Objective-C and COCOA Applications

Transcription

1 Objective-C and COCOA Applications Fall, 2012 Prof. Massimiliano "Max" Pala

2 Overview X-Code IDE Basics Objective-C Classes Methods Invocations Important Types Memory Management Protocols Exceptions and Errors Multithreading Notifications Methods Patching Methods

3 X-Code Basics Resources for the ideveloper Apple ios Developer Website Tutorial: Hello World ios SDK 5 Signing and Distributing Code Development Workflow Integrated IDE New Compiler LLVM Apple moved away from GCC / GDB Device Emulators Debugger and Profiler Version Managing (GIT)

4 Objective-C Superset of C++ Object Oriented Polymorphism Single Inheritance Protocols (i.e., Java's Interfaces) Practical Development.m files hold the code (~.cpp files in C++).h files hold the class definitions Compiler Directives are instructions to the Objective-C compiler - prefixed by '@'

5 Objective-C: Classes To Declare a @interface myclass: superclass { // Attributes Declaration } // Methods attributes are instance variables methods can be either instance or class methods - (Address *) getaddress [instance method] + (Address *) getaddress [class method] No class variables (use static variables to share values across instances) When using a class (without accessing methods) you can simply use '@class Address;'

6 Objective-C: Classes-2 To define a class, you need the implementation #import myclass // Methods Method Invocation via message expressions [aobject setx:3 andy:6 andz:5] Use square brackets A message is composed by keywords and parameters If an MsgExp evaluates to an object it can receive a Msg Corresponding method definition -(void) setx: (float) x andy: (float) y andz: (float) z;

7 Objects Every object inherits from NSObject Use two steps approach Allocation - use the alloc method (implemented in the NSObject class) Initialization - use the init method (stub implemented in NSObject class) to initialize the internal structure of your objects

8 Example #import MyObject : NSObject - (void) #import MyObject - (void) dosomething { // Do something here NSLog(@"%s", FUNCTION );

9 Properties Task We want to add variables that we can easily access Use to define a variable Example: Add a property to hold a person's name #import Person : (nonatomic, strong) NSString

10 Properties (cont.) #import firstname; -(id) init { self = [super init]; if (self) { // Init the object... } } Person * newperson = [[Person alloc] init]; newperson.firstname

11 Properties (cont.) Properties generate setter/getter methods for instance variables. For example for an NSString * property 'name': aobject.name ==> [aobject setname:@"myname"]; Property type name; nonatomic - no extra code for multi-thread sync readonly - no changes are possible (no setter) readwrite - both getter and setter are generated (default)

12 Properties (cont.) assign - assign value directly (default) copy - to store a copy of the object (NSCopying protocol) retain - adds a claim to the object (you need to release it) getter=funcname, setter=funcname - changes the default getter / setter names. By default, for property 'zip', the setter is setzip and getter is (nonatomic, copy) NSString *name; -(NSString*) myname { return namel; } -(void) setname(nsstring*) aobj { if (name!= aobj) { [name release]; name = [aobj copy]; } }

13 IOS 5 introduced Automatic Reference Counting no need to use retain/release code compiler-level feature - LLVM is default Properties declaration changes No need to declare ivars (I-WARs) anymore Properties (cont.) IOS 4 required us to declare an ivar (instance variable) #import Person : NSObject { NSString *name; NSString

14 Properties (cont.) LLVM uses three classes of storage strong - automatically retained at runtime. The variable is valid in the scope and automatically released weak (or zeroing weak referencing) - when the object to which this variable points gets deallocated, this value will get set to nil unsafe_unretained - Pointing to another variable. No retaining or automatic zeroing Note that by default all local variables are strong variables, but properties need to be specified

15 Properties (Cont.) Storage specification is mostly used when you declare the properties You can use the storage specifiers also when declaring local variables _strong NSString *yourstring String"; _weak NSString *mystring = yourstring; yourstring = nil; _unsafe_unretained NSString *theirstring = mystring; // What are all the three pointers equal to? If you are not sure what you are doing, avoid unsafe storage class

16 Properties (cont.) _autoreleasing - use this when you want to pass an object by reference the method is responsible to allocate, initializing, and returning an instance of a class the caller does not have responsibility at all to release the returned instance The runtime environment will decide when to release the object

