristics to accommodate the language, cultural , political and legal differences of a foreign market or country.

Localization of iOS Apps?

Making your app available in different languages based on the targeted users.
Apart from the Apps that are downloaded from App Store, there are decent number of iOS Apps that exists on your device by default.

E.g. Phone, Messages, Maps, Calendar, Music, Camera, Stocks, App Store, Game Center, Contacts, Whether, Photos, Notes etc.

The above default apps which are provided by Apple already support localization.

E.g. Settings > General > International > Language

and the select the language you prefer, you can notice all the default apps provided by Apple will reflect the changes according to user preference. This is because all the apps are facilitated with the language and cultural specific content.

These changes might reflect in apps ( downloaded from App Store) also depending on the factor whether they are localized or not.

Approaches

In general there are two ways which are predominantly used to localize the iOS Apps.

Default Approach
Within the App

Default Approach

Naming convention "Localizable.strings" is must and should for default approach. Once that is done, next step is add the supported languages.

In the above step, check all and click on finish for time being. In the later part of this post, it will be clear why we need to check this files after adding each language.

Please check mark all the language in the above step, by default only english is checked.

Now look at the magic Xcode does, for every language you added Xcode automatically creates different version of the same file i,e "Localizable.strings" on the left hand side pane of project window as shown below.

Now Let us try to understand how iOS manages to display the appropriate content from those language specific string files.

Xcode creates a separate .lproj directories for each new language you add. if you open those directories you will see the .string files related to specific language. Apart from .string files you can manually copy-paste all the other resources like images, audio files, video files etc into the directories.

Note: You also realize that the files you checked after adding each language are existing in each of this directories....you can check language specific XIB files over there to appear in this directory.

In the run time iOS loads all the resources from respective directories based on the users language preference. Let us see with some simple example which contains Heading Label and Desc Label and see how it works in real time.

Create Heading and Desc Label in ViewController.m as shown below.

Code Snippet for the above Screenshot:

    UILabel *headingLabel = [[UILabel alloc] initWithFrame:CGRectMake(10, 70, 300, 30)];

//The below line of code is responsible for retrieving the content from appropriate language specific .string file using NSLocalizedString.

    headingLabel.text =[NSString stringWithFormat:NSLocalizedString(@"HeadingLabel", nil)];

    headingLabel.textColor = [UIColor blackColor];

    headingLabel.textAlignment = NSTextAlignmentCenter;

    headingLabel.backgroundColor = [UIColor clearColor];

    headingLabel.font = [UIFont fontWithName:@"Arial-BoldMT" size:16.0];

    headingLabel.hidden = NO;

    headingLabel.highlighted = YES;

    headingLabel.lineBreakMode = YES;

    headingLabel.numberOfLines = 0;

    [self.view addSubview:headingLabel];

    UILabel *descLabel = [[UILabel alloc] initWithFrame:CGRectMake(10, 80, 300, 200)];

//The below line of code is responsible for retrieving the content from appropriate language specific .string file using NSLocalizedString.

    descLabel.text =[NSString stringWithFormat:NSLocalizedString(@"DescLabel", nil)];

    descLabel.textColor = [UIColor blackColor];

    descLabel.textAlignment = NSTextAlignmentLeft;

    descLabel.backgroundColor = [UIColor clearColor];

    descLabel.font = [UIFont fontWithName:@"" size:18.0];

    descLabel.hidden = NO;

    descLabel.highlighted = YES;

    descLabel.lineBreakMode = YES;

    descLabel.numberOfLines = 0;

    [self.view addSubview:descLabel];

Now go to Localizable.strings(English) file and paste the key value pairs for the above UI Elements.

"HeadingLabel" = "LOCALIZATION(ENGLISH)";

"DescLabel"= "Localization is the process of adapting a product to meet the language, cultural and other requirements of a specific target environment or market so that users can use their own languages and conventions when using the app.";

Repeat same thing for Localizable.strings(Spanish).

