3. Background
• Objec)ve-‐C
is
layered
on
top
of
the
C
–
language
– Based
on
SmallTalk-‐80
– Designed
in
early
1980s
• NeXT
SoLware
licensed
Objec)ve-‐C
in
1988
• Apple
Computer
acquired
NeXT
in
1996
• Today:
na)ve
language
for
developing
Mac
OS
X
-‐
and
iPhone
-‐
apps
8. Compiling
and
Running
TB308POHJUS-L-2:point pohjus$ ls -al
total 32
drwxr-xr-x 6 pohjus staff 204 18 Tou 15:32 .
drwxr-xr-x 3 pohjus staff 102 18 Tou 14:52 ..
-rw-r--r--@ 1 pohjus staff 196 18 Tou 15:25 MyPoint.h
-rw-r--r--@ 1 pohjus staff 268 18 Tou 15:23 MyPoint.m
-rw-r--r--@ 1 pohjus staff 339 18 Tou 15:25 main.m
-rw-r--r--@ 1 pohjus staff 120 18 Tou 15:14 makefile
TB308POHJUS-L-2:point pohjus$ make
clang -fno-objc-arc -framework foundation MyPoint.m main.m -o MyPoint
TB308POHJUS-L-2:point pohjus$ make run
./MyPoint
2009-05-18 15:32:46.339 MyPoint[8725:807] X = 0 and Y = 0
2009-05-18 15:32:46.341 MyPoint[8725:807] X = 8 and Y = 7
TB308POHJUS-L-2:point pohjus$
9. Instan)a)ng
an
Object
// Declare a pointer to the object
MyPoint* point;
// Allocate memory for the object
point = [MyPoint alloc];
// Initialize the object
point = [point init];
10. Instan)a)ng
an
Object:
One
Liner
// Allocate and initialize the object
MyPoint* point1 = [[MyPoint alloc] init];
11. Messages
(Methods)
- (void) setX: (int) n;!
method
type:
+
=
class
method
-‐
=
object
method
return
type
selector
name
argument
type
argument
name
12. Messages,
with
Two
Arguments
Declara=on
- (void) setXAndY: (int) x: (int) y
Usage
[object setXAndY: 5: 6];
Declara=on,
be@er
way
- (void) setX: (int) x andY: (int) y
Usage
[object setX: 5 andY: 6];
15. Memory
Handling
in
General
• When
allocate
something
it
must
be
released
– Memory
consump)on
• In
Java,
garbage
collector
takes
care
of
the
release.
Separate
thread
looking
for
objects
that
can
be
released
• In
Obj-‐C
and
C/C++,
programmer
is
responsible
about
the
release.
16. About
Pointers
• int
a
=
5;
– Holds
one
integer
value
– The
integer
is
stored
in
some
memory
address
• Where?
– You
can
get
the
memory
address
by
using
&
in
front
of
the
variable:
&a
17. Example
of
Memory
Address
int main(int argc, char *argv[])
{
int a = 5;
// prints 5
NSLog(@"%i", a);
// prints something like 0x7fff5fbff9cc
NSLog(@"%p", &a);
return 0;
}
18. Pointers
• Pointer
is
a
variable
that
stores
memory
address
• int
a;
– holds
integer
variable
• int*
b;
– holds
memory
address
that
points
to
integer
value
• int*
b
=
&a;
– Now
b
has
the
memory
address
of
a
19. Example
about
Pointers
#import "MyPoint.h"
int main(int argc, char *argv[])
{
int a = 5;
// Store a's memory address to variable b
int *b = &a;
// prints 5
NSLog(@"%i", a);
// prints something like 0x7fff5fbff9cc
NSLog(@"%p", &a);
// prints something like 0x7fff5fbff9cc
NSLog(@"%p", b);
// prints 5
NSLog(@"%i", *b);
return 0;
}
20. What
is
the
result
now?
int main(int argc, char *argv[])
{
int a = 5;
// Store a's memory address to variable b
int *b = &a;
if(b == &a)
{
NSLog(@"Do we go here?");
}
if(*b == a)
{
NSLog(@"What about here?");
}
return 0;
}
21. What
is
the
result
now?
