object-c學習筆記：屬性變數(property)

什麼是property？

是一種代碼產生機制，能夠產生不同類型的getter／setter函數，特別是如果你想要用點（.）操作符號來存取變數的話，你就能必須使用property。

 

如何使用？

用法是固定的，注意下property後面小括弧了跟的參數列表，nonatomic代表非原子性，既不支援多線程的同步，mac上可以根據具體情況考慮，IPhone上就加上把，retain代表對setter的對象加上一個retain操作，同時也會release原有的object，copy顧名思義就是copy setter中參數的對象。看下面的例子：

代碼

@interface Engine : NSObject
{
}
@end

@implementation Engine

- (NSString*) description
{
return (@"engine");
}

@end

@interface Tier : NSObject
{
}
@end


@implementation Tier

- (NSString*) description
{
return (@"tier");
}

@end

@interface Car : NSObject
{
int tier_num;
float engine_power;
    NSString* name;
    Engine* engine;
    Tier* tier;
}

@property (nonatomic) int tier_num;
@property (nonatomic) float engine_power;
@property (nonatomic, copy) NSString* name;
@property (nonatomic, retain) Engine* engine;
@property (nonatomic, retain) Tier* tier;

@end

@implementation Car    

@synthesize tier_num;
@synthesize engine_power;
@synthesize name;
@synthesize engine;
@synthesize tier;

- (id) init
{
if (self = [super init]) {
        tier_num = 4;
        engine_power = 100;
        name = @"BMW";
    }
return self;
}

@end


int main (int argc, const char * argv[]) {
    NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];

    Car* car = [[Car alloc] init];
    NSLog(@"number of tiers is %d\n", car.tier_num);
    NSLog(@"car's name is %a\n", car.name);
    car.name = @"Mazd";

    Engine* newEngine = [[Engine alloc] init];
    car.engine = newEngine;

// insert code here...
    
    [pool drain];
return 0;
}

 

額外的內容

預設的propety變數，總是可讀寫的，如果需要唯讀控制，就用readonly，這時編譯器不會產生setter方法，如

@property (readonly) float something;