Fix #4135, Fix part of #5070: In FractionInteraction UI, leave submit button enabled when answer is empty.

app/src/main/AndroidManifest.xml

@@ -213,6 +213,7 @@
     <activity android:name=".app.testing.DrawableBindingAdaptersTestActivity" />
     <activity android:name=".app.testing.ExplorationInjectionActivity" />
     <activity android:name=".app.testing.ExplorationTestActivity" />
+    <activity android:name=".app.testing.FractionInputInteractionViewTestActivity" />
     <activity
       android:name=".app.testing.TestFontScaleConfigurationUtilActivity"
       android:theme="@style/OppiaThemeWithoutActionBar" />

app/src/main/java/org/oppia/android/app/activity/ActivityComponentImpl.kt

@@ -64,6 +64,7 @@ import org.oppia.android.app.testing.DragDropTestActivity
 import org.oppia.android.app.testing.DrawableBindingAdaptersTestActivity
 import org.oppia.android.app.testing.ExplorationInjectionActivity
 import org.oppia.android.app.testing.ExplorationTestActivity
+import org.oppia.android.app.testing.FractionInputInteractionViewTestActivity
 import org.oppia.android.app.testing.HomeFragmentTestActivity
 import org.oppia.android.app.testing.HomeTestActivity
 import org.oppia.android.app.testing.HtmlParserTestActivity
@@ -139,6 +140,7 @@ interface ActivityComponentImpl :
   fun inject(faqSingleActivity: FAQSingleActivity)
   fun inject(forceNetworkTypeActivity: ForceNetworkTypeActivity)
   fun inject(forceNetworkTypeTestActivity: ForceNetworkTypeTestActivity)
+  fun inject(fractionInputInteractionViewTestActivity: FractionInputInteractionViewTestActivity)
   fun inject(helpActivity: HelpActivity)
   fun inject(homeActivity: HomeActivity)
   fun inject(homeFragmentTestActivity: HomeFragmentTestActivity)

app/src/main/java/org/oppia/android/app/parser/FractionParsingUiError.kt

@@ -20,7 +20,10 @@ enum class FractionParsingUiError(@StringRes private var error: Int?) {
   DIVISION_BY_ZERO(error = R.string.fraction_error_divide_by_zero),
 
   /** Corresponds to [FractionParsingError.NUMBER_TOO_LONG]. */
-  NUMBER_TOO_LONG(error = R.string.fraction_error_larger_than_seven_digits);
+  NUMBER_TOO_LONG(error = R.string.fraction_error_larger_than_seven_digits),
+
+  /** Corresponds to [FractionParsingError.EMPTY_INPUT]. */
+  EMPTY_INPUT(error = R.string.fraction_error_empty_input);
 
   /**
    * Returns the string corresponding to this error's string resources, or null if there is none.
@@ -39,6 +42,7 @@ enum class FractionParsingUiError(@StringRes private var error: Int?) {
         FractionParsingError.INVALID_FORMAT -> INVALID_FORMAT
         FractionParsingError.DIVISION_BY_ZERO -> DIVISION_BY_ZERO
         FractionParsingError.NUMBER_TOO_LONG -> NUMBER_TOO_LONG
+        FractionParsingError.EMPTY_INPUT -> EMPTY_INPUT
       }
     }
   }

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

@@ -43,12 +43,17 @@ class FractionInteractionViewModel private constructor(
         override fun onPropertyChanged(sender: Observable, propertyId: Int) {
           errorOrAvailabilityCheckReceiver.onPendingAnswerErrorOrAvailabilityCheck(
             pendingAnswerError,
-            answerText.isNotEmpty()
+            true // Allow submit on empty answer.
           )
         }
       }
     errorMessage.addOnPropertyChangedCallback(callback)
     isAnswerAvailable.addOnPropertyChangedCallback(callback)
+    // Force-update the UI to reflect the state of the errorMessage and isAnswerAvailable property:
+    errorOrAvailabilityCheckReceiver.onPendingAnswerErrorOrAvailabilityCheck(
+      /* pendingAnswerError= */null,
+      /* inputAnswerAvailable= */true
+    )
   }
 
