ITP 342 Mobile App Dev. Fundamentals

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1 ITP 342 Mobile App Dev Fundamentals

2 Objective-C Classes Encapsulate data with the methods that operate on that data An object is a runtime instance of a class Contains its own in-memory copy of the instance variables declared by that class & pointers to the methods of the class Specification requires 2 distinct pieces: interface (.h) = public header implementation (.m) = private implementation 2

3 The Interface When you define a new class, you have to tell the compiler 3 things: Where the class came from Name its parent class Specify what type of data is to be stored Describe the data that members of the class will contain These members are called the instance variables Define the type of operations, or methods, that can be used 3

4 Methods A class in Obj-C can declare 2 types of methods Instance methods A method whose execution is scoped to a particular instance of the class Before you call an instance method, you must first create an instance of the class Declaration is preceded by a minus (-) sign Class methods Do not require you to create an instance Typically factory methods for creating new instances of the class or accessing some piece of shared info Declaration is preceded by a plus (+) sign 4

5 Define methods Declaring Methods - (void) printinfo; method type return type method name method takes no argument 5

6 Define methods Declaring Methods - (int) getage; method type return type method name method takes no arguments 6

7 Define methods Declaring Methods - (void) setage: (int) num; method type argument type return type method name method takes argument argument name 7

8 Method Example Method declaration syntax 8

9 Object Messaging To get an object to do something, you send it a message telling it to apply a method Message expressions are enclosed in brackets The receiver is an object and the message tells it what to do Message is the name of a method and any arguments The method name serves to select a method implementation Methods names in messages are often referred to as selectors [receiver message]; [person1 printinfo]; 9

10 Messaging Methods can also take parameters or arguments A message with a single argument affixes a colon (:) to the selector name & puts the argument right after the colon [person1 setage:21]; For multiple parameters, method names should interleave the name with the arguments The method s name naturally describes the arguments expected by the method The sub-parts of the method name - of the selector - are not optional, nor can their order be varied [person1 setname:@"trina" age:21]; 10

11 Messaging Example Example of calling an instance method Call the insertobject method by messaging the corresponding object [myarray insertobject:anobj atindex:0]; Example of calling a class method arraywithcapacity: method is a class method on the NSMutableArray class that allocates and initializes a new instance of the class and returns it to your code NSMutableArray* myarray = nil; // Create a new array & assign it to the myarray variable myarray = [NSMutableArray arraywithcapacity:0]; 11

12 Methods Methods can return values BOOL vote; vote = [person1 canvote]; One message expression can be nested inside another [person1 setage:[person2 age]]; 12

13 Variables Variables allow us to store information The C programming language is a statically typed language We have to tell upfront what kind of data a variable is going to hold Format to declare a variable: type name; Examples: int num1; float score; Declare once, use many 13

14 Variables Specify the types of data to be stored in your class along with the names of those data types Data types can be: C basic types like int, float, char Objective-C defined types like BOOL Other classes that you have created or ones that are already created such as NSString Names Begin with a letter or underscore (_) Followed by any combo of letters (upper- or lowercase), underscores, or the digits 0-9 Cannot be a reserved word like int 14

15 Local Variables Variables Within a method, declare using type and name // In an implementation (.m) file, within a method - (void) mymethod { // local variables BOOL canlegallyvote; int numofyears; NSString *name; name Trojan"; } 15

16 Use CamelCase 16

17 Accessor Methods Setter & getter methods are collectively known as accessor methods As of Objective-C 2.0, you can have them automatically generated for you It s a nice convenience provided in the language First, use directive in the interface 17

18 Properties Properties manage an object s internal data A property s data is stored in an instance variable or ivar Xcode generated these variables automatically The property accesses the ivar via getter/ setter methods (aka accessors) in front of the declaration of the ivar We access properties using the self keyword

19 Encapsulation Getter and setter methods Prevent direct access to object data Allow a class to respond to data changes Enable inheritance and overriding Properties Provide automatic encapsulation Enable Key-Value Observing in Cocoa Manage Memory why-user-getters-and-setters 19

20 Placement Put in the interface file (.h) to make them public to other classes // USCViewController : In the class extension in the implementation file (.m) to make them private // USCViewController Note: Older versions of Xcode (before 4.4) required 20

Examples // Primitive type, read-write by default @property int age; // Primitive type, read-only

UITextField *nametf; @property (weak, nonatomic) IBOutlet UILabel *messagelabel; // Objects

21 Examples // Primitive type, read-write by int age; // Primitive type, (readonly) BOOL canlegallyvote; // (weak, nonatomic) IBOutlet UITextField (weak, nonatomic) IBOutlet UILabel *messagelabel; // (strong, nonatomic) NSString *name; // Objects, create only a (readonly) UIView *rootview; 21

Public attributes Put in interface (.h) file Class Attributes Use @property directive to automatically generate setter and getter methods // Interface file (.

22 Public attributes Put in interface (.h) file Class Attributes directive to automatically generate setter and getter methods // Interface file ClassName : ParentName // Public int age; // primitive (strong, nonatomic) NSString *name; // object // Public 22

Private attributes Class Attributes Put in implementation (.m) file in the class extension Use @property directive to automatically generate setter and getter methods // Implementation file (.

