Unable to set value in LiveData-CodePudding

I am unable to set value to LiveData variable which is declared as MutableLiveData. The value i am trying to set is LiveData returned from repository.

Please find below the classes.

Viewmodel.class

    // Variable to hold list of tasks Livedata
    private val _tasks=MutableLiveData<List<TaskEntity>>()
    val tasks:LiveData<List<TaskEntity>>
        get() = _tasks

    init{
        getTasksFromDb()
    }

    private fun getTasksFromDb(){
        viewModelScope.launch {
             try {
                _tasks.value=taskRepository.getAllTasks() // Showing error here
            }catch(exception:Exception){
                Log.d(TAG,"Error " exception.message)
            }
        }
    }

Repository

class TaskRepository (val taskDb: TaskDatabase){

    suspend fun insert(taskEntity: TaskEntity)=
        taskDb.taskDao.insert(taskEntity)

    fun update(taskEntity: TaskEntity)=
        taskDb.taskDao.update(taskEntity)

    fun delete(taskEntity: TaskEntity)=
        taskDb.taskDao.delete(taskEntity)

    fun getAllTasks():LiveData<List<TaskEntity>> =
        taskDb.taskDao.getAllTasks()
}

DAO

@Dao
interface TaskDao {

    @Insert
    fun insert(taskEntity: TaskEntity)

    @Update
    fun update(taskEntity: TaskEntity)

    @Delete
    fun delete(taskEntity: TaskEntity)

    @Query("SELECT * FROM tasks")
    fun getAllTasks():LiveData<List<TaskEntity>>
}

Here the declared variable as well as the value I am trying to assign is also LiveData.Still its giving the error

Type mismatch: 

Required : List<Entity>, Found: LiveData<List<Entity>>

Can somebody help me in finding what is the issue here ?

CodePudding user response：

The error is self-explanatory. It expects a List but you are trying to assign a LiveData. So you could for example just get the value from the LiveData like this:

_tasks.value=taskRepository.getAllTasks().value

That should get rid of the error, although I'm not sure if that would be the correct implementation

CodePudding user response：

If working in some background thread, then you can't use setValue. You have to use postValue here with some observer.

liveData.postValue("someNewData")

CodePudding user response：

First the Livedata.value require a type of Livedata Generic

val liveData = MutableLiveData<Boolean>()
val liveDataTemp = MutableLiveData<Boolean>()
liveData.value = true //current
liveData.value = liveDataTemp //error

If I understand currently you want observe alltask in activity or fragment.
The following code could help you.
ViewModel

fun getAllTask():LiveData<List<TaskEntity>>(){
    return taskRepository.getAllTasks()
}

Activity or Fragment

viewModel.getAllTask().observer(this){
    list -> TODO()
}