HomeKit点滴

最近在研究HomeKit，在更改某个特征值的时候：

当设置了HMAccessoryDelegate的delegate后，在App中，改变HMCharacteristic的特征值时，

- (void)writeValue:(nullable id)value completionHandler:(void (^)(NSError * __nullable error))completion;

代理方法

- (void)accessory:(HMAccessory *)accessory service:(HMService *)service didUpdateValueForCharacteristic:(HMCharacteristic *)characteristic

是不会被触发的。

那么该方法在什么时候被触发呢？当App运行时，特征值被从他的途径修改的时候，比如通过设备的物理开关，才会触发App的改代理方法，目的是App UI与设备保持一致。

详细可参见苹果官方的描述：

Discussion
This method is called as a result of a change in value initiated by the accessory. Programmatic changes initiated by the app do not result in this method being called.

https://developer.apple.com/documentation/homekit/hmaccessorydelegate/1615286-accessory?language=objc