Add Snackbar handling

app/src/main/java/com/jshvarts/conditionalbottomnav/MainActivity.kt

@@ -1,18 +1,19 @@
 package com.jshvarts.conditionalbottomnav
 
+import android.content.res.Resources
 import android.os.Bundle
 import androidx.activity.ComponentActivity
 import androidx.activity.compose.setContent
 import androidx.compose.foundation.isSystemInDarkTheme
 import androidx.compose.foundation.layout.fillMaxSize
 import androidx.compose.foundation.layout.padding
+import androidx.compose.foundation.layout.systemBarsPadding
 import androidx.compose.material.*
-import androidx.compose.runtime.Composable
-import androidx.compose.runtime.DisposableEffect
-import androidx.compose.runtime.Stable
-import androidx.compose.runtime.remember
+import androidx.compose.runtime.*
 import androidx.compose.ui.Modifier
 import androidx.compose.ui.graphics.Color
+import androidx.compose.ui.platform.LocalConfiguration
+import androidx.compose.ui.platform.LocalContext
 import androidx.compose.ui.res.colorResource
 import androidx.compose.ui.res.painterResource
 import androidx.compose.ui.res.stringResource
@@ -25,11 +26,14 @@ import androidx.navigation.compose.NavHost
 import androidx.navigation.compose.currentBackStackEntryAsState
 import androidx.navigation.compose.rememberNavController
 import com.google.accompanist.systemuicontroller.rememberSystemUiController
+import com.jshvarts.conditionalbottomnav.model.SnackbarManager
 import com.jshvarts.conditionalbottomnav.navigation.BottomBarTab
 import com.jshvarts.conditionalbottomnav.navigation.HOME_GRAPH
 import com.jshvarts.conditionalbottomnav.navigation.HomeDestinations.HOME_ITEM_ROUTE
 import com.jshvarts.conditionalbottomnav.navigation.navGraph
 import com.jshvarts.conditionalbottomnav.ui.theme.ConditionalBottomNavTheme
+import kotlinx.coroutines.CoroutineScope
+import kotlinx.coroutines.launch
 
 class MainActivity : ComponentActivity() {
   override fun onCreate(savedInstanceState: Bundle?) {
@@ -58,18 +62,26 @@ class MainActivity : ComponentActivity() {
 @Composable
 fun App() {
   ConditionalBottomNavTheme {
-    val appState = rememberAppState()
-    Scaffold(
-      bottomBar = {
-        if (appState.shouldShowBottomBar) {
-          BottomBar(
-            tabs = appState.bottomBarTabs,
-            currentRoute = appState.currentRoute!!,
-            navigateToRoute = appState::navigateToBottomBarRoute
-          )
-        }
-      }
-    ) { innerPaddingModifier ->
+val appState = rememberAppState()
+Scaffold(
+  bottomBar = {
+    if (appState.shouldShowBottomBar) {
+      BottomBar(
+        tabs = appState.bottomBarTabs,
+        currentRoute = appState.currentRoute!!,
+        navigateToRoute = appState::navigateToBottomBarRoute
+      )
+    }
+  },
+  snackbarHost = {
+    SnackbarHost(
+      hostState = it,
+      modifier = Modifier.systemBarsPadding(),
+      snackbar = { snackbarData -> Snackbar(snackbarData) }
+    )
+  },
+  scaffoldState = appState.scaffoldState
+) { innerPaddingModifier ->
       NavHost(
         navController = appState.navController,
         startDestination = HOME_GRAPH,
@@ -86,16 +98,45 @@ fun App() {
 
 @Composable
 fun rememberAppState(
-  navController: NavHostController = rememberNavController()
+  scaffoldState: ScaffoldState = rememberScaffoldState(),
+  navController: NavHostController = rememberNavController(),
+  snackbarManager: SnackbarManager = SnackbarManager,
+  resources: Resources = resources(),
+  coroutineScope: CoroutineScope = rememberCoroutineScope()
 ) =
-  remember(navController) {
-    AppState(navController)
+  remember(scaffoldState, navController, snackbarManager, resources, coroutineScope) {
+    AppState(scaffoldState, navController, snackbarManager, resources, coroutineScope)
   }
 
