问题描述
我正在尝试实例化viewmodel，以便根据给定的参数显示不同的列表。但是，我对init和构造函数调用感到有些困惑。
以下版本给我一个Mainviewmodel> has no zero argument constructor错误。
版本1
class Mainviewmodel(private val param: String) : viewmodel() {
private var list: ArrayList<ModelDialogoption>? = null
val usermutablelivedata: mutablelivedata<ArrayList<ModelDialogoption>?> = mutablelivedata()
init {
populateList()
usermutablelivedata.value = list!!
}
private fun populateList() {
list = ArrayList()
when (param) {
"Choose your age range" -> {
list!!.add(ModelDialogoption("Prefer not to say",false))
list!!.add(ModelDialogoption("16-39",false))
list!!.add(ModelDialogoption("40-59",true))
list!!.add(ModelDialogoption("60+",false))
}
}
}
}
版本2
这给了我一个没有找到参数的空列表，因为仅在初始化已经发生之后才调用构造函数：
class Mainviewmodel() : viewmodel() {
var param: String? = null
private var list: ArrayList<ModelDialogoption>? = null
val usermutablelivedata: mutablelivedata<ArrayList<ModelDialogoption>?> = mutablelivedata()
init {
populateList()
usermutablelivedata.value = list!!
}
constructor(param: String) : this() {
this.param = param
populateList()
usermutablelivedata.value = list!!
}
private fun populateList() {
list = ArrayList()
when (param) {
"Choose your age range" -> {
list!!.add(ModelDialogoption("Prefer not to say",false))
}
}
}
}
这里还有一个空列表：
版本3
class Mainviewmodel() : viewmodel() {
var param: String? = null
private var list: ArrayList<ModelDialogoption>? = null
val usermutablelivedata: mutablelivedata<ArrayList<ModelDialogoption>?> = mutablelivedata()
constructor(param: String) : this() {
this.param = param
populateList()
usermutablelivedata.value = list!!
}
private fun populateList() {
list = ArrayList()
when (param) {
"Choose your age range" -> {
list!!.add(ModelDialogoption("Prefer not to say",false))
}
}
}
}
版本4
这使我可以填充列表，但是可以确定没有参数，因为没有传递任何参数，只是将其用作起点：
class Mainviewmodel : viewmodel() {
private var list: ArrayList<ModelDialogoption>? = null
val usermutablelivedata: mutablelivedata<ArrayList<ModelDialogoption>?> = mutablelivedata()
init {
populateList()
usermutablelivedata.value = list!!
}
private fun populateList() {
list = ArrayList()
list!!.add(ModelDialogoption("Prefer not to say",false))
}
}
这是我的viewmodelFactory：
public class MyviewmodelFactory implements viewmodelProvider.Factory {
private String param;
public MyviewmodelFactory(String param) {
this.param = param;
}
@NotNull
@Override
public <T extends viewmodel> T create(@NotNull Class<T> modelClass) {
return (T) new Mainviewmodel(param);
}
}
以这种方式启动：
private val viewmodel: Mainviewmodel by activityviewmodels {
MyviewmodelFactoryForHashMap(
arguments?.getString("headerText")
)
}
非常感谢您。
解决方法
自从我回答了您的last question后，我对您的代码流程一无所知
您应该更新它，而不是在ViewModel中传递参数，因为您正在共享和监听两个片段
class CovidCheckInFragment : Fragment(R.layout.fragment_covid_check_in) {
var navController: NavController? = null
private val model: MainViewModel by activityViewModels()
private lateinit var tartTextView:TextView
@RequiresApi(Build.VERSION_CODES.M)
override fun onViewCreated(view: View,savedInstanceState: Bundle?) {
super.onViewCreated(view,savedInstanceState)
tvHeader.text = "COVID Check-in"
navController = Navigation.findNavController(view)
// Listeners
etYourAge.setOnClickListener(onClick)
etYourCounty.setOnClickListener(onClick)
etYourLocality.setOnClickListener(onClick)
rbFemale.setOnClickListener(onClickRb)
rbMale.setOnClickListener(onClickRb)
rbPreferNotToSay.setOnClickListener(onClickRb)
model.userMutableLiveData.observe(viewLifecycleOwner,Observer {
it?.let {
it.filter {
it.selected == true
}.map {
tartTextView.text = it.title
}
}
})
}
private val onClick = View.OnClickListener {
val destination: Int = R.id.action_covidCheckInFragment_to_my_dialog_fragment
val message: String? = when (it.id) {
R.id.etYourAge -> {
tartTextView = etYourAge
model.updateList("Choose your age range")
"Choose your age range"
}
R.id.etYourCounty -> {
tartTextView = etYourCounty
model.updateList("Choose your county")
"Choose your county"
}
R.id.etYourLocality -> {
tartTextView = etYourLocality
model.updateList("Choose your locality")
"Choose your locality"
}
else -> {
""
}
}
val bundle = bundleOf("headerText" to message)
navController = Navigation.findNavController(it)
navController!!.navigate(
destination,bundle
)
}
@RequiresApi(Build.VERSION_CODES.M)
private val onClickRb = View.OnClickListener {
val list = listOf<Button>(rbFemale,rbMale,rbPreferNotToSay)
for (i in list) {
i.setTextColor(resources.getColor(R.color.text))
i.background.setTint(ContextCompat.getColor(activity as MainActivity,R.color.greyEee))
}
if ((it as AppCompatRadioButton).isChecked) {
it.setTextColor(resources.getColor(R.color.white))
it.background.setTint(ContextCompat.getColor(activity as MainActivity,R.color.shadow))
}
}
}
这是您的MainViewModel
class MainViewModel : ViewModel() {
private var list = ArrayList<ModelDialogOption>()
val userMutableLiveData: MutableLiveData<ArrayList<ModelDialogOption>> = MutableLiveData()
fun updateItem(position: Int) {
val itemToUpdate = list[position]
itemToUpdate.selected = !itemToUpdate.selected!!
list[position] = itemToUpdate
}
fun flushItems() {
userMutableLiveData.value = list
}
fun updateList(param: String) {
list = ArrayList()
when (param) {
"Choose your age range" -> {
list.add(ModelDialogOption("Prefer not to say",false))
list.add(ModelDialogOption("16-39",false))
list.add(ModelDialogOption("40-59",false))
list.add(ModelDialogOption("60+",false))
}
"Choose your county" -> {
list.add(ModelDialogOption("Prefer not to say",false))
list.add(ModelDialogOption("County1",false))
list.add(ModelDialogOption("County2",false))
list.add(ModelDialogOption("County3",false))
}
"Choose your locality" -> {
list.add(ModelDialogOption("Prefer not to say",false))
list.add(ModelDialogOption("Locality1",false))
list.add(ModelDialogOption("Locality2",false))
list.add(ModelDialogOption("Locality3",false))
}
}
flushItems()
}
}