MVVM pattern in Android Kotlin - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a ViewModel class in Kotlin.

Android Kotlin

class MyViewModel : [1]() {
  // ViewModel logic here
}

Drag options to blanks, or click blank then click option'

AService

BViewModel

CFragment

DActivity

Attempts:

3 left

💡 Hint

Common Mistakes

Extending Activity or Fragment instead of ViewModel.

Forgetting to extend any class.

The ViewModel class in Android is declared by extending the ViewModel class.

2fill in blank

medium

Complete the code to observe LiveData from the ViewModel in an Activity.

Android Kotlin

viewModel.data.observe([1]) { value ->
  // update UI with value
}

Drag options to blanks, or click blank then click option'

Athis

BlifecycleOwner

CviewLifecycleOwner

Dcontext

Attempts:

3 left

💡 Hint

Common Mistakes

Using viewLifecycleOwner in an Activity.

Passing null or wrong context.

In an Activity, this refers to the LifecycleOwner needed to observe LiveData.

3fill in blank

hard

Fix the error in the ViewModel factory code to create a ViewModel with parameters.

Android Kotlin

class MyViewModelFactory(private val repo: Repository) : ViewModelProvider.[1] {
  override fun <T : ViewModel> create(modelClass: Class<T>): T {
    if (modelClass.isAssignableFrom(MyViewModel::class.java)) {
      return MyViewModel(repo) as T
    }
    throw IllegalArgumentException("Unknown ViewModel class")
  }
}

Drag options to blanks, or click blank then click option'

AFactory

BNewInstanceFactory

CProviderFactory

DViewModelFactory

Attempts:

3 left

💡 Hint

Common Mistakes

Extending a non-existent class.

Not overriding the create method properly.

The correct interface to implement for a ViewModel factory is ViewModelProvider.Factory.

4fill in blank

hard

Fill both blanks to create a LiveData property in ViewModel and expose it as immutable LiveData.

Android Kotlin

private val _data = MutableLiveData<String>()
val data: LiveData<String> = _data[1][2]

Drag options to blanks, or click blank then click option'

AasLiveData()

Bget()

D.value

Attempts:

3 left

💡 Hint

Common Mistakes

Calling .value or asLiveData() unnecessarily.

Trying to create a new LiveData instance.

To expose immutable LiveData, just assign the MutableLiveData to LiveData without extra calls.

5fill in blank

hard

Fill all three blanks to update LiveData value safely from a background thread.

Android Kotlin

fun fetchData() {
  viewModelScope.[1] {
    val result = repository.getData()
    _data.[2] = result
    // or use _data.[3](result) if needed
  }
}

Drag options to blanks, or click blank then click option'

Alaunch

BpostValue

Cvalue

Dasync

Attempts:

3 left

💡 Hint

Common Mistakes

Using async without awaiting.

Setting LiveData value from background thread directly.

Use launch to start a coroutine, update LiveData's value on main thread, or postValue from background thread.