Separate navigation routes and args issue #863 (#931)

* Replaced TopAppBar with CenterAlignedTopAppBar, Fix issue #857 App title moves

* Separate navigation route and args Issue#863

* moved navArguments to Screen class constructor

* Moved Screen class to compose package

app/src/main/java/com/google/samples/apps/sunflower/compose/Screen.kt

@@ -0,0 +1,47 @@
+/*
+ * Copyright 2023 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.google.samples.apps.sunflower.compose
+
+import androidx.navigation.NamedNavArgument
+import androidx.navigation.NavType
+import androidx.navigation.navArgument
+
+sealed class Screen(
+    val route: String,
+    val navArguments: List<NamedNavArgument> = emptyList()
+) {
+    data object Home : Screen("home")
+
+    data object PlantDetail : Screen(
+        route = "plantDetail/{plantId}",
+        navArguments = listOf(navArgument("plantId") {
+            type = NavType.StringType
+        })
+    ) {
+        fun createRoute(plantId: String) = "plantDetail/${plantId}"
+    }
+
+    data object Gallery : Screen(
+        route = "gallery/{plantName}",
+        navArguments = listOf(navArgument("plantName") {
+            type = NavType.StringType
+        })
+    ) {
+        fun createRoute(plantName: String) = "gallery/${plantName}"
+
+    }
+}

app/src/main/java/com/google/samples/apps/sunflower/compose/SunflowerApp.kt

@@ -23,11 +23,9 @@ import androidx.compose.runtime.Composable
 import androidx.compose.ui.platform.LocalContext
 import androidx.core.app.ShareCompat
 import androidx.navigation.NavHostController
-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.google.samples.apps.sunflower.R
 import com.google.samples.apps.sunflower.compose.gallery.GalleryScreen
 import com.google.samples.apps.sunflower.compose.home.HomeScreen
@@ -46,35 +44,39 @@ fun SunFlowerNavHost(
     navController: NavHostController
 ) {
     val activity = (LocalContext.current as Activity)
-    NavHost(navController = navController, startDestination = "home") {
-        composable("home") {
+    NavHost(navController = navController, startDestination = Screen.Home.route) {
+        composable(route = Screen.Home.route) {
             HomeScreen(
                 onPlantClick = {
-                    navController.navigate("plantDetail/${it.plantId}")
+                    navController.navigate(
+                        Screen.PlantDetail.createRoute(
+                            plantId = it.plantId
+                        )
+                    )
                 }
             )
         }
         composable(
-            "plantDetail/{plantId}",
-            arguments = listOf(navArgument("plantId") {
-                type = NavType.StringType
-            })
+            route = Screen.PlantDetail.route,
+            arguments = Screen.PlantDetail.navArguments
         ) {
             PlantDetailsScreen(
                 onBackClick = { navController.navigateUp() },
                 onShareClick = {
                     createShareIntent(activity, it)
                 },
                 onGalleryClick = {
-                    navController.navigate("gallery/${it.name}")
+                    navController.navigate(
+                        Screen.Gallery.createRoute(
+                            plantName = it.name
+                        )
+                    )
                 }
             )
         }
         composable(
-            "gallery/{plantName}",
-            arguments = listOf(navArgument("plantName") {
-                type = NavType.StringType
-            })
+            route = Screen.Gallery.route,
+            arguments = Screen.Gallery.navArguments
         ) {
             GalleryScreen(
                 onPhotoClick = {