23 Private attributes Class Attributes Put in implementation (.m) file in the class extension directive to automatically generate setter and getter methods // Implementation file ClassName () // Private int age; // (strong, nonatomic) NSString *name; ClassName // Implementation of methods (private and 23

24 Class Extensions Extend the internal implementation Can add private properties Can add private methods Must be implemented // USCPerson NSObject *extraproperty; - USCPerson - (void) logextraproperty { NSLog(@"Extra property: %@", self.extraproperty); 24

25 Property (strong, nonatomic) NSString *name; Memory Properties Readable Properties Method Name Properties Threading Properties strong weak copy assign readonly readwrite getter setter nonatomic atomic Setter retains the new value (default under ARC) Assignment doesn't affect object's lifespan Setter makes a copy of the new value For primitives (preceded weak for objects) Only a getter is generated Getter and setter methods generated (default) The method name used for the getter The method name used for the setter Doesn't ensure multi-thread safety of get/set Makes get/set multi-thread safe (default) 25

26 Property Attributes Read-only versus int age; // read-write by (readonly) BOOL canlegallyvote; Memory management policies (only for object (strong, nonatomic) NSString (weak, nonatomic) UILabel *textlabel; Different setter/getter (getter=getage, setter=setage) int age; 26

Property Attributes IBOutlets (Interface Builder components) Use (weak, nonatomic) Class ivars (instance variables) Use (strong, nonatomic) for mobile // IBOutlets @property (weak, nonatomic)

27 Property Attributes IBOutlets (Interface Builder components) Use (weak, nonatomic) Class ivars (instance variables) Use (strong, nonatomic) for mobile // (weak, nonatomic) IBOutlet UITextField (weak, nonatomic) IBOutlet UILabel *messagelabel; // (strong, nonatomic) NSString (strong, nonatomic) NSDate *launchtime; 27

Get & Set Methods When you use @property, the get & set methods are synthesized for you by the complier.

conventions The method used to access the value (the getter method) has the same name as the property.

28 Get & Set Methods When you the get & set methods are synthesized for you by the NSString NSString *lastname; The synthesized methods follow specific naming conventions The method used to access the value (the getter method) has the same name as the property. firstname The method used to set the value (the setter method) starts with the word set and then uses the capitalized property name. setfirstname 28

29 Accessor Methods If you want to use a different name for an accessor method, it s possible to specify a custom name by adding attributes to the property. In the case of Boolean properties (properties that have a YES or NO value), it s customary for the getter method to start with the word (getter=isfinished) BOOL finished; The getter method for a property called finished, for example, should be called (getter=isfinished, setter=setfinished) BOOL finished; 29

30 ivar & NSString NSString *lastname; The ivar (instance variable) is the name of the property prepended by an underscore _firstname When you want to use the property in methods, you need to use self self.firstname 30

31 Dot Syntax Dot syntax is purely a convenient wrapper around accessor method calls. When you use dot syntax, the property is still accessed or changed using the getter and setter methods. someperson.firstname [someperson firstname]; someperson.firstname Trojan"; [someperson setfirstname:@"tommy Trojan"]; 31

32 Getter self.property is the same as [self property] Setter self.property = value; is same as Dot Notation [self setproperty:value]; Note: value is the type of property 32

33 Example // USCViewController.m #import USCViewController (weak, nonatomic) IBOutlet USCViewController - (IBAction)buttonTouched:(id)sender { // There is a property named text on UILabel self.messagelabel.text Trojan"; 33

34 IBOutlets & IBActions Outlets Instance variables that are declared using the keyword IBOutlet A reference from code to an object in Interface Builder Any instance variable that you create and want to connect to an object in IB must be preceded by the IBOutlet keyword Actions Methods that are part of your controller class and declared with the keyword IBAction Tells Interface Builder that this method is an action and can be triggered by a control A method you want a user interface object to be able to call 34

35 2 Ways To Create Objects 1. Drag objects from the Interface Builder Library 2. Write code to allocate and initialize objects Note: Everything we do in Interface Builder can be done in code. The reverse is not true. 35

36 Visual Objects 1. Drag an object into Interface Builder 2. Connect the object with an outlet 3. Send message to the object Example: IBOutlet *UIbob; [bob sayhello]; 36

37 Non-visual Objects 1. Allocate memory for an object 2. Initialize the object 3. Send messages to the object Example: Person *bob = [Person alloc]; bob = [bob init]; [bob sayhello]; 37

38 Person *bob Example The bob variable is a pointer to an object of type Person [bob sayhello]; We send the sayhello message to the object bob 38

39 Memory Allocation NSDate *now = [NSDate alloc]; alloc is a class method inherited from NSObject alloc grabs memory, sets the object s class (NSDate in this class), and zero-initializes the rest 39

40 Initializing the Object now = [now init]; init finishes up the initialization of the object s memory After init is sent, the object is ready to use 40

ITP 342 Mobile App Dev. Fundamentals

ITP 342 Mobile App Dev. Fundamentals ITP 342 Mobile App Dev Fundamentals Object-oriented Programming Object-oriented programming (OOP) is a programming paradigm based on the concept of objects. Classes A class can have attributes & actions