Create stable and reusable MCPeerIDs

README.MD

MCPeerID+Reusable.swift

Documentation

Purpose

MCPeerID objects are used to identify devices in a multi-peer session. It's your app's responsibility to create the PeerID for the local device.

According to Apple, objects created using init(displayName:) are unique, even though they share the same display name.

Use this code to create peer identifiers that are stable over time.

Example Usage

To create a PeerID whose display name is the device's name :

import UIKit
import MultipeerConnectivity

let peerID = MCPeerID.reusableInstance(withDisplayName: UIDevice.current.name)

Test

let reusablePeerID1 = MCPeerID.reusableInstance(withDisplayName: "iPad de Alexis")
let reusablePeerID2 = MCPeerID.reusableInstance(withDisplayName: "iPad de Alexis")
let notReusablePeerID1 = MCPeerID(displayName: "iPad de Alexis")
let notReusablePeerID2 = MCPeerID(displayName: "iPad de Alexis")

XCTAssertEqual(reusablePeerID1, reusablePeerID2)

XCTAssertNotEqual(reusablePeerID1, notReusablePeerID1)
XCTAssertNotEqual(reusablePeerID1, notReusablePeerID2)

XCTAssertNotEqual(reusablePeerID2, notReusablePeerID1)
XCTAssertNotEqual(reusablePeerID2, notReusablePeerID2)

License

The MIT License (MIT)

Copyright (c) 2016 ALEXIS AUBRY RADANOVIC

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NON-INFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

MCPeerID+Reusable.swift

/*
 * ==---------------------------------------------------------------------------------==
 *
 *  File            :   MCPeerID+Reusable.swift
 *  Project         :   MCPeerID+Reusable
 *  Author          :   ALEXIS AUBRY RADANOVIC
 *  Creation Date   :   SEPTEMBER 21 2016
 *
 *  License         :   The MIT License (MIT)
 *
 * ==---------------------------------------------------------------------------------==
 */
 
extension UserDefaults {

    ///
    /// The key used to store the local device's PeerID display name.
    ///
 
    fileprivate static let kLocalPeerDisplayNameKey = "kLocalPeerDisplayNameKey"

    ///
    /// The key used to store the archive of the local device's PeerID.
    ///

    fileprivate static let kLocalPeerIDKey = "kLocalPeerIDKey"

}

extension MCPeerID {
 
    ///
    /// Returns a reusable PeerID for the local device that will be stable over time.
    ///
    /// If a PeerID with the specified display name is saved, it is unarchived and returned. If a Peer ID with the specified name is not saved, it is created, archived, saved and returned.
    ///
    /// - parameter displayName: The display name for the local peer. The maximum allowable length is 63 bytes in UTF-8 encoding. This parameter may not be nil or an empty string.
    ///
    /// - returns: A PeerID that is stable over time.
    ///
 
    public static func reusableInstance(withDisplayName displayName: String) -> MCPeerID {

        let defaults = UserDefaults.standard

        func newPeerID() -> MCPeerID {
            let newPeerID = MCPeerID(displayName: displayName)
            newPeerID.save(in: defaults)
            return newPeerID
        }

        let oldDisplayName = defaults.string(forKey: UserDefaults.kLocalPeerDisplayNameKey)
 
        if oldDisplayName == displayName {
 
            guard let peerData = defaults.data(forKey: UserDefaults.kLocalPeerIDKey), let peerID = NSKeyedUnarchiver.unarchiveObject(with: peerData) as? MCPeerID else {
                return newPeerID()
            }

            return peerID
 
        } else {
            return newPeerID()
        }

    }

    ///
    /// Archives and saves the current peer identifier in the specified user defaults for later reuse.
    ///
    /// - parameter userDefaults: The user defaults suite where the PeerID and its display name will be stored.
    /// 

    private func save(in userDefaults: UserDefaults) {

        let peerIDData = NSKeyedArchiver.archivedData(withRootObject: self)
        userDefaults.set(peerIDData, forKey: UserDefaults.kLocalPeerIDKey)
        userDefaults.set(displayName, forKey: UserDefaults.kLocalPeerDisplayNameKey)
        userDefaults.synchronize()

    }

}