int main(int argc, char *argv[])
{
int a = 5;
int *b = &a;
*b = 10;
NSLog(@"%i", a);
return 0;
}
22. Memory
Areas
• Memory
can
be
divided
into
three
categories
1. Global
or
sta)c
2. Stack
3. Heap
23. Sta)c
• When
something
is
in
sta)c
memory,
it's
there
all
the
)me
when
app
is
running
• So
when
star)ng
the
app,
the
memory
is
allocated
an
when
the
app
closes,
the
memory
is
deallocated
• The
variable
is
stored
in
the
same
memory
address
all
the
)me.
24. Example
of
Sta)c
Memory
int thisIsStoredInStaticMemory = 5;
int main(int argc, char *argv[])
{
static int thisIsAlsoStoredInStaticMemory = 10;
NSLog(@"My number = %i", thisIsStoredInStaticMemory);
NSLog(@"My number = %i", thisIsAlsoStoredInStaticMemory);
return 0;
}
25. Stack
-‐
Memory
• Stack
–
memoryarea
is
usually
small
• If
you
put
too
much
"stuff"
into
stack,
you
might
get
stack
overflow
• Local
variables
are
stored
in
stack!
• Variables
are
released
when
out
of
scope
26. Example
of
Stack
Memory
int main(int argc, char *argv[])
{
int stack1 = 3;
NSLog(@"My number = %i", stack1);
if(YES)
{
int stack2 = 4;
NSLog(@"My number = %i", stack2);
// stack2 is released from memory now.
}
// stack1 is released from memory now.
return 0;
}
27. Example
of
Stack
Memory
int main(int argc, char *argv[])
{
if(YES)
{
int stack2 = 4;
}
// Does this work?
NSLog(@"My number = %i", stack2);
return 0;
}
28. Heap
-‐
Memory
• Heap
–
memory
is
the
large
memory
area
where
almost
all
of
the
objects
go.
• Programmer
is
responsible
for
releasing
the
objects!
29. Example
of
Heap
-‐
memory
#import "MyPoint.h"
int main(int argc, char *argv[])
{
MyPoint* point = [MyPoint alloc];
//...
[point release];
return 0;
}
30. Crea)ng
a
Object
• The
crea)on
of
an
object
is
done
in
two
parts
• 1)
Alloca)ng
memory
– MyPoint* point = [MyPoint alloc];
• 2)
Ini)alize
object
state
– point = [point init];
• Combined
– MyPoint* point = [[MyPoint alloc] init];
• ó
– MyPoint* point = [MyPoint new];
31. What
happens
in
Memory?
• What
happens
in
here?
– MyPoint* p = [MyPoint alloc];
• Two
things!
– MyPoint* p;
– p = [MyPoint alloc];
• p
is
in
stack
–
memory!
• MyPoint
object
is
in
heap
memory!
33. Problem?
#import "MyPoint.h"
int main(int argc, char *argv[])
{
MyPoint* point = [MyPoint alloc];
point = [MyPoint alloc];
[point release];
return 0;
}
34. init-‐method?
• init-‐method
is
implemented
in
NSObject
• You
can
however
implement
your
own
init-‐
method
- (id) initWithName: (NSString*) aName
{
if(self = [super init])
{
name = aName;
}
return self;
}
35. Other
init-‐methods
• Like
in
Java
and
C++,
one
can
have
mul)ple
constructors
• In
Obj-‐C,
one
can
have
mul)ple
init-‐methods
- (id) init
- (id) initWithX: (int) aX;
- (id) initWithX: (int) aX andY: (int) aY
36. Deallocing
Object
and
Reference
Count
• Rules
about
reference
coun=ng
– When
object
is
created
its
reference
count
is
set
to
1
– Incremen)ng
the
reference
count:
• [point retain];
– Decreasing
reference
count
• [point release];
– When
reference
count
reaches
to
0,
dealloca=ng
occurs
• ARC
will
save
you
from
this!