"HeadingLabel"= "LOCALIZACIÓN (SPANISH)";

"DescLabel"= "La localización es del proceso de adaptar un producto para cumplir los requisitos del lenguaje, culturales y otro de un ambiente o de un mercado específico de la blanco de modo que los utilizadores puedan utilizar sus propios lenguajes y";

Repeat same thing for Localizable.strings(Greek).

"HeadingLabel"= "ΕΝΤΟΠΙΣΜΟΣ(GREEK)";

"DescLabel"= "Ο εντοπισμός είναι πολιτιστικές και άλλες απαιτήσεις της διαδικασίας ένα προϊόν για να συναντήσει τη γλώσσα, ενός συγκεκριμένης περιβάλλοντος ή μιας αγοράς στόχων έτσι ώστε τον οι χρήστες μπορούν να χρησιμοποιήσουν.";

Checkout the below screenshot for reference.

Go ahead and run your project using iPhone (or) iPad Simulator.

How do i switch to Spanish or Greek?

Settings > General > International > Language> Spanish or Greek, then press Done

iOS Simulator will reboot the app with new user settings and we need to relaunch the app again to view the reflected changes.

Note: Do not select the language other than what u included, it shows English by default even if you does so.

Navigate to Screen where your app is and relaunch to view the content in Spanish.

Cons of this Approach

Users need to leave the app to change the preferences and relaunch it again.
Language change will be reflected on all other apps that supports Localization.

Pros of this Approach

Easy to Implement because of Xcode built-in Intelligence
Not much of Coding is required.

Within the App Approach

Coming..soon!

Valid architectures of iOS devices?

2013-03-01T17:46:00.002-05:00

iOS Devices are powered by the processors based on ARM architecture, comes in different in versions developed overtime, each one added with some improvements.

iOS developers should ensure to include the valid architectures in project build settings before building the application just to make sure that application runs on all targeted devices.

Apple dropping support for old architectures over the time, the Xcode versions which supports armv7 and armv7s no longer supports armv6. There are some others ways to support all architectures though.

Can I force an iPhone user to upgrade an application?

2012-07-25T18:13:00.000-04:00

In general forcing the user to update our application mandatorily might not go well from user stand point.

In-spite of the above fact, Sometime you do have to force an Upgrade for security or other valid reasons. Lot of gaming applications in the market does this sought of updates.

some of the Financial Enterprise apps which are right there in the App-Store were able to force app users to mandatorily update it to latest version.

How do i do this?

Get Version info Using Itunes web service

NSURL *url = [NSURL URLWithString:@"http://itunes.apple.com/lookup?id=<Your app ID>"];

versionRequest = [ASIFormDataRequest requestWithURL:url];

versionRequest setRequestMethod:@"GET"];

versionRequest setDelegate:self];

versionRequest setTimeOutSeconds:100];

[versionRequest addRequestHeader:@"Content-Type" value:@"application/json"];

[versionRequest startSynchronous];

Response string of our REST call

NSString* jsonResponseString = [versionRequest responseString];

NSDictionary *loginAuthenticationResponse = [jsonResponseString objectFromJSONString];

NSArray *configData = [loginAuthenticationResponse valueForKey:@"results"];

for (id config in configData)

{

version = [config valueForKey:@"version"];

}

Compare Both Versions

NSString *version = @"1.0";

if (![version isEqualToString:[itsUserDefaults objectForKey:@"version"]])

{

UIAlertView *createUserResponseAlert = [[UIAlertView alloc] initWithTitle:@"New Version!!" message: @"A new version of app is available to download" delegate:self cancelButtonTitle:nil otherButtonTitles: @”Update", nil];

[createUserResponseAlert show];

[createUserResponseAlert release];//Avoid if using Automatic reference counting

}

Redirect User

-(void)alertView:(UIAlertView *)actionSheet clickedButtonAtIndex:(NSInteger)buttonIndex

{

NSString *iTunesLink = @"itms-apps://phobos.apple.com/WebObjects/MZStore.woa/wa/viewSoftwareUpdate?id=<appid>&mt=8";

[[UIApplication sharedApplication] openURL:[NSURL URLWithString:iTunesLink]];

}

Which object is create by UIApplicationMain function at app launch time?

