Fix part of #5070: Display empty answer message in text input interaction (#5311)

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check off every point from the Essential Checklist! -->
## Explanation
Fixes part of #5070, In TextInteraction UI, leave submit button enabled
when answer is empty. Show an error on submitting an empty answer.
Created own test suite for text input interaction view.


[text_input.webm](https://github.com/oppia/oppia-android/assets/76042077/a5882904-8152-4422-b9c9-c937cb056dd5)


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Author: Vishwajith-Shettigar

app/src/main/AndroidManifest.xml

@@ -187,9 +187,9 @@
       android:theme="@style/OppiaThemeWithoutActionBar" />
     <activity
       android:name=".app.splash.SplashActivity"
+      android:exported="true"
       android:label="@string/app_name"
       android:screenOrientation="portrait"
-      android:exported="true"
       android:theme="@style/SplashScreenTheme">
       <intent-filter>
         <action android:name="android.intent.action.MAIN" />
@@ -214,6 +214,7 @@
     <activity android:name=".app.testing.ExplorationInjectionActivity" />
     <activity android:name=".app.testing.ExplorationTestActivity" />
     <activity android:name=".app.testing.FractionInputInteractionViewTestActivity" />
+    <activity android:name=".app.testing.TextInputInteractionViewTestActivity" />
     <activity
       android:name=".app.testing.TestFontScaleConfigurationUtilActivity"
       android:theme="@style/OppiaThemeWithoutActionBar" />

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

@@ -83,6 +83,7 @@ import org.oppia.android.app.testing.SpotlightFragmentTestActivity
 import org.oppia.android.app.testing.StateAssemblerMarginBindingAdaptersTestActivity
 import org.oppia.android.app.testing.StateAssemblerPaddingBindingAdaptersTestActivity
 import org.oppia.android.app.testing.TestFontScaleConfigurationUtilActivity
+import org.oppia.android.app.testing.TextInputInteractionViewTestActivity
 import org.oppia.android.app.testing.TextViewBindingAdaptersTestActivity
 import org.oppia.android.app.testing.TopicRevisionTestActivity
 import org.oppia.android.app.testing.TopicTestActivity
@@ -150,6 +151,7 @@ interface ActivityComponentImpl :
   fun inject(imageRegionSelectionTestActivity: ImageRegionSelectionTestActivity)
   fun inject(imageViewBindingAdaptersTestActivity: ImageViewBindingAdaptersTestActivity)
   fun inject(inputInteractionViewTestActivity: InputInteractionViewTestActivity)
+  fun inject(textInputInteractionViewTestActivity: TextInputInteractionViewTestActivity)
   fun inject(ratioInputInteractionViewTestActivity: RatioInputInteractionViewTestActivity)
   fun inject(licenseListActivity: LicenseListActivity)
   fun inject(licenseTextViewerActivity: LicenseTextViewerActivity)

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

@@ -2,13 +2,15 @@ package org.oppia.android.app.player.state.itemviewmodel
 
 import android.text.Editable
 import android.text.TextWatcher
+import androidx.annotation.StringRes
 import androidx.databinding.Observable
 import androidx.databinding.ObservableField
 import org.oppia.android.R
 import org.oppia.android.app.model.Interaction
 import org.oppia.android.app.model.InteractionObject
 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
@@ -28,20 +30,43 @@ class TextInputViewModel private constructor(
 ) : StateItemViewModel(ViewType.TEXT_INPUT_INTERACTION), InteractionAnswerHandler {
   var answerText: CharSequence = ""
   val hintText: CharSequence = deriveHintText(interaction)
+  private var pendingAnswerError: String? = null
 
   var isAnswerAvailable = ObservableField<Boolean>(false)
+  val errorMessage = ObservableField<String>("")
 
   init {
     val callback: Observable.OnPropertyChangedCallback =
       object : Observable.OnPropertyChangedCallback() {
         override fun onPropertyChanged(sender: Observable, propertyId: Int) {
           interactionAnswerErrorOrAvailabilityCheckReceiver.onPendingAnswerErrorOrAvailabilityCheck(
-            /* pendingAnswerError= */ null,
-            answerText.isNotEmpty()
+            pendingAnswerError = pendingAnswerError,
+            inputAnswerAvailable = true // Allow submit on empty answer.
           )
         }
       }
     isAnswerAvailable.addOnPropertyChangedCallback(callback)
+    errorMessage.addOnPropertyChangedCallback(callback)
+
+    // Initializing with default values so that submit button is enabled by default.
+    interactionAnswerErrorOrAvailabilityCheckReceiver.onPendingAnswerErrorOrAvailabilityCheck(
+      pendingAnswerError = null,
+      inputAnswerAvailable = true
+    )
+  }
+
+  override fun checkPendingAnswerError(category: AnswerErrorCategory): String? {
+    return when (category) {
+      AnswerErrorCategory.REAL_TIME -> null
+      AnswerErrorCategory.SUBMIT_TIME -> {
+        TextParsingUiError.createForText(
+          answerText.toString()
+        ).createForText(resourceHandler)
+      }
+    }.also {
+      pendingAnswerError = it
+      errorMessage.set(it)
+    }
   }
 
