Test about live data (View Models)
- Gradle configuration
def lifecycle_version = "2.4.0-alpha02"
implementation "androidx.lifecycle:lifecycle-viewmodel-ktx:$lifecycle_version"
implementation "androidx.lifecycle:lifecycle-livedata-ktx:$lifecycle_version"
implementation "androidx.lifecycle:lifecycle-runtime-ktx:$lifecycle_version"
implementation "androidx.activity:activity-ktx:1.3.5"
implementation "androidx.fragment:fragment-ktx:1.3.5"- ViewModel
- note: Always same pattern.
private val _NAME = MutableLiveData(TYPE)
val NAME: LiveData<TYPE> get() = _NAME
class MainViewModel : ViewModel() {
private val _count = MutableLiveData(0)
val count: LiveData<Int> get() = _count
//Function that interact with private mutable livedata
fun incrementCount() {
_count.value = _count.value?.plus(1) ?: 1
}
}- Activity using ViewModel
class MainActivity : AppCompatActivity() {
private val vm by viewModels<MainViewModel>()
@SuppressLint("SetTextI18n")
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
val binding = ActivityMainBinding.inflate(layoutInflater)
setContentView(binding.root)
binding.button.setOnClickListener { vm.incrementCount() }
vm.count.observe(this, Observer {
binding.textView.text = "Counts: $it"
})
}
}For preserve state livedata, we can do:
- Using saveStateHandle passed as parameter (option 1)
class MainViewModel(private val state: SavedStateHandle) : ViewModel() {
private val _count = MutableLiveData(state["count"] ?: 0)
val count: LiveData<Int> get() = _count
fun incrementCount() {
_count.value = _count.value?.plus(1) ?: 1
state["count"] = _count.value
}
}- Using saveStateHandle passed as parameter (option 2 - easiest)
class MainViewModel(state: SavedStateHandle) : ViewModel() {
private val _count = state.getLiveData("count",0)
val count: LiveData<Int> get() = _count
fun incrementCount() {
_count.value = _count.value?.plus(1) ?: 1
}
}
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