Intercepter les messages de délégué Objective-C dans une sous-class

J'ai une sous-class de UIScrollView dans laquelle je dois répondre en interne au comportement de défilement. Cependant, le viewcontroller aura toujours besoin d'écouter les callbacks des delegates qui défilent, donc je ne peux pas carrément voler le délégué dans mon composant.

Existe-t-il un moyen de conserver la propriété nommée "delegate" et d'écouter uniquement les messages envoyés le long de celle-ci, ou bien de détourner en interne la propriété delegate et de transférer les messages après avoir exécuté du code?

Oui, mais vous devrez replace chaque méthode de délégation dans les documents . Fondamentalement, faites une deuxième propriété de délégué et implémentez le protocole de délégué. Lorsque vos methods de délégué sont appelées, prenez soin de votre entreprise, puis appelez la même méthode sur votre deuxième délégué de la méthode déléguée qui vient d'être exécutée. Par exemple

- (void)scrollViewDidScroll:(UIScrollView *)scrollView { // Do stuff here if ([self.delegate2 respondsToSelector:@selector(scrollViewDidScroll:)]) { [self.delegate2 scrollViewDidScroll:scrollView]; } } 

Pour éviter de replace manuellement toutes les methods de délégué, vous pouvez utiliser le transfert de message. Je viens de mettre en œuvre la même chose en utilisant une class proxy intermédiaire comme suit:

MessageInterceptor.h

 @interface MessageInterceptor : NSObject { id receiver; id middleMan; } @property (nonatomic, assign) id receiver; @property (nonatomic, assign) id middleMan; @end 

MessageInterceptor.m

 @implementation MessageInterceptor @synthesize receiver; @synthesize middleMan; - (id)forwardingTargetForSelector:(SEL)aSelector { if ([middleMan respondsToSelector:aSelector]) { return middleMan; } if ([receiver respondsToSelector:aSelector]) { return receiver; } return [super forwardingTargetForSelector:aSelector]; } - (BOOL)respondsToSelector:(SEL)aSelector { if ([middleMan respondsToSelector:aSelector]) { return YES; } if ([receiver respondsToSelector:aSelector]) { return YES; } return [super respondsToSelector:aSelector]; } @end 

MyScrollView.h

 #import "MessageInterceptor.h" @interface MyScrollView : UIScrollView { MessageInterceptor * delegate_interceptor; //... } //... @end 

MyScrollView.m (Édité, avec merci à Jhabbott ):

 @implementation MyScrollView - (id)delegate { return delegate_interceptor.receiver; } - (void)setDelegate:(id)newDelegate { [super setDelegate:nil]; [delegate_interceptor setReceiver:newDelegate]; [super setDelegate:(id)delegate_interceptor]; } - (id)init* { //... delegate_interceptor = [[MessageInterceptor alloc] init]; [delegate_interceptor setMiddleMan:self]; [super setDelegate:(id)delegate_interceptor]; //... } - (void)dealloc { //... [delegate_interceptor release]; //... } // delegate method override: - (void)scrollViewDidScroll:(UIScrollView *)scrollView { // 1. your custom code goes here // 2. forward to the delegate as usual if ([self.delegate respondsToSelector:@selector(scrollViewDidScroll:)]) { [self.delegate scrollViewDidScroll:scrollView]; } } @end 

Avec cette approche, l'object MessageInterceptor transmet automatiquement tous les messages de délégué à l'object délégué normal, à l' exception de ceux que vous remplacez dans votre sous-class personnalisée.

Le post d'e.James a donné une excellente solution pour la plupart des vues. Mais pour les vues dépendantes du keyboard comme UITextField et UITextView, il en résulte souvent une situation de boucle infinie. Pour m'en débarrasser, je l'ai corrigé avec un code supplémentaire qui vérifie si le sélecteur est contenu dans un ou plusieurs protocoles spécifiques ou non.

WZProtocolInterceptor.h

 #import <Foundation/Foundation.h> @interface WZProtocolInterceptor : NSObject @property (nonatomic, readonly, copy) NSArray * interceptedProtocols; @property (nonatomic, weak) id receiver; @property (nonatomic, weak) id middleMan; - (instancetype)initWithInterceptedProtocol:(Protocol *)interceptedProtocol; - (instancetype)initWithInterceptedProtocols:(Protocol *)firstInterceptedProtocol, ... NS_REQUIRES_NIL_TERMINATION; - (instancetype)initWithArrayOfInterceptedProtocols:(NSArray *)arrayOfInterceptedProtocols; @end 

