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[英]cannot find symbol import com.example.androiddata.databinding.FragmentDetailBindingImpl;
[英]Android kotlin data-binding with fragments error:cannot find symbol import com.example.***.databinding.FragmentUserBindingImpl;
我對 kotlin 比較陌生,並試圖在某些片段中構建一個帶有數據綁定的項目。我有一個名為 UserFragment 的片段,其中有一個 Recyclerview,如下所示:
class UserFragment : Fragment() {
private lateinit var binding: FragmentUserBinding
private lateinit var viewModel: UserListViewModel
override fun onCreateView(
inflater: LayoutInflater, container: ViewGroup?,
savedInstanceState: Bundle?
): View? {
// Inflate the layout for this fragment
binding=DataBindingUtil.inflate(inflater,R.layout.fragment_user, container, false)
binding.userRecycler.layoutManager = LinearLayoutManager(context, RecyclerView.VERTICAL, false)
viewModel = ViewModelProviders.of(this).get(UserListViewModel::class.java)
viewModel.errorMessage.observe(this, Observer {
errorMessage -> if(errorMessage != null) showError(errorMessage) else hideError()
})
binding.mViewModel=viewModel
return binding.root
}
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
//start add activity
val i= Intent(activity,AddUserActivity::class.java)
userFab.setOnClickListener(View.OnClickListener {
startActivity(i)
})
}
private fun showError(@StringRes errorMessage:Int){
errorSnackbar = Snackbar.make(binding.root, errorMessage, Snackbar.LENGTH_INDEFINITE)
errorSnackbar?.setAction(R.string.retry, viewModel.errorClickListener)
errorSnackbar?.show()
}
private fun hideError(){
errorSnackbar?.dismiss()
}
}
xml 布局文件fragment_user.xml如下所示:
<?xml version="1.0" encoding="utf-8"?>
<layout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto" xmlns:tools="http://schemas.android.com/tools">
<data>
<variable
name="mViewModel"
type="com.example.***.ui.User.UserListViewModel" />
</data>
<androidx.constraintlayout.widget.ConstraintLayout
android:layout_width="match_parent"
android:layout_height="match_parent">
<EditText
android:id="@+id/userDateEditText"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:hint="@string/pick_date"
android:background="@drawable/roundededittext"
android:layout_marginEnd="8dp"
app:layout_constraintEnd_toEndOf="parent"
android:layout_marginStart="8dp"
app:layout_constraintStart_toStartOf="parent"
android:layout_marginTop="8dp"
app:layout_constraintTop_toTopOf="parent"/>
<androidx.recyclerview.widget.RecyclerView
android:id="@+id/userRecycler"
android:layout_width="293dp"
android:layout_height="475dp" android:layout_marginTop="8dp"
app:layout_constraintTop_toBottomOf="@+id/userDateEditText"
app:adapter="@{viewModel.getUserListAdapter()}"
app:layout_constraintEnd_toEndOf="parent"
android:layout_marginEnd="8dp" app:layout_constraintStart_toStartOf="parent"
android:layout_marginStart="8dp" android:layout_marginBottom="8dp"
app:layout_constraintBottom_toBottomOf="parent"/>
<com.google.android.material.floatingactionbutton.FloatingActionButton
android:id="@+id/userFab"
android:layout_width="wrap_content"
android:layout_height="wrap_content" android:layout_marginBottom="48dp"
app:layout_constraintBottom_toBottomOf="parent" app:layout_constraintEnd_toEndOf="parent"
android:layout_marginEnd="8dp"/>
<ProgressBar
style="?android:attr/progressBarStyle"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
app:mutableVisibility="@{viewModel.getLoadingVisibility()}"
android:id="@+id/userProgressBar" app:layout_constraintEnd_toEndOf="parent"
android:layout_marginEnd="140dp" app:layout_constraintStart_toStartOf="parent"
android:layout_marginStart="8dp" android:layout_marginTop="8dp"
app:layout_constraintTop_toTopOf="parent" android:layout_marginBottom="8dp"
app:layout_constraintBottom_toBottomOf="parent" app:layout_constraintHorizontal_bias="0.804"
app:layout_constraintVertical_bias="0.499"/>
</androidx.constraintlayout.widget.ConstraintLayout>
</layout>
還有一個類似的適配器類和 item_user.xml:
class UserListAdapter : RecyclerView.Adapter<UserListAdapter.ViewHolder>() {
private lateinit var userModelList:List<UserModel>
override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): UserListAdapter.ViewHolder {
val binding: ItemUserBinding = DataBindingUtil.inflate(LayoutInflater.from(parent.context), R.layout.item_user, parent, false)
return ViewHolder(binding)
}
override fun onBindViewHolder(holder: UserListAdapter.ViewHolder, position: Int) {
holder.bind(userModelList[position])
}
override fun getItemCount(): Int {
return if(::userModelList.isInitialized) userModelList.size else 0
}
fun updateUserList(userModelList:List<UserModel>){
this.userModelList = userModelList
notifyDataSetChanged()
}
class ViewHolder(private val binding: ItemUserBinding):RecyclerView.ViewHolder(binding.root){
private val viewModel = UserViewModel()
fun bind(userModel: UserModel){
viewModel.bind(userModel)
binding.viewModel =viewModel
}
}
}
項目-user.xml :
<?xml version="1.0" encoding="utf-8"?>
<layout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto">
<data>
<variable
name="viewModel"
type="com.example.***.ui.MyUser.UserViewModel" />
</data>
<android.support.constraint.ConstraintLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:paddingLeft="16dp"
android:paddingRight="16dp">
<TextView
android:id="@+id/user_title"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:textStyle="bold"
app:mutableText="@{viewModel.getUserTitle()}"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent" />
<TextView
android:id="@+id/user_description"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_marginTop="8dp"
app:mutableText="@{viewModel.getUserDesc()}"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="@+id/user_title" />
</android.support.constraint.ConstraintLayout>
</layout>
請注意,數據綁定已在 gradle 中啟用,這里非常重要的問題是,在我的片段和適配器中,這一行:
binding.viewModel =viewModel
報告這樣的類型不匹配:
Type mismatch.
