KVO summary

@interface KvoOperation : NSOperation

@property (nonatomic, getter=isFinished) BOOL finished;
@property (nonatomic, strong) NSString *k;

@property (nonatomic, strong) NSMutableArray *mutArr;

-(void)insertObject:(id)object inMutArrAtIndex:(NSInteger)index;

@end

@implementation KvoOperation
@synthesize finished = _finished;
@synthesize k = _k;
@synthesize mutArr = _mutArr;

+ (BOOL)automaticallyNotifiesObserversForKey:(NSString *)key {
    return NO;
}

- (void)setK:(NSString *)k {
    [self willChangeValueForKey:@"k"];
    _k = k;
    [self didChangeValueForKey:@"k"];
}

- (void)setFinished:(BOOL)finished {
    [self willChangeValueForKey:@"isFinished"];
    _finished = finished;
    [self didChangeValueForKey:@"isFinished"];
}

-(void)insertObject:(id)object inMutArrAtIndex:(NSInteger)index {
    [self willChange:(NSKeyValueChangeInsertion) valuesAtIndexes:[NSIndexSet indexSetWithIndex:index] forKey:@"mutArr"];
    [_mutArr insertObject:object atIndex:index];
    [self didChange:NSKeyValueChangeInsertion valuesAtIndexes:[NSIndexSet indexSetWithIndex:index] forKey:@"mutArr"];
}

@end

• + (BOOL)automaticallyNotifiesObserversForKey:(NSString *)key return NO It can shield the native set Method of departure kvo monitor , But for manual implementation kvo Invalid .

• Manually triggered by non collection types kvo ：willChangeValueForKey:、didChangeValueForKey: , Not subject to automaticallyNotifiesObserversForKey: shielding

• Collection types （eg NSMutableArray） increase 、 Delete 、 Replace item Can't trigger kvo, If you use mutableArrayValueForKey: obtain mArr, increase 、 Delete 、 Replace item Can trigger kvo, And by automaticallyNotifiesObserversForKey: Method shielding effect

NSMutableArray *mArr = [_kvoOption mutableArrayValueForKey:@"mutArr"];
[mArr addObject:@"a"];

• Set type increase 、 Delete 、 Replace item Manual trigger kvo ： For example, call the following method when inserting , Can trigger kvo, Not subject to automaticallyNotifiesObserversForKey: shielding

-(void)insertObject:(id)object inMutArrAtIndex:(NSInteger)index {
    [self willChange:(NSKeyValueChangeInsertion) valuesAtIndexes:[NSIndexSet indexSetWithIndex:index] forKey:@"mutArr"];
    [_mutArr insertObject:object atIndex:index];
    [self didChange:NSKeyValueChangeInsertion valuesAtIndexes:[NSIndexSet indexSetWithIndex:index] forKey:@"mutArr"];
}

• Mark：NSOperation finished Property is read-only , Rewrite here , By manually triggering finished kvo, Reach trigger  completionBlock Purpose