iPhone Interview Questions With Answers .

Hello All , find below some iPhone interview questions . I hope this will help you to face the technical interview . I will be modifying this post with some more questions and answers in a couple of days , so keep checking this post for more .

1. What is @interface?

- It’s a keyword used to declare the Class.

2. What is @implementation?

- It’s a keyword used to define the Class.

3. Garbage collector in iPhone?

- iOS 5.0 has got the ARC ( Automated reference counting ).  Objective C does not have a garbage collector rather it uses the reference counting algorithm to manage the memory. This was the developers task until Apple launched iOS 5.0. Again if you are targeting iOS 4.0 or earlier , ARC is no more a choice for you .

4. What is delegate?

- Delegate is an object that handles the events happening on an object. To do that delegate has to follow a protocol specifying the task it is going to handle .

5. What is @synthesize?

- We use @synthesize to generate getters and setters automatically from compiler.  We declare properties and then generate getter and setter method by using @synthesize.

6. What are the features of iOS 5.0 ?

- https://developer.apple.com/technologies/ios5/

7. What is nonatomic ?

- nonatomic and atomic are related to multithreading environment .

 - If a property has an attribute as “nonatomic” that means multiple threads can modify that property concurrently.

- If the attribute is “atomic”, the threads would be given access atomically.

-  So “Atomic” is thread safe while “nonatomic” is thread unsafe.

- Atomic drastically hampers the performance so until and unless not needed you should never go for atomic attribute. ‘nonatomic ’ will do in most of the cases.

8. What are the delegate methods of MKMapView ?

- Check the MKMapViewDelegate in the Documentation. If you don’t have Xcode with you then search on Google.

9. What are the important delegate methods of NSXML parser?

-DidStartElement

-FoundCharecters

-DidEndElement

-FoundError

10. What is @dynamic and any place where it is used ?

- It tells compiler that getter and setter are not implemented by the class but by some other class .

- May be super class or child class .

Example – Core Data

-       The Managed object classes have properties defined by using @dynamic.

11. What is @property?

- It is a keyword used to declare a property.

12. What is data source?

- The datasource is an object that implements the required datasource protocol that is needed to create a complex control.

Ex UITableView is a view that needs a datasource object to which will help building the table. Often it’s the controller that is displaying the table view. The protocol that dataSource object ( mostly controller it self) has to implement is “UITableViewDataSource” .

13. What is model view controller?

- MVC is a Design pattern .

Model stands for the database  object which will manage all the database transaction .

- View stands for the UI i.e. the UI visible to the user. User will be interacting with the view.

- Controller is an object who handles the view events and also render the database changes to the UI. In short , it bridges the interaction between Modal and View.

14. what is @ protocol?

- @protocol is a keyword used to define a protocol. A protocol is a set of method declarations defining specific purpose. It only lists out the methods prototype , the actual implantation would be provided by the class that implements /  follows the protocol.

15. what is id?

- id is a generic reference type. The variable declared using id data-type can hold any object. Most of the methods that returns an object has ‘id’ as return type. Ex – init.

16. Explain memory management?

- Most of the object oriented languages have the Garbage Collector .  All the objects are allocated on the heap memory. The Garbage Collector is a thread that runs periodically to check all the objects, which are no more being referenced from the program. Garbage collector then de-allocates all these unreferenced objects on the Heap. In this environment programmer does not need to worry about de-allocating the objects explicitly.

In Objective – C we don’t have garbage collector. ( Note: Its available from iOS 5.0 only). So in this environment we have to explicitly take care of allocation and deallocation of all the objects in our program.  And to manage this Objective C uses ‘reference counting’ algorithm as the memory management algorithm. 

Reference Counting: In this algorithm every object keeps track of it owners ( I,e reference variables from the program ) . No of owners is represented by the property retainCount declared in NSObject. If this retainCount goes to ‘0’ the object gets deallocated automatically.  We never call dealloc method on any object explicitly.

