RecyclerView适配器方法未被调用kotlin

Question

在Adapter方法中。我能够在updateUsers(newUsers:list(中打印列表元素，这意味着我正在Adapter中获取数据集，但没有调用任何Adapter方法。我也设置了布局管理器。

我为CreateViewHolder和BindViewHolder上的所有适配器方法都设置了断点。但是控制没有进入代码块。

class MainActivity : AppCompatActivity() {
lateinit var viewModel: ListViewModel
private val usersAdapter = UserListAdapter(arrayListOf(),this)
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
viewModel = ViewModelProviders.of(this).get(ListViewModel::class.java)
viewModel.refresh()

usersList.apply {
layoutManager = LinearLayoutManager(this.context)
adapter = usersAdapter
}
usersList.adapter = usersAdapter

observeViewModel()
}
fun observeViewModel() {
viewModel.users.observe(this, Observer {
it?.let {
it.forEach {
Log.d("Each Item", it.toString());
}
loading_view.visibility = View.VISIBLE
usersAdapter.updateUsers(it)
}
})

viewModel.userLoadError.observe(this, Observer {
it?.let {
list_error.visibility = if (it) View.VISIBLE else View.GONE
}
})
viewModel.loading.observe(this, Observer {
it?.let {
loading_view.visibility = if (it) View.VISIBLE else View.GONE
if (it) {
list_error.visibility = View.GONE
usersList.visibility = View.GONE
}
}
})

}

}

class UserListAdapter(private var users: ArrayList<User>, private val context : Context) : RecyclerView.Adapter<UserListAdapter.UserViewHolder>() {
fun updateUsers(newUsers: List<User>) {
newUsers.forEach() {
Log.d("updateUsers", it.firstName)
}
users.clear()
users.addAll(newUsers)
notifyDataSetChanged()
}
override fun onCreateViewHolder(parent: ViewGroup, viewType: Int) : UserViewHolder{
val layoutInflator = LayoutInflater.from(parent.context)
val view = layoutInflator.inflate(R.layout.item_layout,parent,false)
return UserViewHolder(view)
}
override fun getItemCount():Int {
return users.size
}
override fun onBindViewHolder(holder: UserViewHolder, position: Int) {
holder.bind(users[position])
}

class UserViewHolder(view: View) : RecyclerView.ViewHolder(view) {
private val imageView = view.imageView
private val userName = view.name
private val userEmail = view.email
fun bind(country: User) {
userName.text = country.firstName + " " + country.lastName
userEmail.text = country.email
imageView.loadImage(country.avatar)
}
}
}

Answer 1

我不太清楚为什么你的代码不起作用，在这里我已经使用你的代码实现了，它起作用了。

主要活动

class MainActivity : AppCompatActivity() {
private lateinit var viewModel: ListViewModel
private val usersAdapter = UserListAdapter(arrayListOf(), this)
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
viewModel = ViewModelProviders.of(this).get(ListViewModel::class.java)
viewModel.refresh()
usersList.apply {
layoutManager = LinearLayoutManager(this.context, 
RecyclerView.VERTICAL, false)
adapter = usersAdapter
}
// usersList.adapter = usersAdapter // Don't need, you already set the 
//      adapter above.
observeViewModel()
}
private fun observeViewModel() {
viewModel.users.observe(this, Observer {
it?.let {
it.forEach {
Log.d("Each Item", it.toString());
}
//loading_view.visibility = View.VISIBLE
usersAdapter.updateUsers(it)
}
})
// commented for simplicity
//viewModel.userLoadError.observe(this, Observer {
// it?.let {
//list_error.visibility = if (it) View.VISIBLE else View.GONE
// }
//})
// viewModel.loading.observe(this, Observer {
// it?.let {
// loading_view.visibility = if (it) View.VISIBLE else View.GONE
// if (it) {
// list_error.visibility = View.GONE
// usersList.visibility = View.GONE
//  }
//
// }
// })
}
}

UserListAdapter

class UserListAdapter(private var users: ArrayList<User>, private val context : Context) : RecyclerView.Adapter<UserListAdapter.UserViewHolder>() {
fun updateUsers(newUsers: List<User>) {
newUsers.forEach() {
Log.d("updateUsers", it.firstName)
}
users.clear()
users.addAll(newUsers)
notifyDataSetChanged()
}
override fun onCreateViewHolder(parent: ViewGroup, viewType: Int) : UserViewHolder {
val inflater = LayoutInflater.from(parent.context)
val view = inflater.inflate(R.layout.item_layout,parent,false)
return UserViewHolder(view)
}
override fun getItemCount():Int {
return users.size
}
override fun onBindViewHolder(holder: UserViewHolder, position: Int) {
holder.bind(users[position])
}

class UserViewHolder(view: View) : RecyclerView.ViewHolder(view) {
private val imageView = view.imageView
private val userName = view.name
private val userEmail = view.email
fun bind(country: User) {
userName.text = country.firstName + " " + country.lastName
userEmail.text = country.email
//imageView.loadImage(country.avatar)
}
}
}

ListViewModel

class ListViewModel: ViewModel() {
val users : MutableLiveData<List<User>> = MutableLiveData()
fun refresh() {
val userList = mutableListOf<User>()
userList.add(User(
"User1 First Name",
"User1 last Name",
"[e-mail]"
))
userList.add(User(
"User2 First Name",
"User2 First Name",
"[e-mail]"
))
userList.add(User(
"User3 First Name",
"User3 First Name",
"[e-mail]"
))
userList.add(User(
"User4 First Name",
"User4 First Name",
"[e-mail]"
))
userList.add(User(
"User5 First Name",
"User5 First Name",
"[e-mail]"
))
userList.add(User(
"User6 First Name",
"User6 First Name",
"[e-mail]"
))
users.value = userList
}

}

希望这能有所帮助。