코코아에서 KVO/BINDINGS 호환 브리지 패턴 구현
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03-07-2019 - |
문제
나는 Cocoa에서 간단한 물체 브리지를 구현하려고 노력하고 있으며, 여기서 브리지 객체는 임의의 다른 nsobject 인스턴스에 대한 KVO/바인딩 호환 드롭으로 작용합니다.
다음은 내 문제입니다 (아래 코드의 자세한 내용) :
브리지 객체는 NSString* 속성이있는 사람-객체의 하락 역할을합니다. 이름 그리고 주소* 속성 주소. 다리의 키패스 "이름"또는 "주소"에 바인딩하는 것이 잘 작동합니다. 브리지의 "주소"에 어떤 객체를 바인딩 할 때 문제가 시작되고 새로운 주소 객체가 사람의 경우에 설정됩니다. 주소 재산. 이로 인해 KVO 관련 예외가 발생합니다.
Cannot remove an observer <NSKeyValueObservance 0x126b00> for the key path "street" from <Address 0x12f1d0> because it is not registered as an observer
브리지가 "주소"-프로페티의 변화를 알아 차리고 WillChangeValueforkeyPath/didchangevalueforkeyPath 튜플을 방출하더라도 이것은 발생합니다.
아래 코드는 문제를 생성합니다. "bridgedemo.m"파일로 저장할 수있는 자체 포함 대상 C 코드입니다.
gcc -o test BridgeDemo.m -framework AppKit -framework Foundation; ./test
이 문제에 대한 해결책을 알고 있거나 동일한 문제를 해결하는 더 나은 접근 방식을 제공 할 수 있다면 매우 행복한 프로그래머!
bridgedemo.m :
#import <Foundation/Foundation.h>
#import <AppKit/AppKit.h>
/* --- Address ----------------------------------------- */
@interface Address : NSObject {
NSString* street;
NSNumber* zipCode;
NSString* city;
}
@property(retain) NSString* street;
@property(retain) NSNumber* zipCode;
@property(retain) NSString* city;
@end
@implementation Address
@synthesize street, zipCode, city;
-(id)init {
if( !( self = [super init] ) ) { return nil; }
self.street = @"Elm Street";
self.zipCode = @"12345";
self.city = @"Crashington";
return self;
}
-(void) modifyStreet {
self.street = @"Main Street";
}
-(void)dealloc {
[street release]; [zipCode release]; [city release];
[super dealloc];
}
@end
/* --- Person ----------------------------------------- */
@interface Person : NSObject {
NSString* name;
Address* address;
}
@property(retain) NSString* name;
@property(retain) Address* address;
@end
@implementation Person
@synthesize address, name;
-(id)init {
if( !( self = [super init] ) ) { return nil; }
self.name = @"Tom";
self.address = [[Address new] autorelease];
return self;
}
- (void)modifyAddress {
Address* a = [[Address new] autorelease];
a.street = @"Jump Street";
a.zipCode = @"54321";
a.city = @"Memleakville";
self.address = a;
}
- (void)dealloc { [address release]; [name release]; [super dealloc]; }
@end
/* --- Bridge ----------------------------------------- */
@interface Bridge : NSObject {
NSMutableDictionary* observedKeys;
NSObject* obj;
}
@property(retain) NSObject* obj;
@end
@implementation Bridge
@synthesize obj;
- (id)init {
if( !( self = [super init] ) ) { return nil; }
observedKeys = [NSMutableDictionary new];
return self;
}
- (void)forwardInvocation:(NSInvocation*)inv {
[inv invokeWithTarget:obj];
}
- (NSMethodSignature *)methodSignatureForSelector:(SEL)aSelector {
return [obj methodSignatureForSelector:aSelector];
}
- (void) observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context
{
NSLog( @">>>> Detected Change in keyPath: %@", keyPath );
[self willChangeValueForKey:keyPath];
[self didChangeValueForKey:keyPath];
}
-(id)valueForUndefinedKey:(NSString*)key {
/* Register an observer for the key, if not already done */
if( ![observedKeys objectForKey:key] ) {
[observedKeys setObject:[NSNumber numberWithBool:YES] forKey:key];
[obj addObserver:self forKeyPath:key options:NSKeyValueObservingOptionNew context:nil];
}
return [obj valueForKey:key];
}
- (void)dealloc {
for( NSString* key in [observedKeys allKeys] ) {
[obj removeObserver:self forKeyPath:key];
}
[obj release];
[observedKeys release];
[super dealloc];
}
@end
/* --- MyObserver ------------------------------------ */
