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

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)
+    // Apply defaults:
+    errorOrAvailabilityCheckReceiver.onPendingAnswerErrorOrAvailabilityCheck(
+      null,
+      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/res/values/strings.xml

@@ -166,6 +166,7 @@
   <string name="fraction_error_invalid_format">Please enter a valid fraction (e.g., 5/3 or 1 2/3)</string>
   <string name="fraction_error_divide_by_zero">Please do not put 0 in the denominator</string>
   <string name="fraction_error_larger_than_seven_digits">None of the numbers in the fraction should have more than 7 digits.</string>
+  <string name="fraction_error_empty_input">Enter a fraction to continue</string>
   <string name="number_error_starting_with_floating_point">Please begin your answer with a number (e.g.,”0” in 0.5).</string>
   <string name="number_error_invalid_format">Please enter a valid number.</string>
   <string name="number_error_larger_than_fifteen_characters">The answer can contain at most 15 digits (0–9) or symbols (. or -).</string>

app/src/test/java/org/oppia/android/app/parser/FractionParsingUiErrorTest.kt

@@ -165,7 +165,7 @@ class FractionParsingUiErrorTest {
         .toUiError()
         .getErrorMessageFromStringRes(activity.appLanguageResourceHandler)
       assertThat(errorMessage)
-        .isEqualTo("Please enter a valid fraction (e.g., 5/3 or 1 2/3)")
+        .isEqualTo("Enter a fraction to continue")
     }
   }
 

utility/src/main/java/org/oppia/android/util/math/FractionParser.kt

@@ -1,5 +1,6 @@
 package org.oppia.android.util.math
 
+import android.text.TextUtils
 import org.oppia.android.app.model.Fraction
 import org.oppia.android.util.extensions.normalizeWhitespace
 
@@ -24,6 +25,9 @@ class FractionParser {
    * detection should be done using [getRealTimeAnswerError], instead.
    */
   fun getSubmitTimeError(text: String): FractionParsingError {
+    if (TextUtils.isEmpty(text)) {
+      return FractionParsingError.EMPTY_INPUT
+    }
     if (invalidCharsLengthRegex.find(text) != null) {
       return FractionParsingError.NUMBER_TOO_LONG
     }
@@ -130,6 +134,9 @@ class FractionParser {
      * Indicates that at least one of the numbers present in the string is too long to be
      * precisely represented in a fraction.
      */
-    NUMBER_TOO_LONG
+    NUMBER_TOO_LONG,
+
+    /** The input text was empty. */
+    EMPTY_INPUT
   }
 }

utility/src/test/java/org/oppia/android/util/math/FractionParserTest.kt

@@ -85,9 +85,9 @@ class FractionParserTest {
   }
 
   @Test
-  fun testSubmitTimeError_emptyString_returnsInvalidFormat() {
+  fun testSubmitTimeError_emptyString_returnsEmptyInput() {
     val error = fractionParser.getSubmitTimeError("")
-    assertThat(error).isEqualTo(FractionParser.FractionParsingError.INVALID_FORMAT)
+    assertThat(error).isEqualTo(FractionParser.FractionParsingError.EMPTY_INPUT)
   }
 
   @Test