2012-07-18T11:43:00.003-04:00

The app delegate object is created by UIApplicationMain function at app launch time. The app delegate object's main job is to handle state transitions within the app.

How main function of an app gets called during the app launch cycle?

2012-07-18T11:21:00.001-04:00

During app launching, the system creates a main thread for the app and calls the app’s main function on that main thread. The Xcode project's default main function hands over control to the UIKit framework, which takes care of initializing the app before it is run.

Name the application thread from where UIKit classes should be used?

2012-07-18T11:14:00.002-04:00

UIKit classes should be used only from an application’s main thread. Note: The derived classes of UIResponder and the classes which manipulate application’s user interface should be used from application’s main thread.

Does iOS support multitasking?

2012-07-18T11:04:00.000-04:00

iOS 4 and above supports multi-tasking and allows apps to remain in the background until they are launched again or until they are terminated

Native vs Mobile Web vs Hybrid -Apps

2011-12-15T14:55:00.001-05:00

About Native:
Native applications are those which are platform and hardware dependent. These are built using specific programming language like Objective C for iOS, Java for Android and .Net for Windows.

These mobile applications are fast, reliable, responsive and powerful but are tied to a specific platform.

Must be deployed or downloaded. Most apps requires approval and you have to wait for them to get approved.

Access to hardware sensors like Camera, Gyroscope, Microphone, Compass.

Few problems with Audio and Video. Flash works but only if device supports it.

Specific tools required for some platforms ( like Apple's) , You have to built a new app for each target platform.

Tight control over typefaces and layout.

You can charge whatever you wish for your application but most App distributors take a slice up to 30%.
About Mobile-Web:
Mobile-Web applications are simply the web-pages designed for the Mobile devices, i,e optimizing your websites for use on smaller screens.

Mobile-Web Apps refers to the use of internet connected applications, or browser based access to the internet from a mobile device, which is connected to a wireless network.

Mobile-Web applications holds the promise of overcoming this fragmentation in Mobile OS's and Apple Store marketplaces by enabling you to develop apps that will run across platforms, across devices using open web technologies such as HTML, CSS, JavaScript.

These Apps can be hosted on your already existing web-server and accessed at a standard URL through the device web-browser.

Since these are platform agnostic, content can be reformatted with CSS to suit any device.

Browsers can be clunky but new advancements in JavaScript like jQuery Mobile are catching up fast.

W3C’s Geo-location API is a simple JavaScript API that when plugged into your app can enhance the user’s interaction with your service by pinpointing their exact position using the GPS sensors built into today’s devices. Supported by many of today’s Mobile WebKit browsers on all the main platforms. Google Maps uses this for their mobile web app.

Developing and delivering Mobile-Web apps means no high-level coding languages, no payments to App Store platforms, no approval process.

Scope of Mobile-Web Apps with HTML5:

With HTML5's introduction of the new video element , web developers can now include video within their pages without the need of embedding it in a plugin like flash. Given the high profile case of Apple refusing to support flash on their massively popular iOS devices, this is something of a huge relief to Mobile-Web developers.

The HTML 5 specification contains a standard for local storage that is implemented by a wide variety of browsers. Using the localStorage API You can create applications that store their data locally on the user’s phone rather than on your servers. This can be used to enable applications that use dynamic data such as calendars to also be used offline, or to support personalization of the app by users without them needing to log in or have an account on your site.

Giving your apps some level of offline capability can bring it closer to the native experience as your key interface features – buttons, images, styles, scripts, etc – can all still work even if the user has a poor internet connection.

HTML5 enables developers to specify which files should be stored locally on the user’s device. This saves your app from ending up being a blank page if the user doesn’t have a connection, thus improving the user experience.

HTML5’s Web Workers specification provides applications with the ability to use scripts that run in the background without interacting with users.

Your mobile users will often have to key in information on your app. HTML5 brings new form types that are recognised by the browsers and formatted accordingly, presenting the user with the keyboard they need, no longer needing lengthy JavaScripts... just declared straight in the HTML.

