我有一个UIScrollView的子类,我需要在内部响应滚动行为。但是,viewcontroller仍然需要监听滚动的委托回调,所以我不能直接在我的组件中窃取委托。
有没有办法让属性名为“delegate”,只是监听沿着它发送的消息,或者以某种方式内部劫持委托属性并在运行某些代码后向外转发消息?
答案 0 :(得分:85)
为避免手动覆盖所有委托方法,您可以使用邮件转发。我刚刚使用中间代理类实现了相同的功能,如下所示:
<强> MessageInterceptor.h 强>
@interface MessageInterceptor : NSObject {
id receiver;
id middleMan;
}
@property (nonatomic, assign) id receiver;
@property (nonatomic, assign) id middleMan;
@end
<强> MessageInterceptor.m 强>
@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
<强> MyScrollView.h 强>
#import "MessageInterceptor.h"
@interface MyScrollView : UIScrollView {
MessageInterceptor * delegate_interceptor;
//...
}
//...
@end
MyScrollView.m (已编辑,感谢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
使用这种方法,MessageInterceptor
对象将自动将所有委托消息转发给常规委托对象,除了,用于在自定义子类中覆盖的对象。
答案 1 :(得分:66)
e.James的帖子为大多数观点提供了出色的解决方案。但对于像UITextField和UITextView这样的键盘相关视图,它通常会导致无限循环的情况。为了摆脱它,我用一些额外的代码修复它,检查选择器是否包含在特定的协议中。
<强> WZProtocolInterceptor.h 强>
#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
<强> WZProtocolInterceptor.m 强>
#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;
}
这是Swift 2版本:
//
// 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
subclasses 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 { NSStringFromProtocol($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 string 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: String,
salt: UInt?)
-> NSObject.Type
{
let className: String = {
let basicClassName = "_" +
NSStringFromClass(NSProtocolInterceptor.self) +
"_" + concatenatedName
if let salt = salt { return basicClassName + "_\(salt)" }
else { return basicClassName }
}()
let nextSalt = salt.map {$0 + 1}
if let theClass = NSClassFromString(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
}
答案 2 :(得分:5)
实际上,这对我有用:
@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
...在e.James给出的令人敬畏的答案中使子类成为消息拦截器。
答案 3 :(得分:-4)
是的,但您必须覆盖the docs中的每个委托方法。基本上,创建第二个委托属性并实现委托协议。调用委托方法时,请注意您的业务,然后从刚刚运行的委托方法调用第二个委托上的相同方法。例如。
- (void)scrollViewDidScroll:(UIScrollView *)scrollView {
// Do stuff here
if ([self.delegate2 respondsToSelector:@selector(scrollViewDidScroll:)]) {
[self.delegate2 scrollViewDidScroll:scrollView];
}
}