观察 MediatorLiveData 问题

Question

我的ViewModel中有以下LiveData变量（简化示例）：

 val currentUser: LiveData<UserObject> val allSites: LiveData<ArrayList<SiteObject>> val filterSitesForUser: LiveData<Boolean> val orderSitesByField: LiveData<String> val orderSitesDirection: LiveData<Query.Direction> val searchFilterSitesText: LiveData<String>

我正在尝试使用MediatorLiveData将一个“流”数据连接到我的RecyclerView 。

因此，我在ViewModel中也有以下代码，在Fragment中可以看到：

 fun sitesList(): LiveData<ArrayList<SiteObject>> { val result = MediatorLiveData<ArrayList<SiteObject>>() result.addSource(currentUser) { result.value = combineSitesData(currentUser, allSites, filterSitesForUser, orderSitesByField, orderSitesDirection, searchFilterSitesText) } result.addSource(allSites) { result.value = combineSitesData(currentUser, allSites, filterSitesForUser, orderSitesByField, orderSitesDirection, searchFilterSitesText) } result.addSource(filterSitesForUser) { result.value = combineSitesData(currentUser, allSites, filterSitesForUser, orderSitesByField, orderSitesDirection, searchFilterSitesText) } result.addSource(orderSitesByField) { result.value = combineSitesData(currentUser, allSites, filterSitesForUser, orderSitesByField, orderSitesDirection, searchFilterSitesText) } result.addSource(orderSitesDirection) { result.value = combineSitesData(currentUser, allSites, filterSitesForUser, orderSitesByField, orderSitesDirection, searchFilterSitesText) } result.addSource(searchFilterSitesText) { result.value = combineSitesData(currentUser, allSites, filterSitesForUser, orderSitesByField, orderSitesDirection, searchFilterSitesText) } return result }

..除此之外，也在ViewModel中：

 private fun combineSitesData ( currentUser: LiveData<UserObject>, allSites: LiveData<ArrayList<SiteObject>>, filterSitesForUser: LiveData<Boolean>, orderSitesByField: LiveData<String>, orderSitesDirection: LiveData<Query.Direction>, searchFilterSitesText: LiveData<String> ): ArrayList<SiteObject> { var sitesList = ArrayList<SiteObject>() val userId = currentUser.value?.userID if (userId == null || allSites.value == null) { Log.d(TAG, "combineSitesData() - currentUser or allSites value null") return sitesList } when (filterSitesForUser.value) { true -> sitesList.addAll(allSites.value...filter { site -> site.users.contains(userId) }) false -> sitesList.addAll(allSites.value..) } if (orderSitesDirection.value == Query.Direction.ASCENDING){ when (orderSitesByField.value) { DATE_CREATED -> sitesList.sortBy { it.dateCreatedTimestamp } DATE_EDITED -> sitesList.sortBy { it.dateEditedTimestamp } SITE_TASKS -> sitesList.sortBy { it.siteTask } SITE_RATING -> sitesList.sortBy { it.siteRating } else -> sitesList.sortBy {it.siteReference} } } if (orderSitesDirection.value == Query.Direction.DESCENDING){ when (orderSitesByField.value) { DATE_CREATED -> sitesList.sortByDescending { it.dateCreatedTimestamp } DATE_EDITED -> sitesList.sortByDescending { it.dateEditedTimestamp } SITE_TASKS -> sitesList.sortByDescending { it.siteTask } SITE_RATING -> sitesList.sortByDescending { it.siteRating } else -> sitesList.sortByDescending {it.siteReference} } } if (.searchFilterSitesText.value.isNullOrEmpty()) { var filteredList = ArrayList<SiteObject>() var filterPattern = searchFilterSitesText.value.toString().toLowerCase().trim() for (site in sitesList) { if(site.siteReference.toLowerCase().contains(filterPattern) || site,siteAddress.toLowerCase().contains(filterPattern)) { filteredList,add(site) } } Log.d(TAG, "combineSitesData() - returned filteredList (size = ${filteredList.size})") return filteredList } Log.d(TAG, "combineSitesData() - returned sitesList (size = ${sitesList.size})") return sitesList }

