我有allRecords
-通过存储库从 session 室获得的实时数据值。
我希望handleSelectedItem
方法更改与ID匹配的LiveData<List<...>>
中一项的值。
我尝试使用Transformation.map()完成此操作,但是此代码不起作用
class RecordListViewModel @Inject constructor(val repository: RecordRepository): ViewModel() {
private var allRecords : LiveData<List<RecordItem>> = Transformations.map(repository.getAllRecording()){
records -> return@map records.map{ it.toItem()}
}
fun getAllRecords() : LiveData<List<RecordItem>>{
return allRecords
}
fun handleSelectedItem(id : Int) {
Log.d("HandleSelectedItem", "Test1")
allRecords = Transformations.map(allRecords) { records ->
return@map records.map {
if (it.id == id){
Log.d("HandleSelectedItem", "Test2")
it.copy(isSelected = true)
}
else{
Log.d("HandleSelectedItem", "Test3")
it.copy(isSelected = false)
}
}
}
}
}
帮助解决这个问题
更新
这里提供
MutableLiveData
而不是LiveData
。然后存储库和Dao都应返回MutableLiveData
存储库
fun getAllRecording(): MutableLiveData<List<RecordEntity>> =
appDatabase.getRecordDao().getAllRecording()
道
@Query("SELECT * FROM record")
fun getAllRecording() : MutableLiveData<List<RecordEntity>>
但是Room数据库无法返回MutableLiveData
错误
D:\Project\VoiceRecording\app\build\tmp\kapt3\stubs\debug\ru\ddstudio\voicerecording\data\database\daos\RecordDao.java:17: error: Not sure how to convert a Cursor to this method's return type (androidx.lifecycle.MutableLiveData<java.util.List<ru.ddstudio.voicerecording.data.database.entities.RecordEntity>>).
public abstract androidx.lifecycle.MutableLiveData<java.util.List<ru.ddstudio.voicerecording.data.database.entities.RecordEntity>> getAllRecording();
更新2
private val allRecords = MediatorLiveData<List<RecordItem>>().apply {
val recordsRepository = repository.getAllRecording().map { records -> records.map { it.toItem() } }
addSource(recordsRepository)
}
错误
addSource()
None of the following functions can be called with the arguments supplied:
@MainThread public final fun <S : Any!> addSource(@NonNull p0: LiveData<List<RecordItem>!>, @NonNull p1: (List<RecordItem>!) -> Unit): Unit defined in androidx.lifecycle.MediatorLiveData
@MainThread public open fun <S : Any!> addSource(@NonNull p0: LiveData<List<RecordItem>!>, @NonNull p1: Observer<in List<RecordItem>!>): Unit defined in androidx.lifecycle.MediatorLiveData
最佳答案
您的LiveData
对象应该是val
。使用MutableLiveData
/ MediatorLiveData
和setValue
或postValue
更改LiveData
中的值
class RecordListViewModel @Inject constructor(val repository: RecordRepository): ViewModel() {
private val allRecords = MediatorLiveData<List<RecordItem>>().apply {
val recordsLiveData = repository.getAllRecording().map { records -> records.map { it.toItem() } }
addSource(recordsLiveData) { records ->
value = records
}
}
fun getAllRecords() : LiveData<List<RecordItem>> {
return allRecords
}
fun handleSelectedItem(id : Int) {
Log.d("HandleSelectedItem", "Test1")
allRecords.value?.let { records ->
allRecords.value = records.map { it.copy(isSelected = it.id == id) }
}
}
}
不,不应该。在
LiveData
和DAO
中使用Repository