当我更改player.song.title时,视图需要更新。
当歌曲的属性更改时,它不会自动更新视图。仅当分配了新歌曲时,更改才会反映出来。
我做了2次尝试(下面的代码),都按预期工作。
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
}
}
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)
}
}
问题:随着歌曲中属性的数量增加,它的伸缩性不是很好。
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()
}
}
}
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()
}
}
}
}
我想知道宋是否在上课,我会怎么做
好的,如果我们局限于类,那么解决方案将采用简化设计,如下所示(是的,我更喜欢简单的解决方案)。已通过Xcode 11.4 / iOS 13.4测试。
// << keep your model "as is" in section "Model", instead modify views
struct ContentView: View {
@ObservedObject var player : Player
var body: some View {
VStack {
Text(String(player.duration))
SongDetailsView(song: player.song)
}
}
}
struct SongDetailsView: View {
@ObservedObject var song : Song
var body: some View {
VStack {
Text(song.title)
Text(song.artist)
}
}
}
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我来说两句