The document discusses how to code for accelerometer and Core Location in Objective-C. It provides code snippets for reading accelerometer data using UIAccelerometer and handling orientation changes. It also explains how to get the user's current location using the Core Location framework by initializing a CLLocationManager instance and setting a delegate to receive location updates.

1. How to code for accelerometer
and Core Location?
Desert Code Camp
Phoenix, Arizona 2010

2. Design Pattern
1.

3. Model(delegate) + Controller + View
View Singleton
Include
XIB files
Model Controller
Delegates
3

4. Objective-C
2.

5. Objective-C
 Is a simple computer language designed to enable sophisticated OO programming.
 Extends the standard ANSI C language by providing syntax for defining classes,
methods, and properties, as well as other constructs that promote dynamic
extension of classes.
 Based mostly on Smalltalk (class syntax and design), one of the first object-oriented
programming languages.
 Includes the traditional object-oriented concepts, such as encapsulation,
inheritance, and polymorphism.
5

6. Files
Extension Source Type
.h Header files. Header files contain class, type, function, and
constant declarations.
.m Source files. This is the typical extension used for source
files and can contain both Objective-C and C code.
.mm Source files. A source file with this extension can contain C+
+ code in addition to Objective-C and C code.
This extension should be used only if you actually refer to C+
+ classes or features from your Objective-C code.
6

7. #import
 To include header files in your source code, you can use the standard #include, but….
 Objective-C provides a better way #import. it makes sure that the same file is never
included more than once.
#import
“MyAppDelegate.h”
#import
“MyViewController.h”
#import
<UIKit/UIKit.h>
7

8. Class
 The specification of a class in Objective-C requires two distinct pieces: the
interface (.h files) and the implementation (.m files).
 The interface portion contains the class declaration and defines the instance
variables and methods associated with the class.
@interface
…
@end
 The implementation portion contains the actual code for the methods of the
class.
@implementation
…
@end
8

9. Class
Class name
@interface
MyClass
:
NSObject
Parent class
{
int
count;
id
data;
Instance variables
NSString*
name;
}
-­‐
(id)initWithString:(NSString
*)aName;
methods
+
(MyClass
*)createMyClassWithString:
(NSString
*)
aName;
@end
9

10. Class
Class name
@implementation
MyClass
-­‐
(id)initWithString:(NSString
*)
aName
{
if
(self
=
[super
init])
{
count
=
0;
data
=
nil;
methods
name
=
[aName
copy];
return
self;
}
}
+
(MyClass
*)createMyClassWithString:
(NSString
*)
aName
{
return
[[[self
alloc]
initWithString:aName]
autorelease];
}
@end
10

11. Methods
 A class in Objective-C can declare two types of methods:
 Instance method is a method whose execution is scoped to a particular instance of the
class. In other words, before you call an instance method, you must first create an
instance of the class.
 Class methods, by comparison, do not require you to create an instance.
Method type identifier One or more signature keywords
-­‐(void)insertObject:(id)anObject
atIndex:(NSUInteger)index;
Return type Parameters with (type) and name
11

12. Methods
So
the
declaration
of
the
method
insertObject
would
be:
-­‐(void)insertObject:(id)anObject
atIndex:(NSUInteger)index
Method type identifier, is (-) to instance methods, (+) to class methods.
And
the
line
to
call
the
method
would
be:
[myArray
insertObject:anObj
atIndex:0];
12

13. Properties
 They are simply a shorthand for defining methods (getters and setters) that
access existing instance variables.
 Properties do not create new instance variables in your class declaration.
 Reduce the amount of redundant code you have to write. Because most
accessor methods are implemented in similar ways
 You specify the behavior you want using the property declaration and then
synthesize actual getter and setter methods based on that declaration at
compile time.
13

14. Properties
In the interface we have:
{
BOOL
flag;
NSString*
myObject;
UIView*
rootView;
}
@property
BOOL
flag;
@property
(copy)
NSString*
myObject;
//
Copy
the
object
during
assignement
@property
(readonly)
UIView*
rootView;
//
Create
only
a
getter
method.
…
And in the implementation side we have:
@syntetize
flag;
@syntetize
myObject;
@syntetize
rootView;
…
myObject.flag
=
YES;
CGRect
viewFrame
=
myObject.rootView.frame;
14

15. Properties
Writability
 Readwrite. You can read/write it. This is the default value.
 Readonly. You can only read it.
Setter semantics (mutually exclusive)
 Assign. Specifies that the setter uses simple assignment. This is the default value.
 Retain. Specifies that a pointer should be retained.
 Copy. Specifies that a copy of the object should be used for assignment.
Atomicity (multithreading)
 Nonatomic. Specifies that accessor methods are not atomic.
 The default value is atomic but there is no need to specify it.
15

16. Protocols and Delegates
 Protocols are not classes themselves. They simply define an interface that other objects
are responsible for implementing
 A protocol declares methods that can be implemented by any class.
 In iPhone OS, protocols are used frequently to implement delegate objects. A delegate
object is an object that acts on behalf of, or in coordination with, another object.
 The declaration of a protocol looks similar to that of a class interface, with the exceptions
that protocols do not have a parent class and they do not define instance variables.
 In the case of many delegate protocols, adopting a protocol is simply a matter of
implementing the methods defined by that protocol. There are some protocols that
require you to state explicitly that you support the protocol, and protocols can specify
both required and optional methods.
16

