我已经成功地使用普通的ViewAdapter完成了这个操作，但是使用ListAdapter似乎无法正常工作。
这是我的Fragment，它完成了大部分工作：
class CrimeListFragment: Fragment() {
//Required interface for hosting activities
interface Callbacks {
fun onCrimeSelected(crimeId: UUID)
}
private var callbacks: Callbacks? = null
private lateinit var crimeRecyclerView: RecyclerView
private val crimeListViewModel: CrimeListViewModel by lazy {
ViewModelProviders.of(this).get(CrimeListViewModel::class.java)
}
override fun onAttach(context: Context) {
super.onAttach(context)
callbacks = context as Callbacks?
}
override fun onCreateView(
inflater: LayoutInflater,
container: ViewGroup?,
savedInstanceState: Bundle?
): View? {
val view = inflater.inflate(R.layout.fragment_crime_list, container, false)
crimeRecyclerView =
view.findViewById(R.id.crime_recycler_view) as RecyclerView
crimeRecyclerView.layoutManager = LinearLayoutManager(context)
crimeRecyclerView.adapter = CrimeListAdapter(emptyList())
return view
}
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
crimeListViewModel.crimeListLiveData.observe(
viewLifecycleOwner,
Observer { crimes ->
crimes?.let {
Log.i(TAG, "Got crimes ${crimes.size}")
updateUI(crimes)
}
}
)
}
override fun onDetach() {
super.onDetach()
callbacks = null
}
private fun updateUI(crimes: List<Crime>) {
crimeRecyclerView.adapter = CrimeListAdapter(crimes)
}
companion object {
fun newInstance(): CrimeListFragment {
return CrimeListFragment()
}
}
private inner class CrimeHolder(view: View)
: RecyclerView.ViewHolder(view), View.OnClickListener {
private lateinit var crime: Crime
private val titleTextView = itemView.findViewById<TextView>(R.id.crime_title)
private val dateTextView = itemView.findViewById<TextView>(R.id.crime_date)
private val solvedImageView = itemView.findViewById<ImageView>(R.id.crime_solved)
init {
itemView.setOnClickListener(this)
}
fun bind(crime: Crime) {
this.crime = crime
titleTextView.text = crime.title
dateTextView.text = crime.date.toString()
solvedImageView.visibility = if(crime.isSolved) {
View.VISIBLE
} else {
View.GONE
}
}
override fun onClick(v: View) {
callbacks?.onCrimeSelected(crime.id)
}
}
private inner class CrimeListAdapter(var crimes: List<Crime>)
: ListAdapter<Crime, CrimeHolder>(DiffCallback()) {
override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): CrimeHolder {
val view =
layoutInflater.inflate(R.layout.list_item_crime, parent, false)
return CrimeHolder(view)
}
override fun onBindViewHolder(holder: CrimeHolder, position: Int) {
holder.bind(crimes[position])
}
}
private inner class DiffCallback: DiffUtil.ItemCallback<Crime>() {
override fun areItemsTheSame(oldItem: Crime, newItem: Crime): Boolean {
return oldItem.id == newItem.id
}
override fun areContentsTheSame(oldItem: Crime, newItem: Crime): Boolean {
return oldItem == newItem
}
}
}
这是该片段的视图模型：
class CrimeListViewModel: ViewModel() {
private val crimeRepository = CrimeRepository.get()
val crimeListLiveData = crimeRepository.getCrimes() //returns LiveData<List<Crime>>
}
ListAdapter的相关文档中提到：
虽然使用LiveData是向适配器提供数据的简单方法，但并非必需 - 当有新列表可用时，可以使用submitList(List)。
在更新UI时，我应该提交一个新列表而不是每次创建一个新的ListAdapter对象。但是
crimeRecyclerView.adapter没有.submitList()功能。那么我怎样传递新列表呢？LiveData对我来说仍然很新，所以我不太清楚。我已经观察了存储在我的viewmodel中的LiveData。那么这次我要观察什么？还是只需向现有的Observer添加代码？
最后，当我以此状态运行代码时，手机显示一个空的RecyclerView。只调用了
UpdateUI()，没有调用CrimeListAdapter的任何函数。我不确定这是否是真正的问题，还是上述问题造成的结果。