17. what is retain and release?

- retain and release are two method defined in NSObject . - -

- These methods are related to Memory Mangement .

- retain method when called increases the retainCount by 1.

- release method when called decreases the retainCount by 1

18. what is dealloc?

- dealloc method is called on an object to actually deallocate the memory for that object. ( We should never call dealloc directly )

- In reference counting environment when retainCount of an object reaches to ‘0’, the dealloc method is called on that object automatically to delete the memory space of the object .

- If the object is having some reference type variable holding other objects, then we should call release method on every variable in dealloc.

- If you override then [super dealloc] should be the last line in this method.

19. What is Autorelease pool?

-  Autorelease pool is like a container that holds the autoreleased objects .

- This pool is drained with every run-loop of the Application

- When the pool gets drained, autorelease pool sends a release message to all the objects it was holding.

20. What is Foundation Framework? Can you explain some classes from that?

- Foundation is one of the important frameworks in COCOA Touch.

- It contains the classes like  NSArray , NSString , NSObject etc .

21. What is the difference between NSArray and NSMutableArray?

* NSArray

-        is a static array

-       Once created you can not modify the array

-       Ex you can not add or remove the object in NSArray.

* NSMutableArray

-       is a dynamic array

-       You can add or remove the object dynamically.

22. Write a delegate method of the table view?

 - (void)tableView:( UITableView*)tableView didSelectRowAtIndexPath:(NSIndexPath*)indexPath

23. What are the delegate methods of NSURLConection?

- didReceiveResponse:

- didReceiveData:

- didFinishLoadingData:

- didFailWithError:

24. What is cocoa ?

- COCOA is a collection of frameworks used to write Applications for MAC OS X.

25. Singleton classes

- A singleton class is such a class from which no more that one instance can be created. So there will always be single instance created throughout the program.

Ex UIApplication.

Custom Number pad on iPad

Hello all , recently in one project I had to build a number pad keyboard which will allow user to enter just the number and that's it . On iPad unlike iPhone the UIKeyboardTypeNumberPad does not work . Even if you use this , it brings up the default keyboard . On iPad there is a pretty amount of space , so Apple might not have considered this UIKeyboardTypeNumberPad keyboard as the requirement on iPad . Well second thing about the default keyboard is that it is too big , cause I just want to enter numbers nothing else . So here we go and create our custom number pad to enter the numbers in a text field. To get an idea how it will look , just check out the image below.

Note : This number pad is very specific to iPad , as we will be using UIPopOverController designed for iPad only.

 


Two things we are going to do here .
1) We don't want the default keyboard to pop up when user hits the text field .
2) We want our number pad not to pop up from the bottom of the screen but just right below the text field in a popover .


Lets start with it . Create an iPad project , you can select the view based Application , then next select the iPad from the device list. Name it "CustomNumericKeyboard" . You should see below files in your project .

Drag and drop the below files in the project . You will find these in the sample code attached at the bottom.
1) NumericKBViewController.h
1) NumericKBViewController.m
1) NumericKBViewController.xib

Now your resources pane should look like this .

Next import the "NumericKBViewController.h" at the top of your "CustomNumericKeyboardViewController.h" . Now your class file should look like below .
#import <UIKit/UIKit.h>
#import "NumericKBViewController.h"

@interface CustomNumericKeyboardViewController : UIViewController
{

}
@property(nonatomic,retain) IBOutlet MTextField * textField;

@end

Note down that I have created a custom UITextField class for this purpose , so I am creating an outlet with MTextField object instead of UITextField. MTextField class resides in the "NumericKBViewController.h" that we have added just now to our project. I will shortly highlight why I did this. Next add a text field on the xib file . At this moment don't try to connect the outlet that we have created . Before that you have to set the class for the text field as "MTextField" . How to do that ? check the screen shot below .

