我有一個使用 jetpack compose 建立的電影應用程式。我在其中展示了用戶選擇的最喜歡的電影。收藏夾應該完美地存在於使用者介面中，但是當我從使用者介面中刪除項目時，使用者介面不會立即重新組合以反映變更。怎麼辦？
這是我的使用者介面
@composable
fun favscreen(
movieviewmodel: movieviewmodel
) {
remember { mutablestateof(movieviewmodel.getfavmovies()) }
val shouldshowdialog = remember { mutablestateof(false) }
val uistates = movieviewmodel.favs.collectasstate()
column {
row {
text(
text = "fav movies",
fontsize = 25.sp,
fontfamily = fontfamily(font(r.font.nsb)),
modifier = modifier.padding(20.dp).weight(1f)
)
iconbutton(onclick = {
shouldshowdialog.value = true
}) {
icon(icons.filled.delete, contentdescription = "")
}
}
when(val currentstate = uistates.value){
is movieviewmodel.uistates.loading -> {
box(modifier = modifier.fillmaxsize(), contentalignment = alignment.center) {
circularprogressindicator()
}
}
is movieviewmodel.uistates.favs -> {
val data = currentstate.data
if(data.isempty()){
box(modifier = modifier.fillmaxsize(), contentalignment = alignment.center) {
text(
text = "no fav movies",
fontsize = 25.sp,
fontfamily = fontfamily(font(r.font.nsb)),
modifier = modifier.padding(20.dp))
}
}
else {
lazycolumn(){
items(data){ fav ->
row(modifier = modifier
.padding(20.dp)
.fillmaxwidth()
.clip(roundedcornershape(16.dp))
.background(color = color.darkgray)) {
asyncimage(
model = utils.image_url + fav.imageurl,
contentdescription = "",
contentscale = contentscale.crop,
filterquality = filterquality.high,
modifier = modifier
.width(150.dp)
.height(150.dp))
column(modifier = modifier.padding(20.dp)) {
text(
text = fav.title!!,
fontsize = 20.sp,
fontfamily = fontfamily(font(r.font.nsb)))
text(
text = fav.rating.tostring() + "/10 imdb",
fontsize = 15.sp,
fontfamily = fontfamily(font(r.font.nsb)))
text(
text = "movie id : #" + fav.movieid,
fontsize = 15.sp,
fontfamily = fontfamily(font(r.font.nsb)))
}
}
}
}
}
}
is movieviewmodel.uistates.error -> {
box(modifier = modifier.fillmaxsize(), contentalignment = alignment.center){
text(
text = "no fav movies",
fontsize = 25.sp,
fontfamily = fontfamily(font(r.font.nsb)),
modifier = modifier.padding(20.dp))
}
}
else -> {}
}
}
if (shouldshowdialog.value){
alertdialog(
ondismissrequest = { shouldshowdialog.value = false },
confirmbutton = {
textbutton(onclick = {
movieviewmodel.deletemovies()
shouldshowdialog.value = false
}) {
text(text = "proceed", fontfamily = fontfamily(font(r.font.nsm)))
}
},
dismissbutton = {
textbutton(onclick = {
shouldshowdialog.value = false
}) {
text(text = "cancel", fontfamily = fontfamily(font(r.font.nsm)))
}
},
shape = roundedcornershape(16.dp),
text = { text(text = "favs deletion",fontfamily = fontfamily(font(r.font.nsb)))},
title = { text(text = "do you want to delete all fav movies ?", fontfamily = fontfamily(font(r.font.nsb)))}
)
}
}這是我的視圖模型
@HiltViewModel
class MovieViewModel @Inject constructor(
private val movieRepoImpl: MovieRepoImpl
) : ViewModel() {
private val _favs : MutableStateFlow<UiStates> = MutableStateFlow(UiStates.INITIAL)
val favs get() = _favs.asStateFlow()
// MOVIE DAO
fun getFavMovies() = viewModelScope.launch {
try {
_favs.value = UiStates.LOADING
movieRepoImpl.getFavs().collectLatest {
_favs.value = UiStates.FAVS(it)
}
} catch (ex : Exception){
_favs.value = UiStates.ERROR(ex.localizedMessage!!)