39. dealloc
• You
can
implement
a
dealloc
method
(void) dealloc
{
// Some code
[super dealloc];
}
40. Reference
Count
Example
#import <Foundation/Foundation.h>
@interface Cat : NSObject
{
NSString* name;
}
- (void) setName: (NSString *) theName
@end
@implementation Cat
- (void) setName: (NSString *) theName
{
name = theName;
}
@end
int main(int argc, char *argv[])
{
....
Cat* mirri = [[Cat alloc] init];
[mirri setName: someName];
// What happens now?
[someName release];
}
Since
reference
count
is
0,
dealloca)on
occurs.
This
means,
that
the
Cat
does
not
have
a
name
anymore.
41. Reference
Count
Example
#import <Foundation/Foundation.h>
@interface Cat : NSObject
{
NSString* name;
}
- (void) setName: (NSString *) theName
@end
@implementation Cat
- (void) setName: (NSString *) theName
{
[name release];
name = theName;
[name retain];
}
@end
int main(int argc, char *argv[])
{
....
Cat* mirri = [[Cat alloc] init];
[mirri setName: someName];
// What happens now?
[someName release];
}
Since
reference
count
is
1,
dealloca)on
does
not
occur
and
the
Cat
s)ll
has
it's
name.
42. Copying
a
Object
- (void)setName:(NSString *)theName
}
[name release];
name = [theName copy];
}
43. Autorelease
Pool
• Every
Founda)on
program
must
set
up
autorelease
pool
for
the
Founda)on
objects
• Pool
keeps
track
of
your
objects
for
later
release
– NSAutoreleasePool *pool = [[NSAutoreleasePool
alloc] init];
– ...
– [pool drain];
44. Method
Names
• If
method
name
includes
alloc
or
copy,
it
returns
a
object
that
must
be
released
– // Must be released
– NSObject* object = [[NSObject alloc] init];
– // Must be released
– NSObject* copy = [object copy];
– // Do not have to release
– NSMutableString* string = [NSMutableString string];
• The
above
string
is
released
in
Autorelease
Pool!
45. Problem
// Programmer A code
[[someObject giveCat] eat];
// Programmer B code
- (Cat*) giveCat
{
// Must be released!
Cat* myCat = [[Cat alloc] init];
// But where? Should the programmer who calls this method be
// responsible for deallocation of the Cat? How does the programmer
// know this?
return myCat;
}
..
46. Solu)on
// Programmer A code
[[someObject giveCat] eat];
// Programmer B code
- (Cat*) giveCat
{
// Must be released!
Cat* myCat = [[Cat alloc] init];
// But where? When autopool is drained!
[myCat autorelease];
return myCat;
}
47. Delayed
Release
• Autorelease
means
"send
release
message
later".
• Release
message
is
sent
when
Autorelease
Pool
is
released
• Autorelease
Pool
is
created
and
released
in
UIKit
programs
automa=cally!
– Pool
is
created
at
the
beginning
of
an
event
cycle
– Pool
is
released
at
the
end
of
an
event
cycle
48. Autorelease
Pools
App
Loaded
Wait
for
Event
Handle
event
Exit
app
Event
loop
Pool
created
Pool
released
49. Autorelease
Pool
Usage
// Method
- (Cat*) giveCat
{
// Must be released!
Cat* myCat = [[Cat alloc] init];
// But where? When autopool is drained!
[myCat autorelease];
return myCat;
}
// Usage
Cat* someCat = [object giveCat];
// someCat will be released in some time, so if you want to hold it, use
// retain
[someCat retain];
50. Rules
• If
method
name
contains
"alloc",
"new"
or
"copy",
you
must
remember
to
use
release
or
autorelease
– Example:
alloc, newObject, mutableCopy
• If
you
retain something,
you
must
use
release or
autorelease
• Instance
Variables:
retain
or
copy
• autorelease
means
"send
release later"
53. main.m
#import "Cat.h"
int main(int argc, char *argv[])
{
NSAutoreleasePool *pool =
[[NSAutoreleasePool alloc] init];
// Create the string
NSString* catName = [[NSString
alloc] initWithString: @"Jack"];
// Create cat with the string
Cat* cat = [[Cat alloc]
initWithName: catName];
// Just testing. This does not
deallocate catName!
