我有一个NSMutableDictionary对象数组，这些对象显示在主 - 详细信息界面中，该界面有一些文本字段和一堆复选框。控件绑定到字典键，通过数组控制器selection访问。
我想添加一些逻辑，当清除另一个复选框时清除一个复选框，如果在同一个会话中重新检查，则恢复原始值。由于我需要将存储与字典相关联，并且还需要添加代码，我以为我会使用合成来扩展NSMutableDictionary。
这就是我所做的：
LibraryEntry子类，其中包含一个NSMutableDictionary。forwardInvocation:，respondsToSelector:，methodSignatureForSelector:，以及经过一次试错valueForUndefinedKey:。它可以很好地加载数据，但我猜测KVO无法正常工作。我猜测绑定器正在我的对象上调用addObserver:，但我没有实现任何特殊处理它。
我想过简单地覆盖addObserver:并将消息转发到字典。但是，如果我这样做，observeValueForKey:通知将不会来自我的对象（addObserver的原始接收者），而是来自字典。
在我尝试为这些KVO调用实现更透明的转发之前，我认为......这变得越来越混乱。我继续阅读“使用组合，而不是子类”来获得这样的行为。对于这种情况，这只是错误的模式吗？为什么？因为KVO？
如果我放弃作曲并选择其中一种替代方案，似乎我会有更清晰的结果：
这是我的代码，万一它有用（values是字典）：
- (void)forwardInvocation:(NSInvocation *)anInvocation {
if ([values respondsToSelector:[anInvocation selector]])
[anInvocation invokeWithTarget:values];
else
[super forwardInvocation:anInvocation];
}
- (BOOL)respondsToSelector:(SEL)aSelector {
if ( [super respondsToSelector:aSelector] )
return YES;
else
return [values respondsToSelector:aSelector];
}
- (NSMethodSignature*)methodSignatureForSelector:(SEL)selector {
NSMethodSignature* signature = [super methodSignatureForSelector:selector];
if (!signature) signature = [values methodSignatureForSelector:selector];
return signature;
}
-(id)valueForUndefinedKey:(NSString *)key {
return [values valueForKey:key];
}
答案 0 :(得分：1)
我认为结合使用Objective-C相关存储和一些块，您可以将任意行为连接到字典（或任何其他符合KVO的对象）并以这种方式解决您的问题。我提出了以下想法，它实现了一个通用的KVO-triggers-block机制，编码和示例似乎做了你想要它做的事情，并且不涉及子类化或装饰基础集合。
首先是这种机制的公共接口：
typedef void (^KBBehavior)(id object, NSString* keyPath, id oldValue, id newValue, id userInfo);
@interface NSObject (KBKVOBehaviorObserver)
- (void)addBehavior: (KBBehavior)block forKeyPath: (NSString*)keyPath options: (NSKeyValueObservingOptions)options userInfo: (id)userInfo;
- (void)removeBehaviorForKeyPath: (NSString*)keyPath;
@end
这将允许您将基于块的观察/行为附加到任意对象。您使用复选框描述的任务可能如下所示：
- (void)testBehaviors
{
NSMutableDictionary* myModelDictionary = [NSMutableDictionary dictionary];
KBBehavior behaviorBlock = ^(id object, NSString* keyPath, id oldValue, id newValue, id userInfo)
{
NSMutableDictionary* modelDictionary = (NSMutableDictionary*)object;
NSMutableDictionary* previousValues = (NSMutableDictionary*)userInfo;
if (nil == newValue || (![newValue boolValue]))
{
// If the master is turning off, turn off the slave, but make a note of the previous value
id previousValue = [modelDictionary objectForKey: @"slaveCheckbox"];
if (previousValue)
[previousValues setObject: previousValue forKey: @"slaveCheckbox"];
else
[previousValues removeObjectForKey: @"slaveCheckbox"];
[modelDictionary setObject: newValue forKey: @"slaveCheckbox"];
}
else
{
// if the master is turning ON, restore the previous value of the slave
id prevValue = [previousValues objectForKey: @"slaveCheckbox"];
if (prevValue)
[modelDictionary setObject:prevValue forKey: @"slaveCheckbox"];
else
[modelDictionary removeObjectForKey: @"slaveCheckbox"];
}
};
// Set the state...
