prevent the nav gesture if not on start destination

Author: kevinmainairungu

app/src/main/java/com/example/android/navigation/MainActivity.kt

@@ -20,6 +20,8 @@ import android.os.Bundle
 import androidx.appcompat.app.AppCompatActivity
 import androidx.databinding.DataBindingUtil
 import androidx.drawerlayout.widget.DrawerLayout
+import androidx.navigation.NavController
+import androidx.navigation.NavDestination
 import androidx.navigation.findNavController
 import androidx.navigation.ui.AppBarConfiguration
 import androidx.navigation.ui.NavigationUI
@@ -39,6 +41,14 @@ class MainActivity : AppCompatActivity() {
 //        tie the binding object into a view
         NavigationUI.setupActionBarWithNavController(this, navController, drawerLayout)
         appBarConfiguration = AppBarConfiguration(navController.graph, drawerLayout)
+        // prevent nav gesture if not on start destination
+        navController.addOnDestinationChangedListener{ nc : NavController, nd: NavDestination, args: Bundle? ->
+            if (nd.id == nc.graph.startDestination) {
+                drawerLayout.setDrawerLockMode(DrawerLayout.LOCK_MODE_UNLOCKED)
+            } else {
+                drawerLayout.setDrawerLockMode(DrawerLayout.LOCK_MODE_LOCKED_CLOSED)
+            }
+        }
         NavigationUI.setupWithNavController(binding.navView, navController)
     }