Objective C 基本介紹

Interface and
implementation
@interface MyClass : NSObject
-(NSString*) sayGoodnightJames;
@end
@implementation MyClass {
// instance variable declarations go here (starting in iOS5)
}
-(NSString*) sayGoodnightJames {
return @”Good night, James!”;
}
@end

.h & .m ﬁles
@interface MyClass : NSObject
abc.h -(NSString*) sayGoodnightJames;
@end
@implementation MyClass {
// instance variable declarations go here (starting in iOS5)
}
abc.m -(NSString*) sayGoodnightJames {
}
@end

Cocoa’s Own Header
Files

Files

• You can’t see the source code for Cocoa.

Files

• Rely purely on the documentation (and
experimentation).

Files

• Rely purely on the documentation (and
experimentation).
• Can only see the Cocoa header ﬁles.

Class Methods
• Factory method

Class Methods
• Factory method

• UIFont has a class method fontWithName:size:

Class Methods
• Factory method

• Supply a name and a size, and return a UIFont
object.

Class Methods
• Factory method

object.
• Global utility method

Class Methods
• Factory method

object.
• Good place to put a utility method.

Class Methods
• Factory method

object.
• Good place to put a utility method.
• Doesn’t require the overhead of an instance.

How instance are
created
• Ready-Made Instances

How instance are
created
• NSString* s2 = [s uppercaseString];

How instance are
created
• Instatiation from scratch

How instance are
created
• SomeClass* aVariable = [[SomeClass alloc] init];

How instance are
created
• SomeClass* aVariable = [[SomeClass alloc] init];

• Nib-Based Instantiation (見下頁)

Intialization (P. 79)
NSArray* pep =

[NSArray arrayWithObjects:@”cho”, @”james”,
@”calvin”,@”crux”, nil];

NSArray* pep =

[[NSArray alloc] initWithObjects:@”cho”, @”james”,
@”calvin”,@”crux”, nil];

Nib-Based Instatiation
When the app runs and a nib ﬁle is loaded,
those classes are instantiated and initialized.
(P. 80 Figure 5-1)
UIButton* b =

[UIButton buttonWithType:UIButtonTypeRoundedRect]; //factory method

[b setTitle:@”Hello!” forState:UIControlStateNormal]; //set up title

[b setFrame: CGRectMake(100,100,100,35)]; //set up frame

[view addSubview:b]; //place a button in view

Polymorphism
UIButton* b = [UIButton buttonWithType:UIButtonTypeRoundedRect];

UIView* v = b;

[v setTitle:@”James!” forState:UIControlStateNormal];

//compiler will complain!

Polymorphism (cont.)
UIButton* b = [UIButton buttonWithType:UIButtonTypeRoundedRect];

UIView* v = b;

[(UIButton*)v setTitle:@”James!” forState:UIControlStateNormal];

//compiler is happy!

Keyword: self
@implementation MyClass
-(NSString*) greeting {
}
-(NSString*) sayGoodNightJames {
return [self greeting];
}
@end

Keyword: self (cont.)
@implemtation Dog

-(NSString*) bark {

return @”Hi, James”;

}

-(NSString*) speak {

return [self bark];

}

@end

(P. 85 Figure 5-2)

Keyword: self (conc.)
@implemtation Basenji : Dog

-(NSString*) bark {

return @””; //Empty string, Basenjis can’t bark.

}

@end

Basenji* b = [[Basenji alloc] init];

(P. 85 Figure 5-2)

Keyword: super
@implemtation NoisyDog : Dog

-(NSString*) bark {

return [NSString stringWithFormat: @”%@ %@”, [super bark], [super
bark]];

}

@end

(P. 88 a UIView Controller example)

Instance Variables and
Accessors
@implementation Dog {
// ivars can now be declared in the implementation section
int number;
}
-(void) setNumber: (int) n {
self->number = n;
}
-(int) number {
return self->number;
}
@end

Instance Variables and
Accessors
Dog* fido = [[Dog alloc] init];

[fido setNumber: 42];

int n = [fido number];

//n = 42!

Properties
@property(nonatomic) UIViewAutoresizing autoresizingMask

@property(nonatomic) int number

ﬁdo.number = 43;

int n = ﬁdo.number;

Objective C 基本介紹

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Editor's Notes