   override fun getPendingAnswer(): UserAnswer = UserAnswer.newBuilder().apply {
@@ -64,23 +69,25 @@ 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) {
-        AnswerErrorCategory.REAL_TIME -> {
+    when (category) {
+      AnswerErrorCategory.REAL_TIME -> {
+        if (answerText.isNotEmpty()) {
           pendingAnswerError =
             FractionParsingUiError.createFromParsingError(
               fractionParser.getRealTimeAnswerError(answerText.toString())
             ).getErrorMessageFromStringRes(resourceHandler)
+        } else {
+          pendingAnswerError = null
         }
-        AnswerErrorCategory.SUBMIT_TIME -> {
-          pendingAnswerError =
-            FractionParsingUiError.createFromParsingError(
-              fractionParser.getSubmitTimeError(answerText.toString())
-            ).getErrorMessageFromStringRes(resourceHandler)
-        }
       }
-      errorMessage.set(pendingAnswerError)
+      AnswerErrorCategory.SUBMIT_TIME -> {
+        pendingAnswerError =
+          FractionParsingUiError.createFromParsingError(
+            fractionParser.getSubmitTimeError(answerText.toString())
+          ).getErrorMessageFromStringRes(resourceHandler)
+      }
     }
+    errorMessage.set(pendingAnswerError)
     return pendingAnswerError
   }
 

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

@@ -73,6 +73,12 @@ class MathExpressionInteractionsViewModel private constructor(
    * bound to the corresponding edit text.
    */
   var answerText: CharSequence = ""
+    // The value of ths field is set from the Binding and from the TextWatcher. Any
+    // programmatic modification needs to be done here, so that the Binding and the TextWatcher
+    // do not step on each other.
+    set(value) {
+      field = value.toString().trim()
+    }
 
   /**
    * Defines whether an answer is currently available to parse. This is expected to be directly
@@ -166,7 +172,7 @@ class MathExpressionInteractionsViewModel private constructor(
       }
 
       override fun onTextChanged(answer: CharSequence, start: Int, before: Int, count: Int) {
-        answerText = answer.toString().trim()
+        answerText = answer
         val isAnswerTextAvailable = answerText.isNotEmpty()
         if (isAnswerTextAvailable != isAnswerAvailable.get()) {
           isAnswerAvailable.set(isAnswerTextAvailable)

app/src/main/java/org/oppia/android/app/testing/FractionInputInteractionViewTestActivity.kt

@@ -0,0 +1,112 @@
+package org.oppia.android.app.testing
+
+import android.content.Context
+import android.content.Intent
+import android.os.Bundle
+import android.view.View
+import androidx.databinding.DataBindingUtil
+import org.oppia.android.R
+import org.oppia.android.app.activity.ActivityComponentImpl
+import org.oppia.android.app.activity.InjectableAutoLocalizedAppCompatActivity
+import org.oppia.android.app.customview.interaction.FractionInputInteractionView
+import org.oppia.android.app.model.InputInteractionViewTestActivityParams
+import org.oppia.android.app.model.Interaction
+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.InteractionAnswerReceiver
+import org.oppia.android.app.player.state.itemviewmodel.FractionInteractionViewModel
+import org.oppia.android.app.player.state.itemviewmodel.StateItemViewModel
+import org.oppia.android.app.player.state.itemviewmodel.StateItemViewModel.InteractionItemFactory
+import org.oppia.android.app.player.state.listener.StateKeyboardButtonListener
+import org.oppia.android.databinding.ActivityFractionInputInteractionViewTestBinding
+import org.oppia.android.util.extensions.getProtoExtra
+import org.oppia.android.util.extensions.putProtoExtra
+import javax.inject.Inject
+
+/**
+ * This is a dummy activity to test [FractionInputInteractionView].
+ */
+class FractionInputInteractionViewTestActivity :
+  InjectableAutoLocalizedAppCompatActivity(),
+  StateKeyboardButtonListener,
+  InteractionAnswerErrorOrAvailabilityCheckReceiver,
+  InteractionAnswerReceiver {
+  private lateinit var binding: ActivityFractionInputInteractionViewTestBinding
+
+  @Inject
+  lateinit var fractionInteractionViewModelFactory: FractionInteractionViewModel.FactoryImpl
+
+  /** Gives access to the [FractionInteractionViewModel]. */
+  val fractionInteractionViewModel by lazy {
+    fractionInteractionViewModelFactory.create<FractionInteractionViewModel>()
+  }
+
+  /** Gives access to the translation context. */
+  lateinit var writtenTranslationContext: WrittenTranslationContext
+
+  override fun onCreate(savedInstanceState: Bundle?) {
+    super.onCreate(savedInstanceState)
+    (activityComponent as ActivityComponentImpl).inject(this)
+    binding = DataBindingUtil.setContentView<ActivityFractionInputInteractionViewTestBinding>(
+      this, R.layout.activity_fraction_input_interaction_view_test
+    )
+
+    val params =
+      intent.getProtoExtra(
+        TEST_ACTIVITY_PARAMS_ARGUMENT_KEY,
+        InputInteractionViewTestActivityParams.getDefaultInstance()
+      )
+    writtenTranslationContext = params.writtenTranslationContext
+    binding.fractionInteractionViewModel = fractionInteractionViewModel
+  }
+
+  /** Checks submit-time errors. */
+  fun getPendingAnswerErrorOnSubmitClick(v: View) {
+    fractionInteractionViewModel.checkPendingAnswerError(AnswerErrorCategory.SUBMIT_TIME)
+  }
+
+  override fun onPendingAnswerErrorOrAvailabilityCheck(
+    pendingAnswerError: String?,
+    inputAnswerAvailable: Boolean
+  ) {
+  }
+
+  override fun onAnswerReadyForSubmission(answer: UserAnswer) {
+  }
+
+  override fun onEditorAction(actionCode: Int) {
+  }
+
+  private inline fun <reified T : StateItemViewModel> InteractionItemFactory.create(
+    interaction: Interaction = Interaction.getDefaultInstance()
+  ): T {
+    return create(
+      entityId = "fake_entity_id",
+      hasConversationView = false,
+      interaction = interaction,
+      interactionAnswerReceiver = this@FractionInputInteractionViewTestActivity,
+      answerErrorReceiver = this@FractionInputInteractionViewTestActivity,
+      hasPreviousButton = false,
+      isSplitView = false,
+      writtenTranslationContext,
+      timeToStartNoticeAnimationMs = null
+    ) as T
+  }
+
+  companion object {
+    private const val TEST_ACTIVITY_PARAMS_ARGUMENT_KEY =
+      "FractionInputInteractionViewTestActivity.params"
+
+    /** Creates an intent to open this activity. */
+    fun createIntent(
+      context: Context,
+      extras: InputInteractionViewTestActivityParams
+    ): Intent {
+      return Intent(context, FractionInputInteractionViewTestActivity::class.java).also {
+        it.putProtoExtra(TEST_ACTIVITY_PARAMS_ARGUMENT_KEY, extras)
+      }
+    }
+  }
+}

