[英]notifyDataSetChanged() not updating RecyclerView Adapter
I am working on a very simple implementation of a RecyclerView that displays data stored in a ViewModel.我正在研究一个非常简单的 RecyclerView 实现,它显示存储在 ViewModel 中的数据。 I am still very new to Android development and am trying to learn the fundamentals.我对 Android 开发还很陌生,正在努力学习基础知识。 In this situation, all the data to be stored in the ViewModel is stored in a simple list, later on I want to use Room to do this but right now I am struggling to get things working.在这种情况下,要存储在 ViewModel 中的所有数据都存储在一个简单的列表中,稍后我想使用 Room 来执行此操作,但现在我正在努力让事情正常进行。 Currently adding an item to the list only adds that item to the private member (_mainList) of the ViewModel, the public member (mainList) is unchanged, and this is the member passed into the adapter constructor call.当前向列表中添加一个项目只是将该项目添加到 ViewModel 的私有成员 (_mainList),公共成员 (mainList) 不变,这是传递给适配器构造函数调用的成员。
ViewModel:视图模型:
class ListViewModel : ViewModel() {
private val _mainList = mutableListOf<String>()
val mainList = _mainList.toList()
fun addMainListItem(item: String) {
_mainList.add(item)
}
}
Adapter:适配器:
class MainAdapter(private var list: List<String>) :
RecyclerView.Adapter<MainAdapter.ViewHolder>() {
class ViewHolder(view: View) : RecyclerView.ViewHolder(view)
override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ViewHolder {
val view = LayoutInflater.from(parent.context).inflate(R.layout.list_item, parent, false)
return ViewHolder(view)
}
override fun onBindViewHolder(holder: ViewHolder, position: Int) {
holder.itemView.list_item_text.text = list[position]
}
override fun getItemCount(): Int {
return list.size
}
}
Fragment that displays the list:显示列表的片段:
class MainListFragment : Fragment() {
private val viewModel: ListViewModel by activityViewModels()
private var _binding: FragmentMainListBinding? = null
private val binding get() = _binding!!
lateinit var adapter: MainAdapter
override fun onCreateView(
inflater: LayoutInflater, container: ViewGroup?,
savedInstanceState: Bundle?
): View {
_binding = FragmentMainListBinding.inflate(inflater, container, false)
val root: View = binding.root
return root
}
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
// Add click listener to floating action button
binding.fabMain.setOnClickListener {
addListItem()
}
adapter = MainAdapter(viewModel.mainList)
main_list_view.adapter = adapter
main_list_view.layoutManager = LinearLayoutManager(requireContext())
}
private fun addListItem() {
val input = EditText(activity)
input.setHint("Enter the name of your new list item")
input.inputType = InputType.TYPE_CLASS_TEXT
activity?.let {
val builder = AlertDialog.Builder(activity)
builder.apply {
setTitle("Add List Item")
setView(input)
setPositiveButton(
"Add"
) { dialog, id ->
val newItem = input.text.toString()
viewModel.addMainListItem(newItem)
adapter.notifyDataSetChanged()
}
setNegativeButton("Cancel"
) { dialog, id ->
dialog.cancel()
}
}
builder.create()
builder.show()
}
}
}
private fun addListItem() {
val input = EditText(activity)
input.setHint("Enter the name of your new list item")
input.inputType = InputType.TYPE_CLASS_TEXT
activity?.let {
val builder = AlertDialog.Builder(activity)
builder.apply {
setTitle("Add List Item")
setView(input)
setPositiveButton(
"Add"
) { dialog, id ->
val newItem = input.text.toString()
viewModel.addMainListItem(newItem)
adapter.addItem(newItem)
}
setNegativeButton("Cancel"
) { dialog, id ->
dialog.cancel()
}
}
builder.create()
builder.show()
}
}
add Method in the adapter also make list to ArrayList and public visibility适配器中的 add 方法也将列表添加到 ArrayList 和公共可见性
fun addItem(item: String){
if(!list.contains(item)){
list.add(item)
}
}
Or if you want to observe changes from ViewModel then add the observing event in your fragment.或者,如果您想观察 ViewModel 的变化,请在您的片段中添加观察事件。 ViewModel list observing events is best practice in your case. ViewModel 列表观察事件是您的最佳做法。
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