KVO总结

@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 返回 NO 可以屏蔽原生 set 方法出发的kvo监听，但是对于手动实现的kvo无效。

• 非集合类型手动触发 kvo ：willChangeValueForKey:、didChangeValueForKey: ，不受automaticallyNotifiesObserversForKey: 屏蔽

• 集合类型（eg NSMutableArray）增、删、替换item不能触发kvo，如果用mutableArrayValueForKey:获取mArr，增、删、替换item 可触发kvo，且受automaticallyNotifiesObserversForKey:方法屏蔽作用

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

• 集合类型增、删、替换 item 手动触发kvo ：例如插入时候调用下面方法，可触发kvo，不受automaticallyNotifiesObserversForKey: 屏蔽

-(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 属性为只读，这里重写，通过手动触发finished kvo，达到触发 completionBlock 目的