Select the text field , go to the right detail pane on the right side . In the third tab ( Identity inspector ) , it will show you the class name as UITextField . Just make it as MTextField . Once you set that , you can connect the IBOutlet that we have created in the class header with this text field on the xib.


In the viewDidLoad method of the view controller , add the below lines of code.


- (void)viewDidLoad
{
    [super viewDidLoad];
    [self.textField addTarget:self action:@selector(textFieldTouched:) forControlEvents:UIControlEventTouchDown];
   
}


Next add a method just after this


- (void)textFieldTouched:(id)sender {
       
    MPopOverController * popOver = [MPopOverController kbPopOverControllerForTextField:self.textField];
    [popOver presentPopoverFromRect:textField.frame inView:self.view permittedArrowDirections:UIPopoverArrowDirectionUp animated:YES];
   
}


And thats it , build and run your project , you should see a nice text field . Click on it and it will bring up the custom number pad which is far much easier and friendlier to enter the number compared to the default keyboard .


Download the Project Code here .


Try to understand the code , its actually quite easy. If you don't, let me explain that to you.


Below are some classes used.


MTextField
text field and few more views have the property called as inputView . This view is nothing but actually the keyboard view in case of the text field . So the thing we did is we are overriding the -(UIView*)inputView getter for the property inputView. Here we return a transparent empty UIView object. Now if users taps the textfield , a transparent view will popup from the bottom instead of the keyboard . Id you want to test this go to this method and try changing the backgroundColor of the view that we return over here and you will see what happens.


NumbericKBViewController
Its a view controller which actually displays our number pad . It actually holds the reference of the text field for which we are displaying this view controller . For more info , you can check out the IBOutlets and IBActions on how it manages the number entry part .


MPopOverController
Well Its simply a UIPopOverController subclass customized to suit our need . I will be using this custom number pad at lots of places in my project , so just wanted to make it a concrete independent utility that I can use with few lines of code at any place . And thats how even the demo project attached above uses it.


Well thats all for now . I hope this post will help you understand How to create Custom Keyboard , PopOverController to make things easy and really beautiful on iPad Apps . Keep checking for more posts soon . For any queries feel free to main me on bharat.jagtap@bitcode.in … Thank You !!

IPhone Interview Questions

Hello All , download the iPhone interview questions from the below link .

iPhone Interview Questions

If you have few more questions , feel free to post those as comments to this blog post . I will add those to the file. Take care and Happy iphone programming :-)

Using RESTfull services | Parsing JSON | Google Translate API

In this tutorial we are going to see three things

1) How to consume RESTfull Services in iOS.

2) How to parse JSON response.

3) Google Translate APIs.

Basically there are two types of web-services .

1) SOAP services.

2) REST Services.

SOAP services deal with SOAP protocol. It uses xml . While using SOAP services you have to follow the set of strict rules to create and receive SOAP messages. We would talk about that in details in the SOAP services post.

As now a days the most widely used services are REST services , we will focus on that in this tutorial. Some advantages using REST services are as below

1) It can use JSON . ( Very light weight way for data communication compared to XML )

2) Easy to implement .

3) Parsing JSON is quit easy.

4) Because of all the above , you achieve the quick response time .

( Note : Again whether to go for REST or SOAP completely depends on the server side programmer who is creating the web services . If you are responsible for both side work ( iPhone and sever side coding ) then REST service with JSON would almost solve the purpose. )

Ok that is enough talk about the web services. If you want you simply google the terms RESTfull web services or SOAP web services to know more about them .Lets get to the implementation part.

Now in this tutorial we are going to user google's REST services for language translation. I am talking about the Google Translate APIs. Our final output will look like below screenshot.

User will be entering some text in English . User will have some choices of languages to choose for the translation. When user presses the translate button , we will do the web service consuming task and will display the translated text in the label at the bottom.