Required:MyUser.UserListViewModel?
Found:com.example.***.ui.MyUser.UserListViewModel
當我構建我的項目時,錯誤如下:
error: cannot find symbol
import com.example.***.databinding.FragmentUserBindingImpl;
第一個錯誤非常明確:binding.viewModel 需要一個可為空的 UserListViewModel? 並獲得一個不可為空的 UserListViewModel(請參閱kotlin null 安全文檔)。 你可以嘗試這樣的事情來擺脫它:
將您的 viewModel 聲明為
private var viewModel: UserListViewModel? = null
並以這種方式設置您的綁定:
viewModel?.let{binding.viewModel = it}
關於第二個錯誤,您的聲明似乎沒有問題,但有時 Android Studio 的緩存已損壞,請嘗試使緩存無效/重新啟動,它可能會有所幫助。
類型不匹配。 必需:MyUser.UserListViewModel? 找到:com.example.***.ui.MyUser.UserListViewModel
基本上錯誤是告訴你
binding.viewModel //is a nullable type and there for it expects a nullable
//type to be assigned as well
因此,只需通過添加? 在其 delacarion 之后的 simbol(注意后期初始化類型不允許為空類型)。 像這樣試試
private var viewModel: UserListViewModel? = null
關於第二個錯誤數據綁定庫需要編譯才能自動生成綁定類,只需重建項目,這個錯誤就會消失。
請隨意使用此模板作為基礎,以避免所有樣板代碼
@Retention(AnnotationRetention.RUNTIME)
@Target(AnnotationTarget.CLASS)
annotation class ContentView(@LayoutRes val id: Int)
fun ViewGroup.inflate(@LayoutRes layoutId: Int,
addContainer: Boolean = false): View {
return LayoutInflater.from(context).inflate(layoutId,this,addContainer)
}
@Suppress("UNCHECKED_CAST")
abstract class BaseFragment<Model : ViewModel, Binding : ViewDataBinding> : Fragment() {
/**
* Data binding class variable all view elements declared on the
* Xml file will be available within this instance if a view model
* Is required for the xml to work we will need to bind it on @onBindViewModel
*/
protected lateinit var binding: WeakReference<Binding?>
/**
* Fragments view model according to MVVM android architecture
* Each fragment class should have one , in order to facilitate
* Live Data and Binding library features, tho we can skip it
*/
protected lateinit var viewModel: WeakReference<Model?>
/**
* Here is where most likely you will get not null data , both binding and
* view model references can be destroyed by garbage collector
* If this application reaches low memory levels
*
* This optional method is used to bind the required view model inside the
* Xml file, this is optional to use tho is recommended
* Bind them by calling the view model binding.customViewModel = viewModel
*/
protected open fun onBindViewModel(viewModel: Model?, binding: Binding?) {}
/**
* There will be the occasion where custom params will be needed on view model's
* Constructor in this case will want to override the default creation @see ViewModelFactory
*/
protected open fun onCreateViewModel(modelType: Class<Model>): Model? = if (modelType != ViewModel::class.java)
ViewModelProviders.of(requireActivity()).get(modelType) else null
/**
* Here we will inherit view model and binding values based on the class
* Parameters and store them in global variables so any class extending
* From Base activity has access to binding and view model instances by default
*/
override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
val layout = this.javaClass.annotations.find { it.annotationClass == ContentView::class } as ContentView?
?: throw RuntimeException("You annotate this class with @ContentView and provide a layout resource")
container?.let { binding = WeakReference(DataBindingUtil.bind(it.inflate(layout.id))!!) }
?: run { binding = WeakReference(DataBindingUtil.bind(inflater.inflate(layout.id, null))) }
viewModel = WeakReference(
onCreateViewModel(
(this.javaClass.genericSuperclass
as ParameterizedType).actualTypeArguments[0] as Class<Model>
)
)
setHasOptionsMenu(true)
onBindViewModel(viewModel.get(), binding.get())
return binding.get()?.root
}
}
就像這樣使用它(看看有多少樣板代碼消失了)
@ContentView(R.layout.fragment_user)
class UserFragment: BaseFragment<UserListViewModel, FragmentUserBinding> {
override fun onBindViewModel(viewModel: UserListViewModel?, binding: FragmentUserBinding?) {
binding.viewModel = viewModel
}
}
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