 @Stable
 class AppState(
-  val navController: NavHostController
+  val scaffoldState: ScaffoldState,
+  val navController: NavHostController,
+  private val snackbarManager: SnackbarManager,
+  private val resources: Resources,
+  coroutineScope: CoroutineScope
 ) {
+  // Process snackbars coming from SnackbarManager
+  init {
+    coroutineScope.launch {
+      snackbarManager.messages.collect { currentMessages ->
+        if (currentMessages.isNotEmpty()) {
+          val message = currentMessages[0]
+          val text = resources.getText(message.messageId)
+
+          // Display the snackbar on the screen. `showSnackbar` is a function
+          // that suspends until the snackbar disappears from the screen
+          scaffoldState.snackbarHostState.showSnackbar(text.toString())
+          // Once the snackbar is gone or dismissed, notify the SnackbarManager
+          snackbarManager.setMessageShown(message.id)
+        }
+      }
+    }
+  }
+
+  // ----------------------------------------------------------
+  // BottomBar state source of truth
+  // ----------------------------------------------------------
   val bottomBarTabs = BottomBarTab.values()
   private val bottomBarRoutes = bottomBarTabs.map { it.route }
 
@@ -140,6 +181,17 @@ private tailrec fun findStartDestination(graph: NavDestination): NavDestination
   return if (graph is NavGraph) findStartDestination(graph.startDestination!!) else graph
 }
 
+/**
+ * A composable function that returns the [Resources]. It will be recomposed when `Configuration`
+ * gets updated.
+ */
+@Composable
+@ReadOnlyComposable
+private fun resources(): Resources {
+  LocalConfiguration.current
+  return LocalContext.current.resources
+}
+
 @Composable
 fun BottomBar(
   tabs: Array<BottomBarTab>,

app/src/main/java/com/jshvarts/conditionalbottomnav/Screens.kt

@@ -16,6 +16,8 @@ import androidx.compose.ui.Modifier
 import androidx.compose.ui.graphics.Color
 import androidx.compose.ui.res.stringResource
 import androidx.compose.ui.unit.dp
+import com.jshvarts.conditionalbottomnav.model.SnackbarManager
+import kotlin.random.Random
 
 @Composable
 fun HomeScreen(
@@ -98,10 +100,14 @@ fun HomeItemDetailScreen(
         .padding(innerPaddingModifier)
         .fillMaxSize()
     ) {
-      Text(
-        text = "Home Item $itemId",
-        style = MaterialTheme.typography.h6
-      )
+      if (ifRandomlyFailed()) {
+        SnackbarManager.showMessage(R.string.item_lookup_failed_error)
+      } else {
+        Text(
+          text = "Home Item $itemId",
+          style = MaterialTheme.typography.h6
+        )
+      }
     }
   }
 }
@@ -128,3 +134,5 @@ fun HomeItemCard(
     )
   }
 }
+
+private fun ifRandomlyFailed() = Random.nextBoolean()

app/src/main/java/com/jshvarts/conditionalbottomnav/model/SnackbarManager.kt

@@ -0,0 +1,35 @@
+package com.jshvarts.conditionalbottomnav.model
+
+import androidx.annotation.StringRes
+import kotlinx.coroutines.flow.MutableStateFlow
+import kotlinx.coroutines.flow.StateFlow
+import kotlinx.coroutines.flow.asStateFlow
+import kotlinx.coroutines.flow.update
+import java.util.*
+
+
+data class Message(val id: Long, @StringRes val messageId: Int)
+
+/**
+ * Class responsible for managing Snackbar messages to show on the screen
+ */
+object SnackbarManager {
+
+  private val _messages: MutableStateFlow<List<Message>> = MutableStateFlow(emptyList())
+  val messages: StateFlow<List<Message>> get() = _messages.asStateFlow()
+
+  fun showMessage(@StringRes messageTextId: Int) {
+    _messages.update { currentMessages ->
+      currentMessages + Message(
+        id = UUID.randomUUID().mostSignificantBits,
+        messageId = messageTextId
+      )
+    }
+  }
+
+  fun setMessageShown(messageId: Long) {
+    _messages.update { currentMessages ->
+      currentMessages.filterNot { it.id == messageId }
+    }
+  }
+}

app/src/main/res/values/strings.xml

@@ -5,4 +5,5 @@
     <string name="chat">Chat</string>
     <string name="item_detail">Item Detail</string>
     <string name="close">Close</string>
+    <string name="item_lookup_failed_error">Item lookup failed</string>
 </resources>