Android 开发新手,正在尝试了解最新的架构组件。使用 Android Studio 3.2、Room、LiveData、ViewModel、数据绑定(bind)和 RecyclerView,我已经与数据绑定(bind)斗争了好几天。我的 Activity 中有一个 fragment ,而应该显示来 self 的 ViewModel/查询的数据的 RecyclerView 部分是空白/空的。即使相关的 Room 查询有效并返回项目,适配器的 getItemCount 中的 Log.d 显示零个项目。
请用线索棒打我,让我知道我错过了什么。我的代码的相关部分:
实体与道
import org.threeten.bp.Instant
data class ActionDetails(val time: Instant,
val firstName: String,
... )
@Query("SELECT time, first_name as firstName...")
fun liveStatus(): LiveData<List<ActionDetails>>
fragment 类
class MainFragment : Fragment() {
...
private lateinit var viewModel: MainViewModel
private lateinit var adapter: ViewAdapter
override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?,
savedInstanceState: Bundle?): View {
val binding = MainFragmentBinding.inflate(inflater, container, false)
val context = context ?: return binding.root
val factory = Utilities.provideMainViewModelFactory(context)
viewModel = ViewModelProviders.of(this, factory).get(MainViewModel::class.java)
adapter = ViewAdapter(listOf())
binding.apply {
rvActionDetails.setHasFixedSize(true)
rvActionDetails.layoutManager = LinearLayoutManager(context)
rvActionDetails.adapter = adapter
vm = viewModel
setLifecycleOwner(this@MainFragment)
}
return binding.root
}
View 模型
class MainViewModel(private val repository: DataRepository) : ViewModel() {
val actions: LiveData<List<ActionDetails>> = repository.liveStatus()
}
适配器
import ...FragmentActionDetailBinding
class ViewAdapter(private val actions: List<ActionDetails>) : RecyclerView.Adapter<ViewAdapter.ViewHolder>() {
private val TAG = this::class.java.simpleName
class ViewHolder(val binding: FragmentActionDetailBinding) : RecyclerView.ViewHolder(binding.root) {
fun bind(action: ActionDetails) {
binding.apply {
vm = action
executePendingBindings()
}
}
}
override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ViewHolder {
val inflater = LayoutInflater.from(parent.context)
val binding = FragmentActionDetailBinding.inflate(inflater, parent, false)
return ViewHolder(binding)
}
override fun onBindViewHolder(holder: ViewHolder, position: Int) {
holder.bind(actions[position])
}
override fun getItemCount(): Int {
Log.d(TAG, "Adapter has ${actions.size} items!")
return actions.size
}
}
主要 fragment
<layout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools">
<data>
<variable
name="vm" type=".MainViewModel" />
</data>
<androidx.constraintlayout.widget.ConstraintLayout
xmlns:app="http://schemas.android.com/apk/res-auto"
android:id="@+id/main"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainFragment" >
...
<androidx.recyclerview.widget.RecyclerView
android:id="@+id/rv_action_details"
android:layout_width="match_parent"
android:layout_height="wrap_content"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layoutManager="androidx.recyclerview.widget.LinearLayoutManager"
tools:listitem="@layout/fragment_action_detail" />
</androidx.constraintlayout.widget.ConstraintLayout>
XML fragment
<layout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools">
<data>
<variable
name="vm" type=".ActionDetails" />
</data>
<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
tools:context=".ActionDetailFragment" >
<TextView
android:id="@+id/first_name"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="@{vm.firstName}"
tools:text="John"/>
...
</LinearLayout>
最佳答案
终于解决这个问题了。不确定到底是什么解决了这个问题 - 我认为这是由于在 fragment 中的 binding.apply 中配置 RecyclerView 之前移动了 ViewModel 并运行了executePendingBindings(),但我不确定 - 因为我在学习后还做了一些其他更改关于 BindingAdapter。
我的更改如下,如果对其他人有帮助的话,我也很感激任何关于如何改进这一点的评论。
干杯。
fragment 类
class MainFragment : Fragment() {
...
override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?,
savedInstanceState: Bundle?): View {
...
binding.apply {
//Need to do this before configuring the RecyclerView
vm = viewModel
setLifecycleOwner(this@MainFragment)
executePendingBindings()
rvActionDetails.setHasFixedSize(true)
rvActionDetails.layoutManager = LinearLayoutManager(context)
rvActionDetails.adapter = adapter
}
return binding.root
}
适配器
import ...FragmentActionDetailBinding
class ViewAdapter(private val actions: List<ActionDetails>) : RecyclerView.Adapter<ViewAdapter.ViewHolder>() {
...
override fun setData(data: List<ActionDetails>) {
actions = data
notifyDataSetChanged()
}
绑定(bind)适配器
@BindingAdapter("listData")
fun <T> setRecyclerViewList (recyclerView: RecyclerView, data: T) {
if (recyclerView.adapter is BindableListAdapter<*>) {
(recyclerView.adapter as BindableListAdapter<T>).setData(data)
}
}
interface BindableListAdapter<T> {
fun setData(data: T)
}
主要 fragment
<layout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools">
<data>
<variable
name="vm" type=".MainViewModel" />
</data>
<androidx.constraintlayout.widget.ConstraintLayout
...
<androidx.recyclerview.widget.RecyclerView
android:id="@+id/rv_action_details"
android:layout_width="match_parent"
android:layout_height="wrap_content"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layoutManager="androidx.recyclerview.widget.LinearLayoutManager"
app:listData="@{vm.actions}"
tools:listitem="@layout/fragment_action_detail" />
</androidx.constraintlayout.widget.ConstraintLayout>
XML fragment
<layout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools">
<data>
<variable
name="vm" type=".ActionDetails" />
</data>
<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
tools:context=".ActionDetailFragment" >
<TextView
android:id="@+id/first_name"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="@{vm.firstName}"
tools:text="John"/>
...
</LinearLayout>
关于android - RecyclerView、数据绑定(bind)和 ViewModel 没有数据,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/52503212/