CS 185C/286 - Lecture 10

Cay S. Horstmann

Lecture 10 Quiz 1

No quiz today, but there will be one on Thursday

Homework 5 asks about your progress reports etc.

Today's Lecture/Lab

• A brief intro into iOS and Objective-C

Introducing iOS Development

• You must use a Mac.
• Install XCode from the Appstore
• You must program in Objective-C
• Adds Smalltalk-like OO features to C
• Dates from the 1980
• Used in NeXTSTEP, the predecessor to Mac OS X
• Used in Mac OS X and iOS

Messages

• In Java, C++, you call a method:

  obj.method(arg1, arg2)

• In Smalltalk and Objective-C, you send a message
• Message send is more dynamic
• Object can change its mind how to deal with a message...but it usually doesn't.
• Syntax is different

  [obj method: arg1 param2: arg2]

• The [obj method: arg] part is just another syntax for obj.method(arg)
• The param2: part is a Smalltalk idiosyncracy, somewhat but not quite like “named parameters” in languages such as C#, Groovy, or Scala
• Ex. [myArray insertObject: obj atIndex: 1], calls method insertObject:atIndex:

Defining Classes

• Separate interfaces and implementation (like in C++)
• Interface in .h file
• Use + for class (static) methods, - for instance methods

• @interface classname : superclassname {
   // instance variables
  }
  + (return_type)classMethod:(param1_type)param1_varName;
  - (return_type)instanceMethod:(param1_type)param1_varName :(param2_type)param2_varName;
  @end

Implementation

• In .m file

• @implementation classname
  + (return_type)classMethod
  {
   // implementation
  }
  - (return_type)instanceMethod
  {
   // implementation
  }
  @end

Constructing Objects

• Send the alloc and init methods to an object: [[NSDate alloc] init]
• These are class methods.

Properties

• Property is like getter/setter pair in Java
• In Objective-C, you don't use get: name/setName
• @property (nonatomic, retain) NSString *name;
• Ignore nonatomic and retain for now.
• The @property declaration goes in the .h file
• In the .m file, place @synthesize name;
• Now can use dot notation with property: q.name

Miscellaneous

• nil is a null reference
• Strings are written as @"Hello"
• self is like this in Java
• NSString, NSArray, NSMutableArray, NSMutableDictionary
• API reference is here
• Remember to use pointers for all object references: NSString *greeting = @"Hello";
• However, id is a generic object reference that doesn't require an asterisk: id greeting = ...;

Integration with InterfaceBuilder

• Apple's Objective-C has morphed into a DSL for InterfaceBuilder
• IBOutlet: Object linked to .xib file entity

  @property (nonatomic, retain) IBOutlet UITextView *choice_text;

• IBAction: Method that can be called from UI

Reading Before Next Class

• Dr. Pollett recommends the book by Hillegass for learning Objective-C.
• Read chapters 12 - 16

Lab

• Bring your laptop to the lab
• You will work with a buddy
• For this lab, match yourself up with a buddy who has a Mac
• Submit lab work to git

Hello, World

• Start XCode and make new single-view iOS application. Call it Lab10
• Set the prefix to SJSU
• Check only the second checkbox (Use automatic reference counting)
• On the left, select the .xib file
• Locate the library in the bottom right (Figure 2-16 of Beginning iOS 5 Development)
• Click on the cube and search for Label
• Drag the label on the center of the UI builder in the middle
• Double-click on Label and change to Hello, World!
• Select Product → Run from the menu

Some Code

• In SJSUViewController.h, add

  @property (nonatomic, retain) NSArray *choices;

• In SJSUViewController.m, add

  @synthesize choices;

  after @implementation
• In viewDidLoad, add the following code after [super viewDidLoad];:

  self.choices = [NSArray arrayWithObjects: @"Android", @"Blackberry", @"iOS", @"Windows Mobile"];

• You get a warning triangle. What's the message?
• Apply the suggested fix. What happens?
• In viewDidReceiveMemoryWarning, add

  self.choices = nil;

  This helps with the semi-automatic memory management.
• In SJSUViewController.h, add the following under the array:

  @property (nonatomic, retain) IBOutlet UILabel *choice_text;
  -(IBAction)choice_btn_touch:(id)sender;

• choice_text is a property, so what do you need to do in ViewController.m?
• And in ViewDidReceiveMemoryWarning?
• Now we add the implementation of the button callback. Add it before @end in the .m file:

  -(IBAction)choice_btn_touch:(id)sender {
      int count = [self.choices count];
    	int index = arc4random() % count;
    	NSString *choice = [self.choices objectAtIndex:index];
  	  self.choice_text.text = choice;      
  }

• Now select the .xib file. Keep the label from the previous step and add a Round Rect Button.
• Select View → Assistant Editor
• Right-click the label and drag to the choice_text property.
• Right-click the button. Drag to the callback function.
• Run your program. What does it do when you click the button?