Prevent showing Empty MediaPreview screen and avoid Camera/Gallery Stack.

app/src/main/java/org/thoughtcrime/securesms/mediasend/v2/MediaSelectionNavigator.kt

@@ -29,6 +29,10 @@ class MediaSelectionNavigator(
     navController.safeNavigate(toGallery)
   }
 
+  fun isPreviousScreenMediaReview(navController: NavController): Boolean {
+    return navController.previousBackStackEntry?.destination?.id == R.id.mediaReviewFragment
+  }
+
   companion object {
     fun Fragment.requestPermissionsForCamera(
       onGranted: () -> Unit

app/src/main/java/org/thoughtcrime/securesms/mediasend/v2/MediaSelectionViewModel.kt

@@ -264,6 +264,10 @@ class MediaSelectionViewModel(
     lastMediaDrag = Pair(0, 0)
   }
 
+  fun isSelectedMediaEmpty(): Boolean {
+    return store.state.selectedMedia.isEmpty()
+  }
+
   fun removeMedia(media: Media) {
     val snapshot = store.state
     val newMediaList = snapshot.selectedMedia - media

app/src/main/java/org/thoughtcrime/securesms/mediasend/v2/capture/MediaCaptureFragment.kt

@@ -119,7 +119,7 @@ class MediaCaptureFragment : Fragment(R.layout.fragment_container), CameraFragme
       }
     }
 
-    if (isFirst()) {
+    if (isFirst() || sharedViewModel.isSelectedMediaEmpty()) {
       requireActivity().onBackPressedDispatcher.addCallback(
         viewLifecycleOwner,
         object : OnBackPressedCallback(true) {

app/src/main/java/org/thoughtcrime/securesms/mediasend/v2/gallery/MediaSelectionGalleryFragment.kt

@@ -53,16 +53,14 @@ class MediaSelectionGalleryFragment : Fragment(R.layout.fragment_container), Med
       mediaGalleryFragment.onViewStateUpdated(MediaGalleryFragment.ViewState(state.selectedMedia))
     }
 
-    if (arguments?.containsKey("first") == true) {
-      requireActivity().onBackPressedDispatcher.addCallback(
-        viewLifecycleOwner,
-        object : OnBackPressedCallback(true) {
-          override fun handleOnBackPressed() {
-            requireActivity().finish()
-          }
+    requireActivity().onBackPressedDispatcher.addCallback(
+      viewLifecycleOwner,
+      object : OnBackPressedCallback(true) {
+        override fun handleOnBackPressed() {
+          onBackPressed()
         }
-      )
-    }
+      }
+    )
 
     lifecycleDisposable.bindTo(viewLifecycleOwner)
     lifecycleDisposable += sharedViewModel.mediaErrors
@@ -139,6 +137,19 @@ class MediaSelectionGalleryFragment : Fragment(R.layout.fragment_container), Med
   }
 
   override fun onToolbarNavigationClicked() {
-    requireActivity().onBackPressed()
+    onBackPressed()
+  }
+
+  fun onBackPressed() {
+    if (arguments?.containsKey("first") == true) {
+      requireActivity().finish()
+      return
+    }
+
+    if (navigator.isPreviousScreenMediaReview(findNavController()) && sharedViewModel.isSelectedMediaEmpty()) {
+      requireActivity().finish()
+    } else {
+      findNavController().popBackStack()
+    }
   }
 }