WZProtocolInterceptor.m

 #import <objc/runtime.h> #import "WZProtocolInterceptor.h" static inline BOOL selector_belongsToProtocol(SEL selector, Protocol * protocol); @implementation WZProtocolInterceptor - (id)forwardingTargetForSelector:(SEL)aSelector { if ([self.middleMan respondsToSelector:aSelector] && [self isSelectorContainedInInterceptedProtocols: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] && [self isSelectorContainedInInterceptedProtocols:aSelector]) return YES; if ([self.receiver respondsToSelector:aSelector]) return YES; return [super respondsToSelector:aSelector]; } - (instancetype)initWithInterceptedProtocol:(Protocol *)interceptedProtocol { self = [super init]; if (self) { _interceptedProtocols = @[interceptedProtocol]; } return self; } - (instancetype)initWithInterceptedProtocols:(Protocol *)firstInterceptedProtocol, ...; { self = [super init]; if (self) { NSMutableArray * mutableProtocols = [NSMutableArray array]; Protocol * eachInterceptedProtocol; va_list argumentList; if (firstInterceptedProtocol) { [mutableProtocols addObject:firstInterceptedProtocol]; va_start(argumentList, firstInterceptedProtocol); while ((eachInterceptedProtocol = va_arg(argumentList, id))) { [mutableProtocols addObject:eachInterceptedProtocol]; } va_end(argumentList); } _interceptedProtocols = [mutableProtocols copy]; } return self; } - (instancetype)initWithArrayOfInterceptedProtocols:(NSArray *)arrayOfInterceptedProtocols { self = [super init]; if (self) { _interceptedProtocols = [arrayOfInterceptedProtocols copy]; } return self; } - (void)dealloc { _interceptedProtocols = nil; } - (BOOL)isSelectorContainedInInterceptedProtocols:(SEL)aSelector { __block BOOL isSelectorContainedInInterceptedProtocols = NO; [self.interceptedProtocols enumerateObjectsUsingBlock:^(Protocol * protocol, NSUInteger idx, BOOL *stop) { isSelectorContainedInInterceptedProtocols = selector_belongsToProtocol(aSelector, protocol); * stop = isSelectorContainedInInterceptedProtocols; }]; return isSelectorContainedInInterceptedProtocols; } @end BOOL selector_belongsToProtocol(SEL selector, Protocol * protocol) { // Reference: https://gist.github.com/numist/3838169 for (int optionbits = 0; optionbits < (1 << 2); optionbits++) { BOOL required = optionbits & 1; BOOL instance = !(optionbits & (1 << 1)); struct objc_method_description hasMethod = protocol_getMethodDescription(protocol, selector, required, instance); if (hasMethod.name || hasMethod.types) { return YES; } } return NO; } 

Et voici la version Swift 2:

