States.md

State restoring

An advanced feature of PanelKit is the ability to save and restore the state of panels. This allows you to save all the floating and pinned states at a particular moment in your app's life, store it (e.g. to disk), and restore to the exact same state at any moment.

How to implement

Panels

Each panel that wants its state to be able to save and restore needs to implement the PanelStateCoder protocol. This procotol has one single requirement:

var panelId: Int { get }

panelId is a unique id to identify a panel. Used when restoring the panel’s state. A panel’s id should be the same across app launches to successfully restore its state.

PanelManager

Saving

The PanelManager protocol has the following API:

var panelStates: [Int: PanelState] { get }

This returns a dictionary with the panel ids as keys and panel states as values. The PanelState struct conforms to the Codable protocol.

Restoring

Restoring can be done via the following API:

func restorePanelStates(_ states: [Int: PanelState])

Example implementation

extension MyPanelManager {

    func savePanelStates() {

        let states = self.panelStates
		
        let encoder = JSONEncoder()
		
        guard let json = try? encoder.encode(states) else {
            return
        }
		
        UserDefaults.standard.set(json, forKey: "panelStates")
		
    }
	
    func restorePanelStatesFromDisk() {
		
        guard let jsonData = UserDefaults.standard.data(forKey: "panelStates") else {
            return
        }
		
        let decoder = JSONDecoder()
        guard let states = try? decoder.decode([Int: PanelState].self, from: jsonData) else {
            return
        }
		
        restorePanelStates(states)
		
    }
	
}