Project Setup

We are going to parse the JSON in this project so lets download the JSON parsing library for our project. The most widely used in iOS is SB-JSON. Its the third party library for parsing JSON text. Download the files from below link.

https://github.com/downloads/stig/json-framework/SBJson_v3.0.4.zip

Download the file , save this on your mac as you would be needing this lot many times in the future projects. Ok , next expand the zip . You can see some folders like classes , examples etc.. What we need is the classes folder .You can see a number of files in the classes folder. Drag all these files into the Xcode project that you have created . When you add the files to the project , make sure the copy files if Needed checkbox is checked. This will actually copy all the files to your project.

(Note : You can just create a group in the project to add all these files so that it would look cleaner and is always better to manage ).

You can now build the project just to make sure that JSON parser files have been successfully integrated with the project.

Next , lets add a new file that is UIViewController subclass . I have named it MyViewController with the XIB for user interface . The xib view will look like this.

The view contains following controls.

• A picker for displaying different languages.
• A text filed for user to enter the text ( English text ).
• A button.
• A label to display the translated text.

Make sure you set the datasource and delegate of the picker to the file's owner. Also set the delegate of the textField to the files owner.

Lets go to MyViewController.h. It should look like this.

You can see three outlets , one for each picker, textField and valueLabel. There are two methods

-(IBAction)translate:(id)sender; -(void)parseJSONString:(NSString*)string;

-(IBAction)translate:(id)sender;

This method would be invoked on the translate button touch up.

-(void)parseJSONString:(NSString*)string;

This method would be used to parse the JSON response.

We have got two arrays langNames and langCodes. langNames array will store the languages names like Hindi , French , Arabic etc. langCodes array will store the corresponding language codes like "hi" for Hindi , "fr" for french etc..

Lets have a loot at the initWithNibName method.

Implement the following textField and UIPickerView datasource and delegate methods. You can simply copy these in your MyViewController.m

#pragma TextField Delegate Methods

- (BOOL)textFieldShouldReturn:(UITextField *)textField

{

[textField resignFirstResponder];

return YES;

}

#pragma Picker Methods

- (NSInteger)numberOfComponentsInPickerView:(UIPickerView *)pickerView

{

return 1;

}

- (NSInteger)pickerView:(UIPickerView *)pickerViewnumberOfRowsInComponent:(NSInteger)component

{

return [langNames count];

}

- (NSString *)pickerView:(UIPickerView *)pickerView titleForRow:(NSInteger)rowforComponent:(NSInteger)component

{

return [langNames objectAtIndex:row];

}

Now this will display the languages in the picker. Next Lets have a look at the method that would be called on translate button touch.

-(IBAction)translate:(id)sender

{

// get theselectec langauge number and with that fetch the correposing language code fromthe langCodes array.

int selected = [langPicker selectedRowInComponent:0];

NSString * langCode =[langCodes objectAtIndex:selected];

// Below isthe webservice URL. It takes two parameters in the query string , 1) text to betranslated and then langpair=en|%@" from en to %@ language.

// q=%@ ( for text to be translated )

// v=1.0 (this is the only version for google translate api available , so no worries).

//langpair=en|%@ ( It is of the form from_language|to_language ).

NSString *serviceURLString = @"https://ajax.googleapis.com/ajax/services/language/translate?q=%@&v=1.0&langpair=en|%@";

// Here wereplaces the placeholder with the actual values.

NSString *serviceURLFinalString = [NSString stringWithFormat:serviceURLString,englishField.text,langCode];

// Here wereplaces the empty spaces , '|' , etc characters with correspoing %escapes.( wecan not have a black space in the URL )

serviceURLFinalString =[serviceURLFinalString stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding];

// Create aNSURL object from the string.

NSURL *serviceURLFinal = [NSURL URLWithString:serviceURLFinalString];

// fetchingthe contents from the string.

NSString * response =[NSString stringWithContentsOfURL:serviceURLFinalencoding:NSUTF8StringEncoding error:nil];

NSLog(@"Response: %@ ",response);

[self parseJSONString:response];

}

The above method is well commented , so you can read the comments to understand what we are doing exactly. We are logging the response on the console. So for the time being you can comment the line [self parseJSONString:response]; and simply check the what response we are getting on the console . If I enter a text "We are iPhone programmers." then the response we get is a JSON response as below.