 // // NSProtocolInterpreter.swift // Nest // // Created by Manfred Lau on 11/28/14. // Copyright (c) 2014 WeZZard. All rights reserved. // import Foundation /** `NSProtocolInterceptor` is a proxy which intercepts messages to the middle man which originally intended to send to the receiver. - Discussion: `NSProtocolInterceptor` is a class cluster which dynamically subclasss itself to conform to the intercepted protocols at the runtime. */ public final class NSProtocolInterceptor: NSObject { /// Returns the intercepted protocols public var interceptedProtocols: [Protocol] { return _interceptedProtocols } private var _interceptedProtocols: [Protocol] = [] /// The receiver receives messages public weak var receiver: NSObjectProtocol? /// The middle man intercepts messages public weak var middleMan: NSObjectProtocol? private func doesSelectorBelongToAnyInterceptedProtocol( aSelector: Selector) -> Bool { for aProtocol in _interceptedProtocols where sel_belongsToProtocol(aSelector, aProtocol) { return true } return false } /// Returns the object to which unrecognized messages should first be /// directed. public override func forwardingTargetForSelector(aSelector: Selector) -> AnyObject? { if middleMan?.respondsToSelector(aSelector) == true && doesSelectorBelongToAnyInterceptedProtocol(aSelector) { return middleMan } if receiver?.respondsToSelector(aSelector) == true { return receiver } return super.forwardingTargetForSelector(aSelector) } /// Returns a Boolean value that indicates whether the receiver implements /// or inherits a method that can respond to a specified message. public override func respondsToSelector(aSelector: Selector) -> Bool { if middleMan?.respondsToSelector(aSelector) == true && doesSelectorBelongToAnyInterceptedProtocol(aSelector) { return true } if receiver?.respondsToSelector(aSelector) == true { return true } return super.respondsToSelector(aSelector) } /** Create a protocol interceptor which intercepts a single Objecitve-C protocol. - Parameter protocols: An Objective-C protocol, such as UITableViewDelegate.self. */ public class func forProtocol(aProtocol: Protocol) -> NSProtocolInterceptor { return forProtocols([aProtocol]) } /** Create a protocol interceptor which intercepts a variable-length sort of Objecitve-C protocols. - Parameter protocols: A variable length sort of Objective-C protocol, such as UITableViewDelegate.self. */ public class func forProtocols(protocols: Protocol ...) -> NSProtocolInterceptor { return forProtocols(protocols) } /** Create a protocol interceptor which intercepts an array of Objecitve-C protocols. - Parameter protocols: An array of Objective-C protocols, such as [UITableViewDelegate.self]. */ public class func forProtocols(protocols: [Protocol]) -> NSProtocolInterceptor { let protocolNames = protocols.map { NSSsortingngFromProtocol($0) } let sortedProtocolNames = protocolNames.sort() let concatenatedName = sortedProtocolNames.joinWithSeparator(",") let theConcreteClass = concreteClassWithProtocols(protocols, concatenatedName: concatenatedName, salt: nil) let protocolInterceptor = theConcreteClass.init() as! NSProtocolInterceptor protocolInterceptor._interceptedProtocols = protocols return protocolInterceptor } /** Return a subclass of `NSProtocolInterceptor` which conforms to specified protocols. - Parameter protocols: An array of Objective-C protocols. The subclass returned from this function will conform to these protocols. - Parameter concatenatedName: A ssortingng which came from concatenating names of `protocols`. - Parameter salt: A UInt number appended to the class name which used for distinguishing the class name itself from the duplicated. - Discussion: The return value type of this function can only be `NSObject.Type`, because if you return with `NSProtocolInterceptor.Type`, you can only init the returned class to be a `NSProtocolInterceptor` but not its subclass. */ private class func concreteClassWithProtocols(protocols: [Protocol], concatenatedName: Ssortingng, salt: UInt?) -> NSObject.Type { let className: Ssortingng = { let basicClassName = "_" + NSSsortingngFromClass(NSProtocolInterceptor.self) + "_" + concatenatedName if let salt = salt { return basicClassName + "_\(salt)" } else { return basicClassName } }() let nextSalt = salt.map {$0 + 1} if let theClass = NSClassFromSsortingng(className) { switch theClass { case let anInterceptorClass as NSProtocolInterceptor.Type: let isClassConformsToAllProtocols: Bool = { // Check if the found class conforms to the protocols for eachProtocol in protocols where !class_conformsToProtocol(anInterceptorClass, eachProtocol) { return false } return true }() if isClassConformsToAllProtocols { return anInterceptorClass } else { return concreteClassWithProtocols(protocols, concatenatedName: concatenatedName, salt: nextSalt) } default: return concreteClassWithProtocols(protocols, concatenatedName: concatenatedName, salt: nextSalt) } } else { let subclass = objc_allocateClassPair(NSProtocolInterceptor.self, className, 0) as! NSObject.Type for eachProtocol in protocols { class_addProtocol(subclass, eachProtocol) } objc_registerClassPair(subclass) return subclass } } } /** Returns true when the given selector belongs to the given protocol. */ public func sel_belongsToProtocol(aSelector: Selector, _ aProtocol: Protocol) -> Bool { for optionBits: UInt in 0..<(1 << 2) { let isRequired = optionBits & 1 != 0 let isInstance = !(optionBits & (1 << 1) != 0) let methodDescription = protocol_getMethodDescription(aProtocol, aSelector, isRequired, isInstance) if !objc_method_description_isEmpty(methodDescription) { return true } } return false } public func objc_method_description_isEmpty( var methodDescription: objc_method_description) -> Bool { let ptr = withUnsafePointer(&methodDescription) { UnsafePointer<Int8>($0) } for offset in 0..<sizeof(objc_method_description) { if ptr[offset] != 0 { return false } } return true } 

En fait, cela a fonctionné pour moi:

 @implementation MySubclass { id _actualDelegate; } // There is no need to set the value of _actualDelegate in an init* method - (void)setDelegate:(id)newDelegate { [super setDelegate:nil]; _actualDelegate = newDelegate; [super setDelegate:(id)self]; } - (id)delegate { return self; } - (id)forwardingTargetForSelector:(SEL)aSelector { if ([_actualDelegate respondsToSelector:aSelector]) { return _actualDelegate; } return [super forwardingTargetForSelector:aSelector]; } - (BOOL)respondsToSelector:(SEL)aSelector { return [super respondsToSelector:aSelector] || [_actualDelegate respondsToSelector:aSelector]; } @end 

… faisant de la sous-class l'intercepteur de message dans la réponse géniale donnée par e.James.