NSOperation KVO完成

3 回答

• -2

  NSOperationQueue 实现将观察您的操作的"isFinished"属性（使用KVO），因此它知道何时从队列中删除它 . isFinished 很可能在被告知其值的变化后被内部Apple代码调用 .

  回复于 2024-05-02T17:26:35+08:00
• 1

  添加到quellish的答案，这是你如何覆盖执行，完成，取消 .

  //.m
  @interface MyOperation ()  //class extension, make these otherwise read-only properties read-write, we must synthesize
  @property(atomic, assign, readwrite, getter=isExecuting) BOOL executing;
  @property(atomic, assign, readwrite, getter=isFinished) BOOL finished;
  @property(atomic, assign, readwrite, getter=isCancelled) BOOL cancelled;
  @end
  
  @implementation CoreLocationOperation
  @synthesize executing, finished, cancelled;
  
  + (BOOL)automaticallyNotifiesObserversForKey {
    return YES;
  }
  
  + (NSSet *)keyPathsForValuesAffectingIsCancelled {
    NSSet *result = [NSSet setWithObject:@"cancelled"];
    return result;
  }
  
  + (NSSet *)keyPathsForValuesAffectingIsExecuting {
    NSSet *result = [NSSet setWithObject:@"executing"];
        return result;
  }
  
   + (NSSet *)keyPathsForValuesAffectingIsFinished {
      NSSet *result = [NSSet setWithObject:@"finished"];
     return result;
   }
  
  
  - (void)start {
   //..
    //You can use self.executing = YES; (note we can change executing which would otherwise be read-only because we synthesized our own ivar.
    [self setExecuting:YES];
  ...
  }
  
  - (void)cancel {
  //..
    //super will change the properties executing/finished for us or we can do it manually
    [super cancel];
  ...
  
  }
      @end
  

  我认为这比有更清楚

  [self willChangeValueForKey:_NSURLOperationIsFinished];
      [self setIsFinished:YES];
      [self didChangeValueForKey:_NSURLOperationIsFinished];
  

  回复于 2024-05-02T17:26:35+08:00
• 2

  首先，您不需要进行手动KVO通知 . 对于 NSOperation 子类，除非您的类通过实现 +automaticallyNotifiesObserversForKey 或 +automaticallyNotifiesObserversOf<Key> 返回NO而选择退出自动KVO通知，否则应自动发送KVO通知 .

  除非将子类添加到 NSOperationQueue ，否则 NSOperation 子类不是很有用 . 将操作添加到队列时，队列使用KVO来观察指示状态更改的属性，例如 finished ， executing ， cancelled 等 . 请注意，这些不是 isFinished ， isExecuting 或 isCancelled - 这些是合成获取这些属性的访问器 .

  在您的问题中，您包含以下代码：

  [self willChangeValueForKey:@"isFinished"];
  [self willChangeValueForKey:@"isExecuting"]
  finished = YES;
  executing = NO;
  [self didChangeValueForKey:@"isFinished"];
  [self didChangeValueForKey:@"isExecuting"];
  

  你在这里做的是为get访问者发送手动KVO通知，而不是观察到的属性 . 相反，这将完成你似乎想要做的事情：

  [self setFinished:YES];
  [self setExecuting:NO];
  

  不是直接访问实例变量，而是使用访问器方法 . 这将正确发送这些属性的自动更改通知 .

  如果您是关于KVO的 truly paranoid 并且想要发送get访问者密钥路径（例如 isFinished ）的通知，请将您的属性注册为密钥路径的依赖项：

  + (NSSet *) keyPathsForValuesAffectingIsFinished {
      NSSet   *result = [NSSet setWithObject:@"finished"];
      return result;
  }
  

  Registering dependencies is part of KVO compliance.

  回复于 2024-05-02T17:26:35+08:00