fix: Enable submit button after linking items in Drag & Drop Sort Int…

…eraction

app/src/main/java/org/oppia/android/app/player/state/itemviewmodel/DragAndDropSortInteractionViewModel.kt

@@ -219,8 +219,12 @@ class DragAndDropSortInteractionViewModel private constructor(
       dragDropInteractionContentViewModel.itemIndex = index
       dragDropInteractionContentViewModel.listSize = _choiceItems.size
     }
-    // to update the content of grouped item
+
+    // To update the list
     (adapter as BindableAdapter<*>).setDataUnchecked(_choiceItems)
+
+    // *Trigger pending answer check* to re-enable submit button
+    checkPendingAnswerError(AnswerErrorCategory.REAL_TIME)
   }
 
   fun unlinkElement(itemIndex: Int, adapter: RecyclerView.Adapter<RecyclerView.ViewHolder>) {
@@ -246,15 +250,24 @@ class DragAndDropSortInteractionViewModel private constructor(
       dragDropInteractionContentViewModel.itemIndex = index
       dragDropInteractionContentViewModel.listSize = _choiceItems.size
     }
-    // to update the list
+
+    // *Update the list*
     (adapter as BindableAdapter<*>).setDataUnchecked(_choiceItems)
+
+    // *Trigger pending answer check* to re-enable submit button
+    checkPendingAnswerError(AnswerErrorCategory.REAL_TIME)
   }
 
   private fun getSubmitTimeError(): DragAndDropSortInteractionError {
-    return if (_originalChoiceItems == _choiceItems) {
+    val hasItemsChanged = _originalChoiceItems.size != _choiceItems.size ||
+      _originalChoiceItems.zip(_choiceItems).any { (originalItem, currentItem) ->
+        originalItem.htmlContent != currentItem.htmlContent
+      }
+    return if (!hasItemsChanged) {
       DragAndDropSortInteractionError.EMPTY_INPUT
-    } else
+    } else {
       DragAndDropSortInteractionError.VALID
+    }
   }
 
   /** Implementation of [StateItemViewModel.InteractionItemFactory] for this view model. */