How to reduce code duplication for class properties (Swift 3) - swift

Question

In my application I want to implement separate class to keep all the temporary variables of Now Playing item for Music Player.
It has lots of properties with different types, but they should be handled in the same way. They should be handled in the class method "updateData" (see the end of code)
This is my code:
struct DataDefaults {
//MARK: Default properties
let albumTitle: String? = "Unknown Album"
let albumArtist: String? = "Unknown Artist"
let title: String? = "Unknown Title"
let artist: String? = "Unknown Artist"
let artwork: UIImage? = UIImage(named: "noartwork")!
let genre: String? = ""
let lyrics: String? = "No Lyrics"
let releaseDate: Date? = nil
let playbackDuration: TimeInterval? = 0
let rating: Int? = 0
let assetURL: URL? = nil
let isExplicitItem: Bool? = false
let isCloudItem: Bool? = false
let hasProtectedAsset: Bool? = false
}
class SongInfo: NSObject {
static let sharedData = SongInfo()
let defaults = DataDefaults()
//MARK: Properties
var albumTitle: String
var albumArtist: String
var title: String
var artist: String
var artwork: UIImage
var genre: String
var lyrics: String
var releaseDate: Date?
var playbackDuration: TimeInterval
var rating: Int
var assetURL: URL?
var isExplicitItem: Bool
var isCloudItem: Bool
var hasProtectedAsset: Bool
//MARK: Init
private override init () {
self.albumTitle = defaults.albumTitle!
self.albumArtist = defaults.albumArtist!
self.title = defaults.title!
self.artist = defaults.artist!
self.artwork = defaults.artwork!
self.genre = defaults.genre!
self.lyrics = defaults.lyrics!
self.releaseDate = defaults.releaseDate
self.playbackDuration = defaults.playbackDuration!
self.rating = defaults.rating!
self.assetURL = defaults.assetURL
self.isExplicitItem = defaults.isExplicitItem!
self.isCloudItem = defaults.isCloudItem!
self.hasProtectedAsset = defaults.hasProtectedAsset!
}
//MARK: Set properties
func updateData(allData: DataDefaults) {
var wasUpdated: Bool = false
if allData.albumTitle == self.albumTitle {
//pass
} else if allData.albumTitle == nil || allData.albumTitle == "" {
self.albumTitle = defaults.albumTitle!
wasUpdated = true
} else {
self.albumTitle = allData.albumTitle!
wasUpdated = true
}
//Need to repeat same IF for all properties
}
}
Is there any way I can use property name to make some reusage of the same code instead of duplicating it?

Answer 1

Rather than trying to find a solution to a weird design, I re-designed for what you're trying to accomplish 🙂
struct SongData: Equatable {
static let defaultData = SongData(albumTitle: "Unknown Album",
albumArtist: "Unknown Artist",
title: "Unknown Title",
artist: "Unknown Artist",
artwork: UIImage(named: "noartwork"),
genre:"",
lyrics: "No Lyrics",
releaseDate: nil,
playbackDuration: 0,
rating: 0,
assetURL: nil,
isExplicitItem: false,
isCloudItem: false,
hasProtectedAsset: false)
//MARK: Default properties
var albumTitle: String?
var albumArtist: String?
var title: String?
var artist: String?
var artwork: UIImage?
var genre: String?
var lyrics: String?
var releaseDate: Date?
var playbackDuration: TimeInterval?
var rating: Int?
var assetURL: URL?
var isExplicitItem: Bool?
var isCloudItem: Bool?
var hasProtectedAsset: Bool?
/// This initializer will set the properties to the defaultData properties if a passed value is nil
init(albumTitle: String?, albumArtist: String?, title: String?, artist: String?, artwork: UIImage?, genre: String?, lyrics: String?, releaseDate: Date?, playbackDuration: TimeInterval?, rating: Int?, assetURL: URL?, isExplicitItem: Bool?, isCloudItem: Bool?, hasProtectedAsset: Bool?) {
// initialize properties where the default is nil
self.releaseDate = releaseDate
self.assetURL = assetURL
//initialize other properties with the passed values, or use the default value if nil
self.albumTitle = SongData.valueOrDefault(albumTitle, SongData.defaultData.albumTitle)
self.albumArtist = SongData.valueOrDefault(albumArtist, SongData.defaultData.albumArtist)
self.title = SongData.valueOrDefault(title, SongData.defaultData.title)
self.artist = SongData.valueOrDefault(artist, SongData.defaultData.artist)
self.artwork = artwork ?? SongData.defaultData.artwork
self.genre = SongData.valueOrDefault(genre, SongData.defaultData.genre)
self.lyrics = SongData.valueOrDefault(lyrics, SongData.defaultData.lyrics)
self.playbackDuration = playbackDuration ?? SongData.defaultData.playbackDuration
self.rating = rating ?? SongData.defaultData.rating
self.isExplicitItem = isExplicitItem ?? SongData.defaultData.isExplicitItem
self.isCloudItem = isCloudItem ?? SongData.defaultData.isCloudItem
self.hasProtectedAsset = hasProtectedAsset ?? SongData.defaultData.hasProtectedAsset
}
static func ==(leftItem: SongData, rightItem: SongData) -> Bool {
return (leftItem.albumTitle == rightItem.albumTitle) &&
(leftItem.albumArtist == rightItem.albumArtist) &&
(leftItem.title == rightItem.title) &&
// Comparing a reference type here. may need to be handled differently if that's a problem
(leftItem.artwork === rightItem.artwork) &&
(leftItem.genre == rightItem.genre) &&
(leftItem.lyrics == rightItem.lyrics) &&
(leftItem.releaseDate == rightItem.releaseDate) &&
(leftItem.playbackDuration == rightItem.playbackDuration) &&
(leftItem.rating == rightItem.rating) &&
(leftItem.assetURL == rightItem.assetURL) &&
(leftItem.isExplicitItem == rightItem.isExplicitItem) &&
(leftItem.isCloudItem == rightItem.isCloudItem) &&
(leftItem.hasProtectedAsset == rightItem.hasProtectedAsset)
}
//simple helper function to avoid long turneries in the init
static func valueOrDefault(_ value: String?, _ defaultValue: String?) -> String? {
guard let value = value, !value.isEmpty else {
return defaultValue
}
return value
}
}
class SongInfo {
static let sharedData = SongInfo()
var data: SongData
//MARK: Init
private init ()
{
self.data = SongData.defaultData
}
//MARK: Set properties
func updateData(newData: SongData) {
if(newData != self.data) {
self.data = newData
}
}
}
I changed your struct to act more like it appears you're wanting it to be used, and the struct's init will fall back to using the default values if the init values are nil. My design also contains no force unwraps, which are almost always bad.

