Swift iOS: Method for monitoring field changes

Swift has kVO’s ability to monitor attribute changes built into it. We often need to monitor changes to certain properties, such as contentSize changes during the first drop-down refresh. The following code can be copied directly:

     private func addObserver() { tableView? .addObserver(self,forKeyPath: "contentSize", options: .new, context: nil)
    }
    private func removeAbserver() { tableView? .removeObserver(self,forKeyPath:"contentSize")
    }
    var curentContentHeight : CGFloat = 0
    override open func observeValue(forKeyPath keyPath: String? , of object: Any? , change: [NSKeyValueChangeKey : Any]? , context: UnsafeMutableRawPointer?) { guard tableView.isUserInteractionEnabledelse {
            return
        }
        print(tableView.contentSize.height)
        curentContentHeight = tableView.contentSize.height
        self.frame.origin.y = curentContentHeight
    }Copy the code

This way, there is no need to use third-party libraries (such as KVOController), which is very easy to test.