app/src/main/java/org/oppia/android/app/testing/InputInteractionViewTestActivity.kt

@@ -8,7 +8,6 @@ import androidx.databinding.DataBindingUtil
 import org.oppia.android.R
 import org.oppia.android.app.activity.ActivityComponentImpl
 import org.oppia.android.app.activity.InjectableAutoLocalizedAppCompatActivity
-import org.oppia.android.app.customview.interaction.FractionInputInteractionView
 import org.oppia.android.app.customview.interaction.NumericInputInteractionView
 import org.oppia.android.app.customview.interaction.TextInputInteractionView
 import org.oppia.android.app.model.InputInteractionViewTestActivityParams
@@ -24,7 +23,6 @@ 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.InteractionAnswerReceiver
-import org.oppia.android.app.player.state.itemviewmodel.FractionInteractionViewModel
 import org.oppia.android.app.player.state.itemviewmodel.MathExpressionInteractionsViewModel
 import org.oppia.android.app.player.state.itemviewmodel.NumericInputViewModel
 import org.oppia.android.app.player.state.itemviewmodel.RatioExpressionInputInteractionViewModel
@@ -40,7 +38,7 @@ import org.oppia.android.app.player.state.itemviewmodel.MathExpressionInteractio
 
 /**
  * This is a dummy activity to test input interaction views.
- * It contains [FractionInputInteractionView], [NumericInputInteractionView],and [TextInputInteractionView].
+ * It contains [NumericInputInteractionView],and [TextInputInteractionView].
  */
 class InputInteractionViewTestActivity :
   InjectableAutoLocalizedAppCompatActivity(),
@@ -55,9 +53,6 @@ class InputInteractionViewTestActivity :
   @Inject
   lateinit var textInputViewModelFactory: TextInputViewModel.FactoryImpl
 
-  @Inject
-  lateinit var fractionInteractionViewModelFactory: FractionInteractionViewModel.FactoryImpl
-
   @Inject
   lateinit var ratioViewModelFactory: RatioExpressionInputInteractionViewModel.FactoryImpl
 
@@ -68,10 +63,6 @@ class InputInteractionViewTestActivity :
 
   val textInputViewModel by lazy { textInputViewModelFactory.create<TextInputViewModel>() }
 