Now our next task would be to parser this JSON and display the translated text in the value label.

The method parseJSONString does the work. Lets have a look at the implementation.

-(void)parseJSONString:(NSString*)string

{

NSDictionary * responseDic= [string JSONValue];

if([[responseDic objectForKey:@"responseStatus"] intValue] == 200 )

{

NSString * value =[[responseDic objectForKey:@"responseData"] objectForKey:@"translatedText"];

valueLabel.text = value;

}

else

{

valueLabel.text = @"Pleaseenter a valid English text !!!";

}

}

Explanation : The above method parses the JSON response string.

[string JSONValue]; returns a dictionary of the JSON response. First we check if the reponseStatus is 200 or not . If it is 200 that means we have got the proper response. So next fetch the translated text and assign it to the value label.

Run the program and test it with different languages . Lets have a look at the output.

Hope this post helps you all in handling restful services , parsing JSON and integrating the Google Translate APIs. If you have any doubts or issues , feel free to post them as comments. Keep checking the blog for more posts soon !!!

Thank You!!!

XML parsing using NSXMLParser ( SAX Parser for iPhone )

In this post we will see on how to use NSXMLParser to parse an XML file present inside the project bundle but before that lets have a look on what is NSXMLparser and how does it parses an XMLFile

NSXMLParser: Instances of this class parsees XML documents (including DTD declarations) in an event-driven manner. Its an event based parser ( SAX parser). So NSXMLParser notifies its delegate about the items (elements, attributes, CDATA blocks, comments, and so on) that it encounters as it processes an XML document. It also reports parsing errors. For convenience, an NSXMLParser object in the following descriptions is sometimes referred to as a parser object.

Design Phase: This is the output that we will be getting when we parse the XML file, so for the design part you may see from the design that we have to take a UITableViewController and when we are done parsing the xml file, the XML data will be shown in the table.

Step 1: Open Xcode and create a windows based application and add a UITableVIewController subclass file to it with the name XMLTableViewController,. Add a new NSObject subclass file with the name Employee.

Note: The idea behing the Employee class is that we will be parsing the XML files and will be getting the records of the employees. We will allocate and initalise the employee objects from these records in the xml. This is always a better approach. We should never directly use the xml data. It should be clear to you if not now.

Step 2: The XML file that we are going to parse from the bundle looks like this

Select the XMLTableViewController.h file and declare the add the following code

#import <UIKit/UIKit.h>

#import "Employee.h"

@interface XMLTableViewController : UITableViewController {

         NSMutableArray * employees;

         Employee * emp_obj;

         NSXMLParser * Parser;

         NSMutableString * nodeContent;

}

@end

Code Explanation: In the above code you may see that I have declared the object of NSMutableArray class because when our parsing will be done we will be adding the parsed data inside this array and display the content of this array inside the table, The NSMutableString variable named nodeContent will get the data from the xml document and this data will be stored inside the properties of the NSObject subclass called as the Employee, the NSObject subclass is added because even in future if the xml file structure is altered and one new element is added then all you have to do is just add a property inside the Employee file and use the property to get the data from the nodeContent variable of the mutable string. Finally we have declared the object of the NSXMLParser class which will parse the xml file with the help of its delegate methods.

