iOS 多代理的实现

iOS 多代理的实现

正常来讲，根据iOS的框架设计，一个对象有且只能有一个代理，那多代理怎么实现呢，让我们开始吧~

中间件

#import <Foundation/Foundation.h>

@interface ALDInterceptor : NSObject

@property (nonatomic, weak) id receiver;
@property (nonatomic, weak) id middleMan;

@end

@implementation ALDInterceptor

- (id)forwardingTargetForSelector:(SEL)aSelector {
    if ([self.middleMan respondsToSelector:aSelector]) return self.middleMan;
    if ([self.receiver respondsToSelector:aSelector]) return self.receiver;
    return [super forwardingTargetForSelector:aSelector];
}

- (BOOL)respondsToSelector:(SEL)aSelector {
    if ([self.middleMan respondsToSelector:aSelector]) return YES;
    if ([self.receiver respondsToSelector:aSelector]) return YES;
    return [super respondsToSelector:aSelector];
}

@end

如何使用

在你要多代理的class中添加中间件对象

@property (strong, nonatomic) ALDInterceptor *delegateInterceptor;

重写setDelegate的方法，把delegate的对象从receiver换成了中间件对象

- (void)setDelegate:(id<MAMapViewDelegate>)delegate {
	self.delegateInterceptor.receiver = delegate;
	[super setDelegate:(id<MAMapViewDelegate>)self.delegateInterceptor];
}

熟悉iOS的同学就知道了，原理是应用了runtime的消息转发机制。

在调用代理方法的时候，先去询问middleMan是否实现了该代理方法，然后调用middleMan的代理方法，可以在middleMan的方法执行后再去调用receiver的实现方法:

- (void)mapView:(MAMapView *)mapView didSingleTappedAtCoordinate:(CLLocationCoordinate2D)coordinate {
	//tapped here
    if ([self.delegateInterceptor.receiver respondsToSelector:@selector(mapView:didSingleTappedAtCoordinate:)]) {
        [self.delegateInterceptor.receiver mapView:mapView didSingleTappedAtCoordinate:coordinate];
    }
}