Fix issues around configuration changes

app/src/main/java/org/oppia/android/app/player/exploration/ExplorationActivityPresenter.kt

@@ -128,7 +128,7 @@ class ExplorationActivityPresenter @Inject constructor(
 
   fun loadExplorationFragment(readingTextSize: ReadingTextSize) {
     if (getExplorationFragment() == null) {
-      activity.supportFragmentManager.beginTransaction().replace(
+      activity.supportFragmentManager.beginTransaction().add(
         R.id.exploration_fragment_placeholder,
         ExplorationFragment.newInstance(
           profileId, topicId, storyId, explorationId, readingTextSize

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

@@ -180,7 +180,7 @@ class StateFragmentPresenter @Inject constructor(
 
   fun handleAnswerReadyForSubmission(answer: UserAnswer) {
     // An interaction has indicated that an answer is ready for submission.
-    handleSubmitAnswer(answer)
+    handleSubmitAnswer(answer, canSubmitAnswer = true)
   }
 
   fun onContinueButtonClicked() {
@@ -224,9 +224,7 @@ class StateFragmentPresenter @Inject constructor(
 
   fun handleKeyboardAction() {
     hideKeyboard()
-    if (viewModel.getCanSubmitAnswer().get() == true) {
-      handleSubmitAnswer(viewModel.getPendingAnswer(recyclerViewAssembler::getPendingAnswerHandler))
-    }
+    handleSubmitAnswer(viewModel.getPendingAnswer(recyclerViewAssembler::getPendingAnswerHandler))
   }
 
   fun onHintAvailable(helpIndex: HelpIndex, isCurrentStatePendingState: Boolean) {
@@ -425,8 +423,15 @@ class StateFragmentPresenter @Inject constructor(
     }
   }
 
-  private fun handleSubmitAnswer(answer: UserAnswer) {
-    subscribeToAnswerOutcome(explorationProgressController.submitAnswer(answer).toLiveData())
+  private fun handleSubmitAnswer(
+    answer: UserAnswer,
+    canSubmitAnswer: Boolean = viewModel.getCanSubmitAnswer().get() ?: false
+  ) {
+    // This check seems to avoid a crash on configuration change when attempting to resubmit answers
+    // after encountering a submit-time error, but it's also more correct to keep it.
+    if (canSubmitAnswer) {
+      subscribeToAnswerOutcome(explorationProgressController.submitAnswer(answer).toLiveData())
+    }
   }
 
   fun dismissConceptCard() {

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

@@ -329,7 +329,10 @@ class StatePlayerRecyclerViewAssembler private constructor(
       hasPreviousButton,
       isSplitView.get()!!,
       writtenTranslationContext
-    )
+    ).also {
+      // Ensure that potential errors are re-detected in cases of configuration changes.
+      (it as? InteractionAnswerHandler)?.checkPendingAnswerError(rawUserAnswer.lastErrorCategory)
+    }
   }
 
   private fun addContentItem(

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

@@ -4,9 +4,9 @@ import androidx.databinding.ObservableField
 import androidx.databinding.ObservableList
 import androidx.lifecycle.ViewModel
 import org.oppia.android.app.fragment.FragmentScope
+import org.oppia.android.app.model.AnswerErrorCategory
 import org.oppia.android.app.model.RawUserAnswer
 import org.oppia.android.app.model.UserAnswer
-import org.oppia.android.app.player.state.answerhandling.AnswerErrorCategory
 import org.oppia.android.app.player.state.answerhandling.InteractionAnswerHandler
 import org.oppia.android.app.player.state.itemviewmodel.StateItemViewModel
 import org.oppia.android.app.viewmodel.ObservableArrayList

app/src/main/java/org/oppia/android/app/player/state/answerhandling/InteractionAnswerHandler.kt

@@ -1,5 +1,6 @@
 package org.oppia.android.app.player.state.answerhandling
 
+import org.oppia.android.app.model.AnswerErrorCategory
 import org.oppia.android.app.model.RawUserAnswer
 import org.oppia.android.app.model.UserAnswer
 
