obj-c编程19:关联对象

对于一些无法子类化的实例对象来说，如果希望将一个对象与其绑定该如何做呢？

以下示例虚构了一个HyConsoleAlert类，User类将会使用该类在控制台显示定制的告警。如果User中包括多个Alert类则需要手动关联处理每个对应的回调方法，这显得异常麻烦。可以使用objc提供的关联对象模式：将处理例程在生成Alert对象时就与之绑定好，较为漂亮的解决了这个问题。下面上源代码：

#import <Foundation/Foundation.h>

static void *HyAlertkey = "HyAlertkey";

@protocol HyMakeChoose
-(void)makeChoose:(NSUInteger)index alertObject:(id)alertObj;
@end

@interface HyConsoleAlert:NSObject{
@private
NSString *_title,*_msg;
id <HyMakeChoose> __weak _delegate;
}
-(HyConsoleAlert*)initWithTitle:(NSString *) title andMsg:(NSString *) msg
andDelegate:(id <HyMakeChoose>)delegate;
-(void)show;
@end

@implementation HyConsoleAlert
-(id)init{
[NSException raise:@"ERR!" format:@"Invalid init method in HyConsoleAlert"];
return nil;
}

-(HyConsoleAlert*)initWithTitle:(NSString *) title andMsg:(NSString *) msg
andDelegate:(id <HyMakeChoose>) delegate{

self = [super init];
if(self){
_title = [title copy];
_msg = [msg copy];
_delegate = delegate;
}
return self;
}

-(void)show{
NSLog(@"%@\n%@",_title,_msg);
NSLog(@"Yes or No?");
int c;
while(true){
c = getchar();
NSLog(@"DEBUG:getchar : '%c'",c);
if(c == 'y' || c == 'Y')
c = 1;
else if(c == 'n' || c == 'N')
c = 0;
else
continue;

[_delegate makeChoose:c alertObject:self];
break;
}
}
@end

@interface User:NSObject <HyMakeChoose>{
id _alert;
}
-(void)askUserQuestion;
@end

@implementation User

-(id)init{
self = [super init];
return self;
}

-(void)askUserQuestion{
HyConsoleAlert *alert = [[HyConsoleAlert alloc] initWithTitle:@"hopy' question"
andMsg:@"Are you human being"
andDelegate:self];
void (^block)(NSUInteger) = ^(NSUInteger index){
if(index == 1)
NSLog(@"your choose: YES!");
else if(index == 0)
NSLog(@"your choose : NO!");
else
NSLog(@"error!!!");
};
objc_setAssociatedObject(alert,HyAlertkey,block,    OBJC_ASSOCIATION_COPY);
[alert show];
}

-(void)makeChoose:(NSUInteger)index alertObject:(id)alertObj{
NSLog(@"alertObj is %@",alertObj);
void (^block)(NSUInteger) = objc_getAssociatedObject(alertObj,HyAlertkey);
block(index);
/*
if(index == 1)
NSLog(@"your choose: YES!");
else if(index == 0)
NSLog(@"your choose : NO!");
else
NSLog(@"error!!!");
*/
}
@end

int main(void){
@autoreleasepool{
/*
User *user = [User new];
HyConsoleAlert *alert = [[HyConsoleAlert alloc]initWithTitle:@"warning"
andMsg:@"Are you human being?" andDelegate:user];
[alert show];
*/
User *user = [User new];
[user askUserQuestion];
}
return 0;
}