Fix oppia#5615 : Scroll Position For Policies Screen On Orientation C…

…hange (oppia#5616)

## Explanation
This PR fixes oppia#5615 the issue where the scroll position in the policies
screen (Privacy Policy/Terms of Service) would reset after an
orientation change.

### **Changes Made:**
1. **Updated `PoliciesFragmentPresenter`:**
- Added a `scrollPosition` property to save and restore the scroll
state.
- Implemented `onSaveInstanceState` and `onRestoreInstanceState`
handling using a constant key.
- Ensured the scroll position is retained using
`ScrollView.viewTreeObserver` in `onGlobalLayoutListener`.

2. **Modified `PoliciesFragment`:**
   - Delegated `onSaveInstanceState` calls to the presenter.
- Passed the saved instance state to the presenter during fragment view
creation.

### **Testing Performed:**
- Verified that scroll position is correctly retained:
  - Across orientation changes (portrait ↔️ landscape).
  - On both Privacy Policy and Terms of Service screens
---

## Essential Checklist
- [x] The PR title and explanation each start with "Fix #bugnum: ".
- [x] No unnecessary code changes or Android Studio formatting changes
are included.
- [x] The branch is **not** called "develop" and is up-to-date with
"develop".
- [x] Appropriate reviewers are assigned.

---

After Changes :

[Screen_recording_20241223_010758.webm](https://github.com/user-attachments/assets/f9648b03-5b27-4090-9eaa-82946214cd62)

---------

Co-authored-by: Adhiambo Peres <[email protected]>

app/src/main/java/org/oppia/android/app/policies/PoliciesFragment.kt

@@ -49,6 +49,12 @@ class PoliciesFragment : InjectableFragment() {
         POLICIES_FRAGMENT_POLICY_PAGE_ARGUMENT_PROTO,
         PoliciesFragmentArguments.getDefaultInstance()
       )
-    return policiesFragmentPresenter.handleCreateView(inflater, container, policies)
+    return policiesFragmentPresenter
+      .handleCreateView(inflater, container, policies, savedInstanceState)
+  }
+
+  override fun onSaveInstanceState(outState: Bundle) {
+    super.onSaveInstanceState(outState)
+    policiesFragmentPresenter.handleSaveInstanceState(outState)
   }
 }

app/src/main/java/org/oppia/android/app/policies/PoliciesFragmentPresenter.kt

@@ -1,8 +1,10 @@
 package org.oppia.android.app.policies
 
+import android.os.Bundle
 import android.view.LayoutInflater
 import android.view.View
 import android.view.ViewGroup
+import android.widget.ScrollView
 import androidx.appcompat.app.AppCompatActivity
 import org.oppia.android.R
 import org.oppia.android.app.fragment.FragmentScope
@@ -22,21 +24,41 @@ class PoliciesFragmentPresenter @Inject constructor(
   private val resourceHandler: AppLanguageResourceHandler
 ) : HtmlParser.PolicyOppiaTagActionListener {
 
+  private lateinit var binding: PoliciesFragmentBinding
+  private var scrollPosition = 0
+
   /** Handles onCreate() method of the [PoliciesFragment]. */
   fun handleCreateView(
     inflater: LayoutInflater,
     container: ViewGroup?,
-    policiesFragmentArguments: PoliciesFragmentArguments
+    policiesFragmentArguments: PoliciesFragmentArguments,
+    savedInstanceState: Bundle?
   ): View {
-    val binding = PoliciesFragmentBinding.inflate(
+    binding = PoliciesFragmentBinding.inflate(
       inflater,
       container,
       /* attachToRoot= */ false
     )
+
+    savedInstanceState?.let {
+      scrollPosition = it.getInt(KEY_SCROLL_Y, 0)
+    }
+
     setUpContentForTextViews(policiesFragmentArguments.policyPage, binding)
 
+    (binding.root as ScrollView).viewTreeObserver.addOnGlobalLayoutListener {
+      binding.root.scrollTo(0, scrollPosition)
+    }
+
     return binding.root
   }
+  /**
+   * Saves the current scroll position of the policies page into the given [outState].
+   * This helps in restoring the scroll position after orientation changes.
+   */
+  fun handleSaveInstanceState(outState: Bundle) {
+    outState.putInt(KEY_SCROLL_Y, (binding.root as ScrollView).scrollY)
+  }
 
   private fun setUpContentForTextViews(
     policyPage: PolicyPage,
@@ -86,4 +108,8 @@ class PoliciesFragmentPresenter @Inject constructor(
         (activity as RouteToPoliciesListener).onRouteToPolicies(PolicyPage.TERMS_OF_SERVICE)
     }
   }
+
+  companion object {
+    private const val KEY_SCROLL_Y = "policies_scroll_y"
+  }
 }

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

@@ -3,6 +3,7 @@
   xmlns:app="http://schemas.android.com/apk/res-auto">
 
   <ScrollView
+    android:id="@+id/policy_scroll_view"
     android:layout_width="match_parent"
     android:layout_height="match_parent"
     android:background="@color/component_color_shared_screen_tertiary_background_color"

app/src/sharedTest/java/org/oppia/android/app/policies/PoliciesFragmentTest.kt

@@ -4,8 +4,10 @@ import android.app.Application
 import android.app.Instrumentation.ActivityResult
 import android.content.Context
 import android.content.Intent
+import android.content.pm.ActivityInfo
 import android.text.Spannable
 import android.text.style.ClickableSpan
+import android.widget.ScrollView
 import android.widget.TextView
 import androidx.appcompat.app.AppCompatActivity
 import androidx.test.core.app.ActivityScenario.launch
@@ -304,6 +306,34 @@ class PoliciesFragmentTest {
     }
   }
 
+  @Test
+  fun testPoliciesFragment_privacyPolicy_retainsScrollPositionAfterOrientationChange() {
+    launch<PoliciesFragmentTestActivity>(
+      createPoliciesFragmentTestActivity(
+        getApplicationContext(),
+        PolicyPage.PRIVACY_POLICY
+      )
+    ).use { scenario ->
+      scenario.onActivity { activity ->
+        val scrollView = activity.findViewById<ScrollView>(R.id.policy_scroll_view)
+        scrollView.scrollTo(0, 500)
+        testCoroutineDispatchers.runCurrent()
+
+        // Capture the current scroll position.
+        val initialScrollPosition = scrollView.scrollY
+        assertThat(initialScrollPosition).isEqualTo(500)
+
+        // Rotate the screen (simulate an orientation change).
+        activity.requestedOrientation = ActivityInfo.SCREEN_ORIENTATION_LANDSCAPE
+        testCoroutineDispatchers.runCurrent()
+
+        // Verify that the scroll position is retained after the orientation change.
+        val newScrollPosition = scrollView.scrollY
+        assertThat(newScrollPosition).isEqualTo(initialScrollPosition)
+      }
+    }
+  }
+
   @Test
   fun testPoliciesFragment_checkTermsOfServiceWebLink_opensTheLink() {
     launch<PoliciesFragmentTestActivity>(