What is MVVM?

MVVM is a design pattern that separates the presentation logic from the business logic of an application. It consists of three main components:

Model: Represents the data and business logic of the application.

View: Represents the user interface of the application.

ViewModel: Acts as a mediator between the Model and the View. It exposes the data from the Model to the View and handles user actions from the View.

The main advantage of using MVVM is that it makes the code more modular, testable, and maintainable.

What is Jetpack Compose?

Jetpack Compose is a modern toolkit for building Android UIs. It uses a declarative programming model, which means that developers describe the UI components and their properties in a concise and readable way. Compose also provides a powerful layout system that allows developers to create responsive and flexible UIs.

The main advantage of using Jetpack Compose is that it simplifies the UI development process and makes it easier to create beautiful and performant UIs.

How to use Jetpack Compose with MVVM

To use Jetpack Compose with MVVM, we need to follow these steps:

Create the Model: We create a data class that represents the data of our application. For example, if we are building a weather app, we can create a data class that represents the weather data.

Create the ViewModel: We create a ViewModel class that exposes the data from the Model to the View. For example, we can create a ViewModel class that fetches the weather data from an API and exposes it to the View.

Create the View: We create a Composable function that represents the UI of our application. For example, we can create a Composable function that displays the weather data in a card view.

Connect the ViewModel to the View: We use the getViewModel function provided by Koin to create an instance of the ViewModel and pass it to the Composable function. For example, we can use the remember function to create an instance of the WeatherViewModel and pass it to the Composable function that displays the weather data.

Here is an example code snippet that demonstrates how to use Jetpack Compose with MVVM:

data class Weather(val city: String, val temperature: Int)
  
class WeatherViewModel : ViewModel() {
    private val _uiState: MutableStateFlow<Weather> = MutableStateFlow(Weather("", 0))
    val uiState = _uiState.asStateFlow()
  
    fun fetchWeather() {
        // Fetch weather data from API and update _uiState
    }
}

@Composable
fun WeatherView(weatherViewModel: WeatherViewModel) {
    val weather by weatherViewModel.weather.collectAsStateWithLifecycle()
    Card {
        Column {
            Text(text = weather.city)
            Text(text = weather.temperature.toString())
        }
    }
}

@Composable
fun MyApp() {
    val weatherViewModel = getViewModel<WeatherViewModel>()                           
    WeatherView(weatherViewModel)
}

In this example, we create a Weather data class that represents the weather data. We also create a WeatherViewModel class that fetches the weather data from an API and exposes it to the View. We then create a WeatherView Composable function that displays the weather data in a card view. We use the getViewModel function to get the instance of the WeatherViewModel and pass it to the WeatherView Composable function. Finally, to collect state in Compose, use collectAsStateWithLifecycle to make it lifecycle-aware. It starts and stops collecting automatically when the Composable is visible or hidden on the screen, avoiding unnecessary resource usage, even when the app is in the background.

Benefits of using MVVM with Jetpack Compose

One of the benefits of using MVVM with Jetpack Compose is that it allows for reactive programming, which fits well with declarative UI and separation of concerns. Reactive programming is a programming paradigm that emphasizes the propagation of data changes and how those changes affect other parts of an application. In an MVVM architecture, the ViewModel acts as a mediator between the Model and the View, which makes it easier to propagate data changes from the Model to the View in a reactive way.

By using reactive programming with Jetpack Compose, developers can create UIs that automatically update themselves when their underlying data changes. This eliminates the need for manual updates and reduces template code. Additionally, by separating the presentation logic from the business logic, developers can focus on each concern separately and make changes without affecting other parts of the application.

Overall, it also makes code more modular, testable, and maintainable by separating concerns and enabling reactive programming.

Conclusion

In this blog post, we explored how to use Jetpack Compose with MVVM to build a modern Android application. We learned that MVVM is a design pattern that separates the presentation logic from the business logic of an application, while Jetpack Compose is a modern toolkit for building Android UIs. Compose’s declarative nature is an excellent fit for this architectural pattern that use observable UI state as the source of truth for the UI.