@@ -44,11 +45,3 @@ interface InteractionAnswerHandler {
 interface InteractionAnswerReceiver {
   fun onAnswerReadyForSubmission(answer: UserAnswer)
 }
-
-/** Categories of errors that can be inferred from a pending answer.  */
-enum class AnswerErrorCategory {
-  /** Corresponds to errors that may be found while the user is trying to input an answer.  */
-  REAL_TIME,
-  /** Corresponds to errors that may be found only when a user tries to submit an answer.  */
-  SUBMIT_TIME
-}

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

@@ -3,6 +3,7 @@ package org.oppia.android.app.player.state.itemviewmodel
 import androidx.databinding.Observable
 import androidx.databinding.ObservableField
 import androidx.recyclerview.widget.RecyclerView
+import org.oppia.android.app.model.AnswerErrorCategory
 import org.oppia.android.app.model.Interaction
 import org.oppia.android.app.model.InteractionObject
 import org.oppia.android.app.model.ListOfSetsOfHtmlStrings
@@ -143,6 +144,7 @@ class DragAndDropSortInteractionViewModel private constructor(
       ListOfSetsOfTranslatableHtmlContentIds.newBuilder().apply {
         addAllContentIdLists(htmlContentIds)
       }.build()
+    lastErrorCategory = AnswerErrorCategory.NO_ERROR
   }.build()
 
   /** Returns an HTML list containing all of the HTML string elements as items in the list. */

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

@@ -5,13 +5,13 @@ import android.text.TextWatcher
 import androidx.databinding.Observable
 import androidx.databinding.ObservableField
 import org.oppia.android.R
+import org.oppia.android.app.model.AnswerErrorCategory
 import org.oppia.android.app.model.Interaction
 import org.oppia.android.app.model.InteractionObject
 import org.oppia.android.app.model.RawUserAnswer
 import org.oppia.android.app.model.UserAnswer
 import org.oppia.android.app.model.WrittenTranslationContext
 import org.oppia.android.app.parser.FractionParsingUiError
-import org.oppia.android.app.player.state.answerhandling.AnswerErrorCategory
 import org.oppia.android.app.player.state.answerhandling.InteractionAnswerErrorOrAvailabilityCheckReceiver
 import org.oppia.android.app.player.state.answerhandling.InteractionAnswerHandler
 import org.oppia.android.app.player.state.answerhandling.InteractionAnswerReceiver
@@ -32,11 +32,12 @@ class FractionInteractionViewModel private constructor(
   private val translationController: TranslationController
 ) : StateItemViewModel(ViewType.FRACTION_INPUT_INTERACTION), InteractionAnswerHandler {
   private var pendingAnswerError: String? = null
-  var answerText: CharSequence = rawUserAnswer.textualAnswer ?: ""
+  var answerText: CharSequence = rawUserAnswer.textualAnswer
   var isAnswerAvailable = ObservableField<Boolean>(false)
   var errorMessage = ObservableField<String>("")
   val hintText: CharSequence = deriveHintText(interaction)
   private val fractionParser = FractionParser()
+  private var currentErrorCategory = AnswerErrorCategory.NO_ERROR
 
   init {
     val callback: Observable.OnPropertyChangedCallback =
@@ -50,7 +51,6 @@ class FractionInteractionViewModel private constructor(
       }
     errorMessage.addOnPropertyChangedCallback(callback)
     isAnswerAvailable.addOnPropertyChangedCallback(callback)
-    checkPendingAnswerError(AnswerErrorCategory.REAL_TIME)
   }
 
