概述:
- 我有一个名为Player的类和一个名为Song的类。
- Player包含一首歌曲
- 一个视图显示歌曲标题
目标:
当我更改player.song.title时,视图需要更新。
问题:
当歌曲属性更改时,它不会自动更新视图。只有在分配新歌曲时才会反映更改。
我的尝试:
我做了两次尝试(下面是代码),两者都按预期工作。
问题:
- 有更好的方法吗?(这似乎是常见问题,一个人会遇到。) 我的尝试是否合理,第二次尝试是否更好?
- 还是我的设计存在根本性缺陷?(我希望将歌曲放在播放器内,因为它代表了当前的歌曲。)
原始代码(视图不会更新):
模型
import Foundation
import Combine
class Player : ObservableObject {
@Published var duration = 0
@Published var song : Song
init(song: Song) {
self.song = song
}
}
class Song : ObservableObject {
@Published var id : Int
@Published var title : String
@Published var artist : String
init(id: Int,
title: String,
artist: String) {
self.id = id
self.title = title
self.artist = artist
}
}
视图
import SwiftUI
struct ContentView: View {
@ObservedObject var player : Player
var body: some View {
VStack {
Text(String(player.duration))
Text(player.song.title)
Text(player.song.artist)
}
}
}
struct ContentView_Previews: PreviewProvider {
static var previews: some View {
let song = Song(id: 1, title: "title1", artist: "artist1")
let player = Player(song: song)
DispatchQueue.main.asyncAfter(deadline: .now() + 2) {
player.song.title = "title2"
}
return ContentView(player: player)
}
}
尝试1 - 使用CombineLatest
问题:随着歌曲属性数量的增加,使用此方法不太可扩展。
class Player : ObservableObject {
@Published var duration = 0
@Published var song : Song
private var songChangeCanceller : AnyCancellable?
init(song: Song) {
self.song = song
songChangeCanceller = song.$title.combineLatest(song.$artist, song.$id).sink { _, _, _ in
self.objectWillChange.send()
}
}
}
第二种尝试: 使用objectWillChange.sink
class Player : ObservableObject {
@Published var duration = 0
@Published var song : Song
private var songChangeCanceller : AnyCancellable?
private var songAttributesChangeCanceller : AnyCancellable?
init(song: Song) {
self.song = song
songChangeCanceller = $song.sink { newSong in
self.songAttributesChangeCanceller = newSong.objectWillChange.sink { _ in
self.objectWillChange.send()
}
}
}
}