Notes App in Jetpack Compose with Room Database (2026)

package com.example.notes

import android.os.Bundle
import androidx.activity.ComponentActivity
import androidx.activity.compose.setContent
import androidx.activity.enableEdgeToEdge
import androidx.compose.material3.SnackbarHostState
import androidx.compose.material3.SnackbarResult
import androidx.compose.runtime.Composable
import androidx.compose.runtime.LaunchedEffect
import androidx.compose.runtime.getValue
import androidx.compose.runtime.mutableStateOf
import androidx.compose.runtime.remember
import androidx.compose.runtime.rememberCoroutineScope
import androidx.compose.runtime.setValue
import androidx.lifecycle.compose.collectAsStateWithLifecycle
import androidx.lifecycle.viewmodel.compose.viewModel
import androidx.navigation.NavType
import androidx.navigation.compose.NavHost
import androidx.navigation.compose.composable
import androidx.navigation.compose.rememberNavController
import androidx.navigation.navArgument
import com.example.notes.data.Note
import com.example.notes.ui.EditNoteScreen
import com.example.notes.ui.NotesScreen
import com.example.notes.ui.theme.NotesTheme
import kotlinx.coroutines.launch

class MainActivity : ComponentActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        enableEdgeToEdge()
        setContent { NotesTheme { NotesApp() } }
    }
}

/** Two screens: the list ("notes") and the editor ("edit/{id}", where id 0 means a new note). */
@Composable
fun NotesApp(viewModel: NotesViewModel = viewModel()) {
    val nav = rememberNavController()
    val snackbar = remember { SnackbarHostState() }
    val scope = rememberCoroutineScope()

    NavHost(navController = nav, startDestination = "notes") {
        composable("notes") {
            val notes by viewModel.notes.collectAsStateWithLifecycle()
            val query by viewModel.query.collectAsStateWithLifecycle()
            NotesScreen(
                notes = notes,
                query = query,
                snackbar = snackbar,
                onQueryChange = viewModel::onQueryChange,
                onOpen = { nav.navigate("edit/${it.id}") },
                onNew = { nav.navigate("edit/0") },
                onTogglePin = { viewModel.togglePin(it) },
            )
        }
        composable("edit/{id}", arguments = listOf(navArgument("id") { type = NavType.LongType })) { entry ->
            val id = entry.arguments?.getLong("id") ?: 0L
            // Load the note once; a new note starts empty.
            var note by remember { mutableStateOf<Note?>(if (id == 0L) Note(title = "", content = "") else null) }
            LaunchedEffect(id) { if (id != 0L) note = viewModel.load(id) }

            note?.let { current ->
                EditNoteScreen(
                    note = current,
                    onSave = {
                        viewModel.save(it)
                        nav.popBackStack()
                    },
                    onDelete = {
                        viewModel.delete(it)
                        nav.popBackStack()
                        scope.launch {
                            val result = snackbar.showSnackbar("Note deleted", actionLabel = "Undo", withDismissAction = true)
                            if (result == SnackbarResult.ActionPerformed) viewModel.restore(it)
                        }
                    },
                )
            }
        }
    }
}