Objective-C中的KVC和KVO

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@property (nonatomic, copy) NSString *name;

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NSString *n = [object valueForKey:@"name"];

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[object setValue:@"Daniel" forKey:@"name"];

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@property (nonatomic) CGFloat height;

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[object setValue:@(20) forKey:@"height"];

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- (void)registerAsObserver {
/*
Register 'inspector' to receive change notifications for the "openingBalance" property of
the 'account' object and specify that both the old and new values of "openingBalance"
should be provided in the observe… method.
*/
[account addObserver:inspector
forKeyPath:@"openingBalance"
options:(NSKeyValueObservingOptionNew |
NSKeyValueObservingOptionOld)
context:NULL];
}

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id oldValue = change[NSKeyValueChangeOldKey];
id newValue = change[NSKeyValueChangeNewKey];

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- (void)observeValueForKeyPath:(NSString *)keyPath
ofObject:(id)object
change:(NSDictionary *)change
context:(void *)context {

if ([keyPath isEqual:@"openingBalance"]) {
[openingBalanceInspectorField setObjectValue:
[change objectForKey:NSKeyValueChangeNewKey]];
}
/*
Be sure to call the superclass's implementation *if it implements it*.
NSObject does not implement the method.
*/
[super observeValueForKeyPath:keyPath
ofObject:object
change:change
context:context];
}

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NSString *const NSKeyValueChangeKindKey;
NSString *const NSKeyValueChangeNewKey;
NSString *const NSKeyValueChangeOldKey;
NSString *const NSKeyValueChangeIndexesKey;
NSString *const NSKeyValueChangeNotificationIsPriorKey;

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enum {
NSKeyValueChangeSetting = 1,
NSKeyValueChangeInsertion = 2,
NSKeyValueChangeRemoval = 3,
NSKeyValueChangeReplacement = 4
};
typedef NSUInteger NSKeyValueChange;

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if ([change[NSKeyValueChangeNotificationIsPriorKey] boolValue]) {
// 改变之前
} else {
// 改变之后
}

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- (void)unregisterForChangeNotification {
[observedObject removeObserver:inspector forKeyPath:@"openingBalance"];
}

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// Call the accessor method.
[account setName:@"Savings"];

// Use setValue:forKey:.
[account setValue:@"Savings" forKey:@"name"];

// Use a key path, where 'account' is a kvc-compliant property of 'document'.
[document setValue:@"Savings" forKeyPath:@"account.name"];

// Use mutableArrayValueForKey: to retrieve a relationship proxy object.
Transaction *newTransaction = <#Create a new transaction for the account#>;
NSMutableArray *transactions = [account mutableArrayValueForKey:@"transactions"];
[transactions addObject:newTransaction];

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+ (BOOL)automaticallyNotifiesObserversForKey:(NSString *)theKey {

BOOL automatic = NO;
if ([theKey isEqualToString:@"openingBalance"]) {
automatic = NO;
}
else {
automatic = [super automaticallyNotifiesObserversForKey:theKey];
}
return automatic;
}

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- (void)setOpeningBalance:(double)theBalance {
[self willChangeValueForKey:@"openingBalance"];
_openingBalance = theBalance;
[self didChangeValueForKey:@"openingBalance"];
}

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- (void)setOpeningBalance:(double)theBalance {
if (theBalance != _openingBalance) {
[self willChangeValueForKey:@"openingBalance"];
_openingBalance = theBalance;
[self didChangeValueForKey:@"openingBalance"];
}
}

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- (void)setOpeningBalance:(double)theBalance {
[self willChangeValueForKey:@"openingBalance"];
[self willChangeValueForKey:@"itemChanged"];
_openingBalance = theBalance;
_itemChanged = _itemChanged+1;
[self didChangeValueForKey:@"itemChanged"];
[self didChangeValueForKey:@"openingBalance"];
}

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- (void)removeTransactionsAtIndexes:(NSIndexSet *)indexes {
[self willChange:NSKeyValueChangeRemoval
valuesAtIndexes:indexes forKey:@"transactions"];

// Remove the transaction objects at the specified indexes.

[self didChange:NSKeyValueChangeRemoval
valuesAtIndexes:indexes forKey:@"transactions"];
}

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- (NSString *)fullName {
return [NSString stringWithFormat:@"%@ %@",firstName, lastName];
}

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+ (NSSet *)keyPathsForValuesAffectingValueForKey:(NSString *)key {

NSSet *keyPaths = [super keyPathsForValuesAffectingValueForKey:key];

if ([key isEqualToString:@"fullName"]) {
NSArray *affectingKeys = @[@"lastName", @"firstName"];
keyPaths = [keyPaths setByAddingObjectsFromArray:affectingKeys];
}
return keyPaths;
}

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+ (NSSet *)keyPathsForValuesAffectingFullName {
return [NSSet setWithObjects:@"lastName", @"firstName", nil];
}

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- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context {

if (context == totalSalaryContext) {
[self updateTotalSalary];
}
else
// deal with other observations and/or invoke super...
}

- (void)updateTotalSalary {
[self setTotalSalary:[self valueForKeyPath:@"employees.@sum.salary"]];
}

- (void)setTotalSalary:(NSNumber *)newTotalSalary {

if (totalSalary != newTotalSalary) {
[self willChangeValueForKey:@"totalSalary"];
_totalSalary = newTotalSalary;
[self didChangeValueForKey:@"totalSalary"];
}
}

- (NSNumber *)totalSalary {
return _totalSalary;
}

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(lldb) po [observedObject observationInfo]