@interface MyObserver : NSObject {
Address* address;
NSString* street;
}
@property(retain) Address* address;
@property(retain) NSString* street;
@end
@implementation MyObserver
@synthesize street, address;
-(void)dealloc { [street release]; [super dealloc]; }
@end
/* This works fine */
void testBindingToAddress() {
NSLog( @"Testing Binding to 'address' --------------" );
NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];
Bridge* b = [[Bridge new] autorelease];
b.obj = [Person new];
MyObserver* o = [[MyObserver new] autorelease];
[o bind:@"address" toObject:b withKeyPath:@"address"
options:nil];
NSLog( @"Before modifyStreet: %@", o.address.street );
[[b valueForKey:@"address"] performSelector:@selector(modifyStreet)];
NSLog( @"After modifyStreet: %@", o.address.street );
[b performSelector:@selector(modifyAddress)];
NSLog( @"After modifyAdress: %@", o.address.street );
[pool drain];
}
/* This produces an exception */
void testBindingToStreet() {
NSLog( @"Testing Binding to 'address.street' --------------" );
NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];
Bridge* b = [[Bridge new] autorelease];
b.obj = [Person new];
MyObserver* o = [[MyObserver new] autorelease];
[o bind:@"street" toObject:b withKeyPath:@"address.street"
options:nil];
NSLog( @"Before modifyStreet: %@", o.street );
[[b valueForKey:@"address"] performSelector:@selector(modifyStreet)];
NSLog( @"After modifyStreet: %@", o.street );
[b performSelector:@selector(modifyAddress)];
NSLog( @"After modifyAdress: %@", o.street );
[pool drain];
}
/* --- main() ------------------------------------ */
int main (int argc, const char * argv[]) {
testBindingToAddress();
testBindingToStreet();
return 0;
}
해결책
여기에 문제가 있습니다.
Self WillChangeValueforKey : KyyPath]; <---이 시점에서 실제 관찰자는 Street [self didchangevalueforkey : kyypath]를 구독해야합니다. <--- 그리고 새로운 값에 스스로를 추가하십시오.
새로운 가치를 제공하지 않음으로써 관찰자에게 구독을 취소 할 수있는 기회를 거부합니다.
다음은 해킹 된 버전이 작동하고 문제를 보여줍니다.
/* --- Bridge ----------------------------------------- */
....
.....
@interface Bridge : NSObject {
NSMutableDictionary* observedKeys;
NSObject* obj;
//**** Dictionary for old values just before we send the didChangeValue notification.
NSMutableDictionary * oldValues;
}
...
.....
- (id)init {
if( !( self = [super init] ) ) { return nil; }
observedKeys = [NSMutableDictionary new];
//************* Initialize the new dictionary
oldValues = [NSMutableDictionary new];
return self;
}
....
.....
- (void) observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context
{
NSLog( @">>>> Detected Change in keyPath: %@", keyPath );
// **** Cache the old value before telling everyone its going to change.
[oldValues setValue:[change valueForKey:NSKeyValueChangeOldKey] forKey:keyPath];
[self willChangeValueForKey:keyPath];
// **** Simulate the change by removing the old value.
[oldValues removeObjectForKey:keyPath];
// **** Now when we say we did change the value, we are not lying.
[self didChangeValueForKey:keyPath];
}
-(id)valueForUndefinedKey:(NSString*)key {
// **** Important part, return oldvalue if it exists
id oldValue;
if(oldValue = [oldValues valueForKey:key]){
return oldValue;
}
/* Register an observer for the key, if not already done */
if( ![observedKeys objectForKey:key] ) {
[observedKeys setObject:[NSNumber numberWithBool:YES] forKey:key];
NSLog(@"adding observer for:%@", key);
[obj addObserver:self forKeyPath:key options:NSKeyValueObservingOptionNew|NSKeyValueObservingOptionOld context:nil];
}
return [obj valueForKey:key];
}
....
......