i have a spinner defined in the xml like this
<Spinner
android:layout_width="0dp"
android:layout_height="wrap_content"
android:id="@+id/expense_category"
app:sourceData="@{()->createExpenseViewModel.getAllSourceItems(1)}"
app:layout_constraintStart_toStartOf="@+id/textView"
android:layout_marginTop="20dp"
app:layout_constraintTop_toBottomOf="@+id/textView" app:layout_constraintWidth_percent="0.7"
/>
createExpenseViewModel.getAllSourceItems(1) this method returns LiveData <List<Source>>, so i have written a binding adapter for that case
@BindingAdapter("app:sourceData")
fun setSourceData(spinner: Spinner, sourceList: List<Source>) {
val categoryItems = ArrayList<String>()
categoryItems.addAll(sourceList.map { it.sourceName })
val spinnerAdapter =
ArrayAdapter<String>(spinner.context, R.layout.simple_spinner_dropdown_item, categoryItems)
spinner.adapter = spinnerAdapter
}
when building the app, i am getting the following error,
****/ data binding error ****msg:Cannot find the proper callback class for app:sourceData. Tried java.util.List but it has 25 abstract methods, should have 1 abstract methods. file:/home/naveen/Desktop/project-expense/app/src/main/res/layout/activity_create_expense.xml loc:94:34 - 94:80 ****\ data binding error ****
what does this error actually mean,how to resolve this error?
Edit:
what i intend to do is get the list returned by live data and convert to type ArrayList , i need my binding adapter to be triggered once the livedata returns the list, but if i use this app:sourceData="@{createExpenseViewModel.getAllSourceItems(1)}" and set the binding adapter, the adapter get only null list
You are binding a method to app:sourceData, but you're expecting a variable for it in your binding adapter. That cannot work.
I guess you want to populate the List into the Spinner. For that I would create a property in your viewModel and bind this property in the xml. I did just that in an app where I had a list of projects to display in the Spinner. Here's the code including the InverseBindingAdapter to automatically save the selected Project in another variable of the ViewModel.
ViewModel:
// getProjects() returns the LiveData
val projects = metaDataRepository.getProjects()
// use _selectedProject only within ViewModel. Do not expose MediatorLiveData to UI.
// in UI observe selectedProject
private val _selectedProject = MediatorLiveData<Project>()
val selectedProject: LiveData<Project>
get() = _selectedProject
Layout XML:
<Spinner
android:id="@+id/spProjects"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
app:projects="@{viewModel.projects}"
app:selectedProject="@={viewModel.selectedProject}" />
BindingAdapter (to populate data from the viewModel into the UI):
/**
* fill the Spinner with all available projects.
* Set the Spinner selection to selectedProject.
* If the selection changes, call the InverseBindingAdapter
*/
@BindingAdapter(value = ["projects", "selectedProject", "selectedProjectAttrChanged"], requireAll = false)
fun setProjects(spinner: Spinner, projects: List<Project>?, selectedProject: Project, listener: InverseBindingListener) {
if (projects == null) return
spinner.adapter = ProjectAdapter(spinner.context, android.R.layout.simple_spinner_dropdown_item, projects)
setCurrentSelection(spinner, selectedProject)
setSpinnerListener(spinner, listener)
}
Helper Methods for BindingAdapter:
private fun setSpinnerListener(spinner: Spinner, listener: InverseBindingListener) {
spinner.onItemSelectedListener = object : AdapterView.OnItemSelectedListener {
override fun onItemSelected(parent: AdapterView<*>?, view: View?, position: Int, id: Long) = listener.onChange()
override fun onNothingSelected(adapterView: AdapterView<*>) = listener.onChange()
}
}
private fun setCurrentSelection(spinner: Spinner, selectedItem: Project?): Boolean {
if (selectedItem == null) {
return false
}
for (index in 0 until spinner.adapter.count) {
val currentItem = spinner.getItemAtPosition(index) as Project
if (currentItem.name == selectedItem.name) {
spinner.setSelection(index)
return true
}
}
return false
}
Simple Adapter for your Spinner. Change this to your needs:
/**
* Adapter for displaying the name-field of an Project in a Spinner
*/
class ProjectAdapter(context: Context, textViewResourceId: Int, private val values: List<Project>) : ArrayAdapter<Project>(context, textViewResourceId, values) {
override fun getCount() = values.size
override fun getItem(position: Int) = values[position]
override fun getItemId(position: Int) = position.toLong()
override fun getView(position: Int, convertView: View?, parent: ViewGroup): View {
val label = super.getView(position, convertView, parent) as TextView
label.text = values[position].name
return label
}
override fun getDropDownView(position: Int, convertView: View?, parent: ViewGroup): View {
val label = super.getDropDownView(position, convertView, parent) as TextView
label.text = values[position].name
return label
}
}
InverseBindingAdapter (to store the selected Spinner item in the viewModel)
/**
* get the selected projectName and use it to return a
* Project which is then used to set appEntry.value.project
*/
@InverseBindingAdapter(attribute = "selectedProject")
fun getSelectedProject(spinner: Spinner): Project {
return spinner.selectedItem as Project
}
I have followed the core idea of what @muetzenflo suggested, i have created a property on view model like this
class MainViewModel @Inject constructor(
val expenseSourceItems:LiveData<List<Source>> = getAllSourceItems(1)
fun getAllSourceItems(sourceType:Int?): LiveData<List<Source>> {
val res = sourceRepository.getAllSourceItems(sourceType)
return res
}
// the methods below are omitted for brevity
}
then i have bound to the spinner using property access syntax
<Spinner
android:layout_width="0dp"
android:layout_height="wrap_content"
android:id="@+id/expense_category"
app:sourceData="@{createExpenseViewModel.expenseSourceItems}"
app:layout_constraintStart_toStartOf="@+id/textView"
android:layout_marginTop="20dp"
app:layout_constraintTop_toBottomOf="@+id/textView" app:layout_constraintWidth_percent="0.7"
/>
and then used the same binding adapter
@BindingAdapter("app:sourceData")
fun setSourceData(spinner: Spinner, sourceList: List<Source>) {
val categoryItems = ArrayList<String>()
categoryItems.addAll(sourceList.map { it.sourceName })
val spinnerAdapter =
ArrayAdapter<String>(spinner.context, R.layout.simple_spinner_dropdown_item, categoryItems)
spinner.adapter = spinnerAdapter
}
for live data calling a method inside data binding only works for callbacks like onclick, and property access is needed to be used for normal data binding like populating a spinner.