}
}
fun insertMovie(favModel: FavModel) = viewModelScope.launch {
movieRepoImpl.insertFav(favModel)
}
fun deleteMovies() = viewModelScope.launch {
movieRepoImpl.deleteAllMovies()
}
sealed class UiStates {
object LOADING : UiStates()
data class FAVS(val data : MutableList<FavModel>) : UiStates()
data class ERROR(val error : String) : UiStates()
object INITIAL : UiStates()
}
}當您查看 _favs 的寫入用法時，問題變得非常明顯：
只有 getfavmovies 會更新它。
雖然這聽起來像“你應該在刪除功能中更新你的用戶介面狀態”，但我想提出一個替代解決方案：
利用 room flows 的力量！
首先在 viewmodel 中定義 loadingstate，它將儲存為串流：
sealed class loadingstate {
object loading : loadingstate()
data class success : loadingstate()
data class error(val error : string) : loadingstate()
object initial : loadingstate()
}
private val loadingstate = mutablestateflow<loadingstate>(initial)然後，更改 getfavmovies() 函數以使用此機制：
fun getfavmovies() {
viewmodelscope.launch {
try {
_loadingstate.value = loadingstate.loading
movierepoimpl.loadfavs() // a function which triggers e.g. a network call to actually load your movies
_loadingstate.value = loadingstate.success
} catch (ex: exception) {
_loadingstate.value = loadingstate.error(ex.localizedmessage!!)
}
}
}最後，結合你的狀態和數據，讓奇蹟發生。一旦其中一個發生變化，這將自動更新:)
val favs: flow<uistates> = combine(
movierepoimpl.getmovies(),
loadingstate
) { movies, loadingstate ->
when (loadingstate) {
is loadingstate.loading -> uistates.loading
is loadingstate.success -> uistates.success(movies)
is loadingstate.error -> uistates.error(error)
is loadingstate. initial -> uistates.initial
}
}免責聲明：其中可能有拼字錯誤，我沒有方便的 ide
讓我們透過改進程式碼來結束這個答案：
避免將 = 用於不傳回任何內容的函數（getfavmovies、insertmovie、deletemovies）。否則，你會例如期望 getfavmovies 返回電影列表
remember { mutablestateof(movieviewmodel.getfavmovies()) } 並沒有真正的 remember 任何東西，是嗎？這太惱人了。我建議將其移至 viewmodel 中： init { movieviewmodel.getfavmovies() }
val uistates = movieviewmodel.favs.collectasstate()：命名表示這是多個 ui 狀態，請使用單數; uistates 類別本身也是如此。另外，如果這裡直接使用“.value”，可以跳過這裡的重新宣告：when(val currentstate = uistates.value)
您的 uistate 包含 mutablelist<favmodel>。對 ui 狀態使用可變值是一個壞主意，例如它可能會混淆您的 stateflow。一定要避免這種情況。只需使用普通的舊列表:) https://www.php.cn/link/ff685590317f1330efc73f396ac92cd7
使用 collectasstatewithlifecycle() 而不是 collectasstate()。請參閱https://medium.com/androiddevelopers/consuming-flows -安全地在jetpack-compose-cde014d0d5a3
您絕對不應該在 viewmodel 中存取 repoimpl：將儲存庫拆分為介面和實作的整個想法是隱藏實作
定義一個screen-composable 是個好主意，它不需要viewmodel，只需要數據，類似於https://developer.android.com/jetpack/compose/state#state-hoisting：
.
@Composable
private fun FavScreen(
val viewModel: MovieViewModel,
) {
FawScreen(
uiState = viewModel.fav.collectAsStateWithLifecycle().value,
shouldShowDialog = viewModel.shouldShowDialog.collectAsStateWithLifecycle().value
)
}
@Composable
private fun FavScreen(
val uiState: UiStates,
val shouldShowDialog: Boolean
) {
// your current ui
}以上是使用房間資料庫刪除 jetpack 中的所有項目後，UI 未重新組合的詳細內容。更多資訊請關注PHP中文網其他相關文章！