A primary reason that many companies are not already jumping on the HTML5 bandwagon is the belief that HTML apps cannot access native device features. Indeed, pure mobile web apps (i.e., those that run in the browser – not hybrid ones) are currently restricted in their access to features such as the camera, microphone, address book, and so forth.

There is work in progress at the W3C to allow web apps to access such devices services , mobile browsers do not currently provide such functionality – a key requirement for many innovative mobile apps.

About Hybrid-Apps:

A Hybrid-App is a native, downloadable app that runs all or some of its user interface in a embedded browser component.

Hybrid-App development employes native capabilities whiles also serving as a strategic stepping stone towards the adoption of HTML5.

To the user a Hybrid-App is almost indistinguishable from a native one, it is downloaded from the App-Store or Marketplace. It is stored on the device and launched just like any other App.

But to developers there is a huge difference because instead of rewriting the App from scratch for each Mobile-OS, they write at-least some of their application code in HTML, CSS and JavaScript and re-use it across devices.

Hybrid-Apps provide access to hardware sensors, frameworks such as Open-Source PhoneGap Library makes it possible for JavaScript code to query the compass, take pictures, find or create contacts and appointments and tap on many other device features that Mobile-Web apps are barred from accessing.

Unlike the Mobile-Web App, you don't browse to a Hybrid-App, you download and install it.

Also, HTML pages of a hybrid app can be transmitted by a web server, but that’s not a requirement. To improve performance, hybrid apps can include a bundled copy of all required web resources (i.e., HTML, JavaScript, CSS and images) so that users will get instant access to them, without having to wait for a web server to send them over.

what are the different types of iOS provisional Profiles? what is the use of each and how do i create one?

2011-01-12T14:55:00.000-05:00

iOS provisional is profile is something which is introduced by apple for developers , who want to post their apps to App store, Enterprise distribution and test the apps on their devices.

The different types of provision profiles introduced by apple are :
1) Development( to test on iOS devices).
2) Distribution. ( there are two types of Distribution profiles).
a) App store ( distribution to app store).
b) Ad-Hoc ( this is used when you are working on Enterprise application where you were not worried about posting your app to the app store but if you want to distribute it among group of people).

You Need to have a Developer account in-order to create provisional profiles, for more information on this you can visit www. developer.apple.com and click on iOS Dev center.

Frame, Bounds and center in IOS?

2010-09-15T16:55:00.000-04:00

Frame A view's frame (CGRect) is the position of its rectangle in the superview's coordinate system. By default it starts at the top left.

Bounds A view's bounds (CGRect) expresses a view rectangle in its own coordinate system.

Center A center is a CGPoint expressed in terms of the superview's coordinate system and it determines the position of the exact center point of the view.

How to make a NSURL Request and parse the XML response?

2010-09-14T12:52:00.000-04:00

#import "ViewController.h"

#import "XMLReader.h"

//first you need to create a URL using String.

NSURL *url = [NSURL URLWithString:@"feed://feeds.feedburner.com/blogspot/MKGLf?format=xml"];

//Once you create a URL,you are ready make a request.

NSURLRequest *request = [NSURLRequest requestWithURL:url];

//After making request the apparent thing is expecting the response that may be expected response or an Error. so create those objects and initialize them with NULL.

NSURLResponse *response = NULL;

NSError *requestError = NULL;

//Once you have response with you, capture your responseData using NSData.

NSData *responseData = [NSURLConnection sendSynchronousRequest:request returningResponse:&response error:&requestError];

//Convert the response data into response String.

NSString *responseString = [[NSString alloc] initWithData:responseData encoding:NSUTF8StringEncoding];

//Now you can start parsing the data using XML parser. You need XML parser in-order to use the below class method "dictionaryForXMLString"

NSError *parserError = NULL;

NSDictionary *xmlDict = [XMLReader dictionaryForXMLString:responseString error:NULL];

//Once You have xmlDict handy, you can pass this to the any ViewController(like tableview) to populate the data.

What happens when you pass a message to the nil object in Objective C

2010-07-15T15:11:00.000-04:00

Nothing happens, Your app will not get crashed because of that, just Objective C will ignore that.