NSClassFromString //方法原型
Class NSClassFromString (NSString *aClassName
);

NSString * aClassName = @"SunnyClass";
Class class = NSClassFromString(aClassName);

id instance = [[class alloc] init];

if([instance reponseToSelector:@selector(aMethod)])
{[instance aMethod];
}

@interface Fruit : NSObject
- (void)show;
@end@interface Apple : Fruit
@end@interface Banana : Fruit
@end@interface Pear : Fruit
@end

@implementation Fruit
- (void)show
{NSLog(@"I'm a fruit");
}
@end@implementation Apple
- (void)show
{NSLog(@"I'm an apple");
}
@end@implementation Banana
- (void)show
{NSLog(@"I'm a banana");
}
@end@implementation Pear
- (void)show
{NSLog(@"I'm a pear");
}
@end

- (Fruit *)createFruitWithName:(NSString *)fruitName
{Fruit * theFruit;if ([fruitName isEqualToString:@"Apple"]) {theFruit = [[[Apple alloc] init] autorelease];}else if ([fruitName isEqualToString:@"Banana"]){theFruit = [[[Banana alloc] init] autorelease];}else if ([fruitName isEqualToString:@"Pear"]){theFruit = [[[Pear alloc] init] autorelease];}return theFruit;
}

@implementation FruitFactroy- (Fruit *)createFruitWithName:(NSString *)fruitName
{//通过string得到类的结构体Class class = NSClassFromString(fruitName);//通过转化的class得到实例对象Fruit * theFruit = [(Fruit *)[[class alloc] init] autorelease];//调用对象方法if ([theFruit respondsToSelector:@selector(show)]) {[theFruit show];}//返回对象return theFruit;
}
@end

    FruitFactroy * factroy = [[[FruitFactroy alloc] init] autorelease];Fruit * apple = [factroy createFruitWithName:@"Apple"];Fruit * banana = [factroy createFruitWithName:@"Banana"];Fruit * pear = [factroy createFruitWithName:@"Pear"];