   fun getAnswerTextWatcher(): TextWatcher {
@@ -55,6 +80,7 @@ class TextInputViewModel private constructor(
         if (isAnswerTextAvailable != isAnswerAvailable.get()) {
           isAnswerAvailable.set(isAnswerTextAvailable)
         }
+        checkPendingAnswerError(AnswerErrorCategory.REAL_TIME)
       }
 
       override fun afterTextChanged(s: Editable) {
@@ -121,4 +147,22 @@ class TextInputViewModel private constructor(
       )
     }
   }
+
+  private enum class TextParsingUiError(@StringRes private var error: Int?) {
+    /** Corresponds to non empty input. */
+    VALID(error = null),
+
+    /** Corresponds to empty input. */
+    EMPTY_INPUT(error = R.string.text_error_empty_input);
+
+    /** Returns the string corresponding to this error's string resources, or null if there is none. */
+    fun createForText(resourceHandler: AppLanguageResourceHandler): String? =
+      error?.let(resourceHandler::getStringInLocale)
+
+    companion object {
+      /** Returns the [TextParsingUiError] corresponding to the input. */
+      fun createForText(text: String): TextParsingUiError =
+        if (text.isEmpty()) EMPTY_INPUT else VALID
+    }
+  }
 }

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

@@ -9,7 +9,6 @@ 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.NumericInputInteractionView
-import org.oppia.android.app.customview.interaction.TextInputInteractionView
 import org.oppia.android.app.model.InputInteractionViewTestActivityParams
 import org.oppia.android.app.model.InputInteractionViewTestActivityParams.MathInteractionType.ALGEBRAIC_EXPRESSION
 import org.oppia.android.app.model.InputInteractionViewTestActivityParams.MathInteractionType.MATH_EQUATION
@@ -26,7 +25,6 @@ import org.oppia.android.app.player.state.itemviewmodel.MathExpressionInteractio
 import org.oppia.android.app.player.state.itemviewmodel.NumericInputViewModel
 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.itemviewmodel.TextInputViewModel
 import org.oppia.android.app.player.state.listener.StateKeyboardButtonListener
 import org.oppia.android.databinding.ActivityInputInteractionViewTestBinding
 import org.oppia.android.util.extensions.getProtoExtra
@@ -36,7 +34,7 @@ import org.oppia.android.app.player.state.itemviewmodel.MathExpressionInteractio
 
 /**
  * This is a dummy activity to test input interaction views.
- * It contains [NumericInputInteractionView],and [TextInputInteractionView].
+ * It contains [NumericInputInteractionView]
  */
 class InputInteractionViewTestActivity :
   InjectableAutoLocalizedAppCompatActivity(),
@@ -48,16 +46,11 @@ class InputInteractionViewTestActivity :
   @Inject
   lateinit var numericInputViewModelFactory: NumericInputViewModel.FactoryImpl
 
-  @Inject
-  lateinit var textInputViewModelFactory: TextInputViewModel.FactoryImpl
-
   @Inject
   lateinit var mathExpViewModelFactoryFactory: MathExpViewModelFactoryFactoryImpl
 
   val numericInputViewModel by lazy { numericInputViewModelFactory.create<NumericInputViewModel>() }
 
-  val textInputViewModel by lazy { textInputViewModelFactory.create<TextInputViewModel>() }
-
   lateinit var mathExpressionViewModel: MathExpressionInteractionsViewModel
   lateinit var writtenTranslationContext: WrittenTranslationContext
 
@@ -103,7 +96,6 @@ class InputInteractionViewTestActivity :
     }
 
     binding.numericInputViewModel = numericInputViewModel
-    binding.textInputViewModel = textInputViewModel
     binding.mathExpressionInteractionsViewModel = mathExpressionViewModel
   }
 