[myModelDictionary setObject: [NSNumber numberWithBool: YES] forKey: @"slaveCheckbox"];
[myModelDictionary setObject: [NSNumber numberWithBool: YES] forKey: @"masterCheckbox"];
// Add behavior
[myModelDictionary addBehavior: behaviorBlock forKeyPath: @"masterCheckbox" options: NSKeyValueObservingOptionNew userInfo: [NSMutableDictionary dictionary]];
// turn off the master
[myModelDictionary setObject: [NSNumber numberWithBool: NO] forKey: @"masterCheckbox"];
// we now expect the slave to be off...
NSLog(@"slaveCheckbox value: %@", [myModelDictionary objectForKey: @"slaveCheckbox"]);
// turn the master back on...
[myModelDictionary setObject: [NSNumber numberWithBool: YES] forKey: @"masterCheckbox"];
// now we expect the slave to be back on, since that was it's previous value
NSLog(@"slaveCheckbox value: %@", [myModelDictionary objectForKey: @"slaveCheckbox"]);
}
我通过创建一个跟踪块和userInfos的对象来实现块/ KVO连接，然后让它成为KVO观察者。这是我做的：
#import <objc/runtime.h>
static void* kKVOBehaviorsKey = &kKVOBehaviorsKey;
@interface KBKVOBehaviorObserver : NSObject
{
NSMutableDictionary* mBehaviorsByKey;
NSMutableDictionary* mUserInfosByKey;
}
@end
@implementation KBKVOBehaviorObserver
- (id)init
{
if (self = [super init])
{
mBehaviorsByKey = [[NSMutableDictionary alloc] init];
mUserInfosByKey = [[NSMutableDictionary alloc] init];
}
return self;
}
- (void)dealloc
{
[mBehaviorsByKey release];
mBehaviorsByKey = nil;
[mUserInfosByKey release];
mUserInfosByKey = nil;
[super dealloc];
}
- (void)addBehavior: (KBBehavior)block forKeyPath: (NSString*)keyPath userInfo: (id)userInfo
{
@synchronized(self)
{
id copiedBlock = [[block copy] autorelease];
[mBehaviorsByKey setObject: copiedBlock forKey: keyPath];
[mUserInfosByKey setObject: userInfo forKey: keyPath];
}
}
- (void)removeBehaviorForKeyPath: (NSString*)keyPath
{
@synchronized(self)
{
[mUserInfosByKey removeObjectForKey: keyPath];
[mBehaviorsByKey removeObjectForKey: keyPath];
}
}
- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context
{
if (context == kKVOBehaviorsKey)
{
KBBehavior behavior = nil;
id userInfo = nil;
@synchronized(self)
{
behavior = [[[mBehaviorsByKey objectForKey: keyPath] retain] autorelease];
userInfo = [[[mUserInfosByKey objectForKey: keyPath] retain] autorelease];
}
if (behavior)
{
id oldValue = [change objectForKey: NSKeyValueChangeOldKey];
id newValue = [change objectForKey: NSKeyValueChangeNewKey];
behavior(object, keyPath, oldValue, newValue, userInfo);
}
}
}
@end
@implementation NSObject (KBKVOBehaviorObserver)
- (void)addBehavior: (KBBehavior)block forKeyPath: (NSString*)keyPath options: (NSKeyValueObservingOptions)options userInfo: (id)userInfo
{
KBKVOBehaviorObserver* obs = nil;
@synchronized(self)
{
obs = objc_getAssociatedObject(self, kKVOBehaviorsKey);
if (nil == obs)
{
obs = [[[KBKVOBehaviorObserver alloc] init] autorelease];
objc_setAssociatedObject(self, kKVOBehaviorsKey, obs, OBJC_ASSOCIATION_RETAIN);
}
}
// Put the behavior and userInfos into stuff...
[obs addBehavior: block forKeyPath: keyPath userInfo: userInfo];
// add the observation
[self addObserver: obs forKeyPath: keyPath options: options context: kKVOBehaviorsKey];
}
- (void)removeBehaviorForKeyPath: (NSString*)keyPath
{
KBKVOBehaviorObserver* obs = nil;
obs = [[objc_getAssociatedObject(self, kKVOBehaviorsKey) retain] autorelease];
// Remove the observation
[self removeObserver: obs forKeyPath: keyPath context: kKVOBehaviorsKey];
// remove the behavior
[obs removeBehaviorForKeyPath: keyPath];
}
@end
有一点不幸的是，你必须删除观察/行为才能打破原始字典和观察对象之间的传递保留周期，所以如果你不删除这些行为，你就是' ll泄漏集合。但总体而言，这种模式应该是有用的。
希望这有帮助。