IntelliJ File Template for Android App Development work.

01ViewModelTemplate

package ${PACKAGE_NAME}

import androidx.annotation.MainThread
import androidx.lifecycle.*
import kotlinx.coroutines.coroutineScope


#parse("File Header.java")
class ${NAME} (
    private val getFooUseCase: GetFooUseCase
) : ViewModel() {

    // State of ViewModel
    private class State(
        val getFooResult: LiveData<GetFooResult>,
        val selectedFoo: MutableLiveData<SelectedFoo> = MutableLiveData<SelectedFoo>(SelectedFoo.None)
    ) {
        val isAnySelected: Boolean
            get() = selectedFoo.value != SelectedFoo.None

        val result: Result
            get() = Result(getFooResult = getFooResult.value!!)
    }
    // Snapshot of State: customize parameter and add other results on demand.
    data class Result(val getFooResult: GetFooResult)

    private val _state = State(
        getFooResult = liveData(context = viewModelScope.coroutineContext) {
            val result = getFooUseCase.load()
            emit(result)
        }
    )

    private val _result: MutableLiveData<Result> = MutableLiveData()

    val foo: LiveData<Foo>
        get() = _state.getFooResult.filterIsInstance<GetFooResult.Success>()
            .map { it.foo }

    val foos: LiveData<List<Foo>>
        get() = _state.getFooResult.filterIsInstance<GetFooResult.Success2>()
            .map { it.foos }

    val error: LiveData<Throwable>
        get() = _state.getFooResult.filterIsInstance<GetFooResult.Error>()
            .map { it.error }

    val goToNext: LiveData<Result>
        get() = _result

    fun onClickNext() {
        _result.value = _state.result
    }
}

class GetFooUseCase() {
    suspend fun load() = coroutineScope {
        runCatching {
            Foo()
        }.fold(onSuccess = {
            GetFooResult.Success(it)
        }, onFailure = {
            GetFooResult.Error(it)
        })
    }
}

sealed class GetFooResult {
    // customize on demand
    data class Success(val foo: Foo) : GetFooResult()
    data class Success2(val foos: List<Foo>) : GetFooResult()
    data class Error(val error: Throwable) : GetFooResult()
}


data class Foo(val id: String = "dummyId")
sealed class SelectedFoo {
    object None: SelectedFoo()
    // add on demand
}


// replace LiveData extension functions following if defined in other files.

@MainThread
@Suppress("UNCHECKED_CAST")
inline fun <reified R> LiveData<*>.filterIsInstance(): LiveData<R> = filter { it is R } as LiveData<R>

@MainThread
inline fun <X> LiveData<X>.filter(crossinline predicate: (X) -> Boolean): LiveData<X> = this.transform { x ->
    if (predicate(x))  this.value = x
}

@MainThread
inline fun <X, Y> LiveData<X>.transform(
    crossinline transform: MediatorLiveData<Y>.(value: X) -> Unit
): LiveData<Y> {
    val result = MediatorLiveData<Y>()
    result.addSource(
        this
    ) { x ->
        result.transform(x)
    }
    return result
}

02LiveDataEx.kt

@MainThread
@Suppress("UNCHECKED_CAST")
inline fun <reified R> LiveData<*>.filterIsInstance(): LiveData<R> = filter { it is R } as LiveData<R>

@MainThread
inline fun <X> LiveData<X>.filter(crossinline predicate: (X) -> Boolean): LiveData<X> = this.transform { x ->
    if (predicate(x))  this.value = x
}

@MainThread
inline fun <X, Y> LiveData<X>.transform(
    crossinline transform: MediatorLiveData<Y>.(value: X) -> Unit
): LiveData<Y> {
    val result = MediatorLiveData<Y>()
    result.addSource(
        this
    ) { x ->
        result.transform(x)
    }
    return result
}

jp:
01ViewModelTemplate: 一つのファイルで完結できるようにしたものです。
02LiveDataEx.kt: こちらを別ファイルに定義した場合は重複を取り除いてください。

en:
01ViewModelTemplate: It can be completed with one file.
02LiveDataEx.kt: If you define this in another file, please remove the duplication.