Objective-C 複合學習筆記

@interface Car : NSObject
{
	Engine *engine;
	Tire *tires[4];
}

複合既是指用多種對象組成的新的對象。

#import <Foundation/Foundation.h>


// --------------------------------------------------

@interface Tire : NSObject
@end // Tire


@implementation Tire

- (NSString *) description
{
    return (@"I am a tire. I last a while");
} // description

@end // Tire



// --------------------------------------------------

@interface Engine : NSObject
@end // Engine


@implementation Engine

- (NSString *) description
{
    return (@"I am an engine.  Vrooom!");
} // description

@end // Engine


// --------------------------------------------------

@interface Car : NSObject
{
    Engine *engine;
    Tire *tires[4];
}

- (void) print;

@end // Car


@implementation Car

- (id) init
{
    if (self = [super init]) {
        engine = [Engine new];
        
        tires[0] = [Tire new];
        tires[1] = [Tire new];
        tires[2] = [Tire new];
        tires[3] = [Tire new];
    }
    
    return (self);
    
} // init

- (void) print
{
    NSLog (@"%@", engine);
    
    NSLog (@"%@", tires[0]);
    NSLog (@"%@", tires[1]);
    NSLog (@"%@", tires[2]);
    NSLog (@"%@", tires[3]);
    
} // print

@end // Car


// --------------------------------------------------

int main (int argc, const char * argv[])
{
    Car *car;
    
    car = [Car new];
    [car print];
    
    return (0);
    
} // main

自定義NSLog()，重寫desciption，用%@引用

@interface Car : NSObject
{
	Engine *engine;
	Tire *tires[4];
}

- (Engine *) engine;

- (void) setEngine: (Engine *) newEngine;


- (Tire *) tireAtIndex: (int) index;

- (void) setTire: (Tire *) tire
		 atIndex: (int) index;

- (void) print;

@end // Car


- (Engine *) engine
{
	return (engine);
} // engine


- (void) setEngine: (Engine *) newEngine
{
	engine = newEngine;
} // setEngine


- (void) setTire: (Tire *) tire
		 atIndex: (int) index
{
	if (index < 0 || index > 3) {
		NSLog (@"bad index (%d) in setTire:atIndex:",
			   index);
		exit (1);
	}
	
	tires[index] = tire;
	
} // setTire:atIndex:


- (Tire *) tireAtIndex: (int) index
{
	if (index < 0 || index > 3) {
		NSLog (@"bad index (%d) in tireAtIndex:",
			   index);
		exit (1);
	}
	
	return (tires[index]);
	
} // tireAtIndex:

getter用於讀取，setter用於讀入

setter命名以set作爲前綴，getter命名以其返回的屬性名稱命名。