   override fun getPendingAnswer(): UserAnswer = UserAnswer.newBuilder().apply {
@@ -67,20 +67,23 @@ class FractionInteractionViewModel private constructor(
   /** It checks the pending error for the current fraction input, and correspondingly updates the error string based on the specified error category. */
   override fun checkPendingAnswerError(category: AnswerErrorCategory): String? {
     if (answerText.isNotEmpty()) {
-      when (category) {
+      pendingAnswerError = when (category) {
         AnswerErrorCategory.REAL_TIME -> {
-          pendingAnswerError =
-            FractionParsingUiError.createFromParsingError(
-              fractionParser.getRealTimeAnswerError(answerText.toString())
-            ).getErrorMessageFromStringRes(resourceHandler)
+          FractionParsingUiError.createFromParsingError(
+            fractionParser.getRealTimeAnswerError(answerText.toString())
+          ).getErrorMessageFromStringRes(resourceHandler)
         }
         AnswerErrorCategory.SUBMIT_TIME -> {
-          pendingAnswerError =
-            FractionParsingUiError.createFromParsingError(
-              fractionParser.getSubmitTimeError(answerText.toString())
-            ).getErrorMessageFromStringRes(resourceHandler)
+          FractionParsingUiError.createFromParsingError(
+            fractionParser.getSubmitTimeError(answerText.toString())
+          ).getErrorMessageFromStringRes(resourceHandler)
         }
+        AnswerErrorCategory.ANSWER_ERROR_CATEGORY_UNSPECIFIED, AnswerErrorCategory.UNRECOGNIZED,
+        AnswerErrorCategory.NO_ERROR -> null
       }
+      currentErrorCategory = if (pendingAnswerError == null) {
+        AnswerErrorCategory.NO_ERROR
+      } else category
       errorMessage.set(pendingAnswerError)
     }
     return pendingAnswerError
@@ -89,6 +92,7 @@ class FractionInteractionViewModel private constructor(
   override fun getRawUserAnswer(): RawUserAnswer = RawUserAnswer.newBuilder().apply {
     if (answerText.isNotEmpty()) {
       textualAnswer = answerText.toString()
+      lastErrorCategory = currentErrorCategory
     }
   }.build()
 

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

@@ -3,6 +3,7 @@ package org.oppia.android.app.player.state.itemviewmodel
 import androidx.databinding.Observable
 import androidx.databinding.ObservableField
 import org.oppia.android.R
+import org.oppia.android.app.model.AnswerErrorCategory
 import org.oppia.android.app.model.ClickOnImage
 import org.oppia.android.app.model.ImageWithRegions.LabeledRegion
 import org.oppia.android.app.model.Interaction
@@ -89,6 +90,7 @@ class ImageRegionSelectionInteractionViewModel private constructor(
     if (answerText.isNotEmpty()) {
       imageRegionSelection = selectableRegions.find { it.label == answerText.toString() }
     }
+    lastErrorCategory = AnswerErrorCategory.NO_ERROR
   }.build()
 
   private fun parseClickOnImage(answerTextString: String): ClickOnImage {

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

@@ -6,6 +6,7 @@ import androidx.annotation.StringRes
 import androidx.databinding.Observable
 import androidx.databinding.ObservableField
 import org.oppia.android.R
+import org.oppia.android.app.model.AnswerErrorCategory
 import org.oppia.android.app.model.Interaction
 import org.oppia.android.app.model.InteractionObject
 import org.oppia.android.app.model.MathEquation
@@ -14,7 +15,6 @@ import org.oppia.android.app.model.OppiaLanguage
 import org.oppia.android.app.model.RawUserAnswer
 import org.oppia.android.app.model.UserAnswer
 import org.oppia.android.app.model.WrittenTranslationContext
-import org.oppia.android.app.player.state.answerhandling.AnswerErrorCategory
 import org.oppia.android.app.player.state.answerhandling.InteractionAnswerErrorOrAvailabilityCheckReceiver
 import org.oppia.android.app.player.state.answerhandling.InteractionAnswerHandler
 import org.oppia.android.app.player.state.answerhandling.InteractionAnswerReceiver
@@ -74,7 +74,7 @@ class MathExpressionInteractionsViewModel private constructor(
    * Defines the current answer text being entered by the learner. This is expected to be directly
    * bound to the corresponding edit text.
    */
-  var answerText: CharSequence = "" // TODO(#4708): Need to retain state for submit time error.
+  var answerText: CharSequence = rawUserAnswer.textualAnswer
 
   /**
    * Defines whether an answer is currently available to parse. This is expected to be directly
@@ -91,6 +91,8 @@ class MathExpressionInteractionsViewModel private constructor(
   /** Specifies the text to show in the answer box when no text is entered. */
   val hintText: CharSequence = deriveHintText(interaction)
 
