android/ui: show count of Mullvad countries, also fix navigation-related crash when adding new account

Updates tailscale/corp#18202

Signed-off-by: Percy Wegmann <percy@tailscale.com>

android/src/main/java/com/tailscale/ipn/MainActivity.kt

@@ -37,7 +37,6 @@ import androidx.navigation.compose.NavHost
 import androidx.navigation.compose.composable
 import androidx.navigation.compose.rememberNavController
 import androidx.navigation.navArgument
-import androidx.navigation.navigation
 import com.tailscale.ipn.Peer.RequestCodes
 import com.tailscale.ipn.mdm.MDMSettings
 import com.tailscale.ipn.ui.model.Ipn
@@ -74,7 +73,7 @@ import kotlinx.coroutines.launch
 
 class MainActivity : ComponentActivity() {
   private lateinit var requestVpnPermission: ActivityResultLauncher<Unit>
-  private var navController: NavHostController? = null
+  private lateinit var navController: NavHostController
 
   companion object {
     private const val TAG = "Main Activity"
@@ -105,7 +104,7 @@ class MainActivity : ComponentActivity() {
 
     setContent {
       AppTheme {
-        val navController = rememberNavController()
+        navController = rememberNavController()
         Surface(color = MaterialTheme.colorScheme.inverseSurface) { // Background for the letterbox
           Surface(modifier = Modifier.universalFit()) { // Letterbox for AndroidTV
             NavHost(
@@ -162,18 +161,16 @@ class MainActivity : ComponentActivity() {
 
                   composable("main") { MainView(navigation = mainViewNav) }
                   composable("settings") { SettingsView(settingsNav) }
-                  navigation(startDestination = "list", route = "exitNodes") {
-                    composable("list") { ExitNodePicker(exitNodePickerNav) }
-                    composable("mullvad") { MullvadExitNodePickerList(exitNodePickerNav) }
-                    composable(
-                        "mullvad/{countryCode}",
-                        arguments =
-                            listOf(navArgument("countryCode") { type = NavType.StringType })) {
-                          MullvadExitNodePicker(
-                              it.arguments!!.getString("countryCode")!!, exitNodePickerNav)
-                        }
-                    composable("runExitNode") { RunExitNodeView(exitNodePickerNav) }
-                  }
+                  composable("exitNodes") { ExitNodePicker(exitNodePickerNav) }
+                  composable("mullvad") { MullvadExitNodePickerList(exitNodePickerNav) }
+                  composable(
+                      "mullvad/{countryCode}",
+                      arguments =
+                          listOf(navArgument("countryCode") { type = NavType.StringType })) {
+                        MullvadExitNodePicker(
+                            it.arguments!!.getString("countryCode")!!, exitNodePickerNav)
+                      }
+                  composable("runExitNode") { RunExitNodeView(exitNodePickerNav) }
                   composable(
                       "peerDetails/{nodeId}",
                       arguments = listOf(navArgument("nodeId") { type = NavType.StringType })) {
@@ -244,7 +241,7 @@ class MainActivity : ComponentActivity() {
   override fun onNewIntent(intent: Intent?) {
     super.onNewIntent(intent)
     if (intent?.getBooleanExtra(START_AT_ROOT, false) == true) {
-      navController?.popBackStack(route = "main", inclusive = false)
+      navController.popBackStack(route = "main", inclusive = false)
     }
   }
 

android/src/main/java/com/tailscale/ipn/ui/view/ExitNodePicker.kt

@@ -66,7 +66,8 @@ fun ExitNodePicker(
         if (mullvadExitNodeCount > 0) {
           item(key = "mullvad") {
             Lists.SectionDivider()
-            MullvadItem(nav, mullvadExitNodeCount, mullvadExitNodesByCountryCode.selected)
+            MullvadItem(
+                nav, mullvadExitNodesByCountryCode.size, mullvadExitNodesByCountryCode.selected)
           }
         }
 
@@ -128,7 +129,7 @@ fun MullvadItem(nav: ExitNodePickerNav, count: Int, selected: Boolean) {
         },
         supportingContent = {
           Text(
-              "$count ${stringResource(R.string.exit_nodes_available)}",
+              "$count ${stringResource(R.string.countries)}",
               style = MaterialTheme.typography.bodyMedium)
         },
         trailingContent = {

android/src/main/java/com/tailscale/ipn/ui/view/MullvadExitNodePicker.kt

@@ -40,7 +40,7 @@ fun MullvadExitNodePicker(
           topBar = {
             Header(
                 title = { Text("${countryCode.flag()} ${any.country}") },
-                onBack = nav.onNavigateBackToExitNodes)
+                onBack = nav.onNavigateBackToMullvad)
           }) { innerPadding ->
             LazyColumn(modifier = Modifier.padding(innerPadding)) {
               if (nodes.size > 1) {

android/src/main/java/com/tailscale/ipn/ui/view/MullvadExitNodePickerList.kt

@@ -38,7 +38,7 @@ fun MullvadExitNodePickerList(
   LoadingIndicator.Wrap {
     Scaffold(
         topBar = {
-          Header(R.string.choose_mullvad_exit_node, onBack = nav.onNavigateBackToMullvad)
+          Header(R.string.choose_mullvad_exit_node, onBack = nav.onNavigateBackToExitNodes)
         }) { innerPadding ->
           val mullvadExitNodes = model.mullvadExitNodesByCountryCode.collectAsState()
 

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

@@ -159,7 +159,7 @@
     <string name="this_device_is_using_the_system_dns_resolver">This device is using the system DNS resolver.</string>
     <string name="not_using_tailscale_dns">Not using Tailscale DNS</string>
     <string name="allow_lan_access">Allow LAN access</string>
-    <string name="exit_nodes_available">exit nodes available</string>
+    <string name="countries">countries</string>
     <string name="cities_available">cities available</string>
 
     <!-- Strings for MDM Settings Manifest (app_restrictions.xml) -->