Lecture 11

Cover page image

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 - 13

Lab

Bring your laptop to each class
You will work with a buddy
One of you writes code, the other types up answers
Switch roles each lab (not each day)
Submit lab work to Piazza

Hello, World

Start XCode and make new single-view iOS application. Call it Lab11
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
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?