17. Example: Fraction
Fraction.h
Fraction.m
#import
<Foundation/NSObject.h>
#import
"Fraction.h"
#import
<stdio.h>
@interface
Fraction:
NSObject
{
int
numerator;
@implementation
Fraction
int
denominator;
}
@synthesize
numerator;
//Properties
instead
of
getters
and
@synthesize
denominator;
//setters
@property
(nonatomic)
int
numerator;
//
Output
Print
@property
(nonatomic)
int
denominator;
-­‐(void)
print
{
printf("%i/%i",
numerator,denominator);
}
//Output
print
@end
-­‐(void)
print;
@end
17

18. Example: Fraction
main.m
#import <stdio.h>
#import "Fraction.h"
int main( int argc, const char *argv[] ) {
Fraction *frac = [[Fraction alloc] init];
frac.numerator = 1;
frac.denominator=3;
printf( "The fraction is: " );
[frac print];
printf( "n" );
[frac release]
return 0;
}
18

19. Strings
 The NSString class provides an object wrapper.
 Supports storing arbitrary-length strings, support for Unicode, printf-style
formatting utilities, and more.
 Shorthand notation for creating NSString objects from constant values.
Precede a normal, double-quoted string with the @ symbol.
NSString*
myString
=
@”Hello
Worldn";
NSString*
anotherString
=
[NSString
stringWithFormat:@"%d
%s",
1,
@"String”];
19

20. Let us code:
Autorotate and Accelerometer
3

21. Accelerometer
Measure of Gravity acceleration:
0g
1g
2.3g
21

22. Reading the Accelerometer
 UIAccelerometer object in UIKit allow you to access to the raw accelerometer
data directly. This object reports the current accelerometer values.
 To get an instance of this class, call the sharedAccelerometer method of
UIAccelerometer class.
 The updateInterval property define the reporting interval in seconds.
-­‐(void)viewDidLoad
{
UIAccelerometer
*accelerometer
=
[UIAccelerometer
sharedAccelerometer];
accelerometer.delegate
=
self;
accelerometer.updateInterval
=
1.0/60;
[super
viewDidLoad];
}
22

23. Reading the Accelerometer
 A delegate (UIAccelerometerDelegate) will receive acceleration events.
@interface
FooViewController:
UIViewController
<UIAccelerometerDelegate>
 Use accelerometer:didAccelerate: method to process accelerometer data.
-­‐(void)accelerometer:(UIAccelerometer
*)accelerometer
didAccelerate:
(UIAcceleration
*)acceleration
{
NSString
*s
=
[[NSString
alloc]
initWithFormat:@"%f,
%f,
%f",
acceleration.x,
acceleration.y,
acceleration.z];
accLabel.text
=
s;
[s
release];
}
23

24. AutoRotate
The UIViewController class provides the infrastructure needed to rotate your interface and
adjust the position of views automatically in response to orientation changes.
-(BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation interfaceOrientation {
return YES;
//return (interfaceOrientation == UIInterfaceOrientationPortrait);
}
interfaceOrientation values:
 UIInterfaceOrientationPortrait
 UIInterfaceOrientationPortraitUpsideDown
 UIInterfaceOrientationLandscapeLeft
 UIInterfaceOrientationLandscapeRight
24

25. AutoRotate adjustments
25

26. Core Location
4

27. Core Location
The Core Location framework monitors signals coming from cell phone towers
and Wi-Fi hotspots and uses them to triangulate the user's current position.
27

28. Getting the User's Current Location
 Create an instance of CLLocationManager class.
It
is
necessary
to
include
the
CoreLocation.framework
#import
<CoreLocation/CoreLocation.h>
@interface
FooViewController:
UIViewController<CLLocationManagerDelegate>
 To begin receiving notifications, assign a delegate and call the
startUpdatingLocation method.
-­‐(void)viewDidLoad
{
CLLocationManager
*locationManager=
[[CLLocationManager
alloc]
init];
[locationManager
startUpdatingLocation];locationManager.delegate
=
self;
locationManager.distanceFilter
=
kCLDistanceFilterNone;
locationManager.desiredAccuracy
=
kCLLocationAccuracyBest;
}
28

29. Using the Core Location
 We need implement this:
-­‐ (void)locationManager:(CLLocationManager
*)manager
didUpdateToLocation:
(CLLocation
*)newLocation
fromLocation:(CLLocation
*)oldLocation
{
NSString
*latitudeString
=
[[NSString
alloc]
initWithFormat:@"%g°",
newLocation.coordinate.latitude];
latitudeLabel.text
=
latitudeString;
[latitudeString
release];
NSString
*longitudeString
=
[[NSString
alloc]
initWithFormat:@"%g°",
newLocation.coordinate.longitude];
longitudeLabel.text
=
longitudeString;
[longitudeString
release];
}
29

30. Exercises and
References
5

31. iPhone Dev Center
http://developer.apple.com/iphone
31