问题描述
我具有以下功能-
private fun fetchGroupData(callback: (groupModelList: List<GroupModel>) -> Unit) {
val groupModelList = mutablelistof<GroupModel>()
groupviewmodel.getAllGroupEntities().observeOnce(requireActivity(),Observer { groupEntityList ->
groupEntityList.forEach { groupEntity ->
/*
We iterate though all of the available groups,for each group we get all of it's groupMembers models
*/
val groupName = groupEntity.groupName
val groupId = groupEntity.id
taskviewmodel.getGroupTaskCounter(groupId).observeOnce(requireActivity(),Observer { groupTaskCount ->
/*
For each group we observe it's task counter
*/
groupviewmodel.getGroupMembersForGroupId(groupId).observeOnce(requireActivity(),Observer { groupMembers ->
/*
For each group,we iterate through all of the groupMembers and for each of them we use it's userId
to fetch the user model,getting it's full name and adding it to a list of group users full name.
*/
val groupUsersFullNames = mutablelistof<String>()
groupMembers.forEach { groupMember ->
val memberId = groupMember.userId
groupviewmodel.getGroupParticipantForUserId(memberId).observeOnce(requireActivity(),Observer { groupUser ->
groupUsersFullNames.add(groupUser.fullName)
/*
When the groupUsersFullNames size matches the groupMembers size,we can add a model to our list.
*/
if (groupUsersFullNames.size == groupMembers.size)
groupModelList.add(GroupModel(groupId,groupName,groupTaskCount,groupUsersFullNames))
/*
When the new list matches the size of the group list in the DB we call the callback.
*/
if (groupModelList.size == groupEntityList.size)
callback(groupModelList)
})
}
})
})
}
})
}
以下功能正在使用-
private fun initAdapter() {
fetchGroupData { groupModelList ->
if (groupModelList.isEmpty()) {
binding.groupsListNoGroupsMessageTitle.setAsVisible()
binding.groupsListNoGroupsMessageDescription.setAsVisible()
return@fetchGroupData
}
binding.groupsListNoGroupsMessageTitle.setAsGone()
binding.groupsListNoGroupsMessageDescription.setAsGone()
val newList = mutablelistof<GroupModel>()
newList.addAll(groupModelList)
adapter.submitList(groupModelList)
Log.d("submitList","submitList")
binding.groupsListRecyclerview.setAdapterWithItemdecoration(requireContext(),adapter)
}
}
这2个函数代表从本地DB到RecyclerView中的组列表获取。
为了在创建新组时收到通知,我持有一个共享的viewmodel对象,该对象带有一个布尔值,指示是否已创建新组。
在编写这两个函数^的同一片段中,我正在观察此布尔值,如果该值为true,则会触发整个列表的重新提取-
private fun observeSharedinformation() {
sharedinformationviewmodel.value.groupCreatedFlag.observe(requireActivity(),Observer { hasGroupBeenCreated ->
if (!hasGroupBeenCreated) return@Observer
sharedinformationviewmodel.value.groupCreatedFlag.value = false
Log.d("submitList","groupCreatedFlag")
initAdapter()
})
}
在我代码的某个片段中的某个点上,该片段中也有我的共享viewmodel的实例,我触发了Boolean LiveData的值更改-
sharedinformationviewmodel.value.groupCreatedFlag.value = true
依次触发观察者,并重新获取我的群组列表。
我面临的问题是,在重新获取新列表时(因为已添加了新组),我确实获得了当前信息,并且一切都应该可以正常工作,但新数据-新创建的组-不会出现。
此问题有一个例外-如果组列表为空,则当我与一个组一起提交列表时,确实会出现第一个要添加的组。
我想念什么?
