Core App Objects

1-What is the use of controller object UIApplication?
A. Controller object UIApplication is used without subclassing to manage the application event loop.
It coordinates other high-level app behaviors. 
It works along with the app delegate object which contains app-level logic.

2-Which object is create by UIApplicationMain function at app launch time?
A. 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.

3-How is the app delegate is declared by Xcode project templates?
A. App delegate is declared as a subclass of UIResponder by Xcode project templates.

4-Which app specific objects store the app's content?

A. Data model objects are app specific objects and store app’s content. Apps can also use document objects to manage some or all of their data model objects.

5- Are document objects required for an application? What does they offer?

A. Document objects are not required but are very useful in grouping data that belongs in a single file or file package.

6-What are layer objects and what do they represent?

A. Layer objects are data objects which represent visual content. Layer objects are used by views to render their content. Custom layer objects can also be added to the interface to implement complex animations and other types of sophisticated visual effects

7-

What are the App states. Explain them?

A:

• Not running State:  The app has not been launched or was running but was terminated by the system.
• Inactive state: The app is running in the foreground but is currently not receiving events. (It may be executing other code though.) An app usually stays in this state only briefly as it transitions to a different state. The only time it stays inactive for any period of time is when the user locks the screen or the system prompts the user to respond to some event, such as an incoming phone call or SMS message.
• Active state: The app is running in the foreground and is receiving events. This is the normal mode for foreground apps.
• Background state:  The app is in the background and executing code. Most apps enter this state briefly on their way to being suspended. However, an app that requests extra execution time may remain in this state for a period of time. In addition, an app being launched directly into the background enters this state instead of the inactive state. For information about how to execute code while in the background, see “Background Execution and Multitasking.”
• Suspended state:The app is in the background but is not executing code. The system moves apps to this state automatically and does not notify them before doing so. While suspended, an 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 the foreground app.

8-

Explain how the push notification works.

A:

9-

 Why do we need to use @Synthesize?

A:

We can use generated code like nonatomic, atmoic, retain without writing any lines of code. We also have getter and setter methods. To use this, you have 2 other ways: @synthesize or @dynamic: @synthesize, compiler will generate the getter and setter automatically for you, @dynamic: you have to write them yourself.@property is really good for memory management, for example: retain.How can you do retain without @property? 

if (_variable != object)

{

    [_variable release];

    _variable = nil;

    _variable = [object retain];

    }

How can you use it with @property?self.variable = object; When we are calling the above line, we actually call the setter like [self setVariable:object] and then the generated setter will do its job.

10-

 What is code signing?

A:

Signing an application allows the system to identify who signed the application and to verify that the application has not been modified since it was signed. Signing is a requirement for submitting to the App Store (both for iOS and Mac apps). OS X and iOS verify the signature of applications downloaded from the App Store to ensure that they they do not run applications with invalid signatures. This lets users trust that the application was signed by an Apple source and hasn’t been modified since it was signed.

Xcode uses your digital identity to sign your application during the build process. This digital identity consists of a public-private key pair and a certificate. The private key is used by cryptographic functions to generate the signature. The certificate is issued by Apple; it contains the public key and identifies you as the owner of the key pair.

In order to sign applications, you must have both parts of your digital identity installed. Use Xcode or Keychain Access to manage your digital identities. Depending on your role in your development team, you may have multiple digital identities for use in different contexts. For example, the identity you use for signing during development is different from the identity you user for distribution on the App Store. Different digital identities are also used for development on OS X and on iOS.

An application’s executable code is protected by its signature because the signature becomes invalid if any of the executable code in the application bundle changes. Resources such as images and nib files are not signed; a change to these files does not invalidate the signature.

An application’s signature can be removed, and the application can be re-signed using another digital identity. For example, Apple re-signs all applications sold on the App Store. Also, a fully-tested development build of your application can be re-signed for submission to the App Store. Thus the signature is best understood not as indelible proof of the application’s origins but as a verifiable mark placed by the signer

11-

Can you explain what happens when you call autorelease on an object?

A:

When you send an object a autorelease message, its retain count is decremented by 1 at some stage in the future. The object is added to an autorelease pool on the current thread. The main thread loop creates an autorelease pool at the beginning of the function, and release it at the end. This establishes a pool for the lifetime of the task. However, this also means that any autoreleased objects created during the lifetime of the task are not disposed of until the task completes. This may lead to the taskʼs memory footprint increasing unnecessarily. You can also consider creating pools with a narrower scope or use NSOperationQueue with itʼs own autorelease pool. (Also important – You only release or autorelease objects you own

 12-   Whats the NSCoder class used for?

A:

NSCoder is an abstractClass which represents a stream of data. They are used in Archiving and Unarchiving objects. NSCoder objects are usually used in a method that is being implemented so that the class conforms to the protocol. (which has something like encodeObject and decodeObject methods in them