17 Properties (cont.) Example: -(void) generror:(_autoreleasing NSError **) perror {... *perror = [[NSError alloc] initwithdomain:@"myapp" code:1 userinfo:errordictionary]; }... NSError *err = nil; [self generateerrorinvar:&err]; NSLog(@"Error = ", err);

18 strong) NSString strong) NSString weak) NSString *string3;... self.string1 1"; self.string2 = self.string1; self.string3 = self.string1; self.string1 = nil; NSLog(@"String 2 = %@", self.string2); NSLog(@"String 3 = %@", self.string3);

19 Important Types Every class in COCOA has a singleton object A *anobject; COCOA defines a type for a generic object: (id) NSObject Base class of most COCOA classes (runtime methods for allocating and deallocating objects) NSInteger / NSUInteger float NSString / NSMutableString NSArray NSSet

20 Important Types NSString: Use to store any text. This class is immutable (i. e., once assigned a value you can not change it): NSString *text NSString!"; NSMutableString for objects that you want to change values to. NSMutableString *txt String"; txt New String";

21 Important Types (cont.) NSArray: Class to represent array objects NSArray *arr = [NSArray arraywithobjects: a,b,c,nil] (NSMutableArray for mutable arrays) NSSet: Non-ordered fast unique-objects container NSSet *set =[[NSSet @"them"]; - (BOOL) containsobject: (id) anobject if ( [set containsobject:a] == YES)..

22 Memory Management Managed Memory (no Garbage collectors) NSObject implements alloc/release and init (if you override init you should call [super init])

23 Memory Management (cont.) In IOS4, your code is responsible to manage memory for objects you allocated (alloc) you copied you retained (retain) Delayed releasing by using NSAutoReleasePool Every thread should have at least one instance of this class: NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init]; After initialization, any autorelease sent to an object will put a reference into the autorelease pool To release object [pool release] - decrements the referencecount in the object by 1 (each release msg)

24 Memory Management (cont.)

25 Memory Management (cont.) Automatic Reference Counting (ARC) is a compiler-level feature that simplifies the process of managing the lifetimes of Objective-C objects Caveats Do not store object pointers in C structures Do not directly cast between object and nonobject types (for example, between id and void*) You cannot use NSAutoreleasePool objects

26 Protocols Protocols allows multiple inheritance in Objective-C Classes can adopt multiple protocols Similar to Java's Interfaces List of methods A class that adopts a protocol must methods (default) may myprotocol -(int) methodone(id<myprotocol>) anobject; -(int) methodtwo: Citizen : Human <myprotocol, yourprotocol, anyprotocol> if ([ahuman conformstoprotocol:@protocol(myprotocol)])...

27 Categories A category is a method in Objective-C to extend classes even when you don't have the source code To declare a category on an existing class use the parenthesis in the interface NSObject( EnhancedObject) -(NSComparisonResult) NSObject( EnhancedObject) // Methods code

28 Exceptions and Errors COCOA uses both Exceptions and Errors Exceptions: usually errors arising from development errors Errors: generally attributed to the user (behaviour) { // Your Code (NSException *e) { // Code that handles the // Use to re-throw the exception { // Execute Anyway }

29 Exceptions and Errors (cont.) Creating Exceptions: if you want to communicate with a caller by throwing an exception Important data for every NSException: name - identifies the exception reason - string with the explanation of the exception userinfo - optional NSDictionary with additional data To throw an exception, use the NSException's class method +(NSException *)exceptionwithname:(nsstring *)name reason:(nsstring *) reason userinfo:(nsdictionary*) userinfo

30 Exceptions and Errors (cont.) Use ERRORS and handle returned ERRORS COCOA uses NSError (or subclasses) to convey errors Conventions Return of methods should indicate failure or success You can pass a pointer to an NSError as last parameter of a method. If not null, the method stores a new autoreleased version of NSError Important attributes of an NSError domain - scope of the error (e.g. NSCocoaErrorDomain) code - An integer carrying the error (meaningful within the domain) userinfo - A dictionary with additional Info related to the error

31 Exceptions and Errors (cont.) To create a new NSError instance NSError *myerror; NSObject value = [aobj callmymethod:&myerror];... -(id) callmymethod: (NSError **) err {... // Something Bad Happened NSError *error = [[ NSError alloc] initwithdomain:mydom code:12 userinfo:dictionary] autorelease]; *err = error; return nil; }