Copy vs Retain in Objective C

Hi all, in one of my previous posts, we have discussed about memory management in Objective C using retain message. Sending "retain" message to a object will give ownership of the object. Now, lets see what we have to do to get a copy of object instead of just getting ownership of the object.

We have a method called "copy" in Objective C root class "NSObject". Using this method we can we can create a copy of an existing instance. Following is the syntax to do that.

Object *obj2 = [obj1 copy];

Now obj2 is exact copy of obj1. Both are difference objects. Newly created object "obj2" will have a retain count of 1 irrespective of the retain count of obj1.

Now lets take an example. I took NSMutableArray to explain the difference. Don't worry, if you don't know about NSMutableArray. Its just a collection object which holds a bunch of objects. If a object can be copied then it should confirm to NSCopying protocol.

We will discuss about collections and protocols in our next tutorials. For now just take NSMutableArray can hold a collection of objects and we can add or remove objects from it.

    NSMutableArray *array = [[NSMutableArray alloc] initWithObjects:@"First",@"Second", nil];

    NSMutableArray *copiedArray = [array mutableCopy];

    NSMutableArray *retainedArray = [array retain];

    

    [retainedArray addObject:@"Retained Third"];

    [copiedArray addObject:@"Copied Third"];

    

    NSLog(@"array = %@",array);

    NSLog(@"Retained Array = %@",retainedArray);

    NSLog(@"Copied Array = %@",copiedArray);

Now look at the above code. First list shows creating a NSMutableArray object(array) with NSString elements @"First" and @"Second"(In Objective C we represent strings in @"").  copiedArray is copied object of array and retainedArray is retained object of array.

In next code we have added @"Retained Third" object to retained array and @"Copied Third" to copied array. After that I am printing the array values in console. (NSLog is used to print your logs in console. It uses c format specifiers. Apart from those, we can use %@ to print an object.)

Now here is the out put in console :

2013-12-19 17:15:49.379 RetainVsCopy[2876:c07] array = (

    First,

    Second,

    "Retained Third"

)

2013-12-19 17:15:49.380 RetainVsCopy[2876:c07] Retained Array = (

    First,

    Second,

    "Retained Third"

)

2013-12-19 17:15:49.381 RetainVsCopy[2876:c07] Copied Array = (

    First,

    Second,

    "Copied Third"

)

See, both array and Retained Array are having same contents. This is because both are pointing to same  memory/instance/object. Where as contents of Copied Array are different. This is because copy created a separate instance.

I hope this explanation helped you in figuring out difference between copy and retain. Feel free to ask your questions.

You can get source code of this example from here Source Code

Memory management in Objective C

Hi all, today we will discuss about memory management in Objective C. Its an important concept in Objective C. Lets see how it works. Memory is very important for every application. Especially for mobile applications. So, its important to manage memory in our applications.

Thumb rule in Objective C memory management is, who ever creates an object or gets ownership of an object, they are responsible to release that particular object. We discusses in my earlier in my posts that Objective C is object oriented programming language. So, there will be object sharing. To manage this, we have retain count mechanism in Objective C. Retain count represents number of owners to a particular object.

Lets say we have created an object in class A following way :

Object *obj = [[Object alloc] init]; // retain count is 1.

Now, what to do if the same object is shared by another class B? Class B has to get owner ship of obj. Otherwise, if we use obj in class B after it is released by class A, application will be crashed as there are no owners to obj.

Lets retain obj in class B :

[obj retain]; // retain count is 2.

Will increase retain count by 1. Thus indicates class B is also owner of obj. Its responsibility of class B to release obj. Whenever send release message on obj, its retain count will be decremented by 1.

[obj release]; // retain count is 0


Now, retain count of the object obj is 1. After some processing, lets say I am done with using object obj in class A also. I need to release memory related to this object. What I need to do is, just send "release" message on this object.

[obj release];  // retain count 0.

Now, retain count of the obj is 0. There are no owners present for this object. Objective C runtime environment will take care of reclaiming memory allocated to obj.

Following summary explains how memory is managed :


         Class A                     Class B                       Class A                                Class B
           alloc                          retain                         release                                 release
obj (retain count 1)     obj (retain count 2)         obj (retain count 1)          obj (retain count 0)


In our next tutorial we will discuss about autorelease pools and setter methods using memory management.