Answer 2

You could set the defaults directly in your class definition without using a separate struct and have a static unaltered instance with the default values.
For example:
class SongInfo: NSObject {
static let sharedData = SongInfo()
static let defaults = SongInfo()
//MARK: Properties
var albumTitle: String? = "Unknown Album"
var albumArtist: String? = "Unknown Artist"
var title: String? = "Unknown Title"
var artist: String? = "Unknown Artist"
var artwork: UIImage? = UIImage(named: "noartwork")!
var genre: String? = ""
var lyrics: String? = "No Lyrics"
var releaseDate: Date? = nil
var playbackDuration: TimeInterval? = 0
var rating: Int? = 0
var assetURL: URL? = nil
var isExplicitItem: Bool? = false
var isCloudItem: Bool? = false
var hasProtectedAsset: Bool? = false
//MARK: Init
private override init ()
{
// nothing to do here
}
//MARK: Set properties
func updateData(allData: DataDefaults) {
var wasUpdated: Bool = false
if allData.albumTitle == self.albumTitle {
//pass
} else if allData.albumTitle == nil || allData.albumTitle == "" {
self.albumTitle = SongInfo.defaults.albumTitle!
wasUpdated = true
} else {
self.albumTitle = allData.albumTitle!
wasUpdated = true
}
//Need to repeat same IF for all properties
}
}
If you also need to manipulate the basic data without the whole class functionality, you could define a SongInfoData class with only the properties and make SingInfo inherit from that class. Then the static variable for defaults could be in the SongInfoData class and the SingInfo subclass wouldn't need any property declarations.
[EDIT] avoiding code repetition in update function ...
You can generalize the property update process by adding a generic function to your class:
For example:
func assign<T:Equatable>(_ variable:inout T?, _ getValue:(SongInfo)->T?) -> Int
{
let newValue = getValue(self)
if variable == newValue
{ return 0 }
var valueIsEmpty = false
if let stringValue = newValue as? String, stringValue == ""
{ valueIsEmpty = true }
if newValue == nil || valueIsEmpty
{
variable = getValue(SongInfo.defaults)
return 1
}
variable = newValue
return 1
}
func update(with newInfo:SongInfo)
{
let updates = newInfo.assign(&albumTitle) {$0.albumTitle}
+ newInfo.assign(&albumArtist) {$0.albumArtist}
+ newInfo.assign(&title) {$0.title}
+ newInfo.assign(&artist) {$0.artist}
+ newInfo.assign(&artwork) {$0.artwork}
+ newInfo.assign(&genre) {$0.genre}
+ newInfo.assign(&lyrics) {$0.lyrics}
// ...
if updates > 0
{
// react to update
}
}

Answer 3

It seems to me, that you're using MPMedia item.
If so, you don't have to store all these properties at all.
You just need to store persistent ID of the item (convert from UInt64 to string), and later fetch MPMediaItem by using MPMediaQuery with predicate, something like this:
func findSong(persistentIDString: String) -> MPMediaItem? {
let predicate = MPMediaPropertyPredicate(value: persistentIDString, forProperty: MPMediaItemPropertyPersistentID)
let songQuery = MPMediaQuery()
songQuery.addFilterPredicate(predicate)
return songQuery.items.first
}