android: make currentDir reactive

-The composables were reading the currentDir value once and not observing it. This fixes it so that we recompose when the StateFlow changes.
-Use commit() instead of apply() when writing to EncryptedSharedPreferences since we are reading from it immediately and need the writes to happen synchronously
-Remove unused function in PermissionsViewModel

Fixes tailscale/corp#29283

Signed-off-by: kari-ts <kari@tailscale.com>

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

@@ -25,6 +25,7 @@ import androidx.activity.compose.setContent
 import androidx.activity.result.ActivityResultLauncher
 import androidx.activity.result.contract.ActivityResultContract
 import androidx.activity.result.contract.ActivityResultContracts
+import androidx.activity.viewModels
 import androidx.annotation.RequiresApi
 import androidx.browser.customtabs.CustomTabsIntent
 import androidx.compose.animation.core.LinearOutSlowInEasing
@@ -85,6 +86,7 @@ import com.tailscale.ipn.ui.view.UserSwitcherView
 import com.tailscale.ipn.ui.viewModel.ExitNodePickerNav
 import com.tailscale.ipn.ui.viewModel.MainViewModel
 import com.tailscale.ipn.ui.viewModel.MainViewModelFactory
+import com.tailscale.ipn.ui.viewModel.PermissionsViewModel
 import com.tailscale.ipn.ui.viewModel.PingViewModel
 import com.tailscale.ipn.ui.viewModel.SettingsNav
 import com.tailscale.ipn.ui.viewModel.VpnViewModel
@@ -105,6 +107,7 @@ class MainActivity : ComponentActivity() {
     ViewModelProvider(this, MainViewModelFactory(vpnViewModel)).get(MainViewModel::class.java)
   }
   private lateinit var vpnViewModel: VpnViewModel
+  val permissionsViewModel: PermissionsViewModel by viewModels()
 
   companion object {
     private const val TAG = "Main Activity"
@@ -179,6 +182,7 @@ class MainActivity : ComponentActivity() {
                 try {
                   Libtailscale.setDirectFileRoot(uri.toString())
                   TaildropDirectoryStore.saveFileDirectory(uri)
+                  permissionsViewModel.refreshCurrentDir()
                 } catch (e: Exception) {
                   TSLog.e("MainActivity", "Failed to set Taildrop root: $e")
                 }
@@ -333,7 +337,8 @@ class MainActivity : ComponentActivity() {
                         { navController.navigate("notifications") })
                   }
                   composable("taildropDir") {
-                    TaildropDirView(backTo("permissions"), directoryPickerLauncher)
+                    TaildropDirView(
+                        backTo("permissions"), directoryPickerLauncher, permissionsViewModel)
                   }
                   composable("notifications") {
                     NotificationsView(backTo("permissions"), ::openApplicationSettings)

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

@@ -15,7 +15,7 @@ object TaildropDirectoryStore {
   @Throws(IOException::class, GeneralSecurityException::class)
   fun saveFileDirectory(directoryUri: Uri) {
     val prefs = App.get().getEncryptedPrefs()
-    prefs.edit().putString(PREF_KEY_SAF_URI, directoryUri.toString()).apply()
+    prefs.edit().putString(PREF_KEY_SAF_URI, directoryUri.toString()).commit()
     try {
       // Must restart Tailscale because a new LocalBackend with the new directory must be created.
       App.get().startLibtailscale(directoryUri.toString())

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

@@ -13,6 +13,7 @@ import androidx.compose.material3.MaterialTheme
 import androidx.compose.material3.Scaffold
 import androidx.compose.material3.Text
 import androidx.compose.runtime.Composable
+import androidx.compose.runtime.collectAsState
 import androidx.compose.ui.Modifier
 import androidx.compose.ui.res.painterResource
 import androidx.compose.ui.res.stringResource
@@ -73,7 +74,9 @@ fun PermissionsView(
             },
             supportingContent = {
               val displayPath =
-                  permissionsViewModel.currentDir.value?.let { friendlyDirName(it) } ?: "No access"
+                  permissionsViewModel.currentDir.collectAsState().value?.let {
+                    friendlyDirName(it)
+                  } ?: "No access"
 