Please feel free to post your questions.

UIAlertViewStyle property of UIAlertView

Hi Guys,

Hope everybody doing well. Recently I got a requirement in one of my project to create a UIAlertView with "User Name" and "Password" fields. Prior to iOS 5.0, to achieve this functionality we need to subclass UIAlertView and add UITextField as subviews to the UIAlertView.

Initially I thought of subclassing UIAlertView to achieve this functionality, but I came to know that from iOS 5.0 Apple has added a new property "UIAlertViewStyle alertViewStyle" to UIAlertView class.

Following are the various options available for UIAlertViewStyle property :

UIAlertViewStyleDefaultUIAlertViewStyleSecureTextInputUIAlertViewStylePlainTextInputUIAlertViewStyleLoginAndPasswordInput

Now, lets create a single view application and setup the view layout as show below :

Set tags to 1001 to "Default, 1002 to "Secure", 1003 to "Plain" and 1004 to "Login & Password" buttons using xib file.

Add following action method code to your implementation file :

- (IBAction)showAlert:(id)sender

{

    UIAlertView *alertView = [[UIAlertView alloc] init];

    

    switch (((UIButton *)sender).tag)

    {

        // Default Alert View

        case 1001:

            

            alertView.title = @"Default Alert View";

            alertView.message = @"UIAlertViewStyleDefault";

            [alertView addButtonWithTitle:@"OK"];

            

            break;

           

        // Secure Alert View

        case 1002:

            

            alertView.title = @"Secure Alert View";

            alertView.message = @"UIAlertViewStyleSecureTextInput";

            alertView.alertViewStyle = UIAlertViewStyleSecureTextInput;

            [alertView addButtonWithTitle:@"OK"];

            [alertView addButtonWithTitle:@"Cancel"];

            

            break;

            

        // Plain Alert View

        case 1003:

            

            alertView.title = @"Plain Alert View";

            alertView.message = @"UIAlertViewStylePlainTextInput";

            alertView.alertViewStyle = UIAlertViewStylePlainTextInput;

            [alertView addButtonWithTitle:@"OK"];

            [alertView addButtonWithTitle:@"Cancel"];

            break;

          

        // Login ALert View

        case 1004:

            

            alertView.title = @"Login Alert View";

            alertView.alertViewStyle = UIAlertViewStyleLoginAndPasswordInput;

            [alertView addButtonWithTitle:@"OK"];

            [alertView addButtonWithTitle:@"Cancel"];

            break;

    }

    

    [alertView show];

}

Now connect this action to all buttons in xib file to "Touch up inside" UIControlEvent. 

Run application and following is the output :

Default Style :

Secure Style :

Plain Style :

Login & Password :

This saved a lot of time for me. No need to subclass UIAlertView anymore to create a login view. Hope this will save time of your's too.

 

Secure Text Field With Custom Numeric KeyPad

Hi Guys,

Today I have decided to discuss about a custom secure text field with custom numeric keypad. Usually, when we have a UITextField with secure option enabled and using a default keyboard, last character entered by user will be shown for some time and then it will be converted in to a dot. Please see below screenshot.

But this is not same if we use a custom keyboard. If we use a custom keyboard, last digit won't appear to end user. When ever we press a key in custom keyboard, a dot will be added directly with out any animation. Please see the below screenshot.

To have last character animation for custom keyboard, I came up with a Custom secured UITextField called MLKSecuredTextField. Lets see how I have implemented it. 

Create a Single View application as shown below :

Now, create MKLSecureTextField class which will be a subclass of UITextField as shown below :

The logic I have followed is, I have subclasses UITextField and created following initializers :

- (id)init

{

    if( self = [super init] )

    {

        [self setUpTextFieldProperties];

    }

    

    return self;

}

- (id)initWithFrame:(CGRect)frame

{

    if( self = [super initWithFrame:frame] )

    {

        [self setUpTextFieldProperties];

    }

    

    return self;

}

- (void)setUpTextFieldProperties

{

    // Following are default Values. Can assign custom values after creating MLKSecuredTextField.

    self.borderStyle = UITextBorderStyleRoundedRect;

    self.textColor = [UIColor clearColor];

    self.font = [UIFont systemFontOfSize:FONT_SIZE];

    self.clearButtonMode = UITextFieldViewModeAlways;

    self.placeholder = PLACEHOLDER_TEXT;

    self.autoresizingMask = UIViewAutoresizingFlexibleTopMargin;