编辑-
这是我的适配器。
我正在使用一个名为DefaultAdapterDiffUtilCallback的自定义调用,该调用需要一个模型,该模型实现一个为每个模型定义唯一ID的接口,以便我可以比较新模型和旧模型。
class Groupslistadapter(
private val context: Context,private val onClick: (model : GroupModel) -> Unit
) : listadapter<GroupModel,GroupsListViewHolder>(DefaultAdapterDiffUtilCallback<GroupModel>()) {
override fun onCreateViewHolder(parent: ViewGroup,viewType: Int): GroupsListViewHolder {
val binding = GroupsListViewHolderBinding.inflate(LayoutInflater.from(context),parent,false)
return GroupsListViewHolder(binding)
}
override fun onBindViewHolder(holder: GroupsListViewHolder,position: Int) {
holder.bind(getItem(position),onClick)
}
override fun submitList(list: List<GroupModel>?) {
super.submitList(list?.let { ArrayList(it) })
}
}
/**
* Default DiffUtil callback for lists adapters.
* The adapter utilizes the fact that all models in the app implement the "ModelWithId" interfaces,so
* it uses it in order to compare the unique ID of each model for `areItemsTheSame` function.
* As for areContentsTheSame we utilize the fact that Kotlin Data Class implements for us the equals between
* all fields,so use the equals() method to compare one object to another.
*/
class DefaultAdapterDiffUtilCallback<T : ModelWithId> : DiffUtil.ItemCallback<T>() {
override fun areItemsTheSame(oldItem: T,newItem: T) =
oldItem.fetchId() == newItem.fetchId()
@SuppressLint("DiffUtilEquals")
override fun areContentsTheSame(oldItem: T,newItem: T) =
oldItem == newItem
}
/**
* An interface to determine for each model in the app what is the unique ID for it.
* This is used for comparing the unique ID for each model for abstracting the DiffUtil Callback
* and creating a default general one rather than a new class for each new adapter.
*/
interface ModelWithId {
fun fetchId(): String
}
data class GroupModel(val id: String,val groupName: String,var tasksCounter: Int,val usersFullNames: List<String>) : ModelWithId {
override fun fetchId(): String = id
}
edit 2.0-
我的observeOnce()
扩展名-
fun <T> LiveData<T>.observeOnce(lifecycleOwner: LifecycleOwner,observer: Observer<T>) {
observe(lifecycleOwner,object : Observer<T> {
override fun onChanged(t: T?) {
observer.onChanged(t)
removeObserver(this)
}
})
}
解决方法
您是否正在使用“新” ListAdapter
?
import androidx.recyclerview.widget.ListAdapter
在这种情况下,我可以想出您的问题的答案。但是由于我不知道您的确切实现,因此它是基于我的假设,因此您必须验证它是否适用。
为此ListAdapter
,您必须实现areItemsTheSame
和areContentsTheSame
方法。
我曾经有过类似的问题。我正在提交列表,但是它只是没有更新视图中的列表。
我可以通过仔细检查内容是否相同来进行比较来解决此问题。
对于比较功能,请考虑以下因素:
override fun areContentsTheSame(oldItem: GroupModel,newItem: GroupModel): Boolean {
// assuming GroupModel is a class
// this comparison is most likely not getting the result you want
val groupModelsAreMatching = oldItem == newItem // don't do this
// for data classes it usually gives the expected result
val exampleDataClassesMatch = oldItem.dataClass == newItem.dataClass
// But: the properties that need to be compared need to be declared in the primary constructor
// and not in the function body
// compare all relevant custom properties
val groupIdMatches = oldItem.groupId == newItem.groupId
val groupNameMatches = oldItem.groupName == newItem.groupName
val groupTaskCountMatches = oldItem.groupTaskCount == newItem.groupTaskCount
val groupUsersFullNamesMatches = oldItem.groupUsersFullNames == newItem.groupUsersFullNames
return groupIdMatches && groupNameMatches && groupTaskCountMatches && groupUsersFullNamesMatches
}
当然,您需要确保areItemsTheSame
。在这里,您只需要比较groupIds。
您已经这样做了吗?
,我发现了问题。
它与我的提取逻辑无关。
问题出在下面-
创建组时,我要向后堆栈中添加一个新的Fragment,并在完成后将其弹出。
删除群组时,我正在导航至我的主要片段,同时使用popUpTo
和popUpToInclusive
-效果很好。
我需要使用导航,而不是向后弹出堆栈以查看新列表。
这花了我3天的时间来弄清楚。 jeez