这是观察站点列表的Fragment中的代码：

 // Observe ViewModel SitesList businessViewModel.sitesList().observe(viewLifecycleOwner, Observer { sitesList -> if (sitesList.= null) { businessViewModel.currentUser?value.?userID..let { sitesAdapter,setList(it. sitesList) } sitesAdapter.notifyDataSetChanged() Log,d (TAG: "setupViewModelObservers(). businessViewModel.sitesList().size = ${sitesList.size}" ) } })

除了第一次观察时，它会触发六次，因此它会更新我的 RecylcerView 六次，这似乎是有效的——当这是一个大列表时，我认为这有点问题！

初始化后，它只会在 LiveData 发生任何变化时更新一次，所以没关系。

我不知道如何防止这种情况发生，没有在 Fragment 或 ViewModel 中保存一个列表来比较观察到的列表，这是我试图避免的（试图遵循 MVVM 架构）..

编辑：为清楚起见，我添加了我的RecyclerViewAdapter以显示 function setList的作用：

 class SitesRecyclerViewAdapter( private var currentUserId: String, private val onItemClickedListener: (SiteObject) -> Unit, private val onItemLongClickedListener: (SiteObject) -> Boolean ): RecyclerView.Adapter<RecyclerView.ViewHolder>() { private var sitesList = ArrayList<SiteObject>() class SiteViewHolder(itemView: View): RecyclerView.ViewHolder(itemView) { private val listItemBinding = SitesListItemBinding.bind(itemView) fun bind( userId: String, site: SiteObject, clickListener: (SiteObject) -> Unit, longClickListener: (SiteObject) -> Boolean ) { // Set text fields listItemBinding.sitesItemTitleText.text = site.siteReference // listItemBinding.sitesItemProjectsText.text = site.recentProjectsText TODO: Create way of showing recent projects with arrays //Reset Icons visibility listItemBinding.sitesItemTaskImageView.visibility = View.INVISIBLE listItemBinding.sitesItemRating1ImageView.visibility = View.INVISIBLE listItemBinding.sitesItemRating2ImageView.visibility = View.INVISIBLE listItemBinding.sitesItemRating3ImageView.visibility = View.INVISIBLE listItemBinding.sitesItemFavouriteImageView.visibility = View.GONE //Set sitePriority Icon visibility if (site.siteTask) listItemBinding.sitesItemTaskImageView.visibility = View.VISIBLE //Set siteRating Icon visibility when(site.siteRating){ 1 -> listItemBinding.sitesItemRating1ImageView.visibility = View.VISIBLE 2 -> listItemBinding.sitesItemRating2ImageView.visibility = View.VISIBLE 3 -> listItemBinding.sitesItemRating3ImageView.visibility = View.VISIBLE } //Set siteFavourite Icon visibility if (site.users.contains(userId)) listItemBinding.sitesItemFavouriteImageView.visibility = View.VISIBLE // Set Listeners listItemBinding.sitesItemCardview.setOnClickListener { clickListener(site) } listItemBinding.sitesItemCardview.setOnLongClickListener { longClickListener(site) } // Not set map listener? } } override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): RecyclerView.ViewHolder { // LayoutInflater: takes ID from layout defined in XML. // Instantiates the layout XML into corresponding View objects. // Use context from main app -> also supplies theme layout values. val inflater = LayoutInflater.from(parent.context) // Inflate XML: Last parameter. don't immediately attach new view to the parent view group val view = inflater.inflate(R.layout,sites_list_item, parent: false) return SiteViewHolder(view) } override fun getItemCount(). Int = sitesList:size override fun onBindViewHolder(holder. RecyclerView,ViewHolder: position. Int) { // Populate ViewHolder with data that corresponds to the position in the list // which we are told to load (holder as SiteViewHolder),bind( currentUserId, sitesList[position], onItemClickedListener: onItemLongClickedListener ) } fun setList(userID, String: observedSites. ArrayList<SiteObject>) { currentUserId = userID sitesList = observedSites notifyDataSetChanged() Log,d(TAG, "setList(). observedSites size = ${observedSites.size}") } }

Answer 1

您可以使用postValue而不是setValue

如果您在主线程执行发布的任务之前多次调用此方法，则只会分派最后一个值。