Code of the Employee.h file

@interface Employee : NSObject {

         NSString * emp_name;

         NSString * emp_city;

}

@property(nonatomic,retain) NSString * emp_name;

@property(nonatomic,retain) NSString * emp_city;

@end

Code  of the Employee.m file

#import "Employee.h"

@implementation Employee

@synthesize emp_name,emp_city;

@end

Step 3: Initialize every object inside the init method of the XMLTableView.m here’s the code

- (id)initWithStyle:(UITableViewStyle)style {

    if (self = [super initWithStyle:style]) {

            employees=[[NSMutableArray alloc]init];

            nodeContent=[[NSMutableString alloc]init];

            Parser=[NSXMLParser alloc];

            Parser.delegate=self;

            [self loadXML];

            [Parser parse];

    }

    return self;

}

Code Explanation: As you may see from the above code that the Parser which is an object of the NSXMLParser class has to parse an xml file but for doing that you have to supply in the location of the xml file which is present inside the bundle and once you have done that just call a method called parse of the NXMLParser which notifies the object of the NSXMLParser class to begin with the parsing and since the parsing is done with the help of the delegate method of the class we have specified the delegate of the Parser to self. Below given is the function which will just gives the location to of the XMLFIle to the NSXMLParser

-(void) loadXML

{

         NSData * data=[[NSData alloc]initWithContentsOfFile:[[NSBundle mainBundle] pathForResource:@"XMLFile" ofType:@"xml"]];

         [Parser initWithData:data];

         [data release];

        

}

Step 4: The NSXMLParser has 3 delegate method called as

didStartElement: Sent by a parser object to its delegate when it encounters a start tag for an element.

foundCharacters: Sent by a parser object to provide its delegate with a string representing all or part of the characters of the current element.

didEndElement: Sent by a parser object to its delegate when it encounters an end tag for an element.

The above are the three method that are mostly used to parse the xml file of course there are some other methods as well you may use those methods as per your business logic

- (void)parser:(NSXMLParser *)parser didStartElement:(NSString *)elementName namespaceURI:(NSString *)namespaceURI qualifiedName:(NSString *)qualifiedName attributes:(NSDictionary *)attributeDict

{

         if([elementName isEqualToString:@"emp"])

         {

            emp_obj=[[Employee alloc]init];

         }

        

}

Code Explanation: Here you specify the start tag of the xml element from where the parsing should actually begin.

Here’s the code of the foundCharacter

- (void)parser:(NSXMLParser *)parser foundCharacters:(NSString *)string

{

        

[nodeContent appendString:[string stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceAndNewlineCharacterSet]]];

}

Code Explanation: here you append the data from the xml file to the mutable string variable

Here’s the code for the didEndElement

- (void)parser:(NSXMLParser *)parser didEndElement:(NSString *)elementName namespaceURI:(NSString *)namespaceURI qualifiedName:(NSString *)qName

{

         if([elementName isEqualToString:@"name"])

         {

            emp_obj.emp_name=nodeContent;

         }

         else if([elementName isEqualToString:@"city"])

         {

            emp_obj.emp_city=nodeContent;

           

         }

         else if([elementName isEqualToString:@"emp"])

         {

            [employees addObject:emp_obj];

            [emp_obj release];

            emp_obj=nil;

        

         }

         [nodeContent release];

         nodeContent = nil;

         nodeContent = [[NSMutableString alloc]init];

        

        

}

 Code Explanation: Here you add the data from the xml file present inside the nodecontent to the properties that you have created inside the Employee and then add the object of the Employee class to the object of the mutable array. Once the data is inside the mutable array you may display the data present inside the mutable array in the table.

Check out the datasource methods of the table below

- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView {

    return 1;

}

// Customize the number of rows in the table view.

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section {

    return [employees count];

}

// Customize the appearance of table view cells.

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {

   

    static NSString *CellIdentifier = @"Cell";

   

    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];

    if (cell == nil) {

        cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleSubtitle reuseIdentifier:CellIdentifier] autorelease];

    }

    

     Employee * emp = [employees objectAtIndex:indexPath.row];

     cell.textLabel.text=emp.emp_name;

     cell.detailTextLabel.text=emp.emp_city;

    return cell;

}

Step 5: after doing that select the AppDelegate.m file and create the object of the XMLTableViewController in applicationDidFinishLaunching method and run the application here’s the view at the final output.