ViewModel Savedstate Helpers

Helper to access easily save the ViewModel state for Activity restoration.

Installation

In your root build.gradle at the end of repositories:

allprojects {
    repositories {
        ...
        maven { url 'https://jitpack.io' }
    }
}

In your app build.gradle, add the dependencies:

dependencies {
    // Add this if you don't have it already
    implementation 'androidx.lifecycle:lifecycle-viewmodel-savedstate:1.0.0-rc02'

    // viewmodel-savedstate-helpers
    implementation 'com.github.liip:viewmodel-savedstate-helpers:1.0.1-rc02'
}

Usage

Implement your ViewModel

// Import the library
import ch.liip.viewmodelsavedstatehelpers.*

// Define a ViewModel that takes a SavedStateHandle in argument
class MainViewModel(handle: SavedStateHandle) : ViewModel() {
    // Simple string that is saved in the SavedState
    var manualText by handle.delegate<String?>()

    // MutableLiveData that is saved in the SavedState
    val liveDataText by handle.livedata<String?>()
}

Use your ViewModel

Create your ViewModel like explained in the official documentation.

val vm = ViewModelProvider(this, SavedStateVMFactory(this)).get(MainViewModel::class.java)

You can then use the ViewModel like you would do usually. Your data is saved and restored automatically!

override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setContentView(R.layout.activity_main)

    // Obtain the ViewModel with SavedStateVMFactory
    viewModel = ViewModelProviders.of(this, SavedStateVMFactory(this)).get(MainViewModel::class.java)

    // Observe the livedata
    viewModel.liveDataText.observe(this, Observer {
        liveDataText.setText(it)
    })

    // Save the values
    button.setOnClickListener {
        viewModel.liveDataText.value = liveDataText.text.toString()
    }
}

Demo app

You can check the demo Android application to see it in action.

Blogpost

Read the accompanying blogpost on liip.ch.