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

@@ -0,0 +1,89 @@
+package org.oppia.android.app.testing
+
+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.TextInputInteractionView
+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.StateItemViewModel
+import org.oppia.android.app.player.state.itemviewmodel.TextInputViewModel
+import org.oppia.android.app.player.state.listener.StateKeyboardButtonListener
+import org.oppia.android.databinding.ActivityTextInputInteractionViewTestBinding
+import javax.inject.Inject
+
+/**
+ * This is a dummy activity to test input interaction views.
+ * It contains [TextInputInteractionView]
+ */
+class TextInputInteractionViewTestActivity :
+  InjectableAutoLocalizedAppCompatActivity(),
+  StateKeyboardButtonListener,
+  InteractionAnswerErrorOrAvailabilityCheckReceiver,
+  InteractionAnswerReceiver {
+
+  private lateinit var binding: ActivityTextInputInteractionViewTestBinding
+
+  @Inject
+  lateinit var textinputViewModelFactory: TextInputViewModel.FactoryImpl
+
+  /** Gives access to the [TextInputViewModel]. */
+  val textInputViewModel by lazy {
+    textinputViewModelFactory.create<TextInputViewModel>()
+  }
+
+  /** 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(
+      this, R.layout.activity_text_input_interaction_view_test
+    )
+
+    writtenTranslationContext = WrittenTranslationContext.getDefaultInstance()
+    binding.textInputViewModel = textInputViewModel
+  }
+
+  /** Checks submit-time errors. */
+  fun getPendingAnswerErrorOnSubmitClick(v: View) {
+    textInputViewModel.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>
+  StateItemViewModel.InteractionItemFactory.create(
+    interaction: Interaction = Interaction.getDefaultInstance()
+  ): T {
+    return create(
+      entityId = "fake_entity_id",
+      hasConversationView = false,
+      interaction = interaction,
+      interactionAnswerReceiver = this@TextInputInteractionViewTestActivity,
+      answerErrorReceiver = this@TextInputInteractionViewTestActivity,
+      hasPreviousButton = false,
+      isSplitView = false,
+      writtenTranslationContext,
+      timeToStartNoticeAnimationMs = null
+    ) as T
+  }
+}

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

@@ -11,10 +11,6 @@
       name="numericInputViewModel"
       type="org.oppia.android.app.player.state.itemviewmodel.NumericInputViewModel" />
 
-    <variable
-      name="textInputViewModel"
-      type="org.oppia.android.app.player.state.itemviewmodel.TextInputViewModel" />
-
     <variable
       name="mathExpressionInteractionsViewModel"
       type="org.oppia.android.app.player.state.itemviewmodel.MathExpressionInteractionsViewModel" />
@@ -23,6 +19,7 @@
   <ScrollView
     android:layout_width="match_parent"
     android:layout_height="match_parent">
+
     <LinearLayout
       android:layout_width="match_parent"
       android:layout_height="wrap_content"
@@ -36,18 +33,18 @@
         android:id="@+id/test_number_input_interaction_view"
         android:layout_width="match_parent"
         android:layout_height="wrap_content"
-        android:minHeight="48dp"
         android:layout_margin="8dp"
         android:background="@drawable/edit_text_background"
         android:focusable="true"
         android:hint="@string/test_number_input_interaction_hint"
-        android:textColor="@color/component_color_shared_primary_text_color"
-        android:textColorHint="@color/component_color_shared_edit_text_hint_color"
         android:longClickable="false"
         android:maxLength="200"
+        android:minHeight="48dp"
         android:padding="8dp"
         android:singleLine="true"
         android:text="@={numericInputViewModel.answerText}"
+        android:textColor="@color/component_color_shared_primary_text_color"
+        android:textColorHint="@color/component_color_shared_edit_text_hint_color"
         app:textChangedListener="@{numericInputViewModel.answerTextWatcher}" />
 
       <TextView
@@ -64,33 +61,17 @@
         android:textSize="12sp"
         android:visibility="@{numericInputViewModel.errorMessage.length() > 0 ? View.VISIBLE : View.INVISIBLE}" />
 
-      <org.oppia.android.app.customview.interaction.TextInputInteractionView
-        android:id="@+id/test_text_input_interaction_view"
-        android:layout_width="match_parent"
-        android:layout_height="wrap_content"
-        android:minHeight="48dp"
-        android:layout_margin="8dp"
-        android:background="@drawable/edit_text_background"
-        android:focusable="true"
-        android:hint="@string/test_text_input_interaction_hint"
-        android:inputType="text"
-        android:longClickable="false"
-        android:maxLength="200"
-        android:padding="8dp"
-        android:singleLine="true"
-        android:text="@={textInputViewModel.answerText}" />
-
       <org.oppia.android.app.customview.interaction.MathExpressionInteractionsView
         android:id="@+id/test_math_expression_input_interaction_view"
         style="@style/InputInteractionEditText"
-        android:minHeight="48dp"
-        app:placeholder="@{mathExpressionInteractionsViewModel.hintText}"
         android:inputType="text"
+        android:minHeight="48dp"
         android:text="@={mathExpressionInteractionsViewModel.answerText}"
-        app:textChangedListener="@{mathExpressionInteractionsViewModel.answerTextWatcher}"
         app:layout_constraintEnd_toEndOf="parent"
         app:layout_constraintStart_toStartOf="parent"
-        app:layout_constraintTop_toTopOf="parent"/>
+        app:layout_constraintTop_toTopOf="parent"
+        app:placeholder="@{mathExpressionInteractionsViewModel.hintText}"
+        app:textChangedListener="@{mathExpressionInteractionsViewModel.answerTextWatcher}" />
 
       <Button
         android:id="@+id/submit_button"