Top 5 Mistakes Android Developers Make While Using MVVM

Model-View-ViewModel (MVVM) has become the go-to architectural pattern for Android development, helping developers create scalable, testable, and maintainable applications. However, many developers still fall into common pitfalls while implementing MVVM, leading to issues like poor performance, unnecessary complexity, and difficult-to-maintain code.

In this article, we will highlight the top five mistakes developers make when using MVVM and how to avoid them.

1. Putting Business Logic in the ViewModel

One of the most common mistakes in MVVM is placing business logic inside the ViewModel. While ViewModel is responsible for holding UI-related data, business logic should reside in the repository or use-case layer to ensure better separation of concerns.

Why is this a problem?

• Increases the complexity of ViewModel.

• Makes it harder to test since ViewModels become bloated with logic.

• Violates the Single Responsibility Principle (SRP).

Solution:

• Move business logic to repository or use-case classes.

• Keep ViewModel lightweight by only exposing UI state and calling necessary methods from repositories.

2. Using LiveData for Everything

LiveData is a powerful tool, but using it everywhere can lead to unnecessary reactivity and performance issues. Many developers make the mistake of using LiveData even when a simple data holder like a sealed class or a coroutine suspend function would suffice.

Why is this a problem?

• Overuse of LiveData can introduce memory leaks if not handled properly.

• Leads to excessive observer updates, which may slow down UI performance.

• Unnecessary state retention, making debugging harder.

Solution:

• Use LiveData only for UI-related data that needs to be observed.

• For one-time events, use SingleLiveEvent or SharedFlow.

• Use coroutines and suspend functions for simple data retrieval.

3. Not Handling UI State Properly

Managing UI state correctly is crucial for a smooth user experience. Many developers fail to properly handle loading, success, and error states, leading to unpredictable UI behavior.

Why is this a problem?

• Causes unexpected crashes or freezes in the app.

• Leads to a poor user experience due to lack of error handling.

• Makes the code harder to read and maintain.

Solution:

• Use a sealed class to represent different UI states (Loading, Success, Error).

• Implement error handling properly in repositories and propagate errors gracefully.

• Leverage StateFlow or LiveData to update the UI in response to state changes.

Example:

sealed class UIState<out T> {
    object Loading : UIState<Nothing>()
    data class Success<T>(val data: T) : UIState<T>()
    data class Error(val message: String) : UIState<Nothing>()
}

4. Not Using Dependency Injection Properly

Dependency Injection (DI) simplifies object creation and improves code testability. However, many developers either avoid using DI or misuse it, leading to tight coupling and difficult-to-maintain code.

Why is this a problem?

• Makes testing difficult as dependencies cannot be easily replaced.

• Results in tight coupling between components, reducing reusability.

• Leads to code duplication and improper resource management.

Solution:

• Use DI frameworks like Dagger-Hilt or Koin to manage dependencies.

• Inject repositories and other dependencies into ViewModel instead of instantiating them inside.

• Avoid manual dependency creation to keep the architecture clean.

Example Using Hilt:

@HiltViewModel
class MyViewModel @Inject constructor(private val repository: MyRepository) : ViewModel() {
    val data = repository.getData()
}

5. Ignoring Unit Testing

Many developers neglect unit testing in MVVM applications, assuming it is not necessary. However, skipping unit tests can lead to fragile code that is difficult to maintain and debug.

Why is this a problem?

• Bugs become harder to catch before deployment.

• Refactoring becomes risky since there are no tests to ensure existing functionality remains intact.

• Debugging becomes more time-consuming.

Solution:

• Write unit tests for repositories, ViewModels, and use-cases.

• Use Mockito or MockK for mocking dependencies in tests.

• Leverage CoroutineTestRule to test coroutines efficiently.

Example Unit Test for ViewModel:

@RunWith(AndroidJUnit4::class)
class MyViewModelTest {
    private lateinit var viewModel: MyViewModel
    private val repository = mockk<MyRepository>()

    @Before
    fun setUp() {
        viewModel = MyViewModel(repository)
    }

    @Test
    fun `test ViewModel returns correct data`() = runBlockingTest {
        coEvery { repository.getData() } returns flowOf("Test Data")
        assertEquals("Test Data", viewModel.data.value)
    }
}

Conclusion

MVVM is a powerful architecture for Android development, but avoiding these common mistakes is key to making the most of it. By keeping business logic out of ViewModels, using LiveData wisely, managing UI state properly, leveraging dependency injection, and writing unit tests, developers can build cleaner, more maintainable applications.

Have you encountered any of these mistakes in your Android projects? Share your thoughts in the comments below!