viewModel() ใน Composable

Inside a Composable you don’t construct a ViewModel with new. Instead you call the viewModel() function to fetch the right instance.

The viewModel() helper looks up the nearest lifecycle owner and returns the ViewModel scoped to it, creating one only if none exists yet.

Recomposition runs your function many times, yet viewModel() returns the same instance each time, so your state never resets unexpectedly.

Once you hold the ViewModel, read its observable state and your Composable redraws whenever that state changes. The UI follows the data. 🔗

Send user actions to the ViewModel by calling its functions from event lambdas, keeping the decision-making logic out of your Composable.

The function comes from the lifecycle Compose artifact. Import androidx.lifecycle.viewmodel.compose.viewModel to use it.

By default the ViewModel is scoped to the host Activity or navigation destination, so all Composables in that scope share one instance. 🎯

Need to pass dependencies? Provide a factory so the framework knows how to build a ViewModel that has constructor parameters.

Call viewModel() high up, near the screen root, then pass plain state and callbacks down to keep child Composables reusable.

Because viewModel() needs a real owner, design children to take simple parameters so they still render in an isolated @Preview.

The common flow is simple: obtain the ViewModel, read its state, and forward events to its functions. Three steps, every screen. ✨

Check how you obtain a ViewModel from a Composable.

Call viewModel() to fetch a scoped ViewModel, read its state to drive the UI, and forward user events to its functions instead of constructing it yourself.