+  private var currentErrorCategory = AnswerErrorCategory.NO_ERROR
+
   private val allowedVariables = retrieveAllowedVariables(interaction)
   private val useFractionsForDivision =
     interaction.customizationArgsMap["useFractionForDivision"]?.boolValue ?: false
@@ -146,6 +148,7 @@ class MathExpressionInteractionsViewModel private constructor(
     if (answerText.isNotEmpty()) {
       textualAnswer = answerText.toString()
     }
+    lastErrorCategory = currentErrorCategory
   }.build()
 
   override fun checkPendingAnswerError(category: AnswerErrorCategory): String? {
@@ -158,7 +161,12 @@ class MathExpressionInteractionsViewModel private constructor(
             answerText.toString(), allowedVariables, resourceHandler
           )
         }
+        AnswerErrorCategory.ANSWER_ERROR_CATEGORY_UNSPECIFIED, AnswerErrorCategory.UNRECOGNIZED,
+        AnswerErrorCategory.NO_ERROR -> null
       }
+      currentErrorCategory = if (pendingAnswerError == null) {
+        AnswerErrorCategory.NO_ERROR
+      } else category
       errorMessage.set(pendingAnswerError)
     }
     return pendingAnswerError

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

@@ -4,13 +4,13 @@ import android.text.Editable
 import android.text.TextWatcher
 import androidx.databinding.Observable
 import androidx.databinding.ObservableField
+import org.oppia.android.app.model.AnswerErrorCategory
 import org.oppia.android.app.model.Interaction
 import org.oppia.android.app.model.InteractionObject
 import org.oppia.android.app.model.RawUserAnswer
 import org.oppia.android.app.model.UserAnswer
 import org.oppia.android.app.model.WrittenTranslationContext
 import org.oppia.android.app.parser.StringToNumberParser
-import org.oppia.android.app.player.state.answerhandling.AnswerErrorCategory
 import org.oppia.android.app.player.state.answerhandling.InteractionAnswerErrorOrAvailabilityCheckReceiver
 import org.oppia.android.app.player.state.answerhandling.InteractionAnswerHandler
 import org.oppia.android.app.player.state.answerhandling.InteractionAnswerReceiver
@@ -26,11 +26,12 @@ class NumericInputViewModel private constructor(
   private val writtenTranslationContext: WrittenTranslationContext,
   private val resourceHandler: AppLanguageResourceHandler
 ) : StateItemViewModel(ViewType.NUMERIC_INPUT_INTERACTION), InteractionAnswerHandler {
-  var answerText: CharSequence = rawUserAnswer.textualAnswer ?: ""
+  var answerText: CharSequence = rawUserAnswer.textualAnswer
   private var pendingAnswerError: String? = null
   val errorMessage = ObservableField<String>("")
   var isAnswerAvailable = ObservableField<Boolean>(false)
   private val stringToNumberParser: StringToNumberParser = StringToNumberParser()
+  private var currentErrorCategory = AnswerErrorCategory.NO_ERROR
 
   init {
     val callback: Observable.OnPropertyChangedCallback =
@@ -45,7 +46,6 @@ class NumericInputViewModel private constructor(
 
     errorMessage.addOnPropertyChangedCallback(callback)
     isAnswerAvailable.addOnPropertyChangedCallback(callback)
-    checkPendingAnswerError(AnswerErrorCategory.REAL_TIME)
   }
 
   /** It checks the pending error for the current numeric input, and correspondingly updates the error string based on the specified error category. */
@@ -58,8 +58,13 @@ class NumericInputViewModel private constructor(
         AnswerErrorCategory.SUBMIT_TIME ->
           stringToNumberParser.getSubmitTimeError(answerText.toString())
             .getErrorMessageFromStringRes(resourceHandler)
+        AnswerErrorCategory.ANSWER_ERROR_CATEGORY_UNSPECIFIED, AnswerErrorCategory.UNRECOGNIZED,
+        AnswerErrorCategory.NO_ERROR -> null
       }
     }
+    currentErrorCategory = if (pendingAnswerError == null) {
+      AnswerErrorCategory.NO_ERROR
+    } else category
     errorMessage.set(pendingAnswerError)
     return pendingAnswerError
   }
@@ -98,6 +103,7 @@ class NumericInputViewModel private constructor(
     if (answerText.isNotEmpty()) {
       textualAnswer = answerText.toString()
     }
+    lastErrorCategory = currentErrorCategory
   }.build()
 
   /** Implementation of [StateItemViewModel.InteractionItemFactory] for this view model. */

