Tips

Use derived props when possible :id=derived

Derived properties are extremely useful at scale because they are so easy to reason about and test. Whenever something can be modeled as a derived property, you probably should put it there. Examples:

data class CounterState(
    val count: Int = 0
) : MavericksState {
    val isEven = count % 2 == 0
}

data class SignUpState(
    val firstName: String = "",
    val lastName: String = "",
    val email: String = ""
) : MavericksState {
    val hasName = firstName.isNotBlank() && lastName.isNotBlank()

    val hasValidEmail = EMAIL_PATTERN.matches(email)

    val canSubmitForm = hasName && hasValidEmail
}

Working with immutable maps

Use custom copy and delete extension functions and treat them similar to data classes:

setState { copy(yourMap = yourMap.copy(“a” to 1, “b” to 2)) }

or

setState { copy(yourMap = yourMap.delete(“a”, “b”)) }

Drive animations from ViewModel.onEach

You may use an onEach callback to drive an animation or show an error for a specific amount of time like this:

viewModel.onAsync(YourState::yourProp, onFail = {
    binding.error.isVisible = true
    delay(4000)
    binding.error.isVisible = false
})

If your Fragment View gets destroyed, Mavericks will stop emitting new values but it will not cancel any existing ones. In this case, if the Fragment view gets destroyed during the delay, your app will crash when you try and access it to hide the error after 4 seconds. To get around this, replace that code with:

viewModel.onAsync(YourState::yourProp, onFail = {
    viewLifecycleOwner.lifecycleScope.whenStarted {
        binding.error.isVisible = true
        delay(4000)
        binding.error.isVisible = false
    }
})

whenStarted is part of Jetpack's lifecycle aware coroutine support.