               Text(displayPath)
             })

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

@@ -15,21 +15,23 @@ import androidx.compose.material3.MaterialTheme
 import androidx.compose.material3.Scaffold
 import androidx.compose.material3.Text
 import androidx.compose.runtime.Composable
+import androidx.compose.runtime.collectAsState
+import androidx.compose.runtime.getValue
 import androidx.compose.ui.Modifier
 import androidx.compose.ui.res.stringResource
 import androidx.compose.ui.unit.dp
-import androidx.lifecycle.viewmodel.compose.viewModel
 import com.tailscale.ipn.R
 import com.tailscale.ipn.ui.theme.exitNodeToggleButton
 import com.tailscale.ipn.ui.util.Lists
 import com.tailscale.ipn.ui.util.friendlyDirName
 import com.tailscale.ipn.ui.viewModel.PermissionsViewModel
+import com.tailscale.ipn.util.TSLog
 
 @Composable
 fun TaildropDirView(
     backToPermissionsView: BackNavigation,
     openDirectoryLauncher: ActivityResultLauncher<Uri?>,
-    permissionsViewModel: PermissionsViewModel = viewModel()
+    permissionsViewModel: PermissionsViewModel
 ) {
   Scaffold(
       topBar = {
@@ -53,7 +55,8 @@ fun TaildropDirView(
           item("divider0") { Lists.SectionDivider() }
 
           item {
-            val currentDir = permissionsViewModel.currentDir.value
+            val currentDir by permissionsViewModel.currentDir.collectAsState()
+            TSLog.d("TaildropDirView", "currentDir in UI: $currentDir")
             val displayPath = currentDir?.let { friendlyDirName(it) } ?: "No access"
 
             ListItem(

android/src/main/java/com/tailscale/ipn/ui/viewModel/PermissionsViewModel.kt

@@ -3,37 +3,20 @@
 
 package com.tailscale.ipn.ui.viewModel
 
-import android.content.Context
-import android.content.Intent
-import android.net.Uri
-import androidx.lifecycle.SavedStateHandle
 import androidx.lifecycle.ViewModel
 import com.tailscale.ipn.TaildropDirectoryStore
+import com.tailscale.ipn.util.TSLog
 import kotlinx.coroutines.flow.MutableStateFlow
 import kotlinx.coroutines.flow.StateFlow
-import libtailscale.Libtailscale
-
-class PermissionsViewModel(private val savedStateHandle: SavedStateHandle) : ViewModel() {
 
+class PermissionsViewModel : ViewModel() {
   private val _currentDir =
-      MutableStateFlow<String?>(TaildropDirectoryStore.loadSavedDir().toString())
+      MutableStateFlow<String?>(TaildropDirectoryStore.loadSavedDir()?.toString())
   val currentDir: StateFlow<String?> = _currentDir
 
-  fun onDirectoryPicked(uri: Uri?, context: Context) {
-    if (uri == null) return
-
-    val flags = Intent.FLAG_GRANT_READ_URI_PERMISSION or Intent.FLAG_GRANT_WRITE_URI_PERMISSION
-    val cr = context.contentResolver
-
-    // Revoke previous grant so you don’t leak one
-    _currentDir.value?.let { old ->
-      runCatching { cr.releasePersistableUriPermission(Uri.parse(old), flags) }
-    }
-
-    cr.takePersistableUriPermission(uri, flags) // may throw SecurityException
-    Libtailscale.setDirectFileRoot(uri.toString())
-    TaildropDirectoryStore.saveFileDirectory(uri)
-
-    _currentDir.value = uri.toString()
+  fun refreshCurrentDir() {
+    val newUri = TaildropDirectoryStore.loadSavedDir()?.toString()
+    TSLog.d("PermissionsViewModel", "refreshCurrentDir: $newUri")
+    _currentDir.value = newUri
   }
 }