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

@@ -5,13 +5,13 @@ import android.text.TextWatcher
 import androidx.databinding.Observable
 import androidx.databinding.ObservableField
 import org.oppia.android.R
+import org.oppia.android.app.model.AnswerErrorCategory
 import org.oppia.android.app.model.Interaction
 import org.oppia.android.app.model.InteractionObject
 import org.oppia.android.app.model.RawUserAnswer
 import org.oppia.android.app.model.UserAnswer
 import org.oppia.android.app.model.WrittenTranslationContext
 import org.oppia.android.app.parser.StringToRatioParser
-import org.oppia.android.app.player.state.answerhandling.AnswerErrorCategory
 import org.oppia.android.app.player.state.answerhandling.InteractionAnswerErrorOrAvailabilityCheckReceiver
 import org.oppia.android.app.player.state.answerhandling.InteractionAnswerHandler
 import org.oppia.android.app.player.state.answerhandling.InteractionAnswerReceiver
@@ -33,9 +33,10 @@ class RatioExpressionInputInteractionViewModel private constructor(
   private val translationController: TranslationController
 ) : StateItemViewModel(ViewType.RATIO_EXPRESSION_INPUT_INTERACTION), InteractionAnswerHandler {
   private var pendingAnswerError: String? = null
-  var answerText: CharSequence = rawUserAnswer.textualAnswer ?: ""
+  var answerText: CharSequence = rawUserAnswer.textualAnswer
   var isAnswerAvailable = ObservableField<Boolean>(false)
   var errorMessage = ObservableField<String>("")
+  private var currentErrorCategory = AnswerErrorCategory.NO_ERROR
 
   val hintText: CharSequence = deriveHintText(interaction)
   private val stringToRatioParser: StringToRatioParser = StringToRatioParser()
@@ -55,7 +56,6 @@ class RatioExpressionInputInteractionViewModel private constructor(
 
     errorMessage.addOnPropertyChangedCallback(callback)
     isAnswerAvailable.addOnPropertyChangedCallback(callback)
-    checkPendingAnswerError(AnswerErrorCategory.REAL_TIME)
   }
 
   override fun getPendingAnswer(): UserAnswer = UserAnswer.newBuilder().apply {
@@ -75,23 +75,29 @@ class RatioExpressionInputInteractionViewModel private constructor(
     if (answerText.isNotEmpty()) {
       textualAnswer = answerText.toString()
     }
+    lastErrorCategory = currentErrorCategory
   }.build()
 
   /** It checks the pending error for the current ratio input, and correspondingly updates the error string based on the specified error category. */
   override fun checkPendingAnswerError(category: AnswerErrorCategory): String? {
     if (answerText.isNotEmpty()) {
-      when (category) {
-        AnswerErrorCategory.REAL_TIME ->
-          pendingAnswerError =
-            stringToRatioParser.getRealTimeAnswerError(answerText.toString())
-              .getErrorMessageFromStringRes(resourceHandler)
-        AnswerErrorCategory.SUBMIT_TIME ->
-          pendingAnswerError =
-            stringToRatioParser.getSubmitTimeError(
-              answerText.toString(),
-              numberOfTerms = numberOfTerms
-            ).getErrorMessageFromStringRes(resourceHandler)
+      pendingAnswerError = when (category) {
+        AnswerErrorCategory.REAL_TIME -> {
+          stringToRatioParser.getRealTimeAnswerError(answerText.toString())
+            .getErrorMessageFromStringRes(resourceHandler)
+        }
+        AnswerErrorCategory.SUBMIT_TIME -> {
+          stringToRatioParser.getSubmitTimeError(
+            answerText.toString(),
+            numberOfTerms = numberOfTerms
+          ).getErrorMessageFromStringRes(resourceHandler)
+        }
+        AnswerErrorCategory.ANSWER_ERROR_CATEGORY_UNSPECIFIED, AnswerErrorCategory.UNRECOGNIZED,
+        AnswerErrorCategory.NO_ERROR -> null
       }
+      currentErrorCategory = if (pendingAnswerError == null) {
+        AnswerErrorCategory.NO_ERROR
+      } else category
       errorMessage.set(pendingAnswerError)
     }
     return pendingAnswerError