object-c学习笔记：属性变量(property)

什么是property？

是一种代码生成机制，能够生成不同类型的getter／setter函数，特别是如果你想要用点（.）操作符号来存取变量的话，你就能必须使用property。

 

如何使用？

用法是固定的，注意下property后面小括号了跟的参数列表，nonatomic代表非原子性，既不支持多线程的同步，mac上可以根据具体情况考虑，IPhone上就加上把，retain代表对setter的对象加上一个retain操作，同时也会release原有的object，copy顾名思义就是copy setter中参数的对象。看下面的例子：

@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;
}

 

额外的内容

默认的propety变量，总是可读写的，如果需要只读控制，就用readonly，这时编译器不会生成setter方法，如

@property (readonly) float something;