-  val fractionInteractionViewModel by lazy {
-    fractionInteractionViewModelFactory.create<FractionInteractionViewModel>()
-  }
-
   val ratioExpressionInputInteractionViewModel by lazy {
     ratioViewModelFactory.create<RatioExpressionInputInteractionViewModel>(
       interaction = Interaction.newBuilder().putCustomizationArgs(
@@ -127,13 +118,11 @@ class InputInteractionViewTestActivity :
 
     binding.numericInputViewModel = numericInputViewModel
     binding.textInputViewModel = textInputViewModel
-    binding.fractionInteractionViewModel = fractionInteractionViewModel
     binding.ratioInteractionInputViewModel = ratioExpressionInputInteractionViewModel
     binding.mathExpressionInteractionsViewModel = mathExpressionViewModel
   }
 
   fun getPendingAnswerErrorOnSubmitClick(v: View) {
-    fractionInteractionViewModel.checkPendingAnswerError(AnswerErrorCategory.SUBMIT_TIME)
     numericInputViewModel.checkPendingAnswerError(AnswerErrorCategory.SUBMIT_TIME)
     ratioExpressionInputInteractionViewModel
       .checkPendingAnswerError(AnswerErrorCategory.SUBMIT_TIME)

app/src/main/res/layout/activity_fraction_input_interaction_view_test.xml

@@ -0,0 +1,75 @@
+<?xml version="1.0" encoding="utf-8"?>
+<layout xmlns:android="http://schemas.android.com/apk/res/android"
+  xmlns:app="http://schemas.android.com/apk/res-auto"
+  xmlns:tools="http://schemas.android.com/tools">
+
+  <data>
+
+    <import type="android.view.View" />
+
+    <variable
+      name="fractionInteractionViewModel"
+      type="org.oppia.android.app.player.state.itemviewmodel.FractionInteractionViewModel" />
+  </data>
+
+  <ScrollView
+    android:layout_width="match_parent"
+    android:layout_height="match_parent">
+    <LinearLayout
+      android:layout_width="match_parent"
+      android:layout_height="wrap_content"
+      android:descendantFocusability="beforeDescendants"
+      android:focusableInTouchMode="true"
+      android:gravity="center"
+      android:orientation="vertical"
+      tools:context=".testing.FractionInputInteractionViewTestActivity">
+
+      <org.oppia.android.app.customview.interaction.FractionInputInteractionView
+        android:id="@+id/test_fraction_input_interaction_view"
+        android:layout_width="match_parent"
+        android:layout_height="wrap_content"
+        android:layout_margin="8dp"
+        android:background="@drawable/edit_text_background"
+        android:fontFamily="sans-serif"
+        android:hint="@{fractionInteractionViewModel.hintText}"
+        android:imeOptions="actionDone"
+        android:longClickable="false"
+        android:maxLength="200"
+        android:minHeight="48dp"
+        android:paddingStart="16dp"
+        android:paddingEnd="16dp"
+        android:paddingBottom="8dp"
+        android:singleLine="true"
+        android:text="@={fractionInteractionViewModel.answerText}"
+        android:textColor="@color/component_color_shared_primary_text_color"
+        android:textColorHint="@color/component_color_shared_edit_text_hint_color"
+        android:textSize="14sp"
+        android:textStyle="italic"
+        app:textChangedListener="@{fractionInteractionViewModel.answerTextWatcher}" />
+
+      <TextView
+        android:id="@+id/fraction_input_error"
+        style="@style/TextViewStart"
+        android:layout_width="match_parent"
+        android:layout_height="wrap_content"
+        android:layout_marginStart="16dp"
+        android:layout_marginEnd="8dp"
+        android:fontFamily="sans-serif"
+        android:minHeight="32dp"
+        android:text="@{fractionInteractionViewModel.errorMessage}"
+        android:textColor="@color/component_color_shared_input_error_color"
+        android:textSize="12sp"
+        android:visibility="@{fractionInteractionViewModel.errorMessage.length() > 0 ? View.VISIBLE : View.INVISIBLE}" />
+
+      <Button
+        android:id="@+id/submit_button"
+        style="@style/StateButtonActive"
+        android:layout_width="match_parent"
+        android:layout_height="wrap_content"
+        android:layout_margin="8dp"
+        android:onClick="getPendingAnswerErrorOnSubmitClick"
+        android:text="@string/submit_button_text"
+        android:textColor="@color/component_color_shared_secondary_4_text_color" />
+    </LinearLayout>
+  </ScrollView>
+</layout>