moko-mvvm

Use EventsDispatcher<T> to send one-time events (like navigation or showing alerts) from a ViewModel to a View. This prevents memory leaks by automatically managing observers based on the lifecycle.

Common Implementation

Define an interface (e.g., EventsListener) that the View will implement. Pass the EventsDispatcher into the ViewModel constructor.

Android Implementation

1. Manual Binding: In an MvvmActivity, call viewModel.eventsDispatcher.bind(lifecycleOwner = this, listener = this) inside onCreate to attach the dispatcher to the Activity lifecycle.
2. Simplified Binding: Implement EventsDispatcherOwner<T> in your ViewModel. Then, use MvvmEventsActivity in your Activity. This automatically handles the binding of the dispatcher to the lifecycle.

iOS Implementation

On iOS, create an instance of EventsDispatcher by passing the listener (the UIViewController) directly into the constructor: EventsDispatcher<ListenerType>(listener: self). Note that bind is not used on iOS.

// commonMain
class EventsViewModel(
    val eventsDispatcher: EventsDispatcher<EventsListener>
) : ViewModel() {

    fun onButtonPressed() {
        eventsDispatcher.dispatchEvent { routeToMainPage() }
    }

    interface EventsListener {
        fun routeToMainPage()
    }
}

To create a basic ViewModel in commonMain, extend the ViewModel class and use MutableLiveData for internal state and LiveData for public exposure. You can use the .map { ... } operator to transform data for the View.

Android Integration

Use MvvmActivity to automatically load a DataBinding layout, resolve the ViewModel, and set the binding variable. You must provide the layoutId, viewModelVariableId (from your BR class), and viewModelClass. Use createViewModelFactory to instantiate your ViewModel.

In your XML layout, declare the viewModel variable in the <data> block and use the .ld suffix (e.g., @{viewModel.counter.ld}) to bind to LiveData values.

iOS Integration

In your UIViewController, instantiate the ViewModel manually. Use the bindText(liveData:) extension from the MultiPlatformLibraryMvvm CocoaPod to bind LiveData to UI elements like UILabel.

// commonMain
class SimpleViewModel : ViewModel() {
    private val _counter: MutableLiveData<Int> = MutableLiveData(0)
    val counter: LiveData<String> = _counter.map { it.toString() }

    fun onCounterButtonPressed() {
        val current = _counter.value
        _counter.value = current + 1
    }
}

The ResourceState sealed class is used to represent the lifecycle and outcome of a data-fetching operation or a resource's availability. It allows you to handle different UI states (like loading spinners, error messages, or empty states) in a type-safe manner.

Available States

• Success<T, E>: Contains the successfully retrieved data of type T.
• Failed<T, E>: Contains an error of type E.
• Loading<T, E>: Represents an ongoing operation.
• Empty<T, E>: Represents a state where no data is available (e.g., an empty list or null result).

// Example usage in a ViewModel or UI layer
val state: ResourceState<String, Exception> = ResourceState.Success("Hello World")

when (state) {
    is ResourceState.Success -> println("Data: ${state.data}")
    is ResourceState.Failed -> println("Error: ${state.error}")
    is ResourceState.Loading -> println("Loading...")
    is ResourceState.Empty -> println("No data found")
}

Combine multiple LiveData objects to create derived state, such as enabling a button only when all input fields are valid.

Using mergeWith

Use email.mergeWith(password) { email, password -> ... } to react to changes in multiple fields simultaneously and return a single calculated value.

Using all

If you have multiple boolean LiveData objects representing validation states, you can combine them using listOf(isEmailValid, isPasswordValid).all(true). This returns a LiveData<Boolean> that is true only when all inputs are true.

// Example: Merging two inputs
class ValidationMergeViewModel : ViewModel() {
    val email: MutableLiveData<String> = MutableLiveData("")
    val password: MutableLiveData<String> = MutableLiveData("")

    val isLoginButtonEnabled: LiveData<Boolean> = email.mergeWith(password) { email, password ->
        email.isNotEmpty() && password.isNotEmpty()
    }
}

// Example: Combining multiple validation flags
class ValidationAllViewModel : ViewModel() {
    val email: MutableLiveData<String> = MutableLiveData("")
    val password: MutableLiveData<String> = MutableLiveData("")

    private val isEmailValid: LiveData<Boolean> = email.map { it.isNotEmpty() }
    private val isPasswordValid: LiveData<Boolean> = password.map { it.isNotEmpty() }
    val isLoginButtonEnabled: LiveData<Boolean> = listOf(isEmailValid, isPasswordValid).all(true)
}

The following modules are available for installation (version 0.16.1):

Common Modules:

• dev.icerock.moko:mvvm-core: Basic ViewModel, EventsDispatcher, and Dispatchers.UI.
• dev.icerock.moko:mvvm-flow: Includes mvvm-core, adds CFlow for native and binding extensions.
• dev.icerock.moko:mvvm-livedata: Includes mvvm-core, adds LiveData and extensions.
• dev.icerock.moko:mvvm-state: Includes mvvm-livedata, adds ResourceState class and extensions.
• dev.icerock.moko:mvvm-livedata-resources: Includes mvvm-core, adds moko-resources extensions for LiveData.
• dev.icerock.moko:mvvm-flow-resources: Includes mvvm-core, adds moko-resources extensions for Flow.

Compose Multiplatform Modules:

• dev.icerock.moko:mvvm-compose: Includes mvvm-core, adds getViewModel for Compose Multiplatform.
• dev.icerock.moko:mvvm-flow-compose: Includes mvvm-flow, adds binding extensions for Compose Multiplatform.
• dev.icerock.moko:mvvm-livedata-compose: Includes mvvm-livedata, adds binding extensions for Compose Multiplatform.

Android Specific Modules:

• dev.icerock.moko:mvvm-livedata-material: Material library extensions.
• dev.icerock.moko:mvvm-livedata-glide: Glide library extensions.
• dev.icerock.moko:mvvm-livedata-swiperefresh: SwipeRefreshLayout library extensions.
• dev.icerock.moko:mvvm-databinding: DataBinding support.
• dev.icerock.moko:mvvm-viewbinding: ViewBinding support.

Testing:

• dev.icerock.moko:mvvm-test: Test utilities.

// Example dependency selection
commonMainApi("dev.icerock.moko:mvvm-core:0.16.1")
commonMainApi("dev.icerock.moko:mvvm-flow:0.16.1")
commonMainApi("dev.icerock.moko:mvvm-livedata:0.16.1")