[catName release];
// Get the name
NSString* name = [cat getName];
// Print the name
NSLog(name);
// Release name and cat
[cat release];
[pool drain];
return 0;
}
55. ARC?
• ARC
(Automa=c
Reference
Coun=ng)
– Compiler
does
automa/c
reference
coun/ng
by
examining
the
source
code
and
then
add
the
retain
and
release
messages
to
objects
• Not
garbage
collec)on,
no
background
process
of
dealloca)on
of
objects!
• Inserts
retain
and
release
statements
based
on
some
fixed
rules
• OS
X
10.7
and
iOS
5
for
all
features
56. Object
lose
owners
// Scenario 1
Person* jack = [[Person alloc] init];
jack = [[Person alloc] init];
// Scenario 2
Person* tina = [[Person alloc] init];
tina = nil;
// Scenario 3
if(yes) {
Person* dave = [[Person alloc] init];
}
57. Some
Fixed
rules
• If
object
is
allocated
and
local
to
method,
release
statement
is
added
near
the
end
of
that
method
• If
allocated
object
is
class
a@ribute,
release
is
added
to
dealloc
• If
the
object
is
return
value,
it
gets
an
autorelease
statement
58. Guidelines
• Don’t
call!
– retain, release, retainCount, autorelease
or dealloc
• You
must
use
@autoreleasepool
syntax
• You
must
enable
ARC
– clang -fobjc-arc -framework foundation
Car.m Motor.m main.m -o App
71. Property
Declara)on
Aoributes:
Writability
• You
can
decorate
a
property
with
aoributes,
example:
– @property (readonly) int x;
• readwrite
– Indicates
that
the
property
is
read/write.
Default
• readonly
– Only
read
– Generates
only
geoer
method
72. Seoer
Seman)cs
• assign
– Simple
seoer.
Default.
• weak
– Non-‐owning
rela)onship
with
an
object
– If
object
is
deallocated,
the
property
is
set
to
nil
• strong
– Owning
rela)onship
with
an
object
• copy
– Specifies
that
a
copy
of
the
object
should
be
used
for
assignment
82. About
Strings
• C
String
– char * // Array of characters
• NSString
– Object,
that
holds
array
of
Unicode
characters
– Is
immutable,
contents
cannot
be
changed
aLerwards!
• NSMutableString
– String
that
can
be
modified
aLerwards
83. Crea)ng
Strings
// Simple way
NSString *temp1 = @"Hello World!";
// Appending, notice that this produces new string
NSString *beginning = @"beginning";
NSString *alphaAndOmega = [beginning
stringByAppendingString:@" and end"];
84. Formapng
• Formapng
– NSString *string1 = [NSString stringWithFormat:@"A
string: %@, a float: %1.2f", @"string", 31415.9265];
– // string1 is "A string: string, a float: 31415.93"
• Format
Specifiers?
– http://developer.apple.com/iphone/
library/documentation/Cocoa/Conceptual/
Strings/Articles/formatSpecifiers.html#//
apple_ref/doc/uid/TP40004265-SW1
88. Protocols?
• Compared
to
Java,
protocols
are
interfaces
• You
define
methods
that
some
object
must
implement
89. Using
Protocols
// MyProtocolName.h
// Notice that the protocol inherites NSObject
// protocol!
@protocol MyProtocolName <NSObject>
//Method declarations go here
@end
// MyObject
@interface Class: NSObject <MyProtocolName>
90. Protocol
as
Variable
• In
Java
– MyInterface object = new MyObject();
• In
Obj-‐C
– id<MyProtocolName> object = [[MyObject
alloc] init];
• As
a
method
argument
– (void) doSomethingWithThisObject:
(id<MyProtocolName>) aObject
• ID
is
a
predefined
pointer
type
for
an
arbitrary
object
