问题描述
我试图解决问题几天都没有成功.每当数据库(数据库室)中特定模型的记录发生更改时,我都希望更新recyclerView.我使用ViewModel处理模型数据,记录列表存储在LiveData中.
I am trying, without success, to solve a problem for days. I would like to update my recyclerView whenever the records of a particular model change in the Database (DB Room). I use ViewModel to handle the model data and the list of records are stored in LiveData.
数据库
@Database(entities = arrayOf(Additive::class), version = ElementDatabase.DB_VERSION, exportSchema = false)
abstract class ElementDatabase() : RoomDatabase() {
companion object {
const val DB_NAME : String = "element_db"
const val DB_VERSION : Int = 1
fun get(appContext : Context) : ElementDatabase {
return Room.databaseBuilder(appContext, ElementDatabase::class.java, DB_NAME).build()
}
}
abstract fun additivesModels() : AdditiveDao
}
模型
@Entity
class Additive {
@PrimaryKey @ColumnInfo(name = "id")
var number : String = ""
var dangerousness : Int = 0
var description : String = ""
var names : String = ""
var notes : String = ""
var risks : String = ""
var advice : String = ""
}
Dao
@Dao
interface AdditiveDao {
@Query("SELECT * FROM Additive")
fun getAllAdditives() : LiveData<List<Additive>>
@Query("SELECT * FROM Additive WHERE id = :arg0")
fun getAdditiveById(id : String) : Additive
@Query("DELETE FROM Additive")
fun deleteAll()
@Insert(onConflict = REPLACE)
fun insert(additive: Additive)
@Update
fun update(additive: Additive)
@Delete
fun delete(additive: Additive)
}
ViewModel
class AdditiveViewModel(application: Application) : AndroidViewModel(application) {
private var elementDatabase : ElementDatabase
private val additivesModels : LiveData<List<Additive>>
init {
this.elementDatabase = ElementDatabase.get(appContext = getApplication())
this.additivesModels = this.elementDatabase.additivesModels().getAllAdditives()
}
fun getAdditivesList() : LiveData<List<Additive>> {
return this.additivesModels
}
fun deleteItem(additive : Additive) {
DeleteAsyncTask(this.elementDatabase).execute(additive)
}
private class DeleteAsyncTask internal constructor(private val db: ElementDatabase) : AsyncTask<Additive, Void, Void>() {
override fun doInBackground(vararg params: Additive): Void? {
db.additivesModels().delete(params[0])
return null
}
}
}
片段
class AdditivesFragment : LifecycleFragment() {
private var viewModel : AdditiveViewModel? = null
private var adapter : AdditivesAdapter? = null
companion object {
fun newInstance() : AdditivesFragment {
val f = AdditivesFragment()
val args = Bundle()
f.arguments = args
return f
}
}
override fun onCreateView(inflater: LayoutInflater?, container: ViewGroup?, savedInstanceState: Bundle?): View? {
return inflater?.inflate(R.layout.fragment_additives, container, false)
}
override fun onActivityCreated(savedInstanceState: Bundle?) {
this.adapter = AdditivesAdapter(ArrayList<Additive>())
this.additives_list.layoutManager = GridLayoutManager(this.context, 2, GridLayoutManager.VERTICAL, false)
this.additives_list.adapter = this.adapter
this.viewModel = ViewModelProviders.of(this).get(AdditiveViewModel::class.java)
this.viewModel?.getAdditivesList()?.observe(this, Observer<List<Additive>> { additivesList ->
if(additivesList != null) {
this.adapter?.addItems(additivesList)
}
})
super.onActivityCreated(savedInstanceState)
}
}
现在,我的问题是为什么观察者只被调用一次(在片段的开头),然后又不被调用呢?如何使观察者不断聆听数据库中的更改(插入,更新,删除),以便可以立即更新我的recyclerView?非常感谢您的任何建议.
Now, my question is why is the observer called only once (at the start of the fragment) and then is not called back again? How can I keep the observer constantly listening to the changes in the DB (insert, update, delete) so that my recyclerView instantly can be updated? Thanks a lot for any suggestion.
推荐答案
这是您犯错的地方:
this.viewModel = ViewModelProviders.of(this).get(AdditiveViewModel::class.java)
当您在fragment
内部时正在传递this
,这对于某些人来说是非常令人不安的,因为这不是语法错误,而是合乎逻辑的.您必须通过activity!!
,它会像这样:
you are passing this
while you are inside the fragment
which is pretty disturbing for some people cause it is not a syntax error but logical. You have to pass activity!!
instead, it will be like this:
this.viewModel = ViewModelProviders.of(activity!!).get(AdditiveViewModel::class.java)
这篇关于使用Room,ViewModel和LiveData更改数据后重新加载RecyclerView的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持!