    

    self.dotViews = [[NSMutableArray alloc] init];

    

    self.textLength = 0;

    self.text = @"";

    

    // Add text changes observer to get notifications whenever text changes

    [self addObserver:self forKeyPath:TEXT options:NSKeyValueObservingOptionNew|NSKeyValueObservingOptionOld context:nil];

}

 setUpTextFieldProperties method will setup the default properties of our custom textfield and adds a observer to "text" property of textfield. We are observing changes made to text of the text field. I am setting the text color as clear color so that whatever text user enters won't appear.

Whenever there is a change in the text, I am updating the last character to dot and showing the current character for some time. If no text entered, last enter character will be changed to dot after 2 seconds time interval. I have used NSTimer to achieve this. Following is the code :

- (void)observeValueForKeyPath:(NSString *)keyPath

                      ofObject:(id)object

                        change:(NSDictionary *)change

                       context:(void *)context {

    

    if ([keyPath isEqual:TEXT])

    {

        [self textChanged];

    }

}

- (void)textChanged

{

    // Remove the dot view if a character removed

    if( self.textLength > [self.text length] )

    {

        [self invalidateDotViewTimerForIndex:([self.text length ]- 1)];

        

        [[self.dotViews objectAtIndex:(self.textLength - 1)] removeFromSuperview];

        [self.dotViews removeObjectAtIndex:(self.textLength - 1)];

    }

    else if( [self.text length] > 0 )

    {

        [self invalidateDotViewTimerForIndex:([self.text length] - 2)];

        

        [self addCharacterLabelAtIndex:([self.text length] - 1)];

        dotViewTimer = [NSTimer scheduledTimerWithTimeInterval:TIMER_INTERVAL target:self selector:@selector(addDotToLastCharacter) userInfo:nil repeats:NO];

    }

    

    // Capture new lenght

    self.textLength = [self.text length];

    

    // User clicked clear text button. Clear all dot views

    if( self.textLength == 0 )

    {

        [self clearAllDotViews];

    }

}

Override following UITextField methods to set the text rect and editing rect for our custom MLKSecureTextField :

- (CGRect)textRectForBounds:(CGRect) bounds

{

    CGRect origValue = [super textRectForBounds: bounds];

    

    return TEXT_LABEL_OFFSET;

}

- (CGRect)editingRectForBounds:(CGRect) bounds

{

    CGRect origValue = [super textRectForBounds: bounds];

    

    return TEXT_LABEL_OFFSET;

}

Now add business logic to add dots, to show last character for time and clearing all dots when user taps clear button on text field.

- (void)addDotToLastCharacter

{

    [self.characterLabel removeFromSuperview];

    [self addDotViewForCharAtIndex:([self.text length] - 1)];

}

- (void)addDotViewForCharAtIndex:(NSInteger)index

{

    UIView *dotView = [[UIView alloc] initWithFrame:DOT_VIEW_RECT];

    dotView.backgroundColor = [UIColor blackColor];

    [dotView.layer setMasksToBounds:YES];

    [dotView.layer setCornerRadius:DOT_RADIUS];

    

    [self addSubview:dotView];

    [self.dotViews addObject:dotView];

}

- (void)addCharacterLabelAtIndex:(NSInteger)index

{

    self.characterLabel = [[UILabel alloc] initWithFrame:CHAR_LABEL_RECT];

    self.characterLabel.text = [NSString stringWithFormat:@"%C",[self.text characterAtIndex:index]];

    self.characterLabel.font = self.font;

    self.characterLabel.backgroundColor = [UIColor clearColor];

    

    [self addSubview:self.characterLabel];

}

- (void)invalidateDotViewTimerForIndex:(NSInteger)index

{

    if( dotViewTimer.isValid )

    {

        [dotViewTimer invalidate];

        [self.characterLabel removeFromSuperview];

        [self addDotViewForCharAtIndex:index];

    }

}

- (void)clearAllDotViews

{

    while( self.dotViews.count )

    {

        [[self.dotViews objectAtIndex:self.dotViews.count-1] removeFromSuperview];

        [self.dotViews removeObjectAtIndex:self.dotViews.count-1];

    }

}

Here are the #defines I have used :

#define DOT_VIEW_RECT       CGRectMake(8 + (index * (9 + 1.5)), 13, 9, 9)

#define CHAR_LABEL_RECT     CGRectMake(8 + (index * (9 + 1.5)), 10, 9, 14)

#define TEXT_LABEL_OFFSET   CGRectOffset(origValue, 0.0f, 3.0f)

#define TEXT            @"text"

#define FONT_SIZE       17

#define TIMER_INTERVAL  2.0

#define DOT_RADIUS      4.5f

#define PLACEHOLDER_TEXT    @"MLKSecuredTextField"

Okay, we have completed creating custom secure text field. Now use it in a view controller and see the output. Create MLKSecureTextField and add it to the View :

secureTextField = [[MLKSecuredTextField alloc] initWithFrame:CGRectMake(20, 20, 280, 30)];

secureTextField.delegate = self;

[self.view addSubview:secureTextField];

For your understanding, I have used three text fields, one MLKTextFieldField with custom numeric keypad, one UITextField with default keypad and one UITextField with custom numeric keypad.

Now try to enter text in the UITextField with default keyboard :

See you are able to see last character for some time, after that it will be converted to a dot. Lets see what is the behavior with UITextField with custom numeric keypad :

Observe the behavior, when ever you press a key it will be directly added as a dot in the text field. Lets see behavior with our custom MLKSecureTextField :

Have you observed that, last character is appeared for some time and after that changed to a dot. Yeah!!!! we got the expected behavior. 

Thats all from this post. Please add your comments and suggestions.

Constructors and Creating Objects in Objective C

Hi, how are you doing guys.... I am back... I hope you guys got some familiarity with the Objective C syntax we discussed in one of my last tutorial. In this tutorial we will learn about how we write constructors/initializers and how to create an object in Objective C.

Lets start.... constructor/initializer is a method which we call while creating a new object in Object Oriented Programming. In this method we write all the code related to initial setup of an object. Objective C have a default construction called init which is present in its root class NSObject. We can override default initializer. It looks like below :

Default Initializer

- (id)init

{

    if( self = [super init] )

    {

        // Initialize your object here

    }

    

    return self;

}

Confused!!!! Lets go one by one line. 

1. - (id)init

- represents it is a class method. id is generic type. It can hold any kind of object. We will see more about id in our next tutorials. init is the initializer name.

2. if( self = [super init] )

self represents current instance/object. [super init] will call the super class initializer.

3. return self;

Finally it returns the properly initialized object.

Custom Initializer 

Okay, now lets create a custom constructor. We will take the same Employee class earlier and will try to initialize his firstName, lastName and salary. Here is the code for it :

Interface 

@interface Employee : NSObject

{

    NSString *firstName;

    NSString *lastName;

    float salary;

}

- (id)initWithFirstName:(NSString *)aFirstName

               lastName:(NSString *)aLastName

                 salary:(float)aSalary;

@end

Implementation 

#import "Employee.h"

@implementation Employee

- (id)initWithFirstName:(NSString *)aFirstName

               lastName:(NSString *)aLastName

                 salary:(float)aSalary

{

    if( self = [super init] )

    {

        firstName = aFirstName;

        lastName = aLastName;

        salary = aSalary;

    }

    

    return self;

}

@end

Above code explains how a class Employee with properties firstName, lastName and salary and a constructor looks like. Now, lets create an object of type Employee....

Object Creation

Option 1:

// Using Default Initializer

Employee *employeeWithDefaultInit = [[Employee alloc] init];

        

// Using Custom Initializer

Employee *employeeWithCustomInit = [[Employee alloc] initWithFirstName:@"Naga" lastName:@"Malleswar" salary:5000];

In the above code I have associated two method calls in single statement. We can make them two separate statements like below, but followed convention is Option 1.

Option 2:

// Using Default Initializer

Employee *employeeWithDefaultInit = [Employee alloc];

employeeWithDefaultInit = [employeeWithDefaultInit init];

        

// Using Custom Initializer

Employee *employeeWithCustomInit = [Employee alloc];

employeeWithCustomInit = [employeeWithCustomInit initWithFirstName:@"Naga" lastName:@"Malleswar" salary:5000];

Both the above options are same. Only thing is convention. Most of the programmers follow Option 1 to create objects. One may get a doubt. What is alloc is??? alloc is a method to allocate memory. Object creation completes only if we send both alloc and init messages to a new object.

Thanks for your time guys. In our next tutorial, we will create set and get methods for the properties in Employee class. Please feel free to add your comments and suggestion.

Introduction to Objective C and its Syntax

Hi Guys, hope all of you are doing good. In this tutorial, I am planning to discuss something about Objective C and how it differs from other programming languages. I am writing this post to help beginners who are learning Objective C to develop Mac OS X or iOS applications. Prior knowledge of OOPS will help to understand Objective C better. Apple have used Objective C for their OS X, iOS and to develop their frameworks COCOA(MAC) and COCOA Touch(iOS) frame works.

Object Oriented Language :

Objective C is Object Oriented C. C is a structured language. We can't create classes and objects in C. Where as in Objective C we can create classes, objects etc how other object oriented languages are doing. Objective C is super set of C. We can compile any C program using a Objective C complier and we can write any C code inside a Objective C class.

Message Passing :

Objective C uses message passing instead of method calling  which is different from other languages like C++, Java etc. Message passing means, the target of the message is resolved during run time. System resolves during run time whether the receiver responds to the method or not. This helps in attaining dynamic binding. In Objective C, if you send a message to nil, it will simply discard the message and nothing happens. Where as in Java, you will get a run time exception.

Syntax :

Objective C syntax differs from Java, C++ and other Object Oriented languages. It follows Small talk kind of syntax. When comes to using primitive data types(int, float, char etc) it follows C syntax.

Lets suppose there is a method called firstName in class Employee. Following code snippet shows how Objective C syntax looks like to send setFirstName message to object emp of class Employee :

Objective C :

// Method Syntax

- (NSString *)firstName

{

return firstName;

}

// Message Passing

[emp firstName];

Java :

// Method Syntax

String firstName()

{

return firstName;

}

// Method Calling

emp.firstName();

C++ :

// Method Syntax

string firstName

{

return firstName;

}

// Method Calling

emp->firstName();

Now, take a look at syntax of method having single argument. Lets say, setSalary with int argument.

Objective C :

// Method Syntax

- (void)setSalary:(int)aSalary

{

}

//  Message Passing

[emp setSalary:10000];

Java :

// Method Syntax

void setSalary()

{

}

// Method Calling

emp. setSalary(1000);

 C++ :

// Method Syntax

void setSalary()

{

}

// Method Calling

emp-> setSalary(1000);

Now, take a look at syntax of method having multiple arguments. For method to set firstName and lastName of employee :

Objective C :

// Method Syntax

- (void)setFirstName:(NSString *)fName andLastName:(NSString *)lName

{

}

// Message passing

[emp setFirstName:fName andLastName:lName];

Java :

// Method Syntax

void setFirstNameAndLastName(String fName, String lName)

{

}

// Method Calling

emp. setFirstNameAndLastName(fName,lName);

C++ :

// Method Syntax

void setFirstNameAndLastName(string fName, string lName)

{

}

// Method Calling

emp->firstName(fName,lName);

Interfaces and implementations

In Objective C, each class has two sections. One is interface and other one is implementation. As per coding conventions, interface will be placed in "Header(.h)" file and implementation placed in "Implementation(.m)" file.

We will continue with Employee class. Interface for an Employee class will look like below:

Interface :

@interface Employee

{

         // Instance variables

         NSString *firstName;

         NSString *lastName:

}

// Instance Methods

- (NSString *)firstName;

- (NSString *)lastName;

- (void)setFirstName:(NSString *)firstName;

- (void)setLastName:(NSString *)lastName;

// Class Methods

+ (int)numberOfEmployees;

@end

Implementation :

@implementation Employee

// Instance Methods

- (NSString *)firstName

{

}

- (NSString *)lastName

{

}

- (void)setFirstName:(NSString *)firstName

{

}

- (void)setLastName:(NSString *)lastName

{

}

// Class Methods

+ (int)numberOfEmployees

{

}

@end

NSObject is the root class of all Objective C classes. Each class of Objective C is inherited from root class NSObject.

Thats all for now. I hope you guys got good understanding about Objective C. Please feel free to add your comments and suggestions.